Thrust washers odd

(Jim XK140 FHC) #1

I have a little too much end float (019mm). I have standard washers fitted(2.34mm) . Is it ok to use one larger washer and one standard ? That will bring me back to spec . Should the large go front or back ?
Thanks Jim

0 Likes

(Mike Spoelker) #2

The thrust wear is generally due to the pressure from the clutch pressure plate, so if I had to mix them, I would put the thicker one to the rear. Before I did that, I would make really, really sure that that few thou didn’t do something unintended up at the distributor and oil pump drive end of things.

1 Like

(Robin O'Connor) #3

Mike, thicker one to the rear? Isn’t the thrust from the clutch towards the front of the engine so the thicker would be on the HB side of the crank. Its probably a moot point really though as the wear is fairly low I think.

0 Likes

(Jim XK140 FHC) #4

My common sense approach is that these washers, are sold singly rather than pairs.Each washer is + 4 thou over standard.
I think the spec for end float is 4- 6 thou. . If you have between 7 and 11 thou float a correction cannot be achieved if fitting an oversize pair.
I can’t imagine front or back would make a whole lot of difference, but that is my guess.

0 Likes

(Robin O'Connor) #5

Just for clarification Jim what is your end float at present?
.019mm 0.19mm 1.9mm???
You did not identify a decimal point (BTW the 1.9mm is totally tongue in cheek :slight_smile: )

0 Likes

(Jim XK140 FHC) #6

My float is 0.19 mm maybe 0.20 mm = 7.5 to 7.9 thou

0 Likes

(Mike Spoelker) #7

With every gear change (or sitting at idle with the clutch pedal depressed) the thrust from the action to release the pressure plate would push the crankshaft forward. The thrust bearing on the rear of the center main bearing restricts that movement.

0 Likes

(Mike Spoelker) #8

The bombproof fix for this is to have thrust surfaces ground undersized to suit the next standard oversize bearings.

0 Likes

(Robin O'Connor) #9

So 2 x +.004 would give 0 end float and 1 x std + 1 x +.004 should be in spec, correct?
And thinking about it it really dosen’t matter which goes where.

0 Likes

(Christopher Potempa) #10

Would placing shim stock cut to size with a pair of scissors next to a thrust washer also be acceptable? I would think something so thin if placed next to the bearing cap followed by the thrust washer would be okay. The recess is deep enough to retain it in place and there would be no movement against it. Plus you’d able to set the thrust gap to a higher order of exactitude than using stock thrust washers alone. I ask because I’m at the same point in my rebuild as Jim. Am I missing anything here?

0 Likes

(Jim XK140 FHC) #11

Thank you Robin
You are correct . I will try the thicker one both sides but I don’t think it will make any difference . I guess the front one takes the most punishment , so I will fit the new one there
Christopher , perhaps a shim might work , but I would be happier with a correct washer if you can achieve it .
Jim

0 Likes

(Paul Wigton) #12

Not a chance would I do such s thing: tooooo much opportunity for a catastrophic failure.

There is no need to improve upon the factory range.

0 Likes

(Christopher Potempa) #13

Okay, I understand it sounds/ reads as a hokey fix but from an academic standpoint, how would it fail? For instance, if an oversize thrust washer of 0.004" larger is needed and all one has on hand are the standard size thrust washers, what would be wrong with inserting an 0.004" shim between the bearing cap and thrust washer? Both shim and thrust washer sit in a recess. I can only see it failing if there’s some sort of rotational force on it. In that position, there’s none there. The thrust washer would have to fail in some way first before the shim would fail.

0 Likes

(Paul Wigton) #14

Try it in your engine: get back to us in 100,000 miles.

I’ll be interested in the results: in the meantime, I think I’d prefer doing it the right way…:grimacing:

0 Likes

(Robin O'Connor) #15

Worst case basis it should work, as you say if it is trapped between the thrust washer and the crankcase then it really has nowhere to go, but I agree with Wiggles, better to go with what Jag supply if you can get it into the required value(s)

0 Likes

(Christopher Potempa) #16

My end float measures 0.006" using the standard size thrust washers so it looks like I won’t be able to continue to stir up the pot here with my idea for what reads as a blasphemous fix.

0 Likes

(Jim XK140 FHC) #17

6 thou is within spec isn’t it ?
I also have a correction , the new washers are sold in pairs not single .
Jim

0 Likes

(Mike Spoelker) #18

Did mic the bearings you removed? Was one thinner than the other?

0 Likes

(Jim XK140 FHC) #19

That is a very good point Mike.
Just measured mine . If I add the thickness of my new pair and subtract the the thickness of my old pair , I get 8.66 thou = 4.33 thou average each . So pretty much no wear on the old ones as the new ones should be +4 thou ( if they are correct size ).
It does seem pretty poor just to offer one size of oversize and why sell them in pairs ? who is going to need to make up add 8 thou ?

0 Likes

(Mike Spoelker) #20

If you are already having the mains ground 0.010" cleaning up the thrust faces to the next oversize would be a logical course of action.

0 Likes