Fly Wheel lightening...?

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Dave in Spokane

Member
Went with the suggestions in my past post, I bagged the 11"set up for my mildly built '40 engine and went with a new Ft. Wayne 9"clutch and pressure plate and just had my stock '40 fly wheel turned. I heard of people lightening the flywheel by cutting down the lip on the clutch side. Good idea or not and if so how much do you trim it down? Thanks again for all of your help. Dave in Spokane
 
Absolutely a great idea! Machining off that lip and using a 9" clutch removes considerable weight from that area, result being a more responsive throttle response, and the old engine will still idle smoothly! Nicer feel at the clutch pedal too. I actually adapt Auburn 9" pressure plates into all my builds instead of the 9" Long PP, to further remove total weight, and they hold up, even behind a 284 in motor.
 
Dave in Spokane said:
Went with the suggestions in my past post, I bagged the 11"set up for my mildly built '40 engine and went with a new Ft. Wayne 9"clutch and pressure plate and just had my stock '40 fly wheel turned. I heard of people lightening the flywheel by cutting down the lip on the clutch side. Good idea or not and if so how much do you trim it down? Thanks again for all of your help. Dave in Spokane
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Turn the lip off and that will get you to about 25 lb...Any more that you can take off wiil be almost unnoticible...Those things have a nasty habit of exploding when made super light and turned 5000.

Be sure the guy you have rebalance the assembly knows how to do it right..
If you are balancing the whole crank assembly, after the crank is done, the flywheel ONLY is bolted on the crank. It is balanced. Then the clutch cover is bolted on. It is PUNCH MARKED and the FLYWHEEL is punchmarked also for indexing. Then the cover is balanced. It is done by drilling the spring guides..NO WELDING weights on...If you have to weld weights, get another cover. You can't balance the disc with the assembly because it is constantly changing relationship with the cover..It is possible to balance the disc by itself on a seperate arbor.

If you are not balancing the crank assembly, this whole procedure is done with an arbor that the flywheel bolts to..It is a good idea before you start to give the arbor a quick spin to check balance and make sure it hasn't gotten dropped and bent etc since the last time you used it.
If you do it by this method it is a good plan to check the runout of the flywheel flange first.
I forgot to mention previously but the crank flange should be checked for runout before balancing the flywheel on the crank.
 
What Pete is talking about here here is exactly what has just been done to my flywheel and clutch. There was a .006 runout on the flywheel on the clutch side and .002 on the engine side. The clutch cover got quite a few holes drilled in it before it was right, and the whole assy ended up at 0.08gram out. Personally I think it was overkill, I told him it's a 4000rpm flathead, not a 9000rpm SBC race motor, but the guy builds race motors, and I think old habits die hard! :D
 
So if I'm reading this right, you should balance a flywheel and pressure plate without the disc installed? I had mine balanced and have a consistant bad vibration around 3000 RPM. It's definitely not drive line related and I installed everything according to the indexing marks on the flywheel and pressure plate. Help!
 
Right or wrong I have balanced my flywheels and p-plate without the clutch disk and no pilot bearing (but I believe that has more to do with the balancing equipment vs anything else).

I also shaved the large lip off of the 9" flywheel in my avatar - a lot of weight saved with it gone ....
 
flathead4rd said:
So if I'm reading this right, you should balance a flywheel and pressure plate without the disc installed? I had mine balanced and have a consistant bad vibration around 3000 RPM. It's definitely not drive line related and I installed everything according to the indexing marks on the flywheel and pressure plate. Help!
Click to expand...

Every time you disengage the clutch, the disc changes position in relation to the flywheel and clutch cover. If it is out of balance and you balance it at one place, it can be out everywhere else.
 
I read everything I could read on flywheel lightening then decided to only have the lip turned off my 59A with a 9" clutch. I was after 24lbs on the flywheel but have not weighed it after balancing.
 
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