just took measurements on the cam/shim clearances on this '00 GS. Check out these results:
Lefthand cylinder
Intake: .53 mm - No, I didn't forget a zero! :mad: The clearance is literally 10 times what it should be
Exhaust: <.04 mm - Not really suprised by this, I've read that they tend to tighten up over time.
Righthand cylinder
Intake: .21 mm - Also wildly out of spec :mad:
Exhaust: .04 mm - again, not suprising
So wtf happened to this bike? I'm afraid to start it up and risk grenading the engine (if it's not already screwed). It's only got 7k miles on it and it's been sitting for the last 2 years. Has anybody ever seen results like these? I don't have the bucket-depressor tool so I haven't taken measurements of the shims yet. What should I do?
-M
What do the plugs look like?
Is the compression good?
If so then you probably don't have carbon build-up on the valves. That means that the last guy in the valve cover probably couldn't use a feeler gauge to save his life.
As far as what it can do, that depends. Check the cam lobes for spalling, and if they're OK don't worry about it.
High valve clearances cause the valves to open late and close early while increasing the acceleration forces within the valvetrain. This can cause increased wear on the cam lobes over extended periods.
With only 7K miles on the clock it shouldn't have needed a cam valve check, unless a over-enthusastic novice mechanic tried and botched a check at the break-in serviceing. Perhaps the EX and IN shims got installed "backwards"?
Before you start tearing at the cams. I would check three things first.
1) Take the carbs off and shine a bright flashlight down the intake ports and manually crank the engine around slowly looking at the vavle seats. Look and see if any gunk or carbon chips might be on the seats holding them slightly open and throwing off the clearances. Spray a good bit of carb cleaner down there for good measure before going on to 2.
2) Manually turn the crank around a few times to make sure there are nothing hanging up and then crank the bike over a few times. This will settle the vavles and should give you a good "working" vavle clearance.
3) If they are still off, measure what difference should be, and then pull out the exhaust shims and see if perhaps they would be a better fit.
If they are still off I guess its time to order some shims, eh? Make sure you post what shims are in there now. They are probably tiny
little thing.
Good luck,
James
Thx for the replies guys. I'm going to go check the condition of the valve seats and cam lobes right now. I went ahead and ordered the motion pro depressor tool so I'll be able to yank those shims out next weekend hopefully. Guess I'd better pick up a dial caliper before then too.
-M
I hope that's not true, but bent valves could give that result as well. You'd have next to no compression then, though.
With large clearances like that be sure to check for sticking valve buckets. It has happened, buckets fit too tight in the head at factory. Does it run OK after it starts to warm up? The tight buckets will loosen as soon as the head starts to warm and run like nothing is wrong.
On the valves with the big clearances, turn the cam lobe away from the bucket and see if you can turn the bucket with your fingertip. If the buckets are fit properly they will turn freely with your finger tip or a screwdriver pushing in the notch. If you have tight buckets, they must be fixed before valves can be adjusted.
Update
Ok, I put the bike back together tonight and it turns over but won't start. This is the first time I've tried to start it, as far as I know it hasn't run in two years. I have a few ideas as to why. It might be fuel pressure; I didn't reinstall the tank but just hooked a hose to the carb input to fill the buckets. I don't know if that's sufficient to get fuel moving through the carbs; I don't see why it wouldn't be.
Upon examination the cam lobes seem to be fine with no gouges or spalling. The valve seats are a mess; shining a light into the intake manifold reveals a build up of black gunk. I don't know if it's varnish or carbon, maybe a mix of both. I hit that with some carb cleaner to clean it up a bit. The engine has compression, but it feels low. Putting my thumb over the plug holes I can feel puffs of air but I was able to hold it there fairly easily.
I'm planning to tear it back down tomorrow and check the valve clearances again. Maybe I'll get different readings having given it a few good cranks. If I see the same results I guess I'll pull the head and have a look.
-M
3/21 Update
Last night I started the steps to remove the head. I got everything except the shims/buckets out before running out of light (I hate not having a garage!) The cams look ok; there is some very slight wear on the faces but I think it's normal. Running my fingernail along the surface I can just barely perceive a difference in texture. I'm going to leave them alone for now unless advised otherwise.
Tonight I plan to get the head off and clean it up. I hope the stock gasket is in good shape so I can re-use it. If not I'll have to wait for a replacement. Here is my theory about what happened:
The last owner put the bike away with the petcock in PRI (it was in PRI when I picked it up). Over the course of time the seals in the carb float valve failed and gas flooded the carb and into the intake manifold (this would explain the absolutely nasty state of the carbs when I opened them up; gunk and varnish totally coating every surface and moving part). As the gas dried it left deposits which are preventing the intake valves from fully seating. This would explain the huge shim clearances and low compression. What do you guys think?
-M
That would make sense to me, especially since it's only the intake valves with the issue.