Question about 3.8 etype flywheel 104 tooth

gsv · Post by **gsv** » Mon Apr 20, 2015 5:28 pm

Is there a minimum thickness for a flywheel?

Does anyone know the original thickness from the base of the ring gear to the surface of the flywheel?

I'm looking at at least 40 thousands off mine and it probably was resurfaced once before I owned the car.

Any help at all would be GREATLY appreciated!!

gsv · Post by **gsv** » Thu Apr 23, 2015 7:06 pm

any thoughts at all?

what was the original thickness of a 3.8 flywheel? from base to face?

Gfhug · Post by **Gfhug** » Thu Apr 23, 2015 7:50 pm

Have you tried contacting any of the engine overhaul companies? My guess is they are more likely to know this than the forum members

gsv · Post by **gsv** » Thu Apr 23, 2015 7:55 pm

I haven't. Do you know of a good one that could advise me?

Gfhug · Post by **Gfhug** » Thu Apr 23, 2015 9:13 pm

You could try Rob Beere or VSE engines. Both are spoken of highly on the forum

PeterCrespin · Post by **PeterCrespin** » Thu Apr 23, 2015 10:40 pm

Sorry. Missed this. The important dimension is the 'web' between the hub and the heavy rim. It's the thinnest section but not easily measured accurately as it is rough and uneven at the back.

I just measured two 4.2 flywheels at the rim as 34.66 and 36.23 mm. The 4.2 is thicker than the 3.8 and the 3.8 comes in two flavours itself - standard and light. All XK flywheels are tough steel, not cast-iron, and are therefore unlikely to 'grenade' and take your ankles off. Why are you taking so much off the front? Is it so badly scored? If you are trying to reduce mass you need to work on the back and especially the rim.

I think you'll be fine, but my opinion is worth what you pay for it...

Pete

gsv · Post by **gsv** » Thu Apr 23, 2015 10:55 pm

it was very badly scored and apparently had been resurfaced unevenly by a previous owner...or bad clutch wear or something b/c one 1/3 was worn more than the rest! Not trying to lighten it at all.

I cannot get a good measure of a 3.8 in it's original state, but I was wondering if it was thinner, so that is good to know.

I've had 2 different machine shops who've done jags for 30+ years say I'd be fine But I had one guy say he had one blow out on him when it was on a dyno and went thru a wall. It had a 'micro crack' that he hadn't seen before. Seeing as how I'm fond of my legs I thought I'd do some asking.

David Oslo · Post by **David Oslo** » Mon Apr 27, 2015 11:31 am

Given that you've posted question on Series 1 and Technical I thought that I'd reply both places :D

I'm at work and my flywheel is at home so I can't measure, but doing some ballpark calcs I get a 40 thou (e.g. 1mm) skim to be around 1 lb in weight reduction.

This is based on inner / outer diameter of the surface being skimmed being around 360mm / 240mm (guestimation)

Not sure if this helps, but maybe puts things a little in perspective, at least if you know how much has previously been skimmed.

gsv · Post by **gsv** » Tue Apr 28, 2015 10:49 pm

thanks David. any and all help is appreciated.

if you have a chance to measure from the base of the ring gear to the surface of the flywheel. I'd be curious to know that too.

gsv · Post by **gsv** » Mon May 04, 2015 7:42 am

For what its worth. A machine shop measured a 3.8 flywheel for me and it was 1.278 inches. He was not sure of the history on it

Dave K · Post by **Dave K** » Mon May 04, 2015 2:09 pm

This probably of no help but I read somewhere that the 3.8 flywheel weighs between 18 and 22lbs.
It appears mine was lightened at some stage because it weighs 18lbs or slightly less now because I had it tub ground when I rebuilt the engine.

Dave

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