Valve replacement

[natelust]

So i want to replace the valves on my bike (gs 650) this summer, the problem is i cant find any were to buy them from! does anyone know where they can be obtained?

[Don-lo]

Why do you want to replace them? Do you know that some are burned? These valves are very durable, and usually just need cleaned and lapped.

[natelust]

re

well i just figured that they had not been changed in the age of the bike, so might as well while replacing all of the gaskets. I have a oil leak some where, as per the cloud when i accelerate. I didnt want to need to rush and order some if i found out there was a problem while doing the replacement, but if you think it is fine...

[nisom512]

well i just figured that they had not been changed in the age of the bike, so might as well while replacing all of the gaskets. I have a oil leak some where, as per the cloud when i accelerate. I didnt want to need to rush and order some if i found out there was a problem while doing the replacement, but if you think it is fine...

how many miles on your bike?

[Steve]

There is a very good chance that your valves are still good.

You say you leave a cloud when acellerating? That is most likely the rings. Depending on the mileage on the bike, you could get by with a hone job and new rings. While you have the head off, change the valve stem seals. You will have new seals in the gasket kit, you may as well use them. While you have the valves out, check to make sure they are not too loose in the guides, then lap them into place to make sure they have a good seal, and put it all back together. Pay particular attention to exactly which 650 you have when you are reading the manual. Some things are just a little different, like the pin count on the cam chain when re-installing the cams. I forget the exact numbers, but I seem to remember that the E model (chain-drive) has one count for cam chain pins, the G models (shaft-drive) have a count that is one pin different. Just be sure which section of the manual you are reading and you will be fine.

.

[Don-lo]

The valves have hardened surfaces, veryyyy durable, but occasionally can get burned due to lean mixture. Much more likely source of smoke are old valve seals: the rubber fatigues from heat eventually. Most of the time, refurbing a head consists of disassembly, cleaning/decarboning, checking valve guides, replacing valve seals and gaskets.

How many miles on the bike? It would be good to verify the rings are sealing before top-end work, so you can decide if you want to go into the pistons.

[chef1366]

If it smokes at hard trottle it's most likely rings. If it smokes all the time or at cold startup it's probably valve stem oil seals.

[Nessism]

well i just figured that they had not been changed in the age of the bike, so might as well while replacing all of the gaskets. I have a oil leak some where, as per the cloud when i accelerate. I didnt want to need to rush and order some if i found out there was a problem while doing the replacement, but if you think it is fine...

I suggest you take your cylinder head to a machine shop that knows motorcycles. They will tell you what need to be done. Ordering parts that may or may not be needed is silly.

[natelust]

I have around 35k miles, but the bike was not taken care of very well before me. You say it is probably rings? as in rings around the pistons? I dont know too much about that. how much trouble is that? what does that entail? i have only heard about it in passing

[Nessism]

Sounds like you need to remove the cylinder and pistons (number them before removing) and take them to the machine shop as well. Have them measured to check condition.

Doing a top end rebuild is not a trivial matter but it's not rocket science either. I trust you have a manual. If not, get one and start educating yourself. Learn to use the Advanced Search function here as well. Lots of good information available. To seek is to find.

[Dave_17954]

I lapped my valves during my rebuild on my 1981 gs650gl. I would guess if it smokes on acceleration sounds more like a ring issue. If I was taking it down that far I would do a re-ring/hone, valve guide seals and decarbon and lap the valves. Heres a pic of one of my valves and this was before I lapped them. I used to have a slight smoke issue upon starting but none now since my rebuild. I had 32,000 miles on mine when I done mine. Would definately seek out a good machine shop and service manual to gain some insight. Like was said its not rocket science but you do have to be very carefull and dont rush it.

[Don-lo]

Nice pic Dave. It gives people some detail as to what they are looking for. Obviously the pic was after the cleaning / decarboning. That seat looks a little pitted. Did you get a smooth continuous seal line after lapping?

[Dave_17954]

Thanks Don...yes I hand lapped all valves/valve seats and then after reassembling done a leak test per the service manual. Actually found one that was still weeping but I relapped it and after rechecking it it sealed up fine.

[doctorgonzo]

That was about the condition of mine, maybe mine a tad worse, I re-cut. Lapping probably would have done it, but APE had the head anyway, so went ahead and did it.

[mike_of_bbg]

I have around 35k miles, but the bike was not taken care of very well before me. You say it is probably rings? as in rings around the pistons? I dont know too much about that. how much trouble is that? what does that entail? i have only heard about it in passing

Yes, rings around the pistons.

I agree that smoking on acceleration probably means worn rings. However, you might want to invest a few dollars in a compression tester, or see if a friend has one that you could borrow. Then run a wet/dry compression test on your motor. A compression test is a really good indicator of the overall health and wear of your motor. It's something good to keep track of over the life of your bike.

Run the motor long enough to get it pretty warm, then take out all of the spark plugs. Screw the compression gauge into each spark plug hole one at a time, hold the throttle wide open, and crank it until the needle stops rising (probably 6 or 7 revs). Note the dry numbers you get. To get the wet numbers, pour about one teaspoon of clean oil into the cylinder through the spark plug hole (this helps to seal the rings temporarily), rev it a couple of times to distribute the oil, then hook the compression tester back up and run it again (remember to hold that throttle open!).

Your warm, dry compression should be above 100psi. Probably 120, 125 or higher is really where you want it (do a dance if you get 140+ ). The cylinders should be fairly even in compression, less than 20 psi different. Your wet numbers should be about 5-10psi higher than dry. Particularly on a hot motor, if your wet numbers are 20+ psi higher than your dry numbers, you are in definite need of a ring job.

What does a ring job entail? Not 100% sure about the 650, but on the 550 it is theoretically possible to service the rings and cylinders without removing the crankcase from the bike. You do have to be very careful about not dropping things (like wrist pin clips) into the open crankcase though. Someone will also surely point out that if your rings are that worn you might want to have a look at some things in the crankcase anyway. Assuming you go on with just a ring job, you'll have to remove the carbs, disconnect the exhaust, remove the valve cover, camshafts (& timing chain), head, and then finally the cylinder block and pistons. It's not really difficult, but an ambitious job for someone with no experience or lacking in mechanical confidence. Wrench-headed friends that can be bribed with cheap beer and pizza are particularly handy. How are you doing on tools? Definitely have multiple manuals in hand. Check BikeCliff's site for the factory manual, then go buy the Clymer or Haynes manual (or both) as well.

Assembly is the reverse of disassembly. Hey! I just wrote a Haynes manual J/K