'82 XJ750J Possible Cam Chain (and Owner) Issues

So this is the story of how I broke my motorcycle.

A couple days ago I did a bunch of work on my bike including;
-changing the oil and filter
-cleaning the oil level sensor
-replacing the copper exhaust header gaskets **possibly important**

Once everything was put back together I started the bike on the center stand and everything sounded lovely.*

Today I decided to fix an issue that I've noticed while working on the valve clearances in the past: the cam chain is too loose. I have two reasons for believing this: first, there are two silver lines cut into the top of the valve cover where the chain has clearly lifted off the gears and scraped the cover. Second, I was actually able to remove the top cam chain guide completely by lifting the chain up and lifting the guide out of its slot. The chain could be pulled up about an inch easily.

Oddly enough I've never noticed any noise or other symptoms of a cam chain tension issue.

To try and fix the issue ( I have already tried the method of turning the engine forward then quickly back to present the tensioner with slack many times. Didn't work), I decided to remove the cam chain tensioner and see if it was faulty. The tensioner looked fine so I cleaned things up, replaced the gasket, and replaced the tensioner.

Two important notes: first, once bolted to the engine I pushed the tensioner in manually with a screwdriver to remove most of the slack. Even after doing this, I still got one more click when I turned the spring and bolt at the back of the assembly in.

Also, There is a bolt with a lock-nut directly beneath the cam chain tensioner. I found that it had mostly backed out and was free to turn. I worked with some people in another forum and the best we could figure was that this bolt is somehow related to the cam chain tension. The procedure they found was to loosen the lock-nut, tighten the bolt until it just starts to resist, then tighten the lock-nut. I followed this procedure and moved on.

After finishing my work I started the bike and...*

Suffice it to say it sounds like a tractor now. It first started up with a loud clicking noise which quickly went away, but there was still a quiet but noticeable popping sound.

What I've tried now:
-tightening the exhaust header bolts (somewhat firmly but carefully of course)
-turning the engine forward and back many times with many different methods
-whacking the tensioner a bit with a heavy metal tool I had in hand

Although the sound makes me think exhaust leak (popping which gets faster/slower with rpm's), it wasn't there yesterday when I finished working on the exhaust. I suppose it's still possible that my new gaskets aren't seated or something.

*I do have some videos of the engine running both before and after today's work, including a clip of the first time I started the bike after screwing with the tensioner. In that clip you can hear the initial loud clicking followed by tractor sounds. I may upload those clips and add them to this thread.

So, what should my next step be in diagnosing this problem? Should I just ride the thing and see what happens? (kidding)

I'd like to ride it in the warm weather this weekend, but I want to make sure I'm not breaking anything first, so I'd appreciate anyone's help.

 

1. Stay away from other forums if you have an XJ. At least come here first.

2. The bolt you found under the cam chain tensioner is what holds the rear cam cahin guide in place. You set it correctly.

3. Your cam chain cut into the valve cover because it is too long. Your cam chain is too long because the rollers have worn. It will need to be replaced.

4. link the clips for us to listen to.

 

Dare I ask what it will take to replace the chain? Better question, can it be done without taking apart the engine?

Before I messed with the tensioner the sound wasn't there. Why can't I get the same tension back into the chain?

 

The chain will need to be split, and a new chain threaded onto the sprockets. Then a new master link will need to be riveted on. All that needs to come off the engine is the cam chain tensioner and the valve cover.

I think you can't get the same tension back into the chain because you moved the rear cam chain guide when you re-set the holding bolt.

 

Is the chain something that I can buy in a generic size or do I have to get one intended for this bike?

Is there a way to reposition the guide so I can get full tension again?

Also I should have mentioned this in my first post. The bike has 26000 miles.

 

Start a conversation with Chacal for parts.

The guide has to be in the proper location for it to work properly. Moving it is just a bandaid, and if the cam chain is worn enough that it can't be tensioned properly (the clue is that it hits the valve cover, and you can remove the upper guide without needing to unbolt the cam sprockets) you will soon be shopping for a new engine instead of a cam chain. I'm surprised that you haven't bent a valve already with how loose the chain is.

 

your rear chain guide might not be under that holding bolt any more. take off the valve cover and see if it's still attached down below. while your in there you can lift out the front guide and see how worn it is, the back one is worn about the same. maybe replacing the guides is all you need. i've seen scrapes in the cover too and didn't replace the chain but i did do guides

 

Dang. Well thanks for the help.

On a side note, is 26000 miles reasonable for this sort of issue?

 

If someone didn't do oil changes, ran it hard, and didn't maintian the bike as required...yes.

+1 on Polock's suggestions. You might only need to replace the guides.

 

Is it simple enough to just reposition the guides? I figured they were retained in some way

 

Was the chain tensioned properly before you adjusted the rear guide holding bolt?
No.
It may be that simple, but you won't know until you try.
Do you have a service manual? The guide placement procedure is in the book. If not I'm sure one of us can type it out or post a photo of it.

You're really not tha far into the engine. Replacing the cam chain guides is easy. Fiddly, but easy.

 

No worries, I have a manual. I'll try to work on the guides tomorrow and hopefully when I have the money I'll replace the chain. I don't believe the bike was abused so it's surprising to me that the chain would fail so soon.

 

Only do the chain if new guides don't get the tension correct. You might start a convo with Chacal anyway just to find out what the link-to-link measurement for the chain is supposed to be so you can figure if the rollers are worn or not. That way you can do the whole shebang at once if the guides are worn, or just the guides, or just the chain depending on what you find.

 

my kind of mechanic
just be careful of that's in your hand

 

Oh it was just a ratchet.
I keep my sledge up on the wall so I'm not tempted to use it

 

if the center guide was that loose is it possible a sprocket jumped a tooth. either before the fact or when the center guide came out.
maybe check that page in the book too

 

Will do. I'll post an update tomorrow for sure

 

So I'm going to start working on the bike soon but before that I thought I should ask about the mystery bolt I messed with yesterday.
I now know the bolt is something like a "cam chain guide retention bolt" and according to http://xjbikes.com/forums/threads/under-the-cam-chain-tensioner.68103/ , it's best left untouched.
Unfortunately I snugged it up a bit yesterday and now I'm wondering if doing so is preventing the auto tensioner from working correctly.

Since it's already too late to say "don't touch it", what is the procedure for adjusting this bolt? For reference I'm talking about the bolt and locknut which is screwed downward into the transmission case directly underneath the tensioner assembly.
It's part # 12 in the Haynes manual diagram for the chain and camshafts - all 750 models (pg. 53).

 

the bottom of the guide is held by that bolt, so in the engine it looks something like this ) the tensioner is pushing the center to the right.
if the tensioner is pushing it and you loosen the bolt it might look like \ when the bottom comes out from under the "don't touch" bolt.
the rear guide has a ball/cylinder shape on the bottom that the bolt hits to hold it in but if the bolt hits the wrong side of the cylinder it will push it out.
take it apart, you'll see all and know all

 

Take it apart? That sounds risky given that the engine is installed and running in the bike. It's not like this is a project engine sitting on a bench, though sometimes I wish it was. Would certainly make resolving some of these issues easier.

I took the valve cover off (I'm actually standing next to the bike right now) and found lots of slack in the chain. I decided to loosen the guide retention bolt about half a turn, sort of an arbitrary decision really. I took the bolt and spring out of the tensioner, stuck a screwdriver inside, and gave it a firm push. The tensioner clicked twice and the chain is now reasonably tight. I can still pull it up but it doesn't go slack when I let go. Instead it straightens back out nicely. I have pictures of before and after if you'd like to double check my work.

I also found something rather scary. The 3rd exhaust cam shim has a very rough patch near its center. Also that cam lobe is noticably foggier on its point than the others (again, photos available upon request). Fortunately the cam is still reflective and the fingernail test proves it's still very highly polished. I can't feel any scratches or roughness in the cam lobe, though it certainly looks iffy on bright light.

I removed the shim and, after recording it's thickness marking, reinstalled it upside-down. I know this isn't a great solution, but it will have to do until I can order a replacement shim.

Right now I'm checking valve clearances to make sure everything is in order there.