Broken Shim. opinions needed.

[Sand_fiend]

Im sure i already know the answer.. these were after market e-bay shims... Not OEM.

this is a new motor with about 20 miles on it now.

while finishing up my project, i was doing some fine tuning before getting it registered.

today I heard something coming apart in the top end so i turned it off.
I got the top cover off to find that a Shim had just shattered in to pieces.
it burred the head and the valve bucket got stuck down.

i took the cams out and found another Cracked shim..
these were two of the three i got off e-bay new..

I have the valve to replace but it also damaged the cam lob. So i have to send the cam to mega cycle and have it welded and re ground.

The valve clearance was only about 6mm. stock is 5 to 6mm the cams call for 4mm but it would not idle with them at 4mm.
It has been running great.

what in you opinion's went wrong with these shims ?

Its a 79 550e with a 635 kit in it.
Mega cycle race/street cams.
The valve springs are about equal grams to stock 750 springs

 

[Sand_fiend]

 

[Steve]

The valve clearance was only about 6mm. stock is 5 to 6mm the cams call for 4mm but it would not idle with them at 4mm.

Excuse me??? I don't know of ANY vehicle that calls for 5 to 6 mm of clearance.

Stock clearance on a GS with shims is 3 to 8 HUNDREDTHS OF A MILLIMETER, or just 1% of what you had there. :-k

.

 

[ged]

Been there done that. Same thing, but going abit faster and causing a bit more damage. I try and use the original OEM shims now and avoid these new aftermarket ones.

 

[GregT]

Those broken shims would appear to be too brittle. Over hardened ? Do you have a brand name for them ?

And please advise just what clearances you were running...

 

[Nessism]

Aftermarket K&L shims were pulled from the market a while ago due to crap like that. According to Z1 Enterprises K&L has gone to a new supplier and fresh stock shims should be filling the distribution channel now. I'd be very leary purchasing from an unknown source because you could get the old crap shims. Go to Z1 and get the newest type otherwise you are gambling.

 

[Sand_fiend]

Excuse me??? I don't know of ANY vehicle that calls for 5 to 6 mm of clearance.

Stock clearance on a GS with shims is 3 to 8 HUNDREDTHS OF A MILLIMETER, or just 1% of what you had there. :-k

.

Yes, sorry you are right.. it is i just typed it in wrong.. :-\\\

they are .005 to .006.. i was still kinda ****ed off... LOL..

 

[Nessism]

Yes, sorry you are right.. it is i just typed it in wrong.. :-\\\

they are .005 to .006.. i was still kinda ****ed off... LOL..

The standard spec is .03-.08 mm, or .001-.003 inch. If you have aftermarket cams the specs may be greater though.

 

[Sand_fiend]

Mega cycle cams call for .004.
.005 to .006 was the closest i could get without getting it to tight the other way with the shims i had. i tried the smaller clearance but it did not run good.

 

[Sand_fiend]

 

[trippivot]

nothing went wrong with the shim - they break when impacted - period.

cheap expensive old new - no difference - hit it with a hammer they all fracture.. all they do is take up a little space and leave a little wiggle room. - shim life is to bounce up and down in the tiny recess.

(usually) Mechanical interference causes shim failure . (rarely) material fatigue is the failure.. (racing) both happen and valve float makes it worse.

weak valve springs - smack the piston- break a shim -- wrong lash and it flies out of place - scatter a shim -- shim over bucket and rev it to 11K they will scoop right out.

Just who assembled the top end? --- there is your problem. installed valve height? keeper to retainer clearance, valve tip to retainer clearance, full lift keeper to guide seal clearance, valve to valve clearance , valve to piston clearance, spring seat pressure, lash,


yeah I know - not everybody checks this stuff, which is why there is a thread about brittle shims.

 

[Sand_fiend]

who, if anyone makes an under bucket shim bucket for these motors ?

 

[Nessism]

You don't need shim under bucket for .380" lift cams.

Did you update the valve spring before installing the cams? Trip has a point. Maybe the shim(s) tried to jump out and got stuck halfway and shattered.

 

[Grimly]

The cam ticket clearly says 4 thou, but you're quoting mm in the OP, so what did you actually measure them in?

 

[Sand_fiend]

i said mm at first but that was wrong. they are set at .005 to .006 thou. I had them under .004 but it would not run right.

Yes, They are new springs i bought from Megacycle cams for this setup per their recommendation .

These were 2 of the 3 shims i bought off e-bay. they were not O.E.M. that shattered

 

[Grimly]

I'd be inclined to blame the shims for being sub-standard. Never had an OEM one fail like that, but they can in the right (wrong) circumstances, if not seated properly and get partially spat out. Assuming you had seated them properly and the cam profile is ok, and the right springs were used (as you say), I don't think operator error is to blame here. Too many reports of bad shims in the last couple of years, and as mentioned above more than one dealer is aware of the problem and has taken steps to rectify it once aware. Some sweatshop knocking them out in a far-flung corner, paying little attention to quality control.

 

[Sand_fiend]

I was doing some final tuning when this happened. i had ridden it around my neighborhood off and on for about two weeks getting it tuned in. it had about 6 or 7 miles on it.
I had the valve cover off last week doing a valve clearance check again so i know they were all the way seated..

I talked to megacycle this morning. it's going to a around $70 to fix the lob.
I guess i got what i payed for cheeping out on not wanting to pay for OEM shim's

 

[Guest]

If they were at .006" or .15mm that may be a big part of the problem. That is quite a lot of clearance, much more than the spec. for the cam.

 

[Chuck78]

I fully agree that more than .004" of lash is too much, & with a lumpy cam, you will have a harder impacting motion of the lobe to the shim/bucket.

On the other hand, I have seen many posts of people breaking shims in recent years, sometimes really screwing up their engines. Absolutely none of these that I have seen were OEM shims, always the square edged K&L's with the ink stamps just like the ones this poster broke.

Basically I agree with Nessism&Z1 completely, but additionally would not recommend anyone using this type of aftermarket shim for aftermarket cams or for a bike that sees a lot of heavy throttle twisting action in the upper rpm powerband.

 

[Sand_fiend]

Darn.... to keep it clean.. I just found that the Guide is cracked in three places on this bent valve..