Engine won't start after spraying carb cleaner

[Blueknyt]

perhaps I am missing something here, or im just really slow on this thread but    "bike started ok and i rode it for 30 minutes...........A week later it didn't start "

um, not starting could be a couple things, but complete loss of compression from a 30 min ride that was running ok and then sat for a week??

Don't think ive ever heard of a back fire bending valves or knocking cam timing off sticking valves could do it

do this, pull the cam box cover and check valve clearences if you have bent valves you will have HUGE gap in valve lash, if cam chain jumped you will see the allignment  of the cam notches will be off and number of pins in the chain (18 i believe) between gear marks will be off.  all this you can see before worring about pulling the head.

[sashkar2000]

Blueknyt, i will follow your advice because AlexT's saga removing the exhaust pipes scared me off a bit.

[Blueknyt]

uh to be clear.  with the rotor mark R-T centered on the left pickup coil. (signal generator behind right hand engine cover) the notches on the end of the cams should both point inward towards each other and be even with the gasket surface of the head. there should be an arrow with a #2 on the exhaust cam gear (front of engine near exhaust pipes) that should be pointed nearly straight up, that arrow is pin 1, counting towards the intake cam (back of engine near carbs) should count 18 pins in the cam chain to a arrow on the intake cam gear next to a #3 that arrow should be pin 18.

Did you by any chance spin the engine backwards using a wrench or the rear wheel with it in gear?  while rare, that COULD, cause the cam chain to slacken enough to POSSIBLY  jump a tooth messing up cam timing.

[sashkar2000]

Thanks for the details Blueknyt. I'll check it out tomorrow. If those things check out and i manage to remove the head, what are the indications of a bad head gasket, does it look any different?

[Blueknyt]

to comp test out to 10psi in both cyl, it wont be a head gasket issue, even if chunks of the gasket are missing. its going to be bent/broken valves or if really lucky cams will be off time.  aside from HOLES in both pistons, even rings worn out you would still see 40-50 psi.  it has been many years ago that i was constantly elbow deep into the GS, (just cuz i loved it) i vaguely remember something about it being very bad to spin the engine backwards beyond a few degrees. i will be resorecting my GS very soon.  any how.  check those things first then on to next step. dont be affraid of breaking bolts, they can be dealt with.

[sashkar2000]

Intake valve has .5 gap, so I proceeded to remove the head. Exhaust bolts were easy but the 8 nuts holding the head are really tough. Will get a long torque wrench tomorrow and a deep socket.

Not sure what to look for once the head is out but hopefully will see the damage tomorrow.

[RossLH]

Intake valve has .5 gap, so I proceeded to remove the head.

Why do you insist on opening the engine? A tight valve just needs a new shim.

[sashkar2000]

A 5mm shim? Neh something must be wrong with those valves.

[sashkar2000]

Blueknyt called it spot on, both intake valves are bent. Which parts should I replace and should I put in new exhaust valves as well to be on the safe side? I guess head gasket should go but what about block gasket, the block did move a bit while lifting the head.

The rest of the engine seems ok but really dirty from all the gunk and sprays. What's the best way to clean it up?




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[sashkar2000]

should i be concerned about rings or anything else since the valves actually bent from the backfire explosion?

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[Blueknyt]

let me guess, when you pulled the head, you found the intakes wernt sitting flat in the ports even with the cams removed right?    now you need a set of valves, you need to check that the valve guides are not hurt, pistons are tougher then valves when it comes to turning the engine by hand so those wont be hurt.  invest in another set of valves (i think the gs1100 uses the same valve size but i could be wrong)  http://www.ferrea.com/Motorcycle-Valves/c8220  have a machine shop redo the head for you.   Get a gasketset it will have a base gasket in it as well as fresh O-ring that go between head and jugs.    other thing you can do is locate another head from a running bike and relap the valves and replace the valve stem seals.... but a gasket set would still be a good idea to put it all back together with.   while its apart you could invest in a set of rings and re-hone the jugs rounding out a top end rebuild.  its up to you and how far you want to take it, either way, inspect the timing chain guides and tensioner parts for wear an tear and replace what you must.

[Blueknyt]

did you notice if the cams were miss-aligned?

[sashkar2000]

Yep, the intakes had about a 2mm gap against the ports. And the valve stems are visibly bent (not immediately noticeable but it's there on close inspection). The timing chain was in the right place and the cams looked fine.

You think getting a used head may be better than getting the valves separately or are you suggesting i throw out the head? The bike has only 8K miles on it so i just want to replace what i may have damaged with the backfire.

So you think the backfire explosion happened with the intake valves open which forced them up and bent them? Are the valve stems the weakest parts to take on that force or do you think the cams took on that as well? and should i be concerned about the exhaust valves? it was a bit tough to remove the buckets, and i didn't see any shims on any buckets, though i haven't seen buckets before so maybe the shims are there but really stuck hard.

thanks a lot for all the advice!

[Blueknyt]

the back fire from intake is the result of fuel in the cyl and the spark plug lighting it off, having bent valves left an easy out for the explosion.    I discribed the valve bending process in your parts cleaning thread.   as to replace the head or rebuild the head, that is your choice.  you could cheap it the best you can and replace just the bent valves and bolt it back together with new gaskets.   the old head , the valve guides need to be inspected to see that they didnt shift or get hurt in anyway.  chances are nothing is wrong but still should be inspected.  new valves, whats the cost? how much for a shop to dress the seats up and lap in the new valves (or good used ones for that matter)  finding another head and do a complete valve job with new stem seals...   regaurdless of the choice you will have to adjust the valve lash again (shims)  seen a couple used heads on ebay for just under 200$,  you could lap the valves in yourself install new stem seals, slap some new gaskets on it and adjust the lash.  just keep in mind. you dont want to do this again in 6 months to a year or less. so make sure what ever you do, go through it and check it all out.

[sashkar2000]

I decided to buy new intake valves and leave the exhausts. Got head and base gaskets and 4 o rings, $130 total but would have needed the gaskets for a replacement head as well.
I wonder what a typical cost of a lapping job is and would a machinist be able to inspect valve guides to spec?

[gsJack]

Just read your 2 threads, had a sticking exhaust bucket on my 02 and one very cold morning it broke an exhaust valve off when it stuck wide open during cranking and intake valve and/or piston collided with it.

Got new valve, bucket, head/base gaskets, cleaned carbon and fixed it.  That was with 20k miles on it and now have 99k without further incident.  The valve guide for the broken valve had it's tip broken off in the port area and I let it go and also didn't change valve seals.  I lapped both the intake and new exhaust valve for that cylinder to insure good seal.  Since you have it all apart suggest you lap in all four valves to make sure you have good seal, only cost you an inexpensive tube of lapping compound from auto parts store.  No tool needed I just turned valve back and forth with my thumb while lapping.

[gsJack]

Looking at pic of your valves it's hard to believe your 02 GS has only 8k miles on it, here's a pic of my broken exhaust valve with 20k miles on it.  Never know for sure buying a used bike, maybe your valve seals are worn?

[sashkar2000]

thanks for suggestion gsJack. What exaclty are valve seals? I thought the valve closed metal to metal against the port, by replacing valve seals do you mean have a machine shop grind them?

I think i caused the valves to look that way during my 30 minutes of opering the bike. I got it from a friend who abandoned it in the garage for 4 years w/o fuel. so tank rusted and fuel lines were gunked up and i was eager to get it to start  so introduced crap into the engine.

Unfortunatley I don't fully understand how the valves got bent (Blueknyt is convinced i turned the engine backwards and caused valve to hit piston, but i don't think i did that). And due to my cleaning efforts i caused 2 huge explosions in the engine which somehow resulted in bent intake valves and 0 compression. So i'm not sure what needs to be replaced. Exhaust valves are kind of expensive so will try to measure them for straightness and try to reuse. Do valve buckets go bad? was the damage visible in your case?

i saw a nice youtube video on lapping valves. doesn't look too hard but i think i want a machine shop to inspect and measure other aspects, like the valve guides, since this is my 1st time ever looking inside an engine.

[Blueknyt]

"At this point I made a terrible judgment call that I really, really regret. I sprayed carb cleaner inside the manifest to dissolve the gunk. And in an attempt to do a better cleaning job, I turned the engine over by rotating the wheel while in gear."


It happens, it does not take much muscle to do it either.  just rocking the wheel back and forth can do it as the engine spins more revolutions then the wheel does. motorcycle valve stems are very thin (unless your talking harley) they are easy to bend.

[musicmarley]

Scary how thin those valves are.  How often should the shims be checked?

Thx,
Sean