Engine is damaged - not an IMS failure!
05-29-2012, 08:37 PM
#183
Race Director
Well folks, I have a broken chain. I'm hoping there can't be too much collateral damage from that other than damaged valves on that bank but I will have to go a little deeper to find out. No debris when I opened it up so that's good. I did some searching on the forum and it doesn't look like this is a common problem. Curious.
I am not making light of your situation but I have to use the cliche and state that a chain is only as strong as its weakest link. If just one link plate (or roller) fails the chain will fail, snap in two like you wouldn't believe. Lost a motorcycle chain once. The chain snapped just like flipping a switch and flew off the countershaft sprocket and I never even found the chain!
Look at the parted link plates very carefully. You might spot an inclusion in the metal of one of the link plates. Look at the roller pins ends too.
If you think something got caught between the chain and one of its sprockets a careful examination of the sprockets and their teeth might turn up signs of this. Then you could expect to find the something in the engine. What it might be though, I can't say.
About all I can think of is possibly a valve spring fragment but you'll know soon as you dig deeper if any springs are broken or if there's any other source of the stray piece of metal assuming this was what happened.
My money's on the chain just being bad defective.
The engine might be rebuildable/repairable. New chains/tensioners/rails/etc of those that are damaged/broken of course along with new intake valves.
If the exhaust valves made contact then new exhaust valves too.
I assume no valves broke and thus one or more valve heads didn't get hammered into the piston/head combustion chambers?
Not sure what I'd do about the pistons even if no valve heads broke free.
Check the rods for straightness and the crank too.
I'm sure you already know this: Go slow and be sure as you can be that the engine is a good rebuild/repair candidate before you sink any more money into parts for it.
Sincerely,
Macster.
05-29-2012, 09:50 PM
#184
Racer
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XR4Tim and alpine 003 - I haven't gotten as far as the chain guide yet. I presume I will find that when I take the head off.
Macster - thanks for your input. The chain is broken in a weird way - it looks like the two center links snapped and the two outer links ripped apart ... can't figure that one out. Could the valves have jammed up against the pistons and stopped the cams cold, making the chain rip apart? I have no money into it yet so I'll keep going until I see what it's going to cost me. My fear is that I need to split the case to insert new chains and I'm not sure I'm up to that. This has sure cured me of my fear of doing a simple clutch job in the future though.
Macster - thanks for your input. The chain is broken in a weird way - it looks like the two center links snapped and the two outer links ripped apart ... can't figure that one out. Could the valves have jammed up against the pistons and stopped the cams cold, making the chain rip apart? I have no money into it yet so I'll keep going until I see what it's going to cost me. My fear is that I need to split the case to insert new chains and I'm not sure I'm up to that. This has sure cured me of my fear of doing a simple clutch job in the future though.
05-29-2012, 10:15 PM
#185
Rennlist Member
It would be interesting to grind the "heads" off and drive out a couple of the link pins to see if there is abnormal wear on any of the other side plates.
or
http://www.powersportsplace.com/part...2825/overview/
or
http://www.powersportsplace.com/part...2825/overview/
05-30-2012, 12:07 AM
#188
Race Director
XR4Tim and alpine 003 - I haven't gotten as far as the chain guide yet. I presume I will find that when I take the head off.
Macster - thanks for your input. The chain is broken in a weird way - it looks like the two center links snapped and the two outer links ripped apart ... can't figure that one out. Could the valves have jammed up against the pistons and stopped the cams cold, making the chain rip apart? I have no money into it yet so I'll keep going until I see what it's going to cost me. My fear is that I need to split the case to insert new chains and I'm not sure I'm up to that. This has sure cured me of my fear of doing a simple clutch job in the future though.
Macster - thanks for your input. The chain is broken in a weird way - it looks like the two center links snapped and the two outer links ripped apart ... can't figure that one out. Could the valves have jammed up against the pistons and stopped the cams cold, making the chain rip apart? I have no money into it yet so I'll keep going until I see what it's going to cost me. My fear is that I need to split the case to insert new chains and I'm not sure I'm up to that. This has sure cured me of my fear of doing a simple clutch job in the future though.
If the valves contact the pistons at slow engine speed the engine stops. Everything stops. At the same time.
(At higher engine speed valves heads break free and the engine can continue to spin but this just pounds the valve heads into their respectiive piston crowns and into their respective combustion chambers, which is almost certainly fatal to the engine.)
Unless I'm totally out in left field (hey where is everybody?) I do not see how the valves contacting the pistons could have caused the chain to snap.
Regardless you may never know or be able to determine what went wrong.
What you of course want to focus on is that you make a good assessment of the engine's suitability for resurrection and if you deem it worthy and you proceed to resurrect the engine you do a proper job. So take your time; measure twice, cut once; as we used to say in the shop.
Sincerely,
Macster.
05-30-2012, 12:32 AM
#189
Three Wheelin'
Well Bill....that's certainly something new to talk about on this forum. I guess you'll remove the heads next then see what you've got?
As far as splitting the case goes...I'm with you...but I bet it's not as complex as you think and when you look back one day it might even seem easy. That is certainly the case with the clutch/flywheel/AOS replacement I just did. It's just nuts and bolts.
It all depends on tools, time, experience, documentation...and money.We know the skills are there. Just gotta lose the fear and doubt.
It's kind of a drag but you're having fun too right??
As far as splitting the case goes...I'm with you...but I bet it's not as complex as you think and when you look back one day it might even seem easy. That is certainly the case with the clutch/flywheel/AOS replacement I just did. It's just nuts and bolts.
It all depends on tools, time, experience, documentation...and money.We know the skills are there. Just gotta lose the fear and doubt.
It's kind of a drag but you're having fun too right??
05-30-2012, 12:47 AM
#190
Racer
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05-30-2012, 01:46 AM
#192
Three Wheelin'
I'd love to drop by and have a peek. Are you home tomorrow at lunch? If so shoot me a quick PM with your address and I'll burn out from work in my 996.
05-30-2012, 01:50 AM
#193
Three Wheelin'
The title of the thread was changed and everything.
Don't let me discourage you from hugging that bearing though. I still agree its good PM.
05-30-2012, 02:58 AM
#194
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05-30-2012, 03:04 AM
#195
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