cam chain tensioner - why did i twist it?

[akier]

This is only partially a question - my other reason for posting is that if I was idiotic enough to do this, maybe someone else can avoid the mistake. I just can't believe how stupid I was ...

What happened: My lovely GS450LX runs beautifully until fully warmed up (20 min of riding), when the idle rises to about 2k RPM. Today, it was hot out and I was stuck in traffic. I started worrying about overheating and I decided to adjust the idle speed. I clearly wasn't thinking very clearly because instead of getting off the bike and taking a moment to figure out what I was touching, I grabbed the large knob and gave it a little wiggle just to see how much play there was, in preparation to twist it slightly. Well, suddenly I'm idling at 2900RPM, with all sorts of top end clatter and racket. I pulled over and killed it. Luckily I was right across the street from a bike shop, so I pulled it in there and we pretty quickly found out what had happened.

In my idiocy, I had grabbed the cam chain tensioner (which in retrospect is nowhere near the idle adjust, nor does it look like it). Bad news for the timing and my valves and pistons. But how bad? One mechanic thought that because the bike was still running until I killed it that the valves might not have bent and that with a timing chain adjust and new shims I'd be ok. The other said that it was more likely the valves bent, or worse, that the pistons would be damaged or burned. After twisting the tensioner, the motor ran for probably 30 sec before I got to the side of the road and shut it down.

Anyone had any experience with this? How bad is it? And most of all, why would you put a huge knob on the outside of the head for a noob like me to be tempted to fiddle with? ARRGH!

[Nessism]

Most likely once you get the tensioner straightened out the bike will be back to normal. Worst thing is you bent the valves. Very unlikely there is any significant piston damage.

[Joe Nardy]

If you bent valves the bike would stop running IMMEDIATELY due to loss of compression (don't ask how I know). Most likely the awful noise you heard was just the cam chain rattling around. I'm not familiar with the 450 motor but on all the GS motors I've worked on you can check to be sure the cam chain hasn't jumped any teeth easily. Just remove the valve cover and ignition cover and look at the timing marks and arrows on the cam gears. Any service manual should tell you how to do this.

Thanks,
Joe

[nert]

Sounds like the bike shop you went to does not work on old zukis.
I agree, can't imagine you caused any permanent damage. Properly re-adjusting the auto-tensioner should return your engine to normal.

[DimitriT]

You're fine. I've done this too. It should readjust itself automatically. The tensioner spring applies some pressure to a little locking lever. Whenever there's any slack the level pushes out a little more and the slack gets tensioned out. When you start your bike it may still rattle a little but this will go away quickly once its done retensioning. If it doesn't retension then you got a problem with the tensioner and you need to service it. There's a great web site on servicing the early Suzuki tensioners. It should be in the FAQ,if its not: http://bwringer.com/gs/

The only damage you may have done is the chain may have skipped. But I doubt it as you were just idling.
BTW, 2k idle is way high. Wassup widdat?

[Billy Ricks]

Here's how to service the tensioner.

With the tensioner removed from the cylinder block loosen the lock nut on the left side of the tensioner and back the slotted bolt out ¼ turn. Turn the knob on the right side of the tensioner, which in the Suzuki service manual is called a lock shaft handle, counterclock-wise. As you are turning the knob counterclock-wise push the pushrod all the way back. Keep turning the knob until it refuses to turn any further.

With the pushrod still pushed in as far as it will go tighten the slotted bolt so that the pushrod will not plunge out.

Remount the tensioner to the cylinder block. If the tensioner is not going in turn the crankshaft clockwise slowly to get slack in the cam chain on the intake side of the block.

Loosen the slotted bolt ¼ turn allowing the pushrod to advance towards the cam chain. Tighten the lock nut but leave the slotted bolt loose by that ¼ turn.

While turning the knob counterclock-wise, slowly rotate the crankshaft in reverse direction, counterclock-wise. This causes the chain to push the pushrod back.

Release the knob and slowly turn the crankshaft in the normal direction, clockwise. You should see the knob rotate as the chain becomes progressively tighter. If it does the pushrod is obviously moving forward under spring pressure signifying the tensioner is in good operable condition. If it moves sluggishly or not at all that means the pushrod or the slotted bolt is sticking. If so remove the tensioner from the block again and inspect the pushrod. It could need cleaning or could be bent or galled. Further crank rotation will take the slack out of the cam chain.

[akier]

thanks - now what about my idle?

thanks for all the comments and advice! now, since i don't have a garage i think i'll be taking it into a shop regardless, and it sounds like it's a good idea to take the valve cover off anyways.

so, another question - could my high idle problem be caused by improper valve clearance? it only happens after it's really good and warmed up - normally, it's 1100 RPM steady. a mechanic (but not an old suzuki mechanic) said that a high hanging idle could be caused by that. as long as the top is already off . . .

and is there anything else i should have the shop look out for or take care of while i'm at it? i'm not excited about spending all this money on labor, but if it's going to happen, i'd like to kill a few birds with my proverbial stone.

[nert]

I don't know that 1100 rpm is high for 450. 1000 give or take is usually normal for the 4 cylinder engines. Its definetly NOT related to valve clearance. I think you need to find another shop QUICK!!!!
If you do have a HOT hanging high idle, probably the cause would be a vacuum leak, or cable issue. Where are you located? Shop around be careful. Sounds like these guys could cause more trouble than you started with.

[Billy Ricks]

thanks for all the comments and advice! now, since i don't have a garage i think i'll be taking it into a shop regardless, and it sounds like it's a good idea to take the valve cover off anyways.

so, another question - could my high idle problem be caused by improper valve clearance? it only happens after it's really good and warmed up - normally, it's 1100 RPM steady. a mechanic (but not an old suzuki mechanic) said that a high hanging idle could be caused by that. as long as the top is already off . . .

and is there anything else i should have the shop look out for or take care of while i'm at it? i'm not excited about spending all this money on labor, but if it's going to happen, i'd like to kill a few birds with my proverbial stone.

Possibly, either that or leaky intake.

[akier]

Nert - no, this is just the shop i happened to be close to when this happened, and were nice enough to store it for the weekend. but they don't work on old bikes, so they were just conjecturing. i have another shop to work on it. and the idle is 1100 normally, and gets up to 2000 when hot.

Mr. Ricks - I have a crappy, non-stock air filter in there now - i'm going to swap it to stock. if that doesn't work, check the boots and seals i imagine. i'm just not excited about the inner boots and their rusty bolts having been seated in my head for 25-odd years. i'd hate to break one of those guys. i seem to cause enough problems with my own ineptitude without having to drill out some bolts.

[Billy Ricks]

Nert - no, this is just the shop i happened to be close to when this happened, and were nice enough to store it for the weekend. but they don't work on old bikes, so they were just conjecturing. i have another shop to work on it. and the idle is 1100 normally, and gets up to 2000 when hot.

Mr. Ricks - I have a crappy, non-stock air filter in there now - i'm going to swap it to stock. if that doesn't work, check the boots and seals i imagine. i'm just not excited about the inner boots and their rusty bolts having been seated in my head for 25-odd years. i'd hate to break one of those guys. i seem to cause enough problems with my own ineptitude without having to drill out some bolts.

Valves do tighten up over time rather which causes them to not seal properly. Try squirting some WD-40 around the intakes and see if the idle changes.

[akier]

update

just got her back from the shop - simple cam chain adjustment and servicing the tensioner did it. not half as expensive as i thought. furthermore, the shop balanced the carbs and adjusted the mixture and that seemed to take care of the majority of the hanging high idle issue.

so, in summary, it's better than before. i'm almost glad i'm an idiot haha.

thanks for all the tips and kind words - did a lot to quell my anxiety, thinking i'd ruined the engine.