has anyone had this done succesfully? a machine shop is telling me this is the answer to a merc crank that they farmed out and in return was ruined. they are telling me it will be 20/20 when turned.
Without welding up the 3&3/4 crank it won't work anyway I can see. What rods and bearings they think they are going to use??? The offset ground Merc cranks used the 39 [?] rods with full floating bearings and that crank pin was 2" in diameter.
how you get 1/4" out of 20 thou is beyond me.. unless they build up with metal spraying? doubt it though.
I have built a lot of experimental engines . A 460 from a 400 Dodge . 440 CAST crank , mains reduced and rods offset ground 030"" (see Chrysler power mag july 1997 , Econo $1500 Big Block) A 380 from a 340 (4.1 bore, 360 crank with mains ground to 318/340 size and rods offset ground .020"" for a 3.6 stroke)And that was Long before Mopar offered the 360 crank for the 318 340 with the reduced mains. A 482 from a 440 with 4.4 bore and 3.96 stroke . I have made two of these cranks. They are not metal sprayed they are Welded with submerged arc then reground after stress relieving. The prototype I arc welded and had ground. My late uncle Wally (Daniells Welding in Midland Ontario) taught me how to arc weld cranks for repair and strokers. It takes about a month to do the welding. (One weld per day, period. No cheating.) A good weld is strongerthan surrounding material. The second one was done on a Peterson Crank Welder which uses submerged arc. Not as strong but a nicer job and quicker. They are then stress relived by an aircraft stress reliver and then finish ground. Sometimes I nitride them and sometimes I have them hard chromed , (my favourite. ) Once ground I defy any of you to find the weld. Also a 426 from a 400 with a 383 Dodge steel crank welded and ground to provide a 3.53 stroke. This engne ran 10.40s for several years in the MIDNITE MIRADA race car which weighs 3450 without driver. It regularily saw and sees 7800 RPM. I put that last in there because I KNOW someone is going to tell me it cant be done but I refuse to listen to that comment when it refers to something I have been doing for years without failure. Trust your guy, dont second guess him. He knows his craft. Don
I don't think the point is that this is in anyway impossible...the point is that the machine shop is saying that they are going to get 1/4" more out of a flathead crank by just grinding. This is VERY common using 4" Merc cranks (it was done on Ford 33/4 ones before 1949, when there were no 4" cranks) to get 4 1/8. With welding, obviously more is possible, but it does not sound like they are welding, and a welded crank would eat far more money than getting another Merc... The .020 is also being misinterpreted I think...I believe they mean that as just the necessary undersize from offsetting an 010 or so worn crank? The Ford crank could only be stroked 1/8 by offsetting with readily available rods, the smaller (and better designed and more expensive...) prewar rods...this would be the same process used to make a Merc into a 4 1/8.
thanks guys for the info.. i was not buying it when over the phone the shop was telling me what they were doing. this is a standard french crank. the so called flathead mastermind joe fazio of sf flatheads told them to do this. they told me they didnt want to use a **** because they were not made here. i told them i would use the **** and it would be the easiest and cheapest way to get themselves out of this mess that i have been dealing with since feb of this year. thanks again, josh
Maybe off the subject a little, but I have had two Merc cranks offset ground to 1.99 rod journals and the both cranks were .010 under before the offset was done. Both turned out fine and one will be going on the dyno soon.
This is awesome information. Stroker motors rule, you obviously know what you are talking about. You can also use big block chevy rods and offset grind the crank to the smaller end of the chevy rod. The difference is considerable, like 2.75 to 2.2 That is .55 x 2 so you can have an extra 1nch.1 of stroke. Plus chevy rods come in lots of different sizes so you can probably make something work. I just bought a 4.65 stroke top fuel crank off ebay for 100. I guess nobody wanted that much stroke. I had the rods turned down to bbc size, no offset grinding, 4.65 was plenty.The cranks go in chrysler 440's with some modification to the balancer keyway. I figured out a combination with a big block chevy flat top piston and chinese h beam rods.Twenty thousandths in the hole. Pistons and rods were so cheap it was astounding. I think it's 565 cubic inches. I got the compression down with copper gaskets, it's about 12.8 to one Short block about a grand.
IIRC the nominal rod journal of 1939-* engines is 2.139". Regrinding that down to 2.000" increases the stroke by a maximum of the difference between the 2 dimensions (and only if both surfaces are perfect, and the grinder removes .0001" from the outer journal surface). A 4.00" Merc crank cut down to 2.000" journal is anywhere up to 4.139" stroke, usually reduced to 4.125" to allow for refinishing of the full OD. The Ford 3.750" becomes a maximum of 3.889", usually reduced to 3-7/8". This process can also de-stroke the crank by up to the same amount for cl*** size purposes. The error may simply be that many people (and shops who should know better) ***ume that the undercut moves the pin offset by the diametric difference (it doesn't), and that the stroke change is double the offset. Re: "The difference is considerable, like 2.75 to 2.2 That is .55 x 2 so you can have an extra 1nch.1 of stroke. " Chevy BBC: 2.20" rod journal (2.75" is the main journal). Chevy SBC: 2.00" rod (1955-67) or 2.10" (1968-*) journal, Maximum stroke increase: .20" (1955-67) or .10" (1968-*) The 3.76" BBC 396/402/427 crank using the late SBC rod becomes 3.86", the 454 crank becomes 4.10".
Maybe i don't understand the problem, but if you are trying to get back where you started with a 4" stroke, stroking a Ford crank seems to be a lot of effort. You will still have to use full floating inserts (cost and care in setting up correctly). Why not use a **** 4 1/8" or 4" with late inserts? I'm a firm believer in the KISS theory, especially with flatheads. Bet your total cost of their solution including the full floaters gets close to the **** and rods with late inserts.
I could never bring myself to put chevy rods in a mopar engine. To start with they are so short. I would rather use small block mopar rods. Stroking has its limits. Once the stroke exceeds the bore you have to ask yourself what you are doing because it is just very possible you would get more power and reliablilty staying with the stroke 90% of the bore. Now I know my slant six dragster is way out of wack with its 4.12 stroke and small bore. if i could I would reverse that and make it a 3.86 stroke and say a 4.12 bore but alas the biggest bore I have been able to make is 3.565 and only on an old 1962 block. Anyway there is a section in my POLYTEK page that explores the pros and cons of stroking for those who would like to dig further. You will note ALL the V8s I listed fall under the 90% bore/stroke rule.
The Jalopy Journal
