Broken Shim. opinions needed.

[Guest]

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.

.

[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.

.

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