Timing chain skipped, now what?

[JRHemmen]

I was on my way to inspection (for the second time) and my bike cut off. It made an awful sound when I tried to crank it so I walked it all the way home and opened it up. The timing was way off and the chain tensioner was spinning when I cranked it, something it shouldn't be doing. I've put 50 miles on the bike so far, I guess the tensioner just loosened up. Anyway, I reset timing, put it back together, and cranked. It spun freely, but there was no pumping sound like air being compressed. I did a compression test and got 0 psi. So are my valves bent? They look fine to me, they all seem to be seated properly. I believe one must have hit a piston though given how the piston looks. What do I do?

I'm so tired of running into new problems on here. I spent 5 months and all of my money building it, I just want to ride it.

Untitled by Bobertbarker, on Flickr

Untitled by Bobertbarker, on Flickr

Untitled by Bobertbarker, on Flickr

 

[dantodd]

Ouch. Sorry man. That is royally screwed. The valve definitely "interfered with the piston and based on zero compression the valve stem is bent, it is very possible that the piston is also a total loss. A used engine is probably cheaper than a full tear down and rebuild if the piston(s) are ruined.

 

[JRHemmen]

I have a second set of valves from a second head I had to buy while rebuilding, so at least I don't have to pay for those.

 

[roeme]

Visually they may seem fine - but only because very few people will be able to make out hundreds of a millimeter by eye. The valve is surely a goner.

I don't think one can get away with a new valve and redoing the seat in this case; but I'd wait for someone more knowledgeable to chime in. It might be possible to replace the head including valves.

 

[dantodd]

I have a second set of valves from a second head I had to buy while rebuilding, so at least I don't have to pay for those.

It may be possible to replace and seat new valves. You'd still have to pull the cylinders and check the piston, rod, bearings, etc. before deciding if a simple valve and seal replacement will help. There are lots of people here who can help with that diagnosis, I'm not there yet so I'll leave that part to them.

 

[JRHemmen]

It may be possible to replace and seat new valves. You'd still have to pull the cylinders and check the piston, rod, bearings, etc. before deciding if a simple valve and seal replacement will help. There are lots of people here who can help with that diagnosis, I'm not there yet so I'll leave that part to them.

After I set the timing and tried to crank it, it spun just fine. I cranked it by hand and it felt like it's always felt. I would think if a rod or bearing was bad that it wouldn't be so smooth. I'm going to pull the valves and inspect the head for any major damage when I get home. I already have a new head gasket in the mail, so I guess all I can do is sit and wait.

 

[dorkburger]

Unbeknownst to me, my bike came to me with a special gift - a screw in the cylinder which ended up between the valve / seat and ultimately bent both intake valves (16v engine) Luckily, the piston survived, and i got off with replacing 2 valves. One was visually bad, and i almost replaced only one, but at the last minute figured that i better check both. i shined light thru the intake (head was off) and saw a tiny bit of light from around the valve. bad also. I lapped the new ones with compound, installed them and was good to go. That was around 2000 -01.

Good luck. Those last minute issues at the end are often the most frustrating.

 

[JRHemmen]

Unbeknownst to me, my bike came to me with a special gift - a screw in the cylinder which ended up between the valve / seat and ultimately bent both intake valves (16v engine) Luckily, the piston survived, and i got off with replacing 2 valves. One was visually bad, and i almost replaced only one, but at the last minute figured that i better check both. i shined light thru the intake (head was off) and saw a tiny bit of light from around the valve. bad also. I lapped the new ones with compound, installed them and was good to go. That was around 2000 -01.

Good luck. Those last minute issues at the end are often the most frustrating.

Good to know someone's had decent luck with it. When I get home I'm going to swap all the valves from my other head into it, just to be safe. I'll lap them obviously. As I've put 50 miles on the bike, would it be unwise to put it all back together and drive to inspection? As I said, I just ordered a new head gasket, and I don't think my old one would be reusable, but I have heard of people doing it. I sure hope my valve clearances aren't all way out of spec now, or else I've got another set of parts to wait on.

 

[JRHemmen]

Also, does someone have some definitive guide on how to attach the chain tensioner so this doesn't happen again? I tightened the 10mm nut on the end of it and it stopped spinning, but I don't know if that was a real fix.

 

[dorkburger]

There is a fairly particular method to setting it. I think the nut you're referring to just holds on the knob. I cant really help here other then to say wait fora response or try a site search. Definitey sort this out before starting it.......

 

[tkent02]

The clock spring needs to be wound up a little bit tighter, so it doesn't bounce around. The Suzuki manual says how many turns, can't remember.

 

[JRHemmen]

Good news, I did a light test and a leak test and only the exhaust valves are bent, both intakes are good.

 

[Steve]

The 10mm nut is NOT used to tension the chain.

As requested, the proper procedure to install the tensioner (assuming the tensioner itself is assembled correctly):
1. Loosen the locknut (12mm wrench) and setscrew (straight-blade screwdriver).
2. Push the plunger in, you will have to rotate the large knob (the one under the 10mm nut) to do so.
3. While holding the plunger in, tighten the setscrew to hold it in place.
4. Verify that the cams are in the proper position with the correct number of pins between the marks on the cam sprockets.
5. Verify that the cams are in the proper position with the correct number of pins between the marks on the cam sprockets. Yes, it's important enough to do it AGAIN.
6. Install the tensioner into its location, torque the retainer bolts into place.
7. Loosen the locknut so the plunger can extend and take up the slack.
8. Snug the setscrew against the plunger, then TURN IT OUT 1/4 TO 1/2 TURN.
9. While holding the setscrew in that position, tighten the locknut.

.

 

[sharpy]

Also, does someone have some definitive guide on how to attach the chain tensioner so this doesn't happen again? I tightened the 10mm nut on the end of it and it stopped spinning, but I don't know if that was a real fix.

OMG. Download a manual and read what you have to do before you stuff up more things. Tightening the 10mm nut was a complete waste of time. grrrrr

 

[tkent02]

OMG. Download a manual and read what you have to do before you stuff up more things. Tightening the 10mm nut was a complete waste of time. grrrrr

Not a waste of time, it probably jammed the plunger and did even more damage.

 

[JRHemmen]

I didn't tighten it while the bike was operable, that was after when I was trying to figure the thing out. I have the manual, and the instructions Steve just provided are the ones I followed, so I'm not sure why it skipped.

 

[Steve]

Most of the time when there is a tensioner problem, it is because somebody will read the manual quickly, then skip the last part of #8 and the first part of #9. They will run the setscrew into the plunger and lock it there, instead of backing it off to allow the plunger to move and locking into THAT position.

How much tension is on the spring-loaded knob (the one under the 10mm nut)? There should be a modest amount of tension, enough to make sure that it's doing its job, but not wound too tightly. If there is not enough tension there, the plunger might have been able to back off, but it should have sprung right back into place with its own spring. The knob only applies pressure to the "check valve" mechanism, not the overall cam chain tension.

.

 

[robertbarr]

Our own BWringer constructed a most thorough web page detailing the rebuilding, checking & setting of the tensioner, here: Likely to be very useful, whether or not you need to rebuild it.

 

[JRHemmen]

Lapped my valves, put them in, set timing, put the chain tensioner in 4 times to make sure I did it right (I followed the instructions exactly), and the bike ran for about 20 seconds before the chain skipped again. Both valves are hitting each other now.

 

[JRHemmen]

Did a compression test, 150 psi on left cylinder, 0 on right.