I am currently in the process of replacing my clutch on my 150.
The flywheel on my car measures 29.8mm thick.
At this measurement I have approx. 4mm clearance from the friction plate spring housings to the flywheel/crankshaft bolt heads.
When is it time to replace the flywheel? Is the original flywheel thickness known?
Regards to all
John Ledbrook
John
It will only get thinner if you have skimmed it, If it has been skimmed a couple of times only then one should replace, otherwise you never have to replace it. My non skimmed original flywheel measures 1.495in just under 1.5inches.
Where are you measuring , 29.8 is way too thin. 1.495 is 37.97mm. I am measuring with calipers over the top of the teeth of ring gear.
Morris
Thanks for your reply.
Yes I am measuring from the back of the
ring gear to the face of the flywheel with callipers.
That’s a lot of difference, 8mm.
Other flywheels I have measured are in the 32 /33mm area. I have owned this car
for fifty years and I can only remember it being skimmed once and that was recently.
On your figures it is definitely time to
start looking for another flywheel. Aluminium or steel ?
Even though they actually have a steel insert friction surface, you won’t get 50 years out of an aluminum flywheel. And it’s fairly pointless if the engine and drivetrain are standard. Should be plenty of good steel ones around.
1 Like
I replaced my flywheel with a Fidanza lightweight, made a vast difference in engine performance and quick revving, with no effect on idle speed, well worth the money. Regards Morris 150 ots 830933
Thanks Morris and Mike.
That’s two different opinions for me
to think about. My car is an original 3.8 S FHC RHD.
I will go to the market now and check the
price range and availability.
Off topic, at the moment while the
northern hemisphere is in a cold snap, I checked the temperature reading on my
cars temp gauge with the car sitting in my garage, with the engine alongside on
the floor , 48degrees C. It has been a bit hot here!!
Lightweight flywheels and I go way back. I installed my first lightweight flywheel in my 1968 Camaro around 1972, a 15lb, nodular iron, low inertia unit from an L88 427 Corvette. I was 19 at the time. The benefit depends a great deal on your driving style. A lightweight flywheel allows the engine to rev more readily, but it can also be a bit trickier to pull away from a dead stop. I actually have a Tilton Engineering aluminum flywheel behind a heavily modified 3.4 in the 120 now.
1 Like
john.
are you able to post pics of your old flywheel particularly the engine side keen to see if the XK150 S had the lightened flywheel as per the 120 and 140 spl equipment
terry
John
Terry McGrath made me look into Viarts book , lo and behold the ‘S’ 150’s already have a lightened flywheel so don’t go looking for another, Standard flywheel part number is C 4809 and the S is C5808.
Regards Morris.
I used a Tilton multiple-plate flywheel/clutch assembly, in my Datsun 1200 race car. It was about the most expensive part of the engine (costing 1200 1984 US dollars, with adaptation costs) and it was a bear to get it off the line–coupled with the fact of its 305 degree duration cam.
In autocross form, the only viable leave-the-line technique was 7000 rpm, then slide your left foot off the clutch pedal!
It did, however, allow a 10,500 rpm redline: I tried lightening a stock 1200 flywheel, for street, but rapidly returned to the stock weight.
Mine is a single disc, but I have driven a friend’s big Healey race car which had a sintered metal multi-disc clutch. That thing was like a light switch, either on or off, nothing in between. Getting out of the pit stall was an adventure.
1 Like
Thanks Morris. Yes I did know the “S”
models had lightened flywheels as standard equipment, but did not have that
part number, it must be hiding somewhere in that spare parts manual!!
Any idea as to what the original flywheel
weighed? My flywheel is 8.1kg’s, weighed on the bathroom scales??
150 S flywheels might be a bit tricky to
find!
Regards
John
My non ‘ S ‘ flywheel weighs 29lbs or 13.15 kg , a difference of 5kg or 11 lbs. Can you send up some heat its - 6 here and heading down , and we live in the banana belt of British Columbia 
1 Like
on this forum in the depths of history I will think you will find exact weights as I am sure we have been over this subject.
The interesting thing is that whilst the part number C4809 is stamped on all the standard flywheels I have never seen the C5808 stamped on a Lightweight wheel. I think that the standard wheel was turned down to make an S wheel and part number went west
1 Like
I see a 7R number on my 21.5 lb. flywheel. Thickness is 1.330. I believe the original weight for XK flywheels (Inc. Mk7) was 28 lbs. I have two other flywheels that measure about 1.380. Over the years I have seen at least two different ways weight was machined from the back of an otherwise std flywheel but I can’t say if that was from Jaguar or local shops.
Terry
There is no sign of a lightweight flywheel in the parts book for the 150 and 150 S, the only number quoted is C 4809.
I know that’s why I asked for a photo of the engine side of the one in john ledbrook’s car. I am sure they have or meant to I erven think the 150S sale lit mentions it
Here is a photo comparison of a factory XK lightweight flywheel (not stamped with any part number) and a heavy flywheel from a 4.2L E-Type (originally fitted to 7E13502).
the 132 tooth wheel on left is the XK lightweight wheel never seen a part number on one
there is a factory lightweight flywheel for the 3.8 litre E type 104 teeth and I think all 3.8 E types had the lightweight wheel
I think the 4.2 wheel is 133 teeth?
I am away from home at the moment, will
see if I can remember how to send photos when I return.
John