So i finally got my bike taken apart. I found that both of my exhaust valves are quite bent. It appears taht they were bent by the intake valves pushing them over.  It also apears that the exhaust valves made contact with the pistons. I havent taken out the valves yet.

SO my questions:
*Is there some sort of trick to taking off the head while the engine is still on the bike? I did get it off, but it was a rather rough process: i think i scratched the head a bit.
*Which gaskets will need to be replaced when i put it all back togeter?
*How do you determine if the valve guide is bad?
*How do i know if my intake valves are still good?
*The pistons and piston walls looked fine (no scratches) but are they?

Thanks,
Weston

I'm not certain of everything, but measure the bore of your cylinder from multiple directions at varying heights, ideally the bore size will not change I dont think. 

If you're replacing the valves, you may as well do the guides too, just to be sure, ya know? thats how I look at things.  I dont know of a way to check those, but I figure it never hurts to know they're good 100% which may or may not be correct logic.  if a piston made contact with the valves, I would inspect the pistons as well for damage, and replace as needed, all 4 valves would PROBABLY be prudent if you want to be 100% since a piston made contact, its possible that more than exhaust valves made contact.

Seems you have a 1990 GS with about 20k miles on it and the bent valves resulted from doing a wheelie.  Probably did some serious over revving for a moment to cause the valves to float and colide.  I've managed to ride over 375k miles without ever thinking of doing a wheelie, must be the generation gap.   

I broke an exhaust valve with about 21k miles on my 02 GS and also broke off part of the valve guide that extends into the port.  Didn't replace the guide; just put in a new exhaust valve, lapped in the intake valve to make sure it was straight, replaced the sticking bucket that caused the problem and put it back together with new head and cylinder base gaskets gaskets.  Have over 66k miles on it now and it never ran better, expect it to go 80-100k miles.



Replacing valve guides is a major project that many shops won't tackle but there is no reason why yours shouldn't be OK with only 20k miles on the bike.  Valve seals might need replacing due to the age of the bike, old low milage bikes frequently have seal leakage problems due to dried out seals.  Only about $4 a piece I think.  I put 0ver 80k miles on my 97 GS with no signs of excessive valve seal wear though.

You can lap in the intake valves with valve lapping compound to make sure they are straight and will seal properly.  Shouldn't be a problem with the pistons or cylinder walls with only 20k miles on the bike if you didn't visibly damage the pistons.

Removing the cylinder head with the engine in the frame is a very tight fit as you discovered but it is doable.  I had to remove a small wire harness and clip from inside the right side of the frame to squeeze the head up and thru.   

Quote from: gsJack on November 24, 2008, 09:27:54 AMI've managed to ride over 375k miles without ever thinking of doing a wheelie, must be the generation gap.   

I'll agree with GSjack.  Get your new valves and a tube of Prussian blue.  Clean the seat gently with Scotch Brite, then put a thin layer of Prussian Blue on the seat.  Gently install the valve in the guide and push it down into the seat with 40lbs or so of force, DON"T TWIST IT.  Then, WITHOUT ROTATING the valve, push it up with your finger from the camshaft side until you can grip the stem from the combustion chamber side.

The valve should have an even ring of blue all the way around the face.  If so, everything is OK.  If not, check for dirt.  If there isn't any dirt on the seat or valve, lap the valve into the seat to try and improve the seating.  If the valve only prints on one side of the circumference, the guide is bent. 

Inspect the pistons carefully for damage from the valves.  If you see no damage, the bottom end should be fine.  Also, inspect both necks of the valve guide for cracks.

I agree with Bob as well.  Remove the intake valves and print them as well.  Just because they don't LOOK bent doesn't mean they aren't bent.

Bikebandit.com is a good resource for exploded parts drawings and prices.  My dealer charges the same as Bikebandit +- a couple percent.

Thanks for the advice guys. I need to track down a valve spring compressor before i move forward, but yeah Ill test the intake valves, and just lap them back in if i can. Then try the exhaust guides with some new valves and see if they are good and hopefully just lap them in as well. Ill check back later....

Welp, i made a valve spring compressor and took out the valves.  Guides look and feel good. All four valves are bent though. So... I might just buy the head thats on ebay right now that has all the valves in it... since im already looking at over $100 in new valves.... plus oil seals.... anyway, does this sound like a good idea? or should I just install new valves in my current head?  does anyone know where you can get cheap valves?

Quote from: Weston on November 29, 2008, 03:11:22 PM
Welp, i made a valve spring compressor and took out the valves.  Guides look and feel good. All four valves are bent though. So... I might just buy the head thats on ebay right now that has all the valves in it... since im already looking at over $100 in new valves.... plus oil seals.... anyway, does this sound like a good idea? or should I just install new valves in my current head?  does anyone know where you can get cheap valves?

the problem with used parts is, they're used. you might end up with an even worse bent valve, or worn guides.

i'd do the work on the known animal, instead of inviting (paying for more parts) the unknown into the shop.

Quote from: gsJack on November 24, 2008, 09:27:54 AM
...the bent valves resulted from doing a wheelie.  Probably did some serious over revving for a moment to cause the valves to float and collide.

I'm missing something, how are bent valves related to doing a wheelie? I understand the concept of floating valves and know its caused by over revving but how does this happen when doing a wheelie? It would make more sense it the driven wheel was off the ground but thats obviously not the case. Can somebody help me feel less stupid?

Clutch/throttle timing?  Weston's description of the causal incident:

http://gstwins.com/gsboard/index.php?topic=44915.msg503108#msg503108

Quote from: ohgood on November 29, 2008, 04:00:10 PM

Quote from: Weston on November 29, 2008, 03:11:22 PM
Welp, i made a valve spring compressor and took out the valves.  Guides look and feel good. All four valves are bent though. So... I might just buy the head thats on ebay right now that has all the valves in it... since im already looking at over $100 in new valves.... plus oil seals.... anyway, does this sound like a good idea? or should I just install new valves in my current head?  does anyone know where you can get cheap valves?

the problem with used parts is, they're used. you might end up with an even worse bent valve, or worn guides.

i'd do the work on the known animal, instead of inviting (paying for more parts) the unknown into the shop.

Agreed...  Fix what you have, it is known quantity.  You never really know what you're getting when it comes to used parts on Ebay.  You can't pick it up, inspect it from all angles, take appropriate measurements, etc.

I've bought bad parts on Ebay and had to fix them.

ke7syv: it was a pretty pathetic wheelie... and it ended with a pretty hard landing. I suspect that the timing chain jumped on only one of the cam sprockets from the impact. Right now the bid is only 19 bucks, so i think ill see if i can get it on minimum bid since thats less than the price of one valve, and since its prettier than mine anyway.  But otherwise ill replace the valves all arround. I am on a tight budget.We'll see how it goes i guess..

Well, I ended up getting the head on ebay for 30 bucks shipped. I took out the valves and inspected the guides. Guides are as good, possibly better than the ones on the old head. All in all it is in better shape. So while I had the valves out i decided the ports needed to be cleaned out because they had alot of carbon in them. Anyway, one thing lead to another and before long I was doing some porting and polishing. I did this using a drill so it was nice and slow and controllable for a noob. I ended up mostly just smoothing out all the casting errors and sharp edges and shortening the valve guides down. After that i cleaned up the old valves and lapped them in nice. Here is what it looks like now:

Tell me what you guys think!

Looks good. While you have it off, check the alignment of the carb boots to the intake ports. You make need to clean up the ports some so they flow smoothly.

Another thing since the exhaust is off, clean up the welds on the inside of the headers. I have seen excessive welds restricting exhaust flow.

Good suggestions. Ill try to do that.