Backfiring causes?

[Allie]

Thanks but I did not adjust any clearances. All shims were measured and inventoried, but went back in their original buckets. Intake valves 2 and 3 were about .06, all the rest are tighter than .05.

[Steve]

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.

She already has v4.2.

.

[Skateguy50]

Thanks but I did not adjust any clearances. All shims were measured and inventoried, but went back in their original buckets. Intake valves 2 and 3 were about .06, all the rest are tighter than .05.

I read your summary to TCK and sorry to hear that taking the cams off and reinstalling per spec didnt clear up your problems... I know how frustrating it can be to repeat the same steps over and over.

What I did for my valve checks is use a measuring shim to get the exact number needed, helps to see how off the valve is. If say the exhaust on 2 was way high maybe the valve was damaged... not sure. I helped a guy from here check his and he had one that was actually a negative clearance when checked that way so not only was it hitting but not even closing on the lowest point of the cam lobe spinning. just knowing <.05 cant rule that out.

Edit here: Just thought the guy I helped had 1 REAL low cylinder, like 30psi and it was the one that had so tight a shim that the exhaust was not shutting. I know the issues started for you after the "check" but until you get the right size shims in or at least measure with a smaller shim to get the exact number I would not rule that out. Basically I use a 2.30 shim, put that in and rotate a few times to seat it then measure. I take that number add it to 2.30 to get the size shim that would basically = 0 clearance. Subtract my .03 and .08 and get my range shim I need. If you are just using a .05 feeler gauge you wont know if its just tight .05 to 0 clearance, or not even shutting with the shim in place being a higher number than the measuring shim + the feeler gauge reading.

Its worth the $12 bucks to grab a low number shim from the dealer to do those checks. That way you know before you have to order shims exactly what you need. some might go down .05 and others .10 (or if you want I can post you my 2.30 shim on loan, my checks are done till spring. Also got 5 spares once Ryan gets his in from the shim swap club you can use to swap with them. As long as I got my extras back by spring its all good and postage on those little bubble wrap envelopes is pretty cheap)

However none of that would really affect your issues on its own... I hate to say it but if you cant ride anyways and are not getting anywhere it might be time to pull the head and start saving up for the oem gaskets to rebuild it once you find the issue. You should probably plan to replace the valve oil seals at least since pulling the valves and checking them is likely required as is removing the cylinders and at least checking them and the rings.

At least you know how to reinstall the cams and do the timing, that is the hardest part of the rebuild.

[Allie]

Skateguy you readed my mind, I'm really wishing I had a low shim to really check the clearances and see wth is going on with them, in particular the #3 exhaust shim. I'm not ready to pull the head 'just' yet, till I check everything I possibly can. I still have the feeling that the engine is coming out and the bike going back up to it's house for the winter. I look at it this way, once that head comes off I DEFINITELY won't be riding until at least the spring. I can afford to take another month or two (more than enough time) to exhaust (har har) all possibilities and -possibly- get a ride or two in for Oct/Nov.

There are a few things I'm going to check today/tomorrow, and stew on it some more. I have the pipes off, I will hook up some air to the cylinder and listen, then take the cams back out, hook air up again and listen for differences. Rapping on the valve again probably won't hurt. The put the cams back in again, (I can use the practice anyway) and check compression again. This is actually pretty fun if I don't think about the open road too much. I definitely need to get ahold of a shim to check with.

[Skateguy50]

I bought mine from the local dealers service department. They gave me free swaps for shims as well but needed to buy the extra, call around and see if the ones local to you will do the same. you obviously cant bring in a pile of shims to swap unless you pull the cams again or buy a few spares in advance. However once you have the measuring shim you can see if some of the ones you have will swap with each other, might only need a few new ones.

[Allie]

The first phase of the leakdown test is done, and I didn't need my fancy stethoscope (a length of vinyl tubing) to hear the hurricane force winds erupting from the exhaust port of cyl #2. (sometimes I call it Cyl #3, but whatev - I must be dyslexic). Yes both valves were closed. None of the other cylinders had anything very audible coming out. Wooo so either tonight or tomorrow I will take the exhaust cam out and do this test again. If I don't hear any air, or not much, it means the valve has some sealing action left in it, and will proceed with a MUCH needed valve adjustment (I know there's a moral in here somewhere that you are all very discreetly and kindly NOT rubbing my face in... ) If I still hear air then it could mean:

a) burned valve
b) bent valve
c) really dirty valve
d) all of the above

In that event I will rap the valve some more and see if I can get it to seat. I may also drain the oil, then fill the cylinder with a marvel mystery oil and PB Blaster cocktail or something to see if I can dissolve some carbon (we're really stretching here buy hey I have time to burn). Those are probably my last ditch efforts before the head comes off for a valve job.

Either way it's plain that whether the cam timing is on or off that valve is going to be a problem so that's my priority I think. So how could the valve have been (sort of) sealing before I started the job, but not now? It may always be a mystery. I could actually have bent the valve, but I doubt it. I don't think a zip tie could have caused THAT much loss of compression. MAYBE when it backfired (did I say gun shot? I meant cannon shot...) it blew a bunch of crap off the valve or the seat, totally killing compression.

[Buffalo Bill]

When does the paperback come out?

Like reading a magazine mystery story. Just add more Jersey'isms, some inky shadows and gunsels.

[Allie]

Like reading a magazine mystery story. Just add more Jersey'isms, some inky shadows and gunsels.

What's a gunsel?? Rose has a shotgun that she intimidates her airbox with, I was thinking of asking her to loan it to me for a while. Would that fill the bill?

[Buffalo Bill]

Who was Dashiell Hammett?

What's a gunsel?? Rose has a shotgun that she intimidates her airbox with, I was thinking of asking her to loan it to me for a while. Would that fill the bill?

See: http://www.google.com/search?client=...=Google+Search
It would work if you chased away a gunsel wit dat', yer sawed off, an' if you barrow it dat's good too.
I can't wait to find out what kill't da cylinder.
Bill

[Allie]

See: http://www.google.com/search?client=...=Google+Search
It would work if you chased away a gunsel wit dat', yer sawed off, an' if you barrow it dat's good too.
I can't wait to find out what kill't da cylinder.
Bill

First definition, a criminal carrying a gun. It's been established that I'm a criminal, all I need is that shotgun...

[TheCafeKid]

Skateguy brings up a very good point. Just knowing that its tighter than .05 isnt enough at this point. I rebuilt my FIRST 750 motor years ago, bought off of ebay. The first thing I did was check valve clearances and was shocked to find that every single one of them was tight. Some I had to go down as many as THREE shim sizes just to get them in spec...fearing the worst, (ie the valves werent ever closing if they were that tight, and may likely be burnt) I stripped the whole motor down in my first endevor at a rebuild. I was lucky, none were burnt, evidently the valves had simply gotten so tight across the board that the motor simply didnt have the compression to start anymore.. And it sat untill the guy sold it to me. After the rebuild, she fired right up, first shot, and ran good numbers across the bank.

Skateguy might have hit the nail on the head with your low comp..the valve simply isnt closing anymore. all your compression is going right out the window.. or the exhaust i suppose. As to number 4...Its hard to say. Im in agreement with your assesment at this point however, time to change out your shims (I have some depending on what you need, that could be lent to the cause.. ) and see where that gets you. You never know.. it may solve at least HALF the problem. Otherwise, a tear down, provided you have everything on hand, and dont need serious machine work, is a weekend job You'll get it sorted, we'll see to it. If not, I will send darling Rose over with her shotgun

[Allie]

Yes I may borrow a 2.30 temporarily but I'll probably buy one just so I always have it. I will be joining the valve shim club too, and probably soon - all the cool kids are doing it.

If you send Rose over to operate the shotgun for 'troubleshooting' do I get some kind of kevlar suit? I'd probably need it even if I operated it.

[kinnet]

If you send Rose over to operate the shotgun for 'troubleshooting' do I get some kind of kevlar suit? I'd probably need it even if I operated it.

You don't actually fire it. Just wave it around menacingly. Works every time.

[1948man]

Wow Allie, what a bummer story. I was planning to check and re-shim my valves next weekend but I'm having doubts now. I can tell you're more mechanical than I am so no telling what I might do. I admire you for jumping in and maintaining perspective and I hope getting the right shims in solves this for you. Is it necessary to disengage the tensioner when checking the valves?

[BassCliff]

Is it necessary to disengage the tensioner when checking the valves?

No.

Just about everything you need to know is in the guide on my little website. Have a look.


Thank you for your indulgence,

BassCliff