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Discussion Starter · #1 ·
Well of course, my first rebuild was running great! I was dialing in the idle/low throttle circuit to get JUST the right color of spark plugs. Was even going to replace the starter clutch to make starting it just a little bit easier than the effort of a single kick. I was riding to a local parking lot after filling up with some fresh gas to mess with the idle speed a bit and get her running just right. When I rolled on the throttle coming off of a stop sign, the engine died immediately. I rolled to a place to park on the side of the street and tried to give her a kick and was met with little to no resistance from compression and the sound of the cylinders just pumping up and down. Luckily I wasn’t too far from home, so while I was mentally preparing to go home and grab some tools, a guy stopped by and said he had some tools at his house around the corner if I could wheel it there. So we got the bike there and we determine there was almost no compression, the bike would roll very easily while in first gear. You could feel the cylinders moving a little though. So after examining the rocker arms lack of movement and seeing the dangling chain after removing the cam chain adjuster, I determine the chain must have broken.
Luckily, it didn’t seem like the valves were in the way of the cylinders at the time because nothing is seized, so hopefully any potential damage is relatively minimal. I don’t know why I would be the guy that had his cam chain break and not totally smash some valves, but maybe I lucked out. I also read it could be the cam sprocket shearing off?
My question is, what would have potentially caused this? I know I’ve gotta get the engine out and at least take the top end apart and check it out, is it possible to fish a new chain on without splitting the cases? There is only so much riding time left this year where I live and would love to get back on the road before too long! I was so close, guys!


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Does the chain have a master link???
Not sure about fishing a chain through the crank case.
There may be pieces of am chain bouncing around the crank case.
 

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Discussion Starter · #3 ·
Does the chain have a master link???
Not sure about fishing a chain through the crank case.
There may be pieces of am chain bouncing around the crank case.
I’m not sure about the old chain, I haven’t opened the engine up yet to take a look at things. During the initial rebuild process I didn’t notice a master link or anything


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There is no master link.

Why did it break ..... 4 decades of tension and abuse combined with marginal maintenance for at least part of those 4 decades.

IMHO if you didn't replace the cam chain and related parts you didn't do a rebuild you did a patch job. Splitting the cases on these bikes is easy and a good opportunity to clean the sludge traps and check out various parts as well as replacing all the seals.
 

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Discussion Starter · #5 ·
There is no master link.

Why did it break ..... 4 decades of tension and abuse combined with marginal maintenance for at least part of those 4 decades.

IMHO if you didn't replace the cam chain and related parts you didn't do a rebuild you did a patch job. Splitting the cases on these bikes is easy and a good opportunity to clean the sludge traps and check out various parts as well as replacing all the seals.
When I rebuilt the engine I cleaned and replaced most everything. The transmission was fine, the cranks were in spec, and all rubber parts were replaced as well as the pistons and rings, and I honed the cylinders. It’s true I neglected to replace the cam chain, but I guess I wrongly assumed it would be fine. To be fair I renovated an engine that I had never actually seen in running condition being that it was the spare that was included when I purchased the bike so I was never sure what sort of abuse the cam chain went through


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If the chain is still hanging from above then it's possible it didn't break and the sprocket bolts came undone, like you mentioned above.
Did you locktite them?

Edit: I guess to confirm you can try and gently turn the rotor generator crank bolt. After like 360 degrees, if the chain is still looped and hanging then it's your sprocket bolts.
 

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Discussion Starter · #7 ·
If the chain is still hanging from above then it's possible it didn't break and the sprocket bolts came undone, like you mentioned above.
Did you locktite them?
I didn’t locktite them. After the research post engine failure I realize I should have. So while it’s very possible the sprocket came loose. I’ve yet to remove the engine and check things out so it’s totally possible the sprocket is just sitting on the cam shaft and the chain is just drooped under the crank sprocket so that it wouldn’t catch. I’ll know for sure soon enough.


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Ah, bummer. Well, you'll want to replace the chain this time anyway, and hopefully the valves were spared, but I'd suspect not. Cam has to stop rotating somehow! Keep us posted!
 

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Discussion Starter · #9 ·
Ah, bummer. Well, you'll want to replace the chain this time anyway, and hopefully the valves were spared, but I'd suspect not. Cam has to stop rotating somehow! Keep us posted!
Well the cam shaft seemed to stop at what would be Tdc for the left cylinder, in that the pin on the points side of the cam is that 12 o clock. So I’m not sure if it’s possible it settled at a path of least resistance as far as the springs go? The engine spins freely as of now like I said, I doubt I’m that lucky, but my fingers are crossed. It never seemed like it was seized at any point during the ordeal. Regardless I’ve got a new chain on the way, and plans to try and get it taken apart and put back together in the next week or so. Just have to wait for the parts to arrive.


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Discussion Starter · #10 ·
Well the cam shaft seemed to stop at what would be Tdc for the left cylinder, in that the pin on the points side of the cam is that 12 o clock. So I’m not sure if it’s possible it settled at a path of least resistance as far as the springs go? The engine spins freely as of now like I said, I doubt I’m that lucky, but my fingers are crossed. It never seemed like it was seized at any point during the ordeal. Regardless I’ve got a new chain on the way, and plans to try and get it taken apart and put back together in the next week or so. Just have to wait for the parts to arrive.


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That’s also given that the valves somehow managed to stay fine. So if that’s the case tack on a few more days to get new valves. I really don’t want to put the bike away for the winter broken


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You'll also want to check the cam case for damage and cam shaft threads.
I have a bunch of cam cases. I can send you one for $5 plus shipping. I hoard cam shafts and cylinder heads/valves, sprockets and bolts, so can't help you out there!



That’s also given that the valves somehow managed to stay fine. So if that’s the case tack on a few more days to get new valves. I really don’t want to put the bike away for the winter broken


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Discussion Starter · #13 ·
Check your valve clearance. Anything above spec and you'll know there might be trouble.
Well I currently can’t really rotate the camshaft to position things exactly where they need to go for valve clearance. I’m gonna take the head off and check them out once I get the engine out again. My only saving grace is that when the failure happened I was at low Rpm


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You don't need to rotate the engine. Just check for excessive clearance.
If there is zero clearance then the cam lobe is pushing the rocker which is pushing the valve open. If there too much clearance then it means a valve could've bent and isn't seating as it should
 

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Discussion Starter · #15 ·
You'll also want to check the cam case for damage and cam shaft threads.
I have a bunch of cam cases. I can send you one for $5 plus shipping. I hoard cam shafts and cylinder heads/valves, sprockets and bolts, so can't help you out there!
It’s likely I’ll take you up on that, especially if you have the sprocket knock bolts if that’s in fact what went wrong. I can’t find them anywhere. Luckily the fall months here have been generally warmer the past few years and we still have 75 degree weather i October so I think if I get off my butt and get it done I can have her back on the road soon


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Discussion Starter · #17 ·
You don't need to rotate the engine. Just check for excessive clearance.
If there is zero clearance then the cam lobe is pushing the rocker which is pushing the valve open. If there too much clearance then it means a valve could've bent and isn't seating as it should
I’m sure something isn’t good. I’m just glad the pistons and cranks are moving freely, the only bummer is the valves were new to the engine. So I probably lost those. But I can replace them easily enough I suppose.


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Discussion Starter · #18 ·
Oh, I also forgot to write, 90-100 past tdc is the safe zone with all valves closed
So an update to my situation, the cam chain was intact broken, and all links were accounted for. The culprit seems to be the cam chain guide. The chain appears to have been rubbing on the top edge of the guide, shaving away at it until it finally bit it hard enough to break it. Surprisingly the valves seem fine, but I’ll do an acetone test while I wait for the new chain guide to arrive. Hopefully I’ll just be replacing gaskets and putting her back together!


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