'82 XJ750J Possible Cam Chain (and Owner) Issues

Well clearances look OK. Everyone is within spec except for the 4th exhaust which is pretty loose. 10 thou fits, 11 doesn't. Should be 6-8 thou. Yes I measured in thou. It's what my feeler gauges read. I'll replace that shim. eventually. Promise.

Even the upside-down 3rd exhaust is still within spec, and yes I turned the engine over a few times to seat the shim.

I was going to hand polish the cam lobe a bit, but I'm not sure it's worth it. It feels absolutely smooth. Heck the surface of the lobe that doesn't contact the shim is more rough than the point.

 

You'll hear this frequently . . .
Out of spec is out of spec.
In spec is in spec.
Bad.
Good.

 

The cam lobes never contact the shims when running (and hardly ever when not running). The oil film/wedge does though. Any wear will be from particulates in the oil, or blocked/restricted oil passages.

Some people do grind their shims to make clearance, so it could be that is what happened to your funny-looking one.

 

http://imgur.com/a/sgWW7
Here is an album of photos from yesterday which should show off the damage.

My primary concern at the moment is if it's safe to start the engine after all of my fiddling with the tensioner. I don't want to blow the thing up after all.

 

There really isn't a specification given for checking the cam chain tension other than making sure that the tensioner is working properly. I'd say that if you have less than 1/4" of lift on the chain at the top guide it's OK to start it. You might turn the engine over a half-dozen times and check that the timing marks line up consistently.

 

I've actually already done that.
Well I was turning the engine over to check valve clearances and to seat the shim and some other things. It probably went over a couple dozen times before I finally got around to checking the timing. It was right where it's always been, the cam dots are just a hairs width off. Nothing that needs to be corrected as far as I know.

 

Your're good to go then.

 

Great!
I'll start it up in a couple hours and let you know how it goes.

Another side question. One of the pictures in the above gallery shows the inside of the valve cover has what looks like over-spray from a paint application. Is this normal? Should I try to remove it? I've already wiped away the really loose stuff but the rest is stuck to the metal.

 

If it's is stuck then just leave it. It's as likely to be baked on oil as it is overspray. You can spray it down with carb-cleaner and use a plastic or brass brush to scrub it off if you want.

 

Oh boy we're in trouble now.

So I ran the engine and long story short, it sounds worse than before, but not because of chain noise.
The chain noise is pretty much completely gone, but now the engine runs like crap. With the choke set on full the engine rpms never climbed as it warmed up like they normally do. Instead it just sat at a steady 1500 rpm. At first it would occasionally surge a couple hundred rpm for just a moment before dropping back down. After a minute it wouldn't even do that but instead just wobbled around just above idle, making a quiet pop or click every few seconds.
Occasionally the engine would make a pop sound and the rpm would drop to 800 or so for a couple seconds.
Revving the engine gently sounded ok, stumbling a bit almost as if it was just running cold.

Now here's the most telling bit. Immediately after shutting the engine off I felt the headers. Cylinder 4 was ice cold as though it wasn't running at all. 2 and 3 felt warm, normal. Then number 1 was screaming hot. So hot I almost burned myself just touching it for a moment.
Once the engine cools off a bit I'll go back out and pull the plugs to see if something is obviously wrong there. I don't think it was running long enough for the plugs to really tell anything, but I'll check anyway.

I'm uploading a video of it running to YouTube right now. I'll add it to the tread once it's up.

What should I check next?

 

Right at the start you can hear the sort of hissing click sound it makes intermittently. This is a totally new sound.

Around 30 seconds in I'm giving it some small revs and as soon as I let off instead of going back to "idle" it drops and sputters/pops for a bit before climbing back up. At 37ish seconds especially I do nothing and it takes several long seconds to climb back up to where it's idling.

 

When you first got the bike, did you bother to rebuild the carbs?

Do you run it with an inline fuel-filter, or are you just relying on the in-tank screen?

 

Carbs were rebuilt and tuned by a mechanic a little over a year ago. They've been flawless ever since. Before I started all this work, even the day before, the engine ran just fine. The only reason I messed with the chain tensioner was because I knew the chain had that ridiculous amount of slack, even though it wasn't making noise. I honestly wish I had just left well enough alone (though I'm glad I found that rough shim before it ate up my camshaft).

I have an inline filter. Speaking of which, I actually just yesterday replaced the fuel line and moved the filter down to between the boots where before it was sitting above the carbs. I only did this so it wouldn't trap air in the filter anymore, though again, I never had any fuel flow problems (I really need to stop fixing things that aren't broken).
When I set the petcock to prime, no fuel entered the filter. I assumed this was because the carbs were already full from running just the day before. By squeezing the line I got some fuel to dribble in and fill the filter. I might go and redo the fuel line to make it like it was before.

 

Relocating the filter could very well be the problem. Also open up the float bowl drains to help the initial fuel flow. Open them one at a time, starting on #1, and close them as soon as you see fuel come out.

 

I'll try that, but unfortunately one of my drain screws is completely stripped at the head. I've undone it exactly one in the lift of the bike, and I should have replaced it then, but oh well.

Still seems a little odd that the carbs would have gone dry in just one day. I would figure it should be able to run for at least a few seconds normally on just what's left in the bowls.

 

I thought you said that the carbs had been rebuilt. Did you strip the screw after that? If not then the carbs were not rebuilt properly (and that small detail is enough to make me suspect ALL of the work that was done by that mechanic. New drain screws come in the rebuild kits).

If there is fuel in the bowls, and they are full, then it takes about 7-10 minutes for them to run low enough to kill the engine.

I think you might need to revisit the carbs...yourself this time.
Classic bikes: either do all of the things yourself at one time to ensure reliability, or do all of the things over and over again.

 

The drain screws were not replaced. I don't remember exactly what was replaced, but it was enough to get the carbs running perfectly. Well, perfectly as long as you don't need to open the drains.

I just pulled the fuel line off the petcock and fuel cam pouring out of the line. Clearly gas was able to go into the line while the engine was running, even though it wouldn't go into the line when the petcock was set to prime without the engine running: when the carbs were already full. I opened the drain on carb 4, the dead cylinder, and gas came pouring out as well. I'm inclined to believe that the carbs are full and the fuel line is working correctly. Obviously this isn't the most thorough examination, but I think it's good enough.

I could put a line on carb 4, open the drain, and leave the petcock on prime just to drain a bunch of gas through the system. This would prove that fuel is moving as it should through the system.

How badly could tightening a loose cam chain throw carbs out of tune? Could the chain be too tight?

 

Not at all. One has nothing to do with the other. Either you have a lack of spark, a lack of compression, or a lack of fuel. Re-confirm that the timing marks are correct, and that you have spark on all four (do a compression check if you can, or re-confirm the valve clearances).

My bet is that the mechanic pulled the float bowls off, sprayed carb cleaner through the jets, and called that rebuilt. You are just now reaping the reward.
I hope that I am wrong.

 

Oh I know for a fact he replaced parts. He showed me the bag of stuff he removed and pointed out some staining and residue which I recognized from when I had the carbs apart a few weeks before. Obviously at the time I didn't have the tools to do the job myself as I couldn't even get the engine running. I know that mechanic through a personal friend and I trust his work, though if the carbs need work now I'll be doing it myself just to avoid the cost and the wait to get into his garage.

I'll check for spark and fuel and if that's not the issue I'll check compression.

 

Were any of those parts the throttle shaft seals?
Are the idle mixture screws still capped, or are they uncovered?

Nevertheless, do the checks. You've got a dead cylinder, and we need to figure out why.