283 flywheel shim

[Stanley S.]

When I disassembled my 1960 motor with 4sp transmission, there was a .050" shim between the crankshaft and the flywheel. The flywheel has casting number 8729004 with casting date E40 for my late May car. I'm reassembling now using the same bell housing, clutch, and transmission. I don't know if the flywheel has ever been surfaced. What is the purpose for this shim? Do I need to reinstall it or can I leave it out?

Thanks.

Stan

[Mike M.]

Re: 283 flywheel shim

never seen nor heard of shim between flywheel and crankshaft ,nor can i image why . but then again, i just got off the boat last month. mike

[David H.]

Re: 283 flywheel shim

Stan

Do you have access to an unused stock flywheel? If so, check thickness.

Spoke to Rick and he indicated, on his race cars, shims were used after flywheel surfacing.

Dave

[Jim L.]

Re: 283 flywheel shim

Stan

Do you have access to an unused stock flywheel? If so, check thickness.

Spoke to Rick and he indicated, on his race cars, shims were used after flywheel surfacing.

Dave

If the shim covers the full 360* of the crank flange and if it is a constant thickness, then the above explanation makes good sense.

If the shim is not constant thickness around the 360* flange, then it's probably there to correct for a warped crank flange.

Same reasoning if the shim covers, say, only 180* of the crank flange... to correct for a bent/warped condition.

Jim

[Stanley S.]

Re: 283 flywheel shim

Dave,

I've attached a photo of what I removed. I don't have a known original flywheel to measure. I can measure mine tomorrow if someone has one not surfaced maybe we can compare.

Stan

[David B.]

Re: 283 flywheel shim

I think you might want to double check your casting #. Should read cast 3729004 which is part # 3739423. Appears correct flywheel. Would strongly suggest reinstalling everything as you found it.

[Joe L.]

Re: 283 flywheel shim

Dave,

I've attached a photo of what I removed. I don't have a known original flywheel to measure. I can measure mine tomorrow if someone has one not surfaced maybe we can compare.

Stan

Stan------

This shim was obviously modified from its original configuration. So, I'd say it could not have been something originally installed at the factory. I strongly suspect it was installed to make up for surfacing of the flywheel. I did not know that such shims were available. However, I think it's a great idea. In fact, it might go a long way towards changing my opinion of using a re-surfaced flywheel.

[Stanley S.]

Re: 283 flywheel shim

All,

Thanks for the comments.

The first digit in the casting # likely is 3. I couldn't decide if it was 3 or 8. The shim is of constant thickness around the perimeter and has .050" stamped. The flywheel thickness measures 1.204" with about .002 variance around the edge. Is this number close to .050" less than it would have been when new?

Stan

[Bill C.]

Re: 283 flywheel shim

Gentlemen,
The shim shown in Stanleys photo is very common and used by a shop or individual that knows what he/they are doing. They have a very important purpose if required.

All GM flywheels of the 50's-60's-70's of our Corvettes and most if not all of GM's line are 1" thick when new from the disc surface to the crank flange mounting surface. Many if not all of our flywheels have been resurfaced, and who knows how many times, or how much. Its very important today dealing with a used factory flywheel ( aftermarket flywheels are NOT all the same, so must always be measure, even if new to ensure that 1" dimension is there) that it is measured correctly and the appropriate shim thickness used to bring back that dimension, I have seen many a used flywheel measuring below .900".

This will change clutch linkage travel and "over center" feel as its moving the clutch assembly that much closer to the engine. The shim moves the face of the flywheel back to its design location.

Dont quote me but I think GM's minimum thickness recommendation was around .950" But there are many being used thinner, they are not raced. Stanleys photo shown is of one MFG design, I suspect it is an ATP unit, designed to accommodate many applications, this on actually had tabs that allow its use on a smaller ID application, designed to just snap off for Stanleys application, which has been done. It was not modified, its just a generic, multi bolt circumference, ID shim. Look close and you can see the slot for the index pin also.

BTW, thats another point, I see so many flywheels reinstalled without using the index pin on the crank. Its there for a reason.

I imagine that back in "the day" these would have been pretty uncommon if around at all. As most flywheels had not been cut or by much at that time. I suggest Stanley remeasure his flywheel at the stated points by laying it face down on a surface plate of plate glass ( Yes, you can use your granite counter top if nobody is looking) as there is no way his stated dimension is correct, I suspect he is measuring total thickness. Whatever the new measured thickness is, subtract from 1.00" and the total thickness shim is the difference, they usually come in .005". .010", .025" and .030". As long as you get within .010" you are OK I know the lack of info on these and the need for them has bitten many and sent many chasing problems with clutch linkage operation, some use an adjustable ball stud to try and make up the difference, and aftermarket flywheels and bellhousings change everything.


I would recomend that Stanley measure his flywheel as stated and install the appropriate shim size needed, which in his case, may be the one already in hand.

These are available through Summit, ATP, Pioneer and many others I'm sure, but here is a pic of one available on Advance Auto Parts website, not certain of this one in pic's specific application, but you get the idea.

[Joe L.]

Re: 283 flywheel shim

Gentlemen,
The shim shown in Stanleys photo is very common and used by a shop or individual that knows what he/they are doing. They have a very important purpose if required.

All GM flywheels of the 50's-60's-70's of our Corvettes and most if not all of GM's line are 1" thick when new from the disc surface to the crank flange mounting surface. Many if not all of our flywheels have been resurfaced, and who knows how many times, or how much. Its very important today dealing with a used factory flywheel ( aftermarket flywheels are NOT all the same, so must always be measure, even if new to ensure that 1" dimension is there) that it is measured correctly and the appropriate shim thickness used to bring back that dimension, I have seen many a used flywheel measuring below .900".

This will change clutch linkage travel and "over center" feel as its moving the clutch assembly that much closer to the engine. The shim moves the face of the flywheel back to its design location.

Dont quote me but I think GM's minimum thickness recommendation was around .950" But there are many being used thinner, they are not raced. Stanleys photo shown is of one MFG design, I suspect it is an ATP unit, designed to accommodate many applications, this on actually had tabs that allow its use on a smaller ID application, designed to just snap off for Stanleys application, which has been done. It was not modified, its just a generic, multi bolt circumference, ID shim. Look close and you can see the slot for the index pin also.

BTW, thats another point, I see so many flywheels reinstalled without using the index pin on the crank. Its there for a reason.

I imagine that back in "the day" these would have been pretty uncommon if around at all. As most flywheels had not been cut or by much at that time. I suggest Stanley remeasure his flywheel at the stated points by laying it face down on a surface plate of plate glass ( Yes, you can use your granite counter top if nobody is looking) as there is no way his stated dimension is correct, I suspect he is measuring total thickness. Whatever the new measured thickness is, subtract from 1.00" and the total thickness shim is the difference, they usually come in .005". .010", .025" and .030". As long as you get within .010" you are OK I know the lack of info on these and the need for them has bitten many and sent many chasing problems with clutch linkage operation, some use an adjustable ball stud to try and make up the difference, and aftermarket flywheels and bellhousings change everything.


I would recomend that Stanley measure his flywheel as stated and install the appropriate shim size needed, which in his case, may be the one already in hand.

These are available through Summit, ATP, Pioneer and many others I'm sure, but here is a pic of one available on Advance Auto Parts website, not certain of this one in pic's specific application, but you get the idea.

Bill------


Most Chevrolet crankshafts do not use an indexing pin. The ones that do include externally balanced engines (400 small block and 454 big block). I believe that 283's also used an indexing pin but I have no idea why.

[Bill C.]

Re: 283 flywheel shim

Hi Joe, you mean they left it out and did not use it? Because all chevy cranks and flywheels I have seen do have it. Even the automatic flywheels. I dont do much with the externally balanced motors.

[Richard G.]

Re: 283 flywheel shim

The pragmatic side of me says the shim would make no functional difference. My bet is the pivot stud length variations could make more difference than a .050 shim would make. I have never heard of a clutch not function because of the flywheel was too close to the crankshaft. So a good idea, possibly.
However, I can also envision the shim causing issues with the flywheel axial run-out if it's no absolutely perfect. I'm going to call it a wash.
Rick

[Joe L.]

Re: 283 flywheel shim

Hi Joe, you mean they left it out and did not use it? Because all chevy cranks and flywheels I have seen do have it. Even the automatic flywheels. I dont do much with the externally balanced motors.

Bill------

If we're talking about the same thing------the dowel pin that is an interference fit in the crankshaft flange and indexes the flywheel, I have not seen such on any Chevrolet V-8 except 400 cid small block and 454 cid big block. Those two engines are externally balanced and the flywheel is counterweighted. This necessitates that the flywheel be installed in only one position relative to the crankshaft and the dowel pin assures this. It's possible that 283's also used a dowel pin but, if so, I do not know why.

Most Chevrolet cranks that I have seen do have a dowel pin hole on the crankshaft flange but no installed dowel pin. I have 2 350 cid engines which I know have never had the dowel pins removed and neither has dowel pins.

In addition, I checked GM sources and GM says that the dowel pins were used only on 70-75 400 cid (never installed in a Corvette), 1970-74 454 cid, and 1955-61 V-8. The dowel pin part number was GM #3701679. It is no longer available from GM.

By the way, the same dowel pin was also later used on 1 piece rear seal crankshafts. Due to the non-counterweighted crankshaft flange on these engines, proper indexing of the flywheel was also required.

[Jim L.]

Re: 283 flywheel shim

It's possible that 283's also used a dowel pin but, if so, I do not know why.

Joe, every 265 and 283 I've worked on has had the dowel pin in the crank flange. Every single one.

[Joe L.]

Re: 283 flywheel shim

Joe, every 265 and 283 I've worked on has had the dowel pin in the crank flange. Every single one.

Jim------


Yes, I think I finally figured out why. Pre 1962 283's, if not all 283's, had a crankshaft without a counter-weighted flange. In such a case, I could see why indexing of the crankshaft flange to the flywheel could be important even though I believe the flywheels were neutral-balanced and not counter-weighted.