Ok, my problem is NOT the cam chain itself, but cam timing..

[Dave_A]

Here's what I have:

I was riding to work on Monday. I had just changed the oil & cleaned the carbs Sunday. The bike started making an odd rattling/buzzing sound over the 'normal' engine noise as I left home. I stopped, checked the cam chain tensioner, and it was real loose (rattling around)... So I assumed that the problem was cam chain tension, tightened the tensioner down a few turns, and rode on. The noise was still there, but not as bad...

Well, a few blocks later, the bike DIES. I am idling at a stop, and I loose power completely...

I try to re-start, and the bike cranks but will not start. After a few start attempts, a final start attempt leaves the bike jammed so that the starter will no longer turn over. I assume the cam chain is busted, and roll it to a nearby parking lot untill I can get a van to bring it home...

Well, today I got the van, brought it hoime, and took the valve cover off...

Cam chain is there, in one piece, on the sprockets...

So I take the right-side cap off (the one that lets you get at the bolt on the side, so you can hand-crank the engine), and hand crank the engine. it will turn backwards (and the cam moves properly), but it sticks trying to rotate forwards (at a certain point)... It does stick a bit going backwards as well...

So, any ideas what's wrong...

I'd like to know where to look before I rip off more covers, and need to replace more gaskets...

As a summary:

The cam chain tensioner is shot (won't hold setting), but the cam chain is fine...

It is not a reg/rect problem. I had enough electrical power to crank the engine AFTER it stalled

There IS oil in the engine, so it should not be an oil-related issue... My oil pressure indicator is functional, as well. It did not light up untill after the engine stalled (like it does whenever the engine is off)...

This happens in neutral AND in gear, so it is not a tranny problem...

Any ideas???

[Don Lobacz]

Most likely your loose cam chain jumped a tooth or 2 and is now bending valves as you rotate the crank ESPECIALLY backwards. When you get the 1&4 "T" mark to line up on the crankshaft, the arrows on the cams should be aligned with the top of the head (all the cam-chain slack should be at the back).

Another slight possibility is that the loose sound was the starter clutch (behind the rotor) and it finally came completely loose.

[Dave_A]

Most likely your loose cam chain jumped a tooth or 2 and is now bending valves as you rotate the crank ESPECIALLY backwards. When you get the 1&4 "T" mark to line up on the crankshaft, the arrows on the cams should be aligned with the top of the head (all the cam-chain slack should be at the back).

Another slight possibility is that the loose sound was the starter clutch (behind the rotor) and it finally came completely loose.

I have a 2cyl bike, and the chain appears to be properly tensioned (goes straight across between the 2 cams)... It APPEARS that the valves are moving in and out properly as the bike turns, and the resistance is at a single point. I have not (and will not) attempted to force it beyond that point: I just stop turning...

A) If the valves move properly (couldn't see in the poorly lit garage... I'll check tomorrow, in daylight), does this mean they're not bent???

B) I assume the starter is under that rectangular panel that sits below the carbs?? Or is it behind the left-side crankcase cover (i.e. the part that's like the one that encloses the clutch basket, but on the other side of the bike)???

[saaz]

I agree with Don. The cam chain will jump teeth if you loosen off the tensioner and turn the motor slowly (trust me, experince talking!), so imagine what it will do with a loose cam chain whene the motor is going.
carefully check the cam timing as per specs and get the tensioner working before running again. The timing as per Don said, on mine (GS1000) the front sprocket is the only one with an arrow that should point to the gasket base, 20 pins (including pin on top of arrow) between the exhuast and inlet cams where the arrows point up)

[Don Lobacz]

The valves will still open and close even when bent, but they do not seat and seal completely: excessive valve clearance and loss of compression are the indicators of bent valves. Cam chain tightness between the cams is meaningless if the cams are out of synch with the crankshaft.

[Dave_A]

Ok, I'm going out to look at the arrows...

[Dave_A]

Ok...

I have both side covers off, and the starter is not interfering (turning the crank forward manually, the starter gears do not turn, but the crank does). Also, with the clutch plates removed, I can see that my bind-up is not in the transmission...

Back to the head:

The bind-up occurrs when the left-cylinder exhaust valve is about to open (regardless of the direction of cranking). It sounds like it's coming from the crankcase, or the left cylinder...

Now, back to my description, and your posts:

IF the cam chain did come loose and jump a tooth on the exhaust sprocket, I can see that causing the stall-and-no-start (if the exhaust valve opened early, there'd be no compression, and thus no start).

Now I was able to crank it with the starter a few times trying to re-start, and then it bound up after a few starting attempts. If I continue on the jump-a-tooth theory, then this might mean that it jumped again due to starter cranking, causing FURTHER mis-timing to the point where my left exhaust valve(s) (82 bike would be a 4-valve per cylinder head, right????) became unintended piston stops???

[Dave_A]

CONFIRMED:

Timing is off, and the valves are opening as the piston is trying to reach TDC... Instead of reaching TDC, the piston hits the open valve... It hits the intake valve when cranked backwards, and the exhaust valve when cranked forwards...

Now...

This piston-hit-valve problem was caused by my re-start attempt after the bike stalled. Prior to that, it was cranking over properly... The only pressure that has been applied to the valves by the piston has come from (a) the starter, and (b) me cranking slowly with a ratchet...

Is either enough to bend valves??? Should I take the whole head off & inspect the valves, or just fix the timing???

Also, there are no 'arrow' markers that I can see. The sprockets say 'IN' or 'EX', have a few 2-digit numbers and the engine-size on them. The cam-ends have rectangular slots, and the top of the head (where those chrome end-caps would go) has a hand-painted white line.

Where are the marks I need to line up???

[Anonymous]

Is either enough to bend valves??? Should I take the whole head off & inspect the valves, or just fix the timing???

You may be able to get away with just doing a compression test after you've fixed the timing problem -- maybe one of the "experts" can confirm this guess.

Michael

[lhanscom]

Is either enough to bend valves??? Should I take the whole head off & inspect the valves, or just fix the timing???

You may be able to get away with just doing a compression test after you've fixed the timing problem -- maybe one of the "experts" can confirm this guess.

Michael

Might as well try, if there bent it will show in the compression test, and you may get lucky.

[Anonymous]

The rectangular notches will be even with eachother at TDC compression. ie. they will be opened towards each other. I don't know where the crank should be with regards to the timing mark.


Steve

[Dave_A]

The rectangular notches will be even with eachother at TDC compression. ie. they will be opened towards each other. I don't know where the crank should be with regards to the timing mark.


Steve

Right now they're not even close...

It's more of a 'V', with one up, and one off at an angle...

[Don Lobacz]

Someone with a manual for your bike will have to send you a picture of your specific setup - our guessing will not be good enough. You really should have a manual yourself. Also, don't do any further testing without resetting the timing AND getting your tensioner to work (or get a new one). After you do that, then check the compression for both cylinders.

[Dave_A]

Someone with a manual for your bike will have to send you a picture of your specific setup - our guessing will not be good enough. You really should have a manual yourself. Also, don't do any further testing without resetting the timing AND getting your tensioner to work (or get a new one). After you do that, then check the compression for both cylinders.

I'll be going to get a Clymer manual from the library tomorrow (that's what I used to get the bike running when I bought it)...

IIRC, there was a section on cam timing...

[Anonymous]

I've also got the Clymer manual if the one in the library is out. It doesn't have my bike in it but its half decent.

Steve