100 Flywheel Weight

[Michael Oritt]

Does anyone know what a stock 100 flywheel should weigh? I am trying to determine if mine has already been lightened.

 

[roscoe]

Michael,
I had mine lightened and as I dimly recall it was 45 or 48 lbs before it was machined. I could be wrong. It is possible that was the weight after I had a bit less than 10 lbs shaved from it. I do know that was roughly what it was lightened by but can't be sure if the 45 lbs was before or after. I think there are plenty of folks who have taken considerably more than 10 lbs off their flywheels with no adverse results. Sorry, who could have imagined that perhaps recording some numbers at the time might help someone in the future......

 

[Michael Oritt]

Thanks Jon. I am going to weigh the flywheel and post a picture showing the back surface. It looks to me like it has been lightened but I could be wrong and if so now is the time for me to have that done.

 

[BoyRacer]

I have a stock flywheel and I'm guessing it's around 35-40 lbs. It's too heavy for my shop scale so I'm guessing based upon the heft of a 3000 flywheel that I know is 28-29 lbs.

 

[BoyRacer]

Update: According to my cheap bathroom scale a stock 100 flywheel weighs 40 lbs.

 

[RCarr]

I get 38lb to 39lb readings on my bathroom scale ... also a cheap made-in-China scale however.

 

[BoyRacer]

Here's my lightened 100/4 flywheel. It weighs just over 22 lbs.

 

[Michael Oritt]

Here's my lightened 100/4 flywheel. It weighs just over 22 lbs.

Richard--

That looks pretty radical though I'd expect nothing less from you,

How do you think taking 20 lbs. off of a street 100's flywheel would affect its driveability?

 

[BoyRacer]

I won't know for at least another year. My chassis is at the stripper so it will be awhile before I can make it a driver. However, I think it will be fine. I have a 22 lb flywheel in my BT7 and I really like it. But that's a 6 cylinder car so I'm not exactly sure what it will feel like behind 4 cylinders. In the past there have been posts by those with similar lightweight flywheels and they were happy.

I wasn't planing on going with one quite so light weight but there was a recent swap meet here in Portland at the All British Field Meet and I found this one for sale. The owner was selling it because he went over to a Tilton aluminum flywheel. That would be a 10 lb flywheel.

 

[Michael Oritt]

At one point I picked up the flywheel to move it onto a table--I don't now want to guess what it weighed but it was heavy. I'll weigh it on my pretty accurate bathroom scale tomorrow and will also post some pictures.

 

[bob hughes]

I had 8 lbs removed from my stock fly wheel and it satisfactory.



Bob

 

[Michael Oritt]

I weighed the flywheel today at 29 pounds. That seems to be about ten pounds lighter than stock according to two posts in this string.
If that's in fact true I'm leaving the flywheel alone. I'll replace the (Toyota) clutch disc, the throwout and the pilot bearings and probably rebuild the slave cylinder while everything is apart and accessible.

I'm attaching a pic of the front (engine) side of the flywheel which seems to show where it was lightened. The pic of the clutch disc shows what the problem was: One of the springs in the disc broke (a remnant of it is alongside the disc). Perhaps pieces of it got into the pilot bearing as when the input shaft was withdrawn one or two balls were missing and the outer race was torn up. In any case this must have been limiting the travel of the throwout bearing making it almost impossible to disengage the clutch.

Does anyone have other suggestions or comments?

 

[BoyRacer]

So Micheal, You have driven your Healey for many miles and were not even aware that your flywheel had been lightened. That tells me that a 29 lb flywheel was not so light that it would be an issue. Based on that information, and the fact that I have a 22 lb flywheel on my BT7 with no adverse effect, I can only assume that a 22 lb flywheel on a 100 motor should work just fine.

 

[BobHaskell]

Michael,
Four and six cylinder engines are different. You might talk to Michael Salter. His Austin-Healey 100 Crank Failures article seems to state that a lightened flywheel is a mixed bag. One of the failures mentioned is the clutch disc spring failure.

 

[BoyRacer]

Here's my conclusion. A big heavy flywheel is good for a big heavy sedan. A lightweight flywheel is good for a sports car.

 

[Legal Bill]

Michael, I’m guessing without knowing that the three indentations in the lower right quadrant of the flywheel picture are balancing relief spots. Maybe I’m not seeing them correctly in the picture, but given the damage suffered by the clutch plate (and not knowing why it happened), I’d bring the flywheel and new pressure plate to a balancing shop to be checked and balanced.

 

[Randy Forbes]

These pictures had been posted here before, but for the sake of consolidation, posted again.

Six (6) cylinder 3000 engine. This conservatively lightened flywheel has been in my BN6 since around 1985.