Valve clearance changed

[Kwaka4me]

Hi, I'm new to club so my first post is seeking some help.
Checking the valve clearances on my 1976 Z900 I got a range of clearances from 0.00" to 0.05" so I needed to see what shim sizes I had.
I used the tool supplied by Zpower to hold down the bucket on No 1 exhaust valve while I removed shim to check size, but the tool kept slipping causing shim to jump sideways out of bucket recess. I had to improvise & use a lever on side of bucket to depress & reset shim into bucket top.
I then made a tool similar to the workshop manual which allowed me to remove the shims & check shim sizes.
Just to be thorough prior to sorting new shims I rechecked the valve clearances again & I was more than surprised to find that No1 exhaust is now at 20thou (0.5mm).
The clearance on No1 exhaust valve was 0.03" prior to shim removal & the shim is 270A.
Cams rotate freely & valves all seem to be operating as they should, but It would seem as if something is holding No1 exhaust valve open.
I can't understand why checking/removing shims should cause this problem. Any one had this happen before, or any ideas prior to me having to remove head to investigate further.

[warren3200gt]

When you first checked the gap it was after the engine had been running and the shim was engine run seated.
The oil under the shim was at engine run density. Once you remove and replace a shim the oil pools and you can t put the shim back in with the same seatedness (if that isn't a word it should be) and consequently doesn't give you the same exact reading. Two thou is next to nowt and doesn't need much to make that difference. One of the reasons I alway shim on the high side of gap spec.

[Kwaka4me]

I appreciate that the oil density can make a difference & if it was only 2 thou I wouldn't be worried, but the clearance went from 0.03" to 0.20" (0.5mm).
I just can't understand why it would change so much, unless something has jammed the valve open.
I don't think I have a choice but to at least remove the exhaust camshaft, with the view to removing the head.

[Mr Bump]

I'm a dozy sod (not saying that you are!) so in your position I'd be thinking that i might have made an error noting the clearance down 1st time and I'd want to completely eliminate that risk before taking the head off.

Is the bike in a condition where you can easily run the engine, or at least turn it over on the starter motor?

Doing a compression test should tell you if a valve is not seating properly shouldn't it? Perhaps set the gaps to what seems correct, then do a compression test. Then recheck the shims and run it if all seems good.


If it's throwing up bad compression on that cylinder, making horrible noises or the shim settings will not stabilise then something is wrong.

Keep in mind also that it is possible to be too hung up on precision. Kawasaki set a tolerance of +/- 0.05 mm because that's accurate enough and there may be some inconsistency in measurement.

Olly

[z1bman]

do a compression test that will tell you if the valve is seating ok

[Kwaka4me]

Thanks for replies. I can only think that the pistons caught the valve while holding it open to remove shim, which has bent the valve head slightly preventing it from closing. Whatever it is I need to remove head to check prior to running engine again.

[chrisNI]

It’s quite easy to bend a valve when the shim tool is in you need to be so careful the slightest ding can bend the valve and it won’t close completely leaving you an increased clearance - I’ve done it it was #1exhaust as well

[rickm]

Surely you would only bend a valve if either you force the valve open with the piston at TDC or if you moved the engine position with the shim tool in place (not easy to do, depending on which type of shim tool you're using) ?

[Kwaka4me]

Head removed & found bent valve, but also small depression in combustion chamber wall opposite plug hole, which suggests something has gone into engine in past. Valve seat & valve also heavily carboned up, which also points to previous damage. Funny how bike was running OK prior to me doing maintenance checks, but at least I've found the problem. Fully head refirb to be carried out.