Tight exhaust Valve bucket

ASUDave · February 20, 2012, 09:07:08 PM

I'm sure this has been answered and I've done some searching and read some related threads, but I just want to be sure before I do anything too crazy.

I am doing my first valve clearance check at 7800 miles. I have 2 really tight exhaust valves (less than .04 mm, the smallest feeler gauge I have). I was able to turn the left bucket, pry the shim out, etc.

The right valve is another story. When I turn the engine to line up the cam lobe, its REALLY tough. The lobe above that valve is marred somewhat. When I do finally get it lined up, I can't turn the bucket in order pry the shim. I loosened the cam a bit and am getting clearance now, but I still can't get this bucket to move. I'd rather not have to take the entire cam off and have to redo timing/tension/etc. Any ideas for how to get this thing unstuck?

gsJack · February 20, 2012, 11:08:29 PM

My 02 GS had a too tight valve bucket (tappet) from the factory and a thumb over the hole compression check showed no compression in that cylinder when cold. As tight as that bucket was when cold it would start and run roughly and then quickly warm and loosen the bucket in a minute or so and the engine would then smooth out and run properly for the rest of the day. I let it go for 20k miles hoping it would wear in but it stuck too tight one freezing cold morning and broke an exhaust valve when first cranking that I had to replace. Buckets loosen and valve clearances increase as the engine warms with an aluminum head and overhead valves because the aluminum expands faster than the steel parts as the engine temps increase.

When I pulled the head to replaced the broken exhaust valve on my 02 GS the head of the valve with a part of the stem was laying loose on the piston when the the head was lifted. I could not budge the tight bucket at all to remove it so I took a long pin punch and drove the remaining part of the valve stem back up thru the guide from inside of head and drove out the bucket, springs, and keepers all together and they all fell apart when out of course.

Only good soution to your tight bucket would be to remove the bucket and replace it with a smaller one. Depending on how tight it is you might have to remove the head and heat it to get that bucket out. I ran my tight bucket for 20k miles before it stuck full open one freezing morning and caused the internal collision that broke the valve. Probably if I never started the bike in below 40F or so ambients I'd never have broke that valve but it really needed to be fixed properly to get a measure for a proper size shim. Exhaust valves that are too tight will run too hot without more cooling seat time and eventually receed into the seat and require more and more shim changes to get clearance. My valve check log:

http://img.photobucket.com/albums/v443/jcp8832/GSvalvelogs.jpg

piresito · February 21, 2012, 03:54:56 AM

Listen to gsJack, he is the man!

Also, you don't have to check and pop the shim with the cam lobe pointing up, from what hear you can pop it in other position if it better suits you, thats what I did in mine, altough I didn't have stuck shims/buckets. I've posted a thread about the valve clearance check methods, suzuki way vs kerrys way and there is lots of information in the thread that my help you: http://gstwins.com/gsboard/index.php?topic=58883.0

I think in that thread there is also an example of why re-timing the engine is not a noob task...

SS Adrenaline · February 21, 2012, 06:16:54 AM

While were on the subject of shims I was woundering if some one can explain this it me. How is it that valves can get tight over time when I had thought that as the cam moves over the shim, the shim will wear. This wearing should increase the gap not decrease it? Sorry if this is a noob question I just cant wrap my head around it?

bombsquad83 · February 21, 2012, 07:09:56 AM

Very good explanation of this from BaltimoreGS here...
http://gstwins.com/gsboard/index.php?topic=59057.msg673419#msg673419

noiseguy · February 21, 2012, 08:07:42 AM

Quote from: SS Adrenaline on February 21, 2012, 06:16:54 AM
How is it that valves can get tight over time when I had thought that as the cam moves over the shim, the shim will wear. This wearing should increase the gap not decrease it?

The shim doesn't wear (much). The head material under the valve itself (inside the combustion chamber) wears. So, valve-to-cam clearance decreases over time, as the valve slowly rises in the head.

SS Adrenaline · February 21, 2012, 09:29:22 AM

The specs for our machines are:
Tappet Clearance (When Cold) = (In And Ex) .03mm to .08mm
So, since there is wear somewear in there wouldnt it be safe to get a shim so that its as close as possible to the .03mm of clearance. That way as it wears the space increases eventually to .08mm. By doing this does it not just increase the time befor it gets out of spec?

bombsquad83 · February 21, 2012, 09:34:17 AM

Quote from: SS Adrenaline on February 21, 2012, 09:29:22 AM
The specs for our machines are:
Tappet Clearance (When Cold) = (In And Ex) .03mm to .08mm
So, since there is wear somewear in there wouldnt it be safe to get a shim so that its as close as possible to the .03mm of clearance. That way as it wears the space increases eventually to .08mm. By doing this does it not just increase the time befor it gets out of spec?

Remember, the clearance gets smaller as it wears. This is because valve slowly sits deeper in the cylinder as it wears, putting it closer to the cam. So you would want to be closer to .08 mm when adjusting. Some people have even gone with clearances up to ~.13 mm with no issues to lengthen the time between reshimming. Look at the animation that I linked to that BaltimoreGS posted. This should make it more clear.

piresito · February 21, 2012, 09:48:38 AM

Well, the clearance is measured between the shim and the lobe, not tappet and lobe. So it is called "shim clearance".
From what I understand about it, the issue is that the valve itselt "dig their hole" more and more as they go up and down.
See the picture here http://gstwins.com/gsboard/index.php?topic=59057.msg673419#msg673419

The bucket is that cylindrical shaped thing that goes up and down and contacts the cam lobes. I'm refering to the valve, as that skinny thing looking like a inverted umbrella, that seems to hang down from the bucket, and goes up and down with it. As the engine wears, the valve recess into the head, going up more and more! See, thats not the tappet that recess, its the valve, so they recess into its hole going up & up, until clearance between shim and the lobe gets lower than spec and you need to change the shim.
What is advised, is to run in the largest clearance between spec or even a little above spec so you dont have to change the shim so frequently.

This is my very basic understanding of it, and its subject to "revision" by a hardcore member...

gsJack · February 21, 2012, 10:24:56 AM

There's a big difference between the intake and exhaust valves. The cool fresh fuel/air mix flowing into the cylinder around an open intake valve feels refreshing compared to the red hot burning just exploded mixture flowing out around an open exhaust valve. The exhaust valve needs some time on the seat between explosions to transfer some of the heat from the valve to the seat or the process of the hot exhaust valve receeding into the valve seat over much time will be accelerated.

It's been my experience over many tens of thousands of GS miles that the intake clearances rarely change while the exhaust valve clearances get tighter due to this recession process. One of the exhaust valves in my 97 GS that ran on the tight side of tolerance began an accelerated process of recession and required more and more shim changes after 40k miles and was down to a min 215 thick shim before 80k miles with no place to go. When the tighter exhaust valve in my 02 GS began the same process around 40k miles I began setting the exhaust clearances wider to allow more cooling seat time and the valve recession progress was all but stopped. Now at 92k miles on the engine I expect to go to 100k miles on mid size shims, if I last that long.

I set my valves now at the stock .001-.003" for the intakes and a larger .003-.005" (.08-.13mm) for the exhaust and my stock GS engine is very happy with it. The stock .001 (.03mm) minimum specked clearance is unusually tight for mc engines. If your going to run redline all day long on a modified engine you might want to give some consideration of the possibility of throwing a shim if the clearance is too great and also there is the cosideration of possibly noisy valves with too much clearance. There's no need to run a stock GS over 9500 rpm since power drop off is fast after the 8500 redline. At least I'd suggest setting your exhaust valves to the loose side of the stock specs if you don't want to go wider. If your going to use your GS for only a year or two before moving "up" don't worry about it. Here's the whole log of my experience:

http://img.photobucket.com/albums/v443/jcp8832/GSvalvelogs.jpg

SS Adrenaline · February 21, 2012, 11:11:45 AM

Quote from: piresito on February 21, 2012, 09:48:38 AM
Well, the clearance is measured between the shim and the lobe, not tappet and lobe. So it is called "shim clearance".
From what I understand about it, the issue is that the valve itselt "dig their hole" more and more as they go up and down.
See the picture here http://gstwins.com/gsboard/index.php?topic=59057.msg673419#msg673419

The bucket is that cylindrical shaped thing that goes up and down and contacts the cam lobes. I'm refering to the valve, as that skinny thing looking like a inverted umbrella, that seems to hang down from the bucket, and goes up and down with it. As the engine wears, the valve recess into the head, going up more and more! See, thats not the tappet that recess, its the valve, so they recess into its hole going up & up, until clearance between shim and the lobe gets lower than spec and you need to change the shim.
What is advised, is to run in the largest clearance between spec or even a little above spec so you dont have to change the shim so frequently.

This is my very basic understanding of it, and its subject to "revision" by a hardcore member...

Ok thanks for that, I finally had the bulb turn on. I was thinking that the valve would wear into the top of the cylinder or away from the cam down, not wear out of the cylinder towards the cam or up. This is why the clearance lessens over time and doesnt increase. I know sounds stupid but I was thinking about the wear the wrong way. Oh and Im keeping my GS for as long as I ride. I dont have a need to upgrade.

piresito · February 21, 2012, 11:31:25 AM

I used to think that way too, its the most obvious way if you look from the top!

Bluesmudge · February 21, 2012, 01:23:52 PM

I have just switched my exhaust valve clearance to about .12mm and the bike seems much happier overall. 1 minute warm-up times at 50 degrees F. I am trying to keep the revs below 9500, but I don't think it matters anyways. Hopefully I can go another 20,000 miles before needing another shim change, but we shall see. I have not ridden enough yet to report changes in fuel economy. YMMV.

OP, if you are working in a cold garage, this can contribute to stuck buckets. I had the same problem when I was rebuilding my top end. 2 minutes with a heat gun pointed at the head and the buckets moved as they should. If I had done the engine work in the summer, I may not have noticed stuck buckets.

ASUDave · February 21, 2012, 01:55:06 PM

Thanks guys. I think I'm going to put everything back together the best I can and take it into the shop. The bike is still under warranty, I believe, and I'll let them deal with the stuck bucket.

Btw, I'm in Phoenix. I would think it rarely gets cold enough to affect the bucket that much.

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Tight exhaust Valve bucket