Hey there lads, quick question.

Bike was idling poorly, and generally not running well at all, cleaned carbs and symptoms remained. Decided to check valves, only to find that it looks entirely possible that they were never checked by previous owner.  I only have a feeler down to .004, and I can't get it under my right exhaust valve.  Cold compression is ok, but when the bike heats up, I lose compression in the right cylinder.  Basically the bike stops running on the right cylinder.  Loosen the cam caps a bit and compression comes back up a bit(not running).  This goes hand in hand with my theory that the shim is too thick on the one side.  The shim is a 268, and I swapped it with the intake, which was a 255, so I am down 12 thou and its still tight.

I am going to go order a 215 tomorrow as a baseline, or should I just pull the head?

Basically what I'm asking is, whats the chance that i just need MUCH smaller shims, or did I likely burn an exhaust valve?

Topher

Well, it is way easier to change shims than pull the head. I'd recommend figuring out what shim size it needs... As the bike heats up, the valve clearance gets larger, so it is possible the bike was running alright when warm... Loosing compression when warm seems opposite of what I'd expect. Are you sure your valve isn't sticking? The the right sized shim in there before you do anything else, then see if your compression problem still exists.

Hard to tell the right shim size when you can;'t get a feeler under?

Get a thiner guage. 1.5 thou is too thick and you're trying a 4 thou.
This is a motorcycle man, not an american push rod V8.
If you rotate the bucket and it spins free but cannot get a feeler guage in (the 1.5 thou) that is still OK, its still not at 0 or tight.
You have a 268 in it. If it is too thick (as in 1.5 wont fit) the damn obvious solution is to try a 265.

The 215 swap causes oil float and you read the clearance lower than its supposed to be, then you put that shim in and its going to be very loose, which will be making tons of noise.

You also cannot spin the motor with a cam cap loose.
You also cannot turn over the motor without a shim in it.
And if you're tight, drop 1 size swap the shims and get it bolted back together and run the bike.
Then if it still is likely to be too thin measure it again after it gets cold.
1 size either way is a really practical way, especially if you're going thinner.

You wont run on 1 cyl after warming up if the valve is tight.
You would lose that cyl 2 seconds after starting and it will come back when you are hot.
Swapping a shim and measuring immediately causes a false tight reading due to oil float. Run the bike and get it through 1 heat cycle. Then test it.

That 215 base line was a shaky concept at best. If anything I'd machine up a bunch of holes in the shim and get the oil into those and use it to test instead of the shim as is. Its got some place to get the oil out from under it atleast.

Now, get the original numbers back in front of you.
If any valve was too tight, drop 1 shim size and this is too tight measured with a 1.5 thou guage not your 4 thou.
If any shim was too loose, yes you can do your calculation about the shim you need etc and fit that it.
Once you fit it in, do not measure it. Nothing is going to be anything other than too tight. Its irrelevant, you need a heat cycle to get it to normal.
So, bolt it back up and ride it, or atleast let it run and see.
Then open up and measure and repeat as needed.
Cool.
Buddha.

Thanks alot, just to clarify, my guage goes down to .004mm, I thought the book said the use a .003?  You mentioned using a .001?

Just a little confused on that. 

I already went down 2 sizes on the shim (from swapping with other shims) and its still tight, as in, I still can't get my .004 in there.  I am going to buy a better feeler right now.

I should also mention, I was able to borrow a 215 from my dealer, he was surprisingly pleasant about lending it to me.  I figure if nothing else, I will have some sort of baseline as to what size I need.

I had a 268, and threw in a 255, and it was still too tight for my feelers, so I figured I had better go way smaller.

.001 min .003 max in inches.

2 sizes is irrelevant, you are floating on oil. Ride the bike then take your next measurement. You can drop 10 sizes and still measure too tight and run like its got a blender full of marbles it will be that loose.

Again 215 is useless. Ride it before measuring and confusing yourself. If you must measure it again, do so after 1 ride.

Cool.
Buddha.

Even with that smaller shim in its place, the bike still didn't seem like it was idling right.  Would it be ok to just idle it for a bit, then recheck?

Quote from: Topher P on March 16, 2009, 12:14:14 PM
Even with that smaller shim in its place, the bike still didn't seem like it was idling right.  Would it be ok to just idle it for a bit, then recheck?

I respect Buddha's expertise, and I love his analysis re oil float, but from recent personal experience, screw all that.  Get a 230 shim in there, crank the engine 6 or 7times with the stator nut (to press out the oil), then check your clearance. 0.230 (the 215 will work too) shim plus gauge minus 0.003 to 0.008 gives you the right shim size.  put that shim in, crank it 6 or 7 times, and recheck.  My bike had 275s in and ran like poop.  I put in 270s, no clearance, ran like poop.  I put in 265s, no clearance, ran like poop.  I said screw this, did my method, came up with 255s, put them in, and it purrs like a kitten.  The thing was off FOUR levels.  Chances are the previous owner figured it was too much of a hassle to deal with the exhaust shims, because it's frankly a PITA.  Chances are good the same is true for you too.

I used an air compressor and blew all the air out of the bucket before putting the new shim in.  Made a mess, but tell me about oil float after THAT!!

I think it is pretty counterproductive to guess at your valve clearance.   Go get some metric feeler gauges that go down to .03-.08mm,  or some good standard gauges that go down to .001.   Measure your clearance correctly, pull the shim and mic it.  Then just get the right shim from the cycle shop and you are done.   If you have to convert from decimal inch to metric multiply by 25.4.   Trust me you will be A lOT happier with the right shims in your bike.   Take your time and do it correctly once.

Remember this is not decimal inch shimming, it is metric, ie., 2,65mm = .1043 inch.   The desired clearance is .03-.08 mm, ie .001-.003 inch.

Quote from: The Buddha on March 16, 2009, 11:51:24 AM
.001 min .003 max in inches.

2 sizes is irrelevant, you are floating on oil. Ride the bike then take your next measurement. You can drop 10 sizes and still measure too tight and run like its got a blender full of marbles it will be that loose.

Again 215 is useless. Ride it before measuring and confusing yourself. If you must measure it again, do so after 1 ride.

Cool.
Buddha.

Buddha; edgeekate me on this.  I am relatively new to the GS500.  My only other shim in bucket cycle is a Honda.  The service manual specifies all clearances are with a cold engine with the oil film removed by compressed air; that is, the float upon oil film and the changes due to hot metal are already figguered into the specs.  Are you saying to measure this one after a ride and with the valve shim seated on the oil film? Or am I mis reading?

prs

Well right now my smallest shim is too tight, so I am going to fire in the 215 and then measure my clearance, and determine the correct sized shim.  And yes I have the proper feeler guages.

SO I threw the 215 in to check and see if I would get compression back, and now I have calculated my correct sizes, but with the 215 in, it still is down a bit on compression.  What are the chances that theres a ton of carbon buildup sitting on the valve seat (due to being run a long time with bad clearances) and that it will seat eventually?

Should I run some combustion chamber cleaner through it?

OK burnt valve/s.
An open shim will not carbon out extra, it will turn ashy white and then like white hot and burn a valve or 2.
Cool.
Buddha.

Quote from: Topher on March 18, 2009, 06:09:37 AM
SO I threw the 215 in to check and see if I would get compression back, and now I have calculated my correct sizes, but with the 215 in, it still is down a bit on compression.  What are the chances that theres a ton of carbon buildup sitting on the valve seat (due to being run a long time with bad clearances) and that it will seat eventually?

Should I run some combustion chamber cleaner through it?

Wait, you've still got the 215 in, but that's not the right shim?  I'm confused...  You ran it with what you knew was a wrong shim and the compression is still bad?

I would tell you to fix one issue at a time in this case.  How bad is the compression exactly?

I can't see what combustion chamber cleaner would hurt, and it might help... why not?

I threw in a 215 and it was way small, lots of clearance, but my compression is still kinda low,.

So the word is pull the head, you dont think I will burn off any carbon and make it seat?

And to extend my though process...

burned valves means pieces of valve missing?

Should be just on the side with the bad clearance??

No point in running it to see if it gets better??

ANybody have a head?
Or is it cheaper to have the work done?

Any chance of piston wash?

Quote from: Topher on March 18, 2009, 06:09:37 AM
SO I threw the 215 in to check and see if I would get compression back, and now I have calculated my correct sizes, but with the 215 in, it still is down a bit on compression.  What are the chances that theres a ton of carbon buildup sitting on the valve seat (due to being run a long time with bad clearances) and that it will seat eventually?

Should I run some combustion chamber cleaner through it?

I would run it and see how it does.  How much is "down a bit"?  I've never even measured my compression!

Mine had one exhaust valve off the seat.  I went down to the correct shim and it ran a TON better, especially coming off idle.  Would it have been better if I pulled the head?  Maybe...

Doesn't cost much to run it with the right shim and find out how it does.  I'd definitely do that before pulling the head!

Quote from: trumpetguy on March 18, 2009, 07:48:07 AM

Quote from: Topher on March 18, 2009, 06:09:37 AM
SO I threw the 215 in to check and see if I would get compression back, and now I have calculated my correct sizes, but with the 215 in, it still is down a bit on compression.  What are the chances that theres a ton of carbon buildup sitting on the valve seat (due to being run a long time with bad clearances) and that it will seat eventually?

Should I run some combustion chamber cleaner through it?

I would run it and see how it does.  How much is "down a bit"?  I've never even measured my compression!

Mine had one exhaust valve off the seat.  I went down to the correct shim and it ran a TON better, especially coming off idle.  Would it have been better if I pulled the head?  Maybe...

Doesn't cost much to run it with the right shim and find out how it does.  I'd definitely do that before pulling the head!

You seem excited by the prospect of pulling the head.  Be careful what you wish for.  I'm with him.  a 7 buck shim vs a heard replacement?  No contest.  Be scientific - start with the easiest solution.  Get the clearance right, spray some cleaner in, maybe some sea foam, run it.  Have you checked things like the plugs, carbs, vacuum?

I'm still not sure on this "Down compression thing..."  Down from what?  Down on both cylinders or one cylinder?

Burnt is just a word for something that has enough grooves and gouges on the edge that it no longer seats and retains pressure.
No chunks missing more than likely.
But I am just saying if a valve was indeed hanging open, that chamber did not have carbon in excess, carbon burnt off and then some of the metal did.
Cool.
Buddha.

Gotcha, thanks man.

As for the other question, compression is down on the right cylinder vs the left.  Head job really doesnt worry me at this point, its like 8 more bolts.