'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.

 

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.

 

The mixture screws were uncapped when I got the bike and the mechanic mentioned adjusting them. The rack wasn't split as far as I know so no new shaft seals. I have checked and rechecked for vacuum leaks on this bike many times and the only one I found on a manifold I sealed with silicone. I know, not the best fix, but it works. I can check for vacuum leaks once I have it running again.

I just drained a good amount of gas out of carbs 3 and 4, the only two with functioning drain screws. Both flowed continuously with the petcock set to prime and the gas that came out was perfectly clean. No rust, dirt, water, or other contaminants visible.

I just removed the plugs and I'm about to do a spark test on all of them. The only thing of note here is that number 4, the dead cylinder, was practically dripping wet. It looks like it doesn't have spark so it never lit any of its gas. I'll know more once I check for spark.

 

Make sure to only check one plug for spark at a time, or you could kill the TCI.
If #4 does not have spark, suspects are: the plug, the resistor in the plug boot, the plug wire.
Swap plugs and see if the problem follows the plug, then swap #1 and #4 plug wires and see if the problem follows the wire.

 

Hah. Unfortunately I just finished testing for spark, on all four cylinders at once. I won't do that again.

The result was perfect bright blue/white spark on all four cylinders.

 

Swap the #4 plug around to #1. Just because it sparks in open air dosen't mean that it will under compression.

 

OK time to add another problem to the list.

I swapped plugs 1 and 4. I also unscrewed the plug end on 4 to check for corrosion or other connection issues. It looked perfectly fine.

Next I checked compression on 4. I was able to quickly get up to 140 psi before the starter motor stopped engaging. It would turn the engine over for a moment then I could hear it freewheeling. Not the standard clattering sound of the clutch disengaging, but a whirring sound of the motor.

Then, when I tried hitting the starter button it engaged, turned the engine a bit, and just stopped. I hit the button a few times quickly but it just clicked (new solenoid btw).

Battery is about 6 months old and has a charge of 12.68 volts, so I don't think it's a voltage issue.

I put the bike into 5th gear and turned the rear wheel to rotate the engine. It turned over just fine with obvious resistance on the compression strokes.

My only guess is that either the motor momentarily locked up (unlikely) or the starter has failed. My only gripes with this explanation is: I've had the starter apart already a I know it's clean and greased inside and the commutator and brushes are clean and well within spec. Also, the bike had a similar issue turning over yesterday although I failed to mention it because it started eventually, but just a few days ago it was spinning over strong with the starter.

How could tightening the cam chain have messed up this engine/starter so badly? It's not like I tore the carbs apart or rebuilt the electrical system or anything that could really mess things up.

 

Have the starter brushes been replaced?

The engine turns with the rear wheel; the chain IS NOT the culprit.

Here's what's going on. You have a relatively neglected 30+ year old motorcycle, and there is maintainance that must be caught up on. You are reaping the rewards of every previous owner who just gassed it up and road it.

 

Starter brushes are pretty long. I think they're only about 1/3 into their wear range. I might try jumping the bike with our minivan (engine off of course) just to rule the battery out.

 

the solenoid clicking really means nothing, the click is the contacts moving into position to make contact but if they will, that's another story.
if it clicks again and nothing happens try crossing the big terminals with a screwdriver.

 

Bad news. Starter motor is completely dead. Even hitting it with 12v from a battery charger (now removed from bike) just sparks a little. I'm going to open it and check the windings.

 

After some intense cleaning, the commutator bars on the starter motor are all shorted together. Looks like one of the seals failed and oil got in. The oil then gummed up the commutator with graphite paste and burned up the motor. What's odd is it looks perfect. No burned resin on the windings or anything like that.

I guess it's of to eBay for a new starter!