Cam chain jumped - Yamaha FJR Forum : Yamaha FJR Owners Forums
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post #1 of 13 (permalink) Old 11-14-2020, 08:14 PM Thread Starter
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Cam chain jumped

My 2006 A with 64K miles has a jumped chain. It looks like I got lucky and the valves are not bent. Bought a borescope and the tops of the pistons look good.

Asking for some help and advice from anyone that has been down this road before.

I pulled the valve cover and the timing cover and when on TDC for #1 the crank gear is 1 tooth advanced.
Timing marks on the cams are correct, cams are in the correct sync, oil holes pointed straight up at 12 o'clock.
Removed the tensioner and did a post-mortem on it, no broken spring. The guides are pristine. I tied the chain to the cams so nothing would move and this is where I stopped.
What I want to do is put it back in time, replace the tensioner and do a compression test.
What is the recommendation for getting the chain off and reinstalling so everything lines up?

Thanks
P.S.
Bike ran fine before this happened, no noise or rattle. Rolled it out of the garage to go for a ride the next day, no start and an irregular cranking rythym noted. Like only one cylinder had compression.
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post #2 of 13 (permalink) Old 11-14-2020, 11:14 PM
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You don't have to remove the chain. BTDT. I just removed the spark plugs, loosened the tensioner and turned the crankshaft nut while giving the chain a little assistance to jump a tooth. It's actually pretty easy to do.
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post #3 of 13 (permalink) Old 11-14-2020, 11:20 PM
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I just went through this on my '04, but it did it at start up. Bike fired up with a clatter and immediately died within 2 seconds.
One tooth off shouldn't have done much damage if any. Once I pulled the head off only two valves(#1 cylinder) were barely leaking when I poured fluid into the intake ports. #2 cylinder was so slight that you just could tell that it had seepage after it sat for a while, #3, and #4 didn't leak a drop. In my haste to get it apart, I pulled a rookie move and did not check to see where the timing marks were. If I would have done what you are doing by setting the timing and installing a new tensioner, my engine would have fired up and ran, but I am glad that I pulled it apart. I had already located a low mile head off of an '05 for a song, so I actually had planned for the worst scenario with all 8 intakes bent.
What you're suggesting is perfect. But I think a leak down test may suit your situation better.
Like yours, when I got the tensioner out there was no broken spring, but it had very little tension left as compared to the new tensioner.
Set the cam timing and do some leak down tests, you may have dodged a bullet.
This is the head I got. Most of this wiped off with a rag and carb cleaner. I hit the exhaust valves with a small wire wheel on my drill. Bike is running like a champ now.
If you do pull the head, remember the head bolts are torque to yield bolts. I went ahead and replaced mine with new ones. Some folks don't.
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post #4 of 13 (permalink) Old 11-15-2020, 10:11 AM Thread Starter
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Thank you, I feel better about going forward with this. My next question is this:
Can I rotate the crankshaft CCW by putting a socket on the crank bolt that holds the sensor wheel on?
I don't want to wind up loosening the bolt and not move the crank.

Thanks
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post #5 of 13 (permalink) Old 11-15-2020, 10:43 AM
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You've likely got the original tensioner, which was redesigned late '07 model, then revised again later. Get the new one with the paint dot on it, better spring.
You can remove the dowel on the timing cover which holds the rear cam chain guide in place. With a little finagling now with a looser chain you can get the chain worked around the crank sprocket one tooth. IF you turn the trigger wheel nut CCW, make sure you have the spark plugs out. IF it loosens, you can simply retorque it but pull it all the way out and use some blue loctite. To retorque just put it in gear with the rear wheel on the ground or something between the spokes. Doesn't take much to hold it.
You did not damage it if off only one tooth... two teeth, well maybe not sure, but three teeth not good. Compression test/leakdown test would confirm (note a certain amount of leakage is normal, 5-10% ok, ideally nothing of course. You will get varying compression readings if the engine is not warmed up. A teaspoon of oil in the spark plug holes will eliminate piston ring leakage. But I suspect you're fine.
One tooth off will affect performance, i.e., may not develop full horsepower at 6000 rpm... it will hesitate to "go fast". Should be OK with all your timing marks lined up.
Lesson learned here to all Gen1 and 2 owners prior to '08... change that freakin' tensioner to the new one... gets awful expensive if you don't.
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post #6 of 13 (permalink) Old 11-15-2020, 04:54 PM
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Quote:
Originally Posted by Kelvin View Post
Thank you, I feel better about going forward with this. My next question is this:
Can I rotate the crankshaft CCW by putting a socket on the crank bolt that holds the sensor wheel on?
I don't want to wind up loosening the bolt and not move the crank.

Thanks
I did.

Russ
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post #7 of 13 (permalink) Old 11-15-2020, 06:28 PM Thread Starter
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I was able to get slack in the chain by taking the dowel out of the guide and was able to rotate the crank CCW until the timing marks lined up. So easy, thanks for the advice. Chain is back on, all marks line up.
Ordered a new tensioner, might be here in a week. I will post up with the results after installation.
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post #8 of 13 (permalink) Old 11-15-2020, 07:46 PM
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With no tensioner, chain can fall... a zippie tie around the chain at the crank sprocket might be a good idea to keep it from falling down.
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post #9 of 13 (permalink) Old 11-15-2020, 11:17 PM
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Quote:
Originally Posted by Kelvin View Post
I was able to get slack in the chain by taking the dowel out of the guide and was able to rotate the crank CCW until the timing marks lined up. So easy, thanks for the advice. Chain is back on, all marks line up.
Ordered a new tensioner, might be here in a week. I will post up with the results after installation.
Cool beans! I too thought it was going to be terrible when I had to do it about a gazillion yrs ago.
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post #10 of 13 (permalink) Old 11-22-2020, 06:48 PM Thread Starter
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Update on my chain tensioner issue: Bad news, after installing new tensioner and checking the timing marks I cranked it over and it has almost no compression.

If you have not replaced your cam chain tensioner yet, I would do it now. I was going to do mine this winter...
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