Shims

Pellet44 · January 04, 2019, 01:29:48 PM

Hi
If this has been covered please point me in the right direction .
I have one cylinder 30psi compression
It still runs.hanging idle.
I ordered some shims for the valve it had a 2.70
In it so I got 2.65 and a 2.60
Still no clearance on .038 feeler Gauge(my smallest )
So I got 2.55 and a 2.50 still no go
The question is
Do I just keep getting smaller shims or could there be something else
Going on ?
Thxs Sean

Pellet44 · January 04, 2019, 01:49:48 PM

I just checked the compression again and the left is 121psi
The right side was 30psi but Is is now 120 psi
So I'm assuming I must be close the right shims.
Should I just order the 2.50 and a 2.45?
Thxs

Joolstacho · January 04, 2019, 02:41:03 PM

I'd just suggest you keep an eye on that suss cylinder, -obviously that valve-seat or valve had been damaged, resulting in it not closing completely (hence previous 30psi).
Is it the exhaust valve?

Pellet44 · January 04, 2019, 04:44:36 PM

Yes it's the exhaust valve on the right hand side
I just did the compression test again this time with throttle open
Both cylinders are st 150psi cold.

twocool · January 04, 2019, 05:10:05 PM

So...my "amateur" diagnosis, is that the valve in question wasn't closing. Thinner and thinner shims....now it closes.

The good news...150 compression, both cylinders... is good ! (always use wide open throttle for compression test)

the bad news... you're getting to the limit on the shim size.

More bad news...what could have possibly happened for that one valve to get so bad?

More bad news...I'm surprised the valve isn't burned...when I had 30 lb compression on my VW bug...it was burned valve...
(but 150 compression means the valve is not burned)

So try to get a valve clearance within limits and go run the bike...what could possibly go wrong?..if it runs, your set...if it doesn't then you have to do a valve job one way or the other...

Cookie

Quote from: Pellet44 on January 04, 2019, 04:44:36 PM
Yes it's the exhaust valve on the right hand side
I just did the compression test again this time with throttle open
Both cylinders are st 150psi cold.

twinstacks · January 08, 2019, 08:06:36 AM

I had the exact same issue. The left cylinder if your sitting on the bike looking forward had zero compression. I stripped everything down and checked pistons and valves and everything was ok. I reground valves back in and changed stem seals and checked for leakages past valves and there were none. I rebuilt engine with new gaskets and again no compression on left cylinder. On further inspection I found all 4 valves were out of clearances and brought 3 out of the 4 back within tolerance but the exhaust valve on left cylinder had to be taken from a 258 down to a 235 and only then did it close but now when it heats up it pops through exhaust on that cylinder and think I need to recheck them all again and possibly put an even smaller one in. Never seen this in all my years of working with bikes.

Pellet44 · January 08, 2019, 05:33:58 PM

So I got down to a 2.40 shim and have .078 clearance on both exhaust valves
Putting it back to get here and hope it runs when I try to kick it over tomorrow.

twinstacks · January 09, 2019, 02:07:10 AM

I think clearance is around .03 on all valves?

The Buddha · January 10, 2019, 02:54:17 AM

I had shims get thicker and thicker on my 50K mile bike. I am not even sure how or why though, but also in 50k miles that bike only went from an average of 250 to maybe 260. Coming to think of it, the thinnest I ever used on it was a 250.
I got a one of ? I ran long commutes in terrible traffic ?
Cool.
Buddha.

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Shims