OK, so I have my 1999 SBC, err 1965 Studebaker 283 just about ready to go in. I've had it mounted in the chassis once without a flywheel to check valve cover clearance at the firewall and such, but pulled it out to install the clutch and flywheel. This is when I discovered how hard it is to put a 168 tooth wheel into a 153 tooth bellhousing. Ditched the small one on Ebay and grabbed a truck bell locally to resolve that issue. (Thanks to Bib Overalls for pointing me to the adapter ring for the bearing retainer!) My clutch is on the way with all new fasteners etc. All good, right? I'm undecided. In my digging for a bellhousing, I considered a couple of scattershields, but cost is always a factor. All the reading I did turned up some neat articles on bellhousing alignment and adjusting it with the off-set alignment dowels. In all my years building and rodding cars, I used more auto trannys than manual, but I don't know off the top of my head anyone that actually needed to change the dowels and adjust alignment with an OE bellhousing. Have any of you? I understand the consequences of misalignment and how it is corrected, but has anyone ever really measured a noteable misalignment and run it anyway, or experienced a failure as a result of doing so? I know it's more likely to be required with a scattershield, so that's why I ask about OE bells.
The original bellhousing was aligned bored to its block, any swapping risks misalignment. I've dialed in a lot of replacement bellhousings, few were close enough to run without offset dowels. Misalignment can lead to hard shifting, premature failure of the front transmission bearing, clutch dragging, popping out of top gear, etc. The job can be made easier with McRobb dowels, kinda pricey but worth it. http://www.robbmcperformance.com/products/dowels.html
Thanks. I've seen those and would probably pick them over the other options. You say "close enough to run". How much is that? Keisler and Lakewood say anything over .005" off-set is excessive? I'll put a dial on mine tomorrow, so I just need to know what I am looking at.
I have an old shop manual from the early days of the SBC, they suggest maximum .008" lateral runout of the bellhousing hole, and .010" out of parallel (longitudinal runout of trans mounting surface).
I have to agree with Root66 although I could be wrong, but the block and bellhousing were manufactured seperately and only came together in the assembly process. Please read this article by Jerry MacNeish (he published the Definative Book on early Z28's and is one of the formost authorities on 67/68/69 Z28 Camaros in the USA) and see what he has to say about factory specs........................... http://www.camaros.org/bellhousings.shtml The first time I measured a Chevy bellhousing on my 68 Z28 it was .009, and this was a factory 302 with original block and bellhousing. It took me about half a day to get it right. Since then I have used offset dowels on every motor/trans I have rebuilt. IMHO
Hydramatic bellhousings on chevy trucks 54-62 had the Phrase "THIS BELLHOUSING MUST REMAIN WITH THIS ENGINE" cast directly into it. This was due to the fact that they were mated for alignment reasons. Any and all bellhousings SHOULD be checked for misalignment if possable. Check a few and you will know why.
Anybody care to elaborate on just how you go about checking bellhousing alignment? I'm putting a A833 behind my 392 hemi project using a QEC torqueflite adapter (spacer plate portion only) and an OEM small block aluminum bellhousing. Thanks in advance.
A Chopped Coupe, Thanks. That's one I had read. Hemifan, take a look at the link above. That article suggest .008-.009 is tollerable for street type driving, consistent with Squirrel's data. Anyone have practical experience to add?
Remember that there are two things to consider on aligment. One that has not been mentioned is the squareness of the transmission mounting face. I have seen those to be off quite a bit, due to either the bellhousing or the block face not being square. This can be checked with a dial indicator and corrected by shims between the block and bellhousing. A thin shim is all that is needed to correct the squareness. I always like to do that process before dialing in the bore concentricity. The bore will change location when you shim for squareness. I always try for the squareness to be within .002 and the bore concentricity to be better than .005
I thought I mentioned that.... anyways, you check the alignment by sticking a dial indicator to the flywheel or crankshaft, and putting the business end inside the hole, and turning the crankshaft. To check the parallelism of the trans mounting surface, put the tip agains tthe back side of the bellhousing and turn the crankshaft.
Practical experience? Total PITA to check/adjust. I can see why people skip it despite the importance. Can't check it with the engine on a stand or dolly, only swinging from a hook or in the car. PITA #1. Rigging the dial indicator mount in a fashion where it won't wobble .003 during a full rotation, PITA #2 (tip- chineese magnet bases are not strong enough) Waiting 3 flippin days for the right degree pins since they're never available anywhere local, PITA #3 Personally, .008 is my limit, any more and I'm gonna adjust til it's under .004. Learned how to do this after fighting a shifting problem with an OT car. Dialing the bell down from .012 improved it's powershift manners. Flippin PITA though. Hate doing it. If I was gonna buy pins ahead of time to avoid hassle number 3, 006-008s will put most problem bells back into range even if not perfectly centered.
Shifty, PITA #1 can be avoided if you do this early and with just the block and crank upside down on the bench with the bellhousing bolted up. Still not fun, but makes turning easier too.
It sounds like the GM parts are less sensitive to runout or parallel misalignment than the Mopar. The factory service manuals indicate a TIR of only 0.007" for the manual bell in the Mopar family. Note to Hemifan, if you do not have a factory service manual let me know and I'll scan the necessary pages for you so you can see what the details look like. Also, I have offset dowels if you need them; .007, .014, .021. Gary .
I don't build on benches, they go straight to the stand. Cleaning a bench to the point of being able to build a block would take longer than dialing in a bellhousing! The lack of ring drag would be a major bonus though.
Tremec's procedure http://www.classicchevy5speed.com/files/GM%20Dial%20Indicating%20-%20RobbMC%20instructions%20Revised%206-15-09A.pdf Plus if you do not have a bell already they will sell you one that they say is in tolerance. How they can do that when they don't have your motor to set up on is beyond me. It is a Z28 knock off................
I think it's important in a high-performance racing application, no doubt. But for a daily driver? The factory wasn't checking it, they were stabbing them together as it went down the line, an of the hundreds of millions of manual trans cars that were built--including Hemi, LS6 and 427 Fords--I've never heard of one having a trans go out because the thing was misaligned by a few thousandths of an inch. -Brad
This will tell you if the trans is concentric with the crankshaft. This is a Studebaker and after I got it aligned I drilled and pinned the the bellhousing flange to the block so that it will be right if it is ever removed and replaced. Studebaker did this ti every engine on the line so you can't just swap bellhousings from one engine to another. I never did it on a Chevy because they have the big alignment pins. It's probably a good idea to check it on a high winding race engine.
Ok, so here's what I found.... My machine shop gave the nasty sucker a bath, so it was tolerable to work with, but still needs more cleaning. I made sure the mating surface was clean on the block and the bell, then assembled with new fasteners tightened pretty well by hand. My flywheel was already mounted to the block with 3 of the six bolts. Leaving the other three out allowed my magnetic base to sit very soundly on the centerline of the crankshaft over the pilot bearing pocket. I started by checking to see that the trans mounting surface was perpendicular in the manner described above by Squirrel. I set the mag base and post as close to the actual centerline as I could, with extensions to hold the dial indicator parallel to the crank centerline, about 3/16 outside the edge of the register bore. Total variation around the entire circumference, lifting the tip over the pivot ball, was .007", within the .010" spec. Then I used a machinist rule as a straight edge to make sure it was flat in about 6 directions. None of my feeler gauges would go under the rule. Now the big question. It took me about 20 minutes to find a decent mounting position for the dial indicator that would allow a reading inside the register bore, from as near the actual center as possible. I didn't get it perfect, but pretty close. Tommy's adapter above looks like the hot ticket. I started in a friendly place and zeroed the indicator, marked the spot as 0 on the piece, then began slow smooth turns in the normal rotation. I was alone and watching it as it was turned was really difficult, so I made a circuit marking every 45 degrees, then I repeated it half way between those points for a total of 16 points. You can see the numbers for each below. My helper came around about the time I finished and allowed me to observe a couple of full revolutions. Making several passes ensured that the dial indicator base was stable and the dial wasn't jumping or sticking. Marking the readings around the hole made it easy to picture the situation. Negative numbers indicate the bore is farther from the crank than the baseline, positive numbers indicate it is closer. As mentioned before, add the two extremes together, then divide by two in order to find the runout of the bore from the crank centerline. Mine was .005 one way, plus .0025 the other way, so .0075/2 = .00375". That is also within the stated spec of .005" I guess I can sleep at night. One thing to note. The extremes were not directly opposite one another. I would have expected the tight spot to be between the 1 & 2 o'clock positions after seeing the loose spot between 7 & 8 o'clock. It was slightly higher. This might be part of my indicator being just a tad off center, but maybe someone good in geometry can explain it. I don't see it as a major concern on my final math and I seem to have some room for safety. If my understanding of the tangent is correct, the angle of my dial indicator would have exagerated the readings, rather than understating them. I am checking this one off. Thanks for all the imput fellas!
I don't know how "foreign" cars did it but Mopars were align bored with the block, the pic below shows the engine plant...note the second block from the left has the bellhousing attached to an empty block.
This has been a neat exercise for me. I was perplexed by the lopsided split on my measurements, so I mapped them out in a CAD program to see what it really looked like. It turned out exactly as the math said it would (go figure). It was off by .003" in the direction of 7 o'clock. It's really amazing that we are able to measure such minute details in a hobby garage with only basic measuring tools.
Hey look.... This search function thingy is pretty cool..... I might be asking the dumb question of the day,but how are you all centering the magnetic base? If we are talking thousandths of an inch I can't imagine eyeballing is quite good enough??? I usually just throw and go with the bellhousing,and have never had a problem. I figured I have the tools (dial indicator) it would be nice to make sure it is right!!!
you don't need to center the magnetic base. Turning the flywheel makes the whole thing (base, indicator, etc) turn about the center of the flywheel. The tricky thing is making sure the base, indicator, etc don't flex.
I get it... I was looking at it in a backwards kinda way. Kinda like the bellhousing is spinning and the flywheel is stationary. I don't know if that makes sense,but I've got it figured out. Thanks for the speedy response!!!
I always do on applications that are going to be raced. I do the same with automatics, checking off the front pump bore. Less than .005 is what I am looking for, try to get it as close to zero as I can.
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