Flywheel bolts nicked

[Martyn T.]

I am changing the clutch (was chattering) on my 78K '69 350/350 and noticed that the flywheel bolts have been slightly nicked by one of the springs in the disc. It (this spring) is partially torn out of it's socket and very loose. I've been told this may be from the flywheel having been cut too much combined with disc wear. I have never heard anything other than a tired throw out bearing.......Are there specs on the original thickness to check this theory ? What else might cause that ?
I would replace the flywheel anyway at this point, as I don't want to go back in there again. Another question: Does a new replacement GM or other new flywheel need to be balanced ? or at least checked ? I know the clutch should be done separately anyway.
Thanks in advance !
Marty

[Timothy B.]

Re: Flywheel bolts nicked

Martyn,

If you check the archives, flywheel part #'s have been discussed, I think your car used a 14" flywheel 168 tooth but I don't know if it's still available. There should be a taper around the edge and if it's machined past this the flywheel should not be used again.

Always balance the pressure plate with the flywheel, it's not that expensive and the shop will mark the installed position so you will know where to clock it. Some say to take the disc but it spins freely so there is no fixed position. I guess it's a good idea to make sure it's zero balanced also.

[Terry M.]

[Martyn T.]

Re: Flywheel bolts nicked

I thought the 350's at least, were internally balanced motors , so the balancer and the flywheel are neutral balanced, meaning you could swap or replace say a new correct replacement flywheel and not affect the motor.
So I guess in addition to the question what might cause the disc springs to hit the flywheel bolts ? are these motors internally balanced ?
I am replacing the original #'s match motor with a Jasper 383 pre '86 350 block with 2 piece rear main and Jasper said just use my exiisting flywheel. True ?
Thanks,
Marty

[John H.]

Re: Flywheel bolts nicked

I thought the 350's at least, were internally balanced motors , so the balancer and the flywheel are neutral balanced, meaning you could swap or replace say a new correct replacement flywheel and not affect the motor.
So I guess in addition to the question what might cause the disc springs to hit the flywheel bolts ? are these motors internally balanced ?
I am replacing the original #'s match motor with a Jasper 383 pre '86 350 block with 2 piece rear main and Jasper said just use my exiisting flywheel. True ?
Thanks,
Marty

Marty -

Pre-'86 350's are internally balanced, as you noted, with neutral harmonic dampers and flywheels/flexplates. Replacing the flywheel with a new one shouldn't be an issue.

I've only seen disc springs hit the flywheel bolts when the disc was installed backwards.

[Steven G.]

Re: Flywheel bolts nicked

Marty, I agree, I have replaced many flywheels and clutch assys. and never had a balancing issue, the 400 ci s/b definately has external flywheel balancing and will cause a vibration on a 350 ci. but thats another story. Steve

[Stuart F.]

Re: Flywheel bolts nicked

That has been my experience as well. That's only supposed to happen to you once in order to learn it.

Stu Fox

[Terry M.]

Re: Flywheel bolts nicked

John,
I certainly don't want to get crossways with an engineer over the fine points of engine balancing -- but I'll at least give you the chance to tell me where I am wrong.

INTERNAL and EXTERNAL balance has nothing (well at least little) to do with the DYNAMIC balance that was done at the engine plant(s). INTERNAL and EXTERNAL balance has to do with the construction of the crankshaft, damper, and flexplate/flywheel.

INTERNAL balance refers to the fact that the crankshaft has all the weight required to STATIC balance the rotating assembly.

In those engines that were EXTERNALLY balanced, some of the STATIC balance weight is contained in the vibration damper and the flywheel/flexplate -- usually because there was not enough room in the crankcase for the requisite mass to be a part of the crankshaft.

Either style of rotating assembly can be DYNAMICALLY balanced as a complete unit by fine adjustments to the mass of the damper and/or the flywheel/flexplate. It is this DYNAMIC balance to which I refer, and which matches the damper and flywheel/flexplate to a given rotating assembly.

Now do I have that right?

[Terry M.]

Re: Flywheel bolts nicked

Sure and let's not talk about internal and external balancing of big blocks. That one will really lead the uninitiated down the path.

For what it is worth Tonawanda DYNAMICALLY balanced the Mark IV engines during hot test, the same way Flint did with the small motors -- BOTH the internally and externally balanced Mark IV engines.

And yes one can get away without dynamically balancing a new rotating component -- sometimes. I know folks who have not been so lucky. Clint Eastwood's line from one of the Dirty Harry movies comes to mind -- "Do you feel lucky ...."

[Timothy B.]

Re: Flywheel bolts nicked

Terry,

You may be correct about how Flint engine balanced but this is how I always thought it is done during rebuild.

Pistons all made the same weight as the lightest and same with rods. This weight attached to the crank journals and then crankshaft balanced. Balancer and flywheel zero balanced then pressure plate balanced to flywheel.

I can't remember exactly but I think we discussed the factory mark for clocking of the pressure plate to flywheel.

[Terry M.]

Re: Flywheel bolts nicked

Yes, on a rebuild that will work, but the question is, as in this case -- what to do when one doesn't want to disassemble the entire engine.

My guess is the engine plant found it easier to dynamically balance the rotating assembly as a unit and not spend time weighing each piston and rod assembly. As it was they selectively fitted pistons to the bore diameter. I am sure there were weight tolerances for the production pistons that got them in the ballpark in terms of mass.

In the field, particularly the way most of us drive (or in some cases don't drive) our babies, the level of balance used by the assembly plant may not be warranted -- but then if we are restoring the car, why stop short of typical factory production. We have long debates about meeting or exceeding that standard for paint, but think nothing about engine balance.

[Bill M.]

Re: Flywheel bolts nicked

Terry,

You may be correct about how Flint engine balanced but this is how I always thought it is done during rebuild.

Pistons all made the same weight as the lightest and same with rods. This weight attached to the crank journals and then crankshaft balanced.

I think the engine plant added weight to the damper hub and/or flywheel (very small weights) that achieved the same thing as an aftermarket balance achieves by adjusting the weight of the crankshaft. This is what Terry is calling dynamic balance.

If you change the weighted damper or flywheel, that fine tuning done by the plant to the engine's balance is lost (unless you remove the balance weight and add it to the new part in the correct location.)

If you change any piston, rod, or crank parts, I think you want to remove that balance weight from the damper or flywheel and rebalance the rotating assembly, aftermarket style.

[Joe L.]

Re: Flywheel bolts nicked

I thought the 350's at least, were internally balanced motors , so the balancer and the flywheel are neutral balanced, meaning you could swap or replace say a new correct replacement flywheel and not affect the motor.
So I guess in addition to the question what might cause the disc springs to hit the flywheel bolts ? are these motors internally balanced ?
I am replacing the original #'s match motor with a Jasper 383 pre '86 350 block with 2 piece rear main and Jasper said just use my exiisting flywheel. True ?
Thanks,
Marty

Martyn-----


You need to check with them and find out what sort of crankshaft was used. A 383 is, basically, a 350 cid block (i.e. 4" bore) with a 400 cid crank (i.e. 3.75"). Stock 400 cid cranks are EXTERNALLY balanced and require counterweighted balancer and flywheel. However, there are some 400 cid cranks on the market that are INTERNALLY balanced. You need to CONFIRM which one is in your engine. If it's an internally balanced crank, then your existing balancer and flywheel will work. If it's externally balanced crank, you'll need a 400 cid balancer and flywheel.

[Martyn T.]

Re: Flywheel bolts nicked

Thanks for all your help. I had an old hot rodder look at my Jasper 383 sitting on the stand today and he immediately said "that's externally balanced " .The balancer had a large section , what I'd call cut out or missing, the crank had a dowel pin for flywheel alignment and then we opened the box shipped with the motor that contains an auto flywheel and sure enough, it had a good size piece welded to it's inside perimeter. One of Jasper's performance people originally told me my '69 350/350 manual flywheel would work fine. But, when I called today, they checked the production # of that 383 and said that I would need a new flywheel for an externally balanced 400. They said, " that would not have been good " if I had used my original flywheel. WOW ! It would have be fun to discover that out after installation.
Anyway, Summit suggested a RAM 14" flywheel. Any reason not to use that brand ? Should I have the new pressure plate balanced ? any opinion on Sachs or should I go GM here Joe ?

[Clem Z.]

Re: Flywheel bolts nicked

i had i corvette owner bring a corvette around and wanted my opinion on the vibration in the engine. it shook so bad you could hardly hold the steering wheel revving it up in the garage. turns out the previous owner had put in a 454 engine which is externally balanced and used the 427 flywheel and damper.