81 GS750E Valve problem (I think)

[Guest]

Hey guys and gals,

I'm brand new here. I was gifted a 1981 GS750E this month. It had been sitting unused for a couple of years. The friend who gave it to me replaced the battery, changed the oil, and put in new spark plugs. Magically, it ran.... for a few days.

I had my brother-in-law ride it, and he told me the secondaries weren't opening up on the carbs, but I could ride it that way for a couple of weeks until I had a chance to dig into it. I took it out yesterday, and had it wide open in 4th gear and noticed I was going 45. Then at the next stop sign it died. I FINALLY got it restarted with full choke and a lot of throttle, and basically rode the clutch a mile home until it ultimately died in my neighborhood. Boy, this is a heavy bike to push home. After it cooled down last night, I got it started again, but same problem after it warmed up.

I plan on giving the carbs a good cleaning, but visited the, "Help, my bike won't run" sticky, and saw that, "Valves>Catbs)".

I watched a youtube video on how to adjust the valves on a GS, and consulted my Clymer manual, then dug in. Got the valve cover off, turned the crank to the correct position, and went to check the clearance on the 4th cylinder. This is where I discovered what I believe is a problem. The arm rocker has a ton of play to it. Please watch the video below, and tell me what you see. Let me first say, this is the first time I've been inside the valve cover on any vehicle, and I know nothing about what it should be like, but it doesn't seem right to me.

https://youtu.be/nG87B3dYsFo

If the YouTube link doesn't work, you can just search my username there (Revbsclark).

Thanks in advance for your help.

[Steve]

"A ton of play" doesn't even come close to describing what you have. I have NEVER seen that much play on a GS valve. Yes, "play", because it's too much to be called "clearance".

You should have heard that. Well, you might have, but didn't know it wasn't proper. That is one good reason that you were not going quickly, those valves were probably not opening at all.

Please don't rely on your brother-in-law for advice on this bike. There are no secondaries on the carbs. There is little doubt that the carbs are operating properly (probably because they need to be cleaned/rebuilt), but there are no secondaries.

To adjust your valves, loosen the locknut on the rocker arm, turn the setscrew until it just about touches the valve stem. Repeat for the other adjuster on that rocker. Insert your feeler gauge, turn the setscrew in until there is just barely some drag on the feeler, tighten the locknut. Repeat on the other adjuster.

On your bike, with the cams positioned the way you have them, there are four pairs of valves that you adjust, then rotate the crank 360° and do the other four pairs. Since you have the luxury of setting them to whatever clearance you want (within limits), go for a clearance on the larger side of the range. The range for your bike is 0.09-0.13mm, so I would shoot for 0.12-0.13mm. When they are all adjusted, I would use the electric starter to crank the engine for a few seconds to make sure everything is seated, then re-check the clearances to be sure they have not changed. Be sure to only do this with a COLD engine.

Since this bike is new to you, it would be good to check some things to establish a good baseline. After adjusting your valves, do a compression check. If the valves have been abused previously, they might be burnt and not sealing properly, yielding low compression numbers.

.

[Revbsclark]

Thanks for your reply. Truly appreciate your help.

"A ton of play" doesn't even come close to describing what you have. I have NEVER seen that much play on a GS valve. Yes, "play", because it's too much to be called "clearance".

You should have heard that. Well, you might have, but didn't know it wasn't proper. That is one good reason that you were not going quickly, those valves were probably not opening at all.

I'm not sure what I would have heard, but I did hear a "clank" when trying to start the engine. To be honest, I've never had a vehicle this old (that still runs), and there are lots of noises I'm not used to.

To adjust your valves, loosen the locknut on the rocker arm, turn the setscrew until it just about touches the valve stem. Repeat for the other adjuster on that rocker. Insert your feeler gauge, turn the setscrew in until there is just barely some drag on the feeler, tighten the locknut. Repeat on the other adjuster.

On your bike, with the cams positioned the way you have them, there are four pairs of valves that you adjust, then rotate the crank 360° and do the other four pairs. Since you have the luxury of setting them to whatever clearance you want (within limits), go for a clearance on the larger side of the range. The range for your bike is 0.09-0.13mm, so I would shoot for 0.12-0.13mm. When they are all adjusted, I would use the electric starter to crank the engine for a few seconds to make sure everything is seated, then re-check the clearances to be sure they have not changed. Be sure to only do this with a COLD engine.

To verify, are you saying not to do anything with that rocker (other than set the clearance)? I could be wrong, but I think I could lower the setscrew all the way, and it still wouldn't come close to being within .005" of the valve stem. I can certainly try it, but I don't think the setscrew is long enough.

Also, do I crank the engine for a few seconds (with the starter) with everything still opened up (valve cover still off)? Again, sorry for the noob question.

Since this bike is new to you, it would be good to check some things to establish a good baseline. After adjusting your valves, do a compression check. If the valves have been abused previously, they might be burnt and not sealing properly, yielding low compression numbers.

Will do. Just have to research how.

Thanks again!!!

[Revbsclark]

Ok, I have new information that may help...

I went out to the garage just to see if the set screws were long enough, and the valve stems were touching the set screws in the full, upright position...

So, apparently, the rocker is pushing the valve stems down, but they are not coming back up right away like the other cylinders do.

I guess I would call them "sticky" as opposed to "stuck", because they did eventually come back up.

I cranked it by hand a few times, and they're back down again...

Thoughts???

[Steve]

Sounds like your engine might need a bit more than a valve adjustment.

If the valves are slow to come back up, it sounds like the stems might be bent. Bent valve stems are usually only caused by a piston hitting a valve face. Pistons hitting valve faces are not 'normal', that is usually caused by over-revving the engine.

Valves with bent heads will not seat properly in the head, which will result in greater clearance at the other end, where you are measuring.

To replace a valve that has been bent, it would be wise to also check/replace the valve guide in the cylinder head, to make sure it hasn't been stretched beyond its limits. There is also the possibility that the piston has been damaged by the contact, but you won't know until the engine is opened up.

To answer your other question about cranking the engine, yes, crank it over with the valve cover off and the spark plugs out. It will not be going that fast, so nothing is going to fly off, but watch the pools of oil around the valves to make sure they don't overflow onto the engine and your floor.

It's a good thing this bike was a gift. Depending on what all is found in the engine and who does the work will determine the repair cost, but plan on at least $500 for parts and gaskets. If you are mechanically-inclined (and can follow instructions), you can do the work yourself. Carbs should be cleaned/rebuilt. About $50 for parts and supplies to do it yourself, $150-200 for one of the several member who offers that service to do them for you. You should also plan on tires and brakes (including pads, new hoses and rebuild kits for master cylinders and calipers). After all that, it will be safe enough to ride, then you can concentrate on any cosmetic issues. Overall, plan on spending about $1000 to get it on the road safely.

.

[Nessism]

Looks like bent valves. Both valves in that same cylinder wouldn't be sticking open at the same time. Most likely there is some cam chain timing issue and the piston hit the valves bending them, thus the clearance since the valves are not closing.

[Revbsclark]

More new information...

I am planning on pulling the top end off and checking the valve stems when I have time. Today I had a few minutes to get started, so I pulled the spark plugs, and the number 4 plug looks like this...

20180927_163715.jpg

I'm guessing that points to the same problem???

[Revbsclark]

Better pic

20180927_163726.jpg

[standswithabeer]

wouldn't bent valve(s) on a cylinder result in zero compression? lacking a compression tester, one could plug #4 with a finger while thumbing the starter button. or, try starting the bike. #4 will be cold.