there is a lot of stove bolt info out there but when you start looking for 261 specific info it gets a little murky pretty quick by being muddled with 235 info. I know they are very closely related but I also know there are some pretty distinct differences. also all the literature I find on stove bolt stuff is primarily 216/235 stuff. I have the HOT ROD soup that chevy article but would like some other view points as well so please post what you know, and if it just something that you've "heard" be sure and say so mild to wild all info is very welcomed!!!
If it were me and I wanted to control what was information was there I would consider starting a inline 261 social group. Then ppst a thread inviting the 261 guys to join. Whenever you want at a later date you can post information on the main board showcasing your social group or someones build from the group there by giving new blood the opportunity to easily find your group. Just a thought. BTW this is not to say that you shouldn't have a 261 thread on the main board.
Im in! I enjoy all the stove bolt stuff. I rely like the performance stuff. I did manage to make mine run pretty good, do miss the good idle though, and the rite off idle torque.
You gotta love the first photo of the mechanic mounting a portable boring machine on an engine with the crankshaft still in place. A coupla carbs,848 head ,blocked decked about .030,3/4 cam,Fenton headers,180 hp,what else is there to know?
I would like more in the 2+ area, Ive already got a 235 thats around 180... the 261 I have is going in a rpu with a lasalle behind it and I want it to be about as nasty as I can and still drive it... so all that said I will start cutting and pasteing all the articles I find on line so we can have a more concise data base so to speak.
and like I said before we all have general info and knowledge, I would like to hear from people that have actually done it and stuck around to yield the results
PM my shadow, notsojollyroger....he speaks 261 fluently. Got one in his 54 tow truck....with a Howard cam, two pots, etc. Sounds like a BB Chevy at idle
You can buy a reprint of the inliners magazine article on the Cadillac 261. It uses 292 rods and early 80's Caddy V-8 pistons. Crank needs to be ground down for the rods. And you end up with a stroked 261. Add overbore and you can get it close to 300 cubic inches. Add cam, carburation, exhaust and serve hot.
I've built a 261 and several 235's. They all ran good for what they are.But we all know the head is the real limitation.There's a 261 on my engine stand as we speak. As far as power,are there any reliable dyno numbers other than the ones printed above from 1955? Are there any reliable 1/4 mile times that can be documneted along with car weight and gearing so we all can get an idea? I used to talk to Leo Santucci quite a bit,the guy who has the 292 turbo Chevy 6 powered Stude and wrote the book for tuning 230-292 engines.He started off drag racing with a built 261 engine.By built I mean a 6000 rpm race engine that has no low speed power and is not streetable and runs only for short durations.He said himself and a few others with all out 261's figured about 280 HP based on 1/4 times. Patrick Dykes told me he saw a few 235's and 261's on dynos with modified heads and never saw more than 200 HP back in the day. So...figuring detuning an all out engine for street use but still a lumpy in town engine might make 220 hp,or not.
K10,Ive never heard of a caddy 261? have any info on this?? Truckedup: see thats kinda the thing I keep hearing conflicting numbers about whats really obtainable? I've heard some say 220 is very do able? soup that chevy barely hits 2 bills? I agree the we need real dyno and time #'s its a shame the 292 family doesnt look nearly as sexy as the stovebolt!
The Forgotten 261 6 Cylinder Engine Between 1954-1962, Chevrolet produced their famous full oil pressure 235 cubic inch six cylinder in trucks and it soon proved to be one of the greats among engines. However, at the same time a lesser known "big brother" to this base engine was being used. This was the quality built 261 cubic inch six cylinder! This 261 was available only in 2 ton (6000 or C60 series) trucks and school buses. During it's early years (1954-1957) it was an extra cost option above the standard 235 six cylinder. In 1958-6192 (the 261 now had a full flow remote oil filter) it became standard in the 2 ton chassis up to 19,000 pounds gross weight. Above that Chevrolet substituted a V-8. This larger six was not offered in US cars, however there was an exception in Canadian built full size Pontiacs. Their base engine, also produced only in Canada, was the 261 not the V-8 as in the US. This provided basic power, great dependability, and better gas mileage. Basically, this larger engine was a 235 with the same crankshaft but GM engineers made various modifications to give it extra strength and horsepower. It's standard bore diameter increased from 3-9/16 inches to 3-3/4 inches. The connecting rods were heavier and attached to increased diameter piston wrist pins. Its higher lift cam shaft, for better breathing, was shared only with the early 235 six cylinder Corvette. A modified larger Rochester carburetor was also a 261 only feature. Unfortunately most of these larger sixes have long since had their original Rochesters replaced with 235's and therefore do not perform to their full potential. In pure big truck form the 261 has a larger thermostat housing holding a double acting thermostat. This is designed to circulate water through the block and head before the thermostat opens to allow hot water into the radiator. Thus, no internal steam hot spots during warm ups, especially in winter. This is particularly important with very cold coolant. Vital engine spots can become very hot before the total coolant becomes hot enough to open a normal thermostat on the front of the block. <TABLE border=1 cellSpacing=0 cellPadding=0 width=500><TBODY><TR><TD>6 Cylinder Engines</TD><TD>Jobmaster</TD><TD>Thriftmaster</TD></TR><TR><TD> </TD><TD> </TD><TD> </TD></TR><TR><TD>Displacement</TD><TD>261 Cu.In.</TD><TD>235.5 Cu. In.</TD></TR><TR><TD>Bore</TD><TD>3 3/4"</TD><TD>3 9/16"</TD></TR><TR><TD>Stroke</TD><TD>3 15/16"</TD><TD>3 15/16"</TD></TR><TR><TD>Firing Order</TD><TD>1-5-3-6-2-4</TD><TD>1-5-3-6-2-4</TD></TR><TR><TD>Compression Ratio</TD><TD>7.8 to 1</TD><TD>8 to 1</TD></TR><TR><TD>Horsepower</TD><TD>33.7 (AMA) 148 (Rated)</TD><TD>30.4 (AMA) 140 (Rated)</TD></TR><TR><TD>No.of Main Bearings</TD><TD>4</TD><TD>4</TD></TR><TR><TD>Wrist Pin Diameter</TD><TD>.927 inches</TD><TD>.875 inches</TD></TR><TR><TD>Rod Shaft Thickness Front to Back</TD><TD>.595 inches</TD><TD>.595 inches</TD></TR><TR><TD>Rod Shaft Thickness Side to Side</TD><TD>.975 inches</TD><TD>.760 inches</TD></TR><TR><TD>Crankshaft Journel Diameter</TD><TD>2.435</TD><TD>2.435</TD></TR><TR><TD>Engine Color in trucks</TD><TD>Green -some later Yellow</TD><TD>Gray</TD></TR></TBODY></TABLE> The block and head surface have three pair of matching small "steam holes" that allow any steam hot pockets to vent away from the open water cooled areas between the cylinders that are not solid metal. Of course, this means the 261 must have its own specialized head gasket. After four years into production, the major quality feature was added to the 261 engine. For the first time a Chevrolet inline six cylinder came standard with a full flow oil filter system. This improvement, used only with the later 261, forced oil through a remote filter cartridge before it reached the engine. It was not like the optional by-pass oil filter system as found on 216 and 235 Chevrolet sixes. This extra helped insure longer life to this larger six cylinder that was often subjected to heavy commercial use. A full flow oil system has been a characteristic of almost all automotive engines for over 40 years but it was just beginning in the mid 1950's. With the 261, the disposable filter is remote and not built in as with later engines. It still resulted in a major design improvement. As with the 235 light truck engine, the 261 came standard with solid valve lifters and an aluminum camshaft timing gear. The passenger car's 235 was equipped with hydraulic valve lifters and a fiber timing gear for quieter operation. During the 1955-1962 Canadian Pontiac application the lifters were the hydraulic type, the cam gear was fiber not aluminum, and it did not have the full flow oil filter. These Canadian made 261's did not add the full flow filter in 1958 as in the U.S. Visually the 261 looks almost identical to the 235. It perfectly replaces the smaller engine and in stock condition increases horsepower from 140 to 148. Those planning on a major rebuild or adding performance options to their Chevrolet inline six should seriously consider locating a 261. Often there is no extra cost in purchasing a re-buildable unit, and the results will be rewarding. If you plan on adding additional carburetion, a higher lift cam, or just want additional performance and more lower end strength in your daily driver, the 261 is for you! Locating and Identifying a 261 Though last placed in larger Chevrolet trucks almost 40 years ago, this now scarce engine can still be located and often at a price no higher than for the smaller 235. Many still remain in the original Chevrolet trucks and are now setting in salvage yards or behind farm buildings. In Canada, the big Pontiac cars are sometimes in the back rows of more isolated older wrecking yards. Don't overlook the wrecked and badly rusted Chevrolet cars of the 1940's and 1950's, particularly those showing signs of some past exterior customizing changes. The Chevrolet enthusiasts of that era knew about the 261 and its potential for added performance. Some of these will already have had extras added such as a higher lift cam shaft, extra carburetion, or dual exhausts. When you have found what you suspect might be a 261, check a few specifies to verify you have the real thing and not the visual almost identical 235. Casting numbers, not stamped numbers, on the 261 head are very visible beside the rocker arm cover. A different set of numbers relate to the 261 block. These seven digits are located on the right side between the fuel pump and starter except for 1954 where it is located forward of the fuel pump. See chart below. <TABLE border=1 cellSpacing=0 cellPadding=0 width=500><TBODY><TR><TD>YEAR</TD><TD>ENGINE SIZE</TD><TD colSpan=3>BLOCK NUMBER</TD><TD colSpan=2>HEAD NUMBER</TD></TR><TR><TD> </TD><TD> </TD><TD> </TD><TD> </TD><TD> </TD><TD> </TD><TD> </TD></TR><TR><TD>54-55</TD><TD>261</TD><TD>3703414</TD><TD>3733950</TD><TD> </TD><TD>3703570</TD><TD>3836850</TD></TR><TR><TD>55-57</TD><TD>261</TD><TD>3733340</TD><TD>3837012</TD><TD> </TD><TD>3703570</TD><TD>3836850</TD></TR><TR><TD>58-62</TD><TD>261</TD><TD>3739365</TD><TD>37369717</TD><TD>3769925</TD><TD>3836850</TD><TD> </TD></TR></TBODY></TABLE> Watch for the "Captain's Bars!" The 261 has two pairs of parallel raised 3/4 inch long bars cast in the block. This is not seen on a 235 except 1954. One pair is above the starter and the second pair is at the top middle of the left side of the block very close to the head. See photos below. The one exception is the early 261 produced in 1954 to mid 1955. It has only one "Captain Bar" above the starter but keeps the pair on the left side. Most used 261 blocks are rebuildable, however often their cylinder heads will have a few very small cracks in the combustion chamber. This is typical due to occasional abuse of over heating in past years. If you choose not to add to your expense by having the cracks repaired, an alternative exists. The more common 235 head is the same except for the three pair of internal steam holes. These can be manually drilled to make the water flow just like in the 261! Sorry, but some 235 heads can be cracked even more than the 261 because they lack heat releasing steam holes. "Warning" When Installing a 261! The stock remote filter system has two very visible 3/4" lines threaded into the block. One is from the pump to the filter and the other from the filter back to the block. Oil must leave and return to the engine by these lines (even if the filter is eliminated) or the engine will fail from lack of lubricant. Many 261 engines have been quickly seized after persons plugged the two oil line holes. They had many years experience on Chevrolet engines without the full flow oil system. Some thought it was an easy fix to just remove the 3/4" lines if one was leaking and cap the holes. This procedure was acceptable on the older 216 and 235 but never on the 1958-1962 261 truck engine. <!-- CONTENT ENDS HERE -->
here's another from Inliners Note: Pat Smith is a long-time tech advisor for Inliners International. His career includes stints as a mechanic/machinist, automotive instructor, and engine builder. Pat is the crew chief for Dyson Racing, reigning Grand-Am Sports racing champions. 261 Street Engine BuildBy Pat SmithBlock: The 261 was introduced in 1954 and was used in Chevrolets "big" trucks and school buses. They can be identified by "Captains Bars" (II) cast in the block above the starter and top center on the driver’s side of the block. The block is similar to the 235 except for the bore, which is now 3.750" (up from 3.5625") and the wrist pin size, which has been enlarged to .927". Almost all other 235 parts are interchangeable! On the later blocks there are provisions, on the driver’s side to plumb a full flow / full pressure, remote oil filter (use at least ½" line). Earlier blocks use the 216/235 "by-pass" oil filter, which steals oil pressure, and filters a very small percentage of the oil. In addition, some of the earlier blocks had no oil passage through the lifter bores, so the use of hydraulic lifters is precluded. Modifications: Normal block stripping and cleaning apply. You have to remove the pan in order to remove the two lower screws, which hold on the timing cover. When apart these holes can be tapped from the outside and bolts installed. The bore can be increased to 3.875 (278 Cu. In.) with fair safety. And, in an emergency, in the case of saving a block, can go another .020" to .030". I like to go .110", which leaves a margin of safety and 276 cu. in. Rings used will be Buick V6 + .060". The top of the block should be milled a minimum amount, just enough to flatten the surface. If possible, find someone who will mill parallel to the crank's centerline. The machinist will have to shim the rear bearing bore, as it is a different size then the front. The 4 main bearings are all different sizes, which precludes align honing and promotes a very expensive line-boring job. NEITHER IS NECESSARY on a street engine, unless a bearing has been spun. BEWARE: These engines did not have tangs on the upper bearings, so it is almost impossible to tell which direction the center caps should go back on!! Mark the caps and adjoining block surface, before you disassemble. Refer to the bearing section for determining bearing sizes and grinding the crank. Pistons: All of the above over-bores depend on very expensive custom pistons. I like JE forged, cam ground pistons. Ross is a slightly cheaper alternative. If you are looking for an even cheaper alternative, stock replacement pistons are available in .030, .060 and .080" oversize. You will be stuck however with odd size, expensive, replacement rings. These are available only in cast iron or chrome! Tom Langdon (Stovebolt Engine Co.) has devised a combination using GMC rods and Buick V6 pistons. I prefer flat top pistons for street use. You may or may not have to cut valve pockets. If you are using GMC rods; be sure you tell the piston manufacturer the width of the small end of the rod. It is wider than the 261 rod. Also, that you will need pin retaining clips, and that the compression height will have to be 1.840" All street pistons should be flat top design, as compression with the 848 head will be right around 9 to 1, which is about perfect for today's regular fuel. Of course you will want to buy high-octane fuel, but paying the price gets pretty old after a short time. To enjoy your rod, you have to use it! Piston to intake valve clearance is a sometimes thing. Because of cam timing, lift, rod length and head milling, you may or may not have a problem. You’ll have to do a trial engine assembly, and check the clearance. You may have to pull the pistons for valve relief cutting. More details will be included later. Connecting rods: Stock rods can be used. They are the same as 235 except for the .927" pin. Caution: These rods are easily twisted when disassembling. Place a rod, which will fit through the pin, into a vise and hold the assembly with that device when the pinch bolt is tightened or loosened. A longer rod can be used to good advantage. The easiest, although not the lightest, is to use a late GMC 270 or early GMC 302 rod. It is a 7" rod compared to the 261 length of 6.810". The best forging number will be a 2135419 as this uses a .990" pin. These are also free floating pins. The rod has to be modified by turning the "big end", equally on both sides, to the 261 width of 1.240" and then rebalanced. GMC rod bearings will have to be used. The GMC has a wide "small end", be sure to tell any piston manufacturer the width. Rings: Any custom pistons should be ordered in a standard, common bore size, that way quality, moly piston rings can be ordered. 3.750" (+. 030", +. 060"), 3.800" (+. 030", +. 060") and 3.875" (+ .030") are all possibilities. These are Chevy V8 or Buick V6 sizes. They all use a modern 5/64, 5/64, 3/16 ring package. Cast iron, chrome and molly rings are available. Stock, replacement, overbore pistons will be limited to an expensive, very wide, ring package in cast iron and chrome ring styles only. The bore must be finished with the right stone grit for the piston rings chosen. Crankshaft: The stock crank is a forged unit, but it is old. It should be hot tanked and magnafluxed. If it has to be turned, the throws can be indexed, so that they are right on the money as far as location. It will of course have to be rebalanced. Balancing, by the way is not done as a V8, i.e. with bob weights, inline cranks are balanced all alone, or possibly with the flywheel and harmonic balancer in place. One more modification should be made. Drill and tap the crank snout for a ½ X 20 balancer retaining bolt from a big block Chevy. V8. This will help install the balancer without damage and retain the balancer if you get carried away with the RPMs. Harmonic Balancer: A 3 groove 292 Chevy 6 balancer, part #10141202 makes an excellent, and improved, replacement for the not so good 261 unit. It should have the rear groove turned off and it’s snout shortened slightly. There was an article on this in an earlier 12 Port News. Or for a Stamped, legal size envelope, I can send you a photocopy. Bearing clearances: Do not get carried away with these. Stock clearances of .0015 to .003" work well. I shoot for a median of .002" for street use. Truthfully, unless you do it right, or unless you have main bearings with adjustment shims, you will have trouble getting the clearances on the mains down to that figure! The right way to do it: Clean your block and main caps, clean and magnaflux your crank. Measure and decide to what size your crank needs to be ground. Buy the main bearings in that size and install them in the empty block. Torque the main bearing caps with a light oil on the threads. Measure the ID of the installed bearings and record it. Subtract the .002" you want for oil clearance and you will have the sizes for the crank grinder to match! If your crank grinder won’t grind to the specified clearances, take your business elsewhere! Rear oil seal: These engines were never equipped, from the factory, with a neoprene, lip type seal. They used rope seals. If you have shimmed main bearing caps, use the rope seal. If you have no shim stack under the main caps, you can use the neoprene lip seal. Personally, I use the rope seal as the engines were designed for. Don't forget to grind the seal surface on the crankshaft on the crankshaft to remove nicks, burrs, grooving and corrosion. PROBLEM; because OSHA or some other big brother agency has decided we should not have asbestos around, there are no good rope seals being manufactured! They new ones are made of fiberglass and don’t seal! Find an original NOS seal*. Something to watch: Oil pans from junkyard engines have had water sitting in them. After hot tanking and glass beading, they can become porous. Look carefully, or you will, as I did, blame the puddle of oil on an innocent rear main seal! Oiling system: A new, stock replacement, oil pump will work fine. Shim the oil pressure relief spring about .060". The pump should be a NAPA or TRW, WITH A GASKET UNDER THE PUMP COVER. This is especially important if you are using hydraulic lifters, as any air in the oiling system will cause the lifters to tick, as air is compressible. Seal all the joints on the pickup for the same reason. When you install the pump in the block, tighten the pointed bolt snug AND THEN BACK IT OFF ½ TURN. Hold it from turning and tighten the lock nut. The pump should wiggle in the block clamp, slightly. I like to go through the adapters on the oil pump tubes. I open them up with the next size drill and taper the holes with a countersink to smooth the flow. Oil Filters: If you have a late 261 with the ½" pipe thread holes on the left side, great! These engines have a full pressure full flow oil filter system. What that means is that 100% of the oil from the pump goes through the filter before it enters the engine. Maybe! Over the lower hole, you will see a boss with a dowel in the middle. If the dowel is out flush with the block, there will be a passage opened between the oil pump outlet and the main oil galley. If the dowel has been pushed in, all the oil has to go through the filter first. I don’t think I would try to move the dowel either in, or out. I would be afraid of breaking the block. Earlier engines had no filter, or a by-pass filter. These took oil, under pressure, from the main oil galley, sent it through the filter and then dumped it back in the pan!! Better than no oil filter, barely. It lowers the oil pressure and filters only a small percentage of the oil. Use a ¼" line to keep the oil pressure as high as it should be. Timing gears: The 235 used fiber timing gears for silence. The 261 truck engines used an aluminum set. I recommend using the stronger aluminum set. You must heat the aluminum gear to get it on the cam without damage. The best way is in a bowl of oil in a furnace. Read the directions! Behind the large camshaft gear is a thrust plate to retain the cam. The thrust plate is not interchangeable with the 250/292 style engines. They are a different thickness. These gears have woodruff keys to locate them on the block and crank. Offset keys are available from Mr. Gasket and all the cam manufacturers for degreeing in the cam. I have NEVER had a 6cyl cam degree in, using the factory marks! You must degree in your new cam. Camshaft: For street use, you will be happiest with a cam having an advertised duration of about 260° intake and 260° to 270° of exhaust duration. That will be about 210° to 212° Intake and 218° to 220° exhaust duration at .050" lift. Lift should be about .450". Small? Yes. Why? Lousy rocker geometry will cause rapid guide wear and you will have less problems with piston to intake valve clearance. Yes, going more will help power but this is a street engine remember. Long life and reasonable fuel mileage are important . Cam cores are becoming increasingly hard to come buy. If you have a cast iron cam, good. It can be suitably reground. Crane, Howard and Iskenderian will regrind your core. Competition Cams still has cores, you must specify a Chevrolet "Blue Flame" six. Recommendations: Isky solid lifter #C4, Crane Hydraulic #H-210/2934-2S-10, Comp Cams Hydraulic #260-7/268-6 H10. These I have used and was quite happy with. There are others. All these cams were installed 4° advanced. Rocker arms: There are no commercially made rockers that I know of. A few custom-made items, but they are few and far between and EXPENSIVE. There are actually 4 different style of rockers on that shaft! Mark them well before disassembly. A good valve train kit can be assembled from replacement parts that will work quite well with the above cams. Lifters: On a cast iron cam, YOU MUST USE a lifter from a ’56 to ’62 solid lifter truck engine, either 235 or 261. Hydraulics should be from the same years 235 passenger car. DO NOT use the "tulip top" lifters which the books call for in the earlier truck engines. These are for stock cams and steel cams only. Pushrods: 5/16 tubular replacement pushrods from Sealed Power are far superior to the stock, ¼" solid, rods. They must be from the same engines as the lifters were ordered for. They will probably be 10 5/8" long. Valve springs: Sissels automotive can supply you with really good springs and retainers. Isky can also supply springs and retainers. Comp cams and Crane seem not to have anything for this engine. Buick 455 springs, Sealed Power #VS715 work well. Valve Spring retainers: Use the stock 235 / 261 spring retainers (without the rotators) with the Buick springs. Valve spring keys: Use heavy-duty keys of the stock angle with the Buick springs and stock retainers. Use keys from Sissell or Isky with their parts. Valve seals: The stock "O" ring seals are notoriously bad. Use a good umbrella type seal. Cylinder Head: All ’54 – ’62 235 / 261 heads seem to be the same as far as ports go. The differences are in the volume of the combustion chamber. Because of the strange design of the combustion chamber and the location of the intake valve, the deck clearance is quite large. Compression is hard to come buy, so you will want the smallest combustion chamber available. The head with the smallest combustion chambers are the ones which contain "848" as the last three casting numbers. These were production heads on ’58 – ’62 235 engines and they were listed as having 8 ¼ to 1 compression. Head milling: Up to .125" can be milled off this head. Of course you will then have to cut valve pockets in the piston and sink the intake valve into the head. A better method would be to mill .030" to .060" maximum off the head. This head, milled .030" and installed on a, .110" over-bored, 261 will give you just a touch over 9 to 1 compression. Just about right for today’s pump gas. Valves: The only larger production valve is the intake valve from a ’50 – ’52 Powerglide 235. They are 1.94" diameter and are still available from TRW. For a street engine, a stainless steel valve from a 265 – 400 Chevy V8 can be used. They come in 1.500" and 1.600". Either may be used. If you use the 1.600, the combustion chamber will require some grinding to un-shroud the valve. Of course that enlarges the chamber volume and lowers the compression. I recommend installing a hard exhaust seat. Porting and polishing: Are beyond my expertise. The bowls under the valves must be opened up and smoothed, but beyond that I would send my head out to be done by a professional. Bill Jenkins used to say; "There isn’t 25 horsepower in the assembly of a short block, but the headwork will cost you hundreds if done wrong." Intake manifolds: Are a very personal thing. Some like the ease of one 4 brl. While others like five 97s on a Howard log. Whatever you choose will take some tinkering. Current thoughts are either two progressive 2 brls or one 4 brl. I think by now you all know the importance of heating the intake manifold. Clifford has redesigned his 4 brl manifolds for water heat at the encouragement of Tom Langdon (Hisself). That was a giant leap towards efficiency. Headers: Fentons have such nostalgic class that I don’t know why you would run any thing else. Add to that, the facts of no warpage, better sealing, and less noise in the front seat. However, tubular headers are lighter and more efficient. They will eke out a few more horsepower. After discussing and experimenting with exhaust systems for sound quality, the following conclusion was reached; The farther forward your muffler is, the more tailpipe you will have behind them and the car will rap more with better the tone! I ended up with 30" glass packs and long tailpipes J . Ignition: Dual points are almost useless on a 6 cyl. Engine. Use a Mallory Unilite electronic adapted from a 250, or a mini HEI from Stovebolt engine company. Whichever you choose, it should be one with a vacuum advance. Sources: Langdon’s Stovebolt Engine Co. 47950 Robin St Utica, MI 48317 Fax/Phone (810) 739-9601 www.stoveboltengineco.com E-mail theboss@stoveboltengineco.com Sissell’s Automotive (Mike Kirby) 1463 Virginia Ave. Baldwin Park CA 91706 (626) 960-1090 Patrick’s Antique Cars & Trucks PO Box 10648 Casa Grande, AZ 85230 (520) 836-1117 www.patricksantiquecars.com
hotdamn,thanks for gathering all that info in one place. One thing that most guys never mention on the 235-261 engines is getting the piston up near zero deck clearance for a tight "quench".The tight quench causes turbulence and a better fuel burn with less tendency to detonate.Tight quench will improve throttle response and fuel mileage and it's important for any performance build. A 261 with the usual flat top stock replacement pistons will sit .040-.070 below the deck from my personal experience with several 261's Combine that that with the stock .055 head gasket thickness,way way too much.On the 261 I built 15 years ago I had the block deck milled .045 and wound up with the piston sitting .015 below deck.So you wind up with about a .065 quench,not the best but ok.I don't know if milling the block deck is a good idea with the bigger overbores.As it is,the 261 block deck is about .500,a little less than a SBC.The 261 on my engine stand now that needs a bore job has .030 pistons and they sit.070 below deck. You might be able to use GMC rods that are about .200 longer and find a inexpensive stock flat top piston with the right compression height.You'll have to make custom small end rod bushings for the GMC rods,cheap if you have the shop tools to do it. The so called Caddy 261 uses 80's Caddy V-8 pistons,292 Chevy Rods I believe and a severely offset ground crankshaft.It seems like a lot of work for a few more cubic inches.I don't like the idea of grinding the fuck out of 60 year old crankshafts...and I believe the quench area is still excessive. Getting a tight quench will also mean paying close attention to the intake valve clearance,especially with a hotter cam.You'll have to dummy up the engine with the cam ,check the clearance and maybe have to slightly notch the piston for intake valve clearance.With the .045 cut I took off the block deck,using a Howards M4F spec grind(.206 duration at .050 lift and .428 actual valve lift,intake clearance was not a problem. Bottom line is all this shit worth it for a few HP and a few more MPG's ? It might be or just do the typical 235-261 build and be happy you wind up with something that runs fine.
thanks Truckedup! I had never heard of "quench" before? thanks for bringing that up, see thats why I did this! also I love the idea of getting more horsepower and better mpg with it 6inarow, where are you? dont hoard all of that knowledge!
Quench or squish area on a 235 head is kinda wierd,but picture a typical "wedge" V-8 head like a Chevy small block.The valves sit in a bowl then there's a the flat area .At TDC the pistom comes up and the fuel air mixture gets "squished" between the piston and flat area causing turbulence to get more complete combustion I'm no expert for sure but this subject is covered by every known engine tuner.It might be more bother than it's worth for some,but my own limited experience says it does make a noticable difference for a street engine.
I read up on quench and block and head milling before my 261 rebuild and once you have an idea of your piston to valve clearances you can work out how much to remove. For some reason my machinist didn't think it was necessary to deck the block— even to get it level. Once I had it home I realized it at least needed decking to level it. That's when I looked into quench factor more. Knowing I needed to remove around .035" (from memory) I took the block to a new machinist who balked at the amount, saying the older blocks have a higher nickel content or something in the iron which makes them very hard, and subsequently tough to cut more than .002" per pass. This meant he would have to make 15 or so passes to remove the .035". And of course that meant a lot of $$ In the end they did a couple of passes to deck the block so I'll never know if milling it more would have made a big difference. I'm still kinda torn, but the short block is assembled now and I really don't want to back track.
OK, so a lot of info here and different ideas. That is what makes this hobby great. On mine, it has 60 over flat top pistons that were in great shape from another motor I have, a 270 flat tappet cam from Clifford, I don't think they even offer it any more, and went with ZERO deck, ya that's rite, zero. I did have to fly cut my pistons for relief of the intake valve, with 848 head. I think, you can't do to much head work on one these. That said, I also would like to have lightened up my crank and fly wheel, couldn't hurt. Mine runs real well, much more power than the 235 that was in my truck, and ran pretty good for what it was. My next move is to build another head, not sure if I am going with another 848, or one of my 261 heads. The new head will get a lot of angle mill, and a lot of porting. By the way, I am running a 4 barrel intake, with a 500 2 barrel Holley, seems to be better than the Edlebrock I was running on it, and certainly easier to fine tune. Just my 2 cents
My next one is likely going to be a 261. I am going to get ahold of my old buddy Nick Arias and have him make me a set of slugs. This one is going to be simple: deck the block so its square, same with the head. Basic 3 angle valve job and let Arias figure out the pistons to take care of a 9:1 compression, Patricks cam, dizzy from GMC Bubbas class last winter, Dickster-ized BXOV-2's and I am set, the 2 groove balancer we did with BHJ Dynamics, and then I am going to balance the thing to within an inch of its life. Of course it will have to get the ol "no-name" polished valve cover - guaranteed for 10 more HP or your money back If I am not a dumb ass, I'll get the right trans and gears and the thing should do OK for me. Hopefully there wont be any 265's or 283's that embarrass me. I think money well spent on the balancing including pistons and harmonic balancer go a long way to helping this
And I have that block of yours out here! BTW, Mark has those Jahns pistons, we need those right? Thanks for a great thread, I will be watching.
Probably need those pistons as long as Dyce doesnt get too carried away on the head. Have mark send me the specs.
OPPY has already brought up angle milling. We used to over size the bolt holes and push the head as far as possible toward the manifold side of the engine. Remember to connect the steam holes, head to block, as required. Watch the Int. valve to cylinder wall clearance when you do this. These two things put more of the chamber over the piston. It also allows for a larger lump on the piston.
well im an in the midst of building my 261 now. oppy i would have to say bought up so good points. i have a buddy that went all out and spent some time and big money on machine work and parts. but im not trying to build a race motor. just some thing reliable and sounds good. i went 40 over took 15 on the block and 10 on the head side. just to clean it all up and get it square. howard cams has new cams for the 261 in stock. to top it off i have a pair of 94s to feed it. i guess you have to ask yourself how far do you wanna go? that langdons is real sharp and offers alot of speed parts for the inliners. give him a call
I am just trying to build mine kind of old school, or cheap, you make the decision on that. I just know from my race car days that if you build a good solid motor with a lot of stock or factory parts, ie., pistons, rods, crank, etc., they seem to last pretty good. In the plain old hot rod world, the real horse power seems to come from the machine work, and the making love to it. I mean the head, breathing. When dealing with the Stove bolt mill, it appears to me the problem with power to dollars spent stops at the head, I to fall prey to this. I am gonna not stop trying to improve mine. I have read that a cam with a longer duration on the exhaust valve, than the intake will also help in the breathing. There is a lot to all of this, I just like hearing all the opinions, ideas, it's all old school for these old mills, just freshening it up for us younger, newer guy's. Keep posting, I'm listening. As far I know, around here, my 6 is pretty fast.
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