Backfiring causes?

[Allie]

Thanks folks and yes it does sound like a good idea to check points again after I get compression back. I'm going to be busy today teaching and apping for a job, but the cams, shims, and buckets (Mrs. Bucket??) are out, and I'm ready to give the valves a good stout thrashing. I'll keep ya posted .

[Skateguy50]

Ask steve for more details if you need, Im not highly qualified... but keep in mind the piston positions when you are giving the valves that thrashing to make sure you only do the ones with the piston at the bottom. then rotate and thrash away at the others

Got any pictures for us? could be of you, or baked goods, or even the bike if you prefer

[Allie]

You see me in my avatar... do I look like the kind of mechanic that would drive a valve inter her piston??

[Skateguy50]

Well, I know I am... I always have to remind myself of the little things... should have told myself to gas up the GS and charge the battery before I went to work... but nope got a lesson in pushing a bike chunk of metal up a hill.

Anyways have fun:

[Allie]

Sk8guy you slay me! Believe me I appreciate every reminder, especially about something as critical and easy to forget as 'put teh piston at teh bottom afore ya throw down on teh valve, stoopit'. The more times I see it the more times I'll remember it.

[Allie]

Ask steve for more details if you need, Im not highly qualified... but keep in mind the piston positions when you are giving the valves that thrashing to make sure you only do the ones with the piston at the bottom. then rotate and thrash away at the others

Got any pictures for us? could be of you, or baked goods, or even the bike if you prefer

The crime scene:



The criminal:



Just kidding:



Hmm the ape has better hair than both of us.

[Allie]

Yesterday afternoon after banging the valves around a little I put the cams back in, with careful attention to timing. Everything seemed to go together well, not much drama. I turned the crank a few times slowly with a wrench to make sure there was no noise or resistance, and all the valves seem to operate fine. I did a quick compression check and got pretty much the same results as from my original no oil test. Drat. I'll probably set timing again today, and check it again. If I can't get compression after I'm sure the cam timing is on, I guess I may try the 'low rent' leak down test I read about on Dan's site. Hook up about 20 psi to your compression gauge hose and listen for leakage noise from the intake ports, exhaust ports, and crank case.

Just a couple of questions; if the valves visibly operate normally and follow the cam lobes, it is unlikely that they are bent, is it not? Not to mention the valve clearances are still tight... unlikely that a valve is sticking open.

Next, is it possible that my No. 2 exhaust valve, which has a gunky looking seating surface, has been hanging open a bit and built carbon up on it, and I disturbed enough of the carbon to kill compression in that cylinder?

I may have to call the pros in for a house call yet.

[TheCafeKid]

Allie wth are you doing? Ya don't take the carbs off for a rebuild/cleaning/boot replacement and magically end up with no compression in one of your cylinders...

Carbon on the seating surface of the valve could def skew your clearance readings, but you'd have to have a crap ton or a serious valve seal leak to have it build up enough to have zero comp on a cylinder. How are you testing compression if the bike can't run? It needs to be warm, tested with the throttle wide open. If I were you, I would assure you're timing is right, put the thing back together, carbs and all doing what you know how to do, and see what happens... If #2 is still a dead pot, it'll be time to pull it all down...

[Buffalo Bill]

Learner's permit…

I guess I may try the 'low rent' leak down test I read about on Dan's site. Hook up about 20 psi to your compression gauge hose and listen for leakage noise from the intake ports, exhaust ports, and crank case.

Just a couple of questions; if the valves visibly operate normally and follow the cam lobes, it is unlikely that they are bent, is it not? Not to mention the valve clearances are still tight... unlikely that a valve is sticking open.

Next, is it possible that my No. 2 exhaust valve, which has a gunky looking seating surface, has been hanging open a bit and built carbon up on it, and I disturbed enough of the carbon to kill compression in that cylinder?

I may have to call the pros in for a house call yet.

That Dan's got a lot of good tips. Blowing compressed air in there and listening for where it comes out makes sense.
A valve could be bent just a mite.
Just today I remembered I bent all the intake valves in a Chevy V-8 because I misunderstood the marks on the cam sprockets.
Today I'm messin' around changing the cams in my GSX750 Katana project. Lots of trial and error and I hope I didn't bend a valve myself.
I won't know for sure until I can do a comp. test.
Best of luck Allie
Bill

[Allie]

Allie wth are you doing? Ya don't take the carbs off for a rebuild/cleaning/boot replacement and magically end up with no compression in one of your cylinders...

Carbon on the seating surface of the valve could def skew your clearance readings, but you'd have to have a crap ton or a serious valve seal leak to have it build up enough to have zero comp on a cylinder. How are you testing compression if the bike can't run? It needs to be warm, tested with the throttle wide open. If I were you, I would assure you're timing is right, put the thing back together, carbs and all doing what you know how to do, and see what happens... If #2 is still a dead pot, it'll be time to pull it all down...

Well yeah no kidding... I don't think the intake work has anything to do with the dead cylinder. However, I did take all the shims out to measure them, and but them back in - and somehow ended up with a dead cylinder. I seriously doubt the cylinder was 'all dead' before I started, though I bet it was on its way... maybe it was only 'mostly dead'?

I'm well aware that a warm engine will give more accurate compression readings, but that's not an option at this point. Nor do I think a warm engine would make much difference for Cylinder #2, and I don't think the bike will run again until the cylinder is not 'all dead'. I'm trying to figure out what I did to kill that cylinder, and exhaust all my options before taking the head off. That's 'wth' I'm doing...

[TheCafeKid]

Well yeah no kidding... I don't think the intake work has anything to do with the dead cylinder. However, I did take all the shims out to measure them, and but them back in - and somehow ended up with a dead cylinder. I seriously doubt the cylinder was 'all dead' before I started, though I bet it was on its way... maybe it was only 'mostly dead'?

I'm well aware that a warm engine will give more accurate compression readings, but that's not an option at this point. Nor do I think a warm engine would make much difference for Cylinder #2, and I don't think the bike will run again until the cylinder is not 'all dead'. I'm trying to figure out what I did to kill that cylinder, and exhaust all my options before taking the head off. That's 'wth' I'm doing...

What was your comp reading on the low pot? Did you try putting a teaspoon of oil into that cylinder to see if the numbers came up? What did the plug out of that cylinder look like? Is the bike puking oil around the base or head gasket? Did all this, the reason you pulled the carbs off and the valve adjustment crop up over night? When's the last time they were adjusted? It's possible that valve was soo tight it wasn't closing and on the exhaust side that could spell bad news, as in torched valve= low compression. But you would probably be able to see that on the leading edge of the valve if you look down into the plug hole and rotate the motor till the valve opens...
I'm not trying to be a jerk so sorry if it sounded that way but if the bike was running well before (certainly sounded so in your video) what happened? Lots of these to check to give you clues. A leak down I suppose will help, but depending, it may not show you anything except your bike is leaky... Yanno?

[Dave8338]

GEEEEEEZ, Allie... I've never seen so many GSR'ers jumping at the chance to help a member out so quickly! GREAT on everyone!

Me thinks that the 'winner' of the "hey I solved the problem" contest...expects a fresh, HOME MADE rhubarb/strawberry pie, express shipped to their front door!

[Allie]

What was your comp reading on the low pot? Did you try putting a teaspoon of oil into that cylinder to see if the numbers came up? What did the plug out of that cylinder look like? Is the bike puking oil around the base or head gasket? Did all this, the reason you pulled the carbs off and the valve adjustment crop up over night? When's the last time they were adjusted? It's possible that valve was soo tight it wasn't closing and on the exhaust side that could spell bad news, as in torched valve= low compression. But you would probably be able to see that on the leading edge of the valve if you look down into the plug hole and rotate the motor till the valve opens...
I'm not trying to be a jerk so sorry if it sounded that way but if the bike was running well before (certainly sounded so in your video) what happened? Lots of these to check to give you clues. A leak down I suppose will help, but depending, it may not show you anything except your bike is leaky... Yanno?

I admit at first I was like, woah! But it really sounded like you didn't slog through all the posts, came in at the end and was like, wtf that doesn't make sense... and you're right it doesn't. Most of the info you ask has been covered already but here's a brief synopsis of the story:

The bike has always been slightly cold blooded, (which I'd assumed was normal for it but I've learned it isn't) but ran really well otherwise. This past year the bike has become downright cantankerous when cold, and top end performance is noticeably not what it was. I've also noticed in this time my valve clatter has all but disappeared. Obviously it's time for me to address maintenance items which I've put off for too long. First up was to be checking valve clearances, and replacing the half moons some of which were leaking quite a bit of oil. I also figured intake O-rings were ready for replacement, and when I saw water blowing from the intake area when the bike was wet I decided the time was NOW. The bike did not really leak oil other than from the half moons and maybe from the tach drive, but mostly the half moons.

I took the carbs off, replaced intake o-rings, cleaned the carbs thoroughly and put all new o-rings in. At the same time I took off the valve cover, checked valve clearances, of which all but two are below .05, my smallest gauge. Then I took each shim out one at a time to measure and inventory them, to try to figure out what I need shim wise. I used a zip tie to hold the valves open. As I noted, the exhaust valve for cyl. #2 appears dirty on the seating area, so it's at least dirty, maybe burned. Nonetheless after I did all this I put it all back together with clean carbs, and the bike won't run. Before fiddling further I did a cold compression test, and cyl number two has almost ZERO compression, with and without oil. All the numbers are given earlier in the thread, you can pick them out easily if you look. Basically number two is dead, three is low, and four is way high, which sounds to the folks here as if the cam timing is off. I forgot to mention I turned the crank by hand a couple times when checking valves before I remembered to put the tensioner back in ... As per advice I took the cams out, rapped on the valves with a wooden dowel and a hammer, reinstalled the cams carefully, and I'm still getting the same compression readings. I will try timing the cams AGAIN, to be sure I have it right, but I still suspect that the cam chain never jumped on the sprockets. Nonetheless SOMETHING happened to make a running bike not run, and that something was perpetrated by me, either directly or indirectly.

The bike still obviously needs the valves adjusted, carbs tuned, etc, but it's not going back together until I solve the mystery of the crazy compression, which may well mean taking the head off. For sure there is some ring wear too, as three cylinders had higher readings with oil, but it may not need a ring job, at least for a while. The thing about the leak down test described by Dan is that it's not the one used on aircraft engines - it's not as practical on bikes. What you do is take the carbs and the pipes off, take your oil cap off, and hook up about 20 psi to your cylinder. Listen at all three locations, and you can get a general idea if something is leaking abnormally - rings = crank case, intake valves = intake ports, exhaust valves = exhaust ports.

That's mostly where I am with this now, and thanks for trying to sift through my mess.

[Allie]

GEEEEEEZ, Allie... I've never seen so many GSR'ers jumping at the chance to help a member out so quickly! GREAT on everyone!

Me thinks that the 'winner' of the "hey I solved the problem" contest...expects a fresh, HOME MADE rhubarb/strawberry pie, express shipped to their front door!

Yes Dave I think we've gone well past the point of no baked goods.

[Dogma]

Allie, I see that you adjusted the valves, but I don't see a specific mention of clearance measurements after installing the new shims. I think I discovered a math error in Valve Adjust 41.xls tonight, in a direction that might cause your problems if you used the spreadsheet and didn't catch it. I've just emailed Steve a few minutes ago, and I thought I should pop in here to mention it too.