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Engine Mechanical TopicsDiscussion for motor builds, cams, head work, stripped bolts and other engine related issues. The good and the bad. If it goes round and around or up and down, post it here.
Initial symptom:
Hard cold start only. Metal bang and intake cough on a cold start attempt. Starts up after rocking bike. Not a valve issue.
I tore down top end and found a cooling failure.
Lack of lubrication on front cylinder. Scored intake side of front piston skirt with matching cylinder markings. No damage on opposite side of piston. Thus, a lack of lubrication issue.
Partial seizure.
I just pulled the pistons and found that the front rod bushing has spun 180 degrees. Looks very odd.
Question: what does a spun rod bushing generally indicate?
Please answer generally, not taking account for the piston/cylinder /lubrication issue. What does a spun rod bushing usually tell you?
Then, please answer specifically, taking in account for the issues I have described with the piston/cylinder/lubrication issue. Knowing the above and now finding the spun bushing, what does this tell you?
So, what next?
Just so you know, I haven’t opened the cam chest yet. I’m about to open cam chest today and inspect all. I can’t wait to see the oil pump (yikes). That’s where I’m betting the issue might be located.
By the way, the piston oil jets appear to be in tact. Piston rings are good, no damage.
The rods are not bound up and they turn the crank/flywheels normally (at first glance).
Experts, please share your thoughts.
Thanks!
Attachments:
Photo of piston and matching cylinder damage.
(intake side)
Some years had issues with the wrist pin bush doing that, known a people it's happened to. You lucked out you found it before the bush mashed completely out and popped a wrist pin keeper letting the pin walk then dig into the cylinder wall. That's the usual story with these.
Initial symptom:
Hard cold start only. Metal bang and intake cough on a cold start attempt. Starts up after rocking bike. Not a valve issue.
I tore down top end and found a cooling failure.
Lack of lubrication on front cylinder. Scored intake side of front piston skirt with matching cylinder markings. No damage on opposite side of piston. Thus, a lack of lubrication issue.
Partial seizure.
I just pulled the pistons and found that the front rod bushing has spun 180 degrees. Looks very odd.
Question: what does a spun rod bushing generally indicate?
Please answer generally, not taking account for the piston/cylinder /lubrication issue. What does a spun rod bushing usually tell you?
Then, please answer specifically, taking in account for the issues I have described with the piston/cylinder/lubrication issue. Knowing the above and now finding the spun bushing, what does this tell you?
So, what next?
Just so you know, I haven’t opened the cam chest yet. I’m about to open cam chest today and inspect all. I can’t wait to see the oil pump (yikes). That’s where I’m betting the issue might be located.
By the way, the piston oil jets appear to be in tact. Piston rings are good, no damage.
The rods are not bound up and they turn the crank/flywheels normally (at first glance).
Experts, please share your thoughts.
Thanks!
Attachments:
Photo of piston and matching cylinder damage.
(intake side)
Photo of spun rod bushing.
Originally Posted by 07SCbobber
Rod bushing = wrist pin bushing.
My bad.
Originally Posted by 07SCbobber
Rod bushing = wrist pin bushing
my mistake
I'm confused, is 07SCbobber the same as the OP SC07Bobber?
Question: what does a spun rod wrist pin bushing generally indicate?
Lack of oil lubrication to the wrist pin. Blockage of the oil passage through the rod to the bushing causing the wrist pin to seize on the bushing thereby spinning the bushing. Check the oil passage in the rod down to the crankcase, there may be debris in there from the cam chest etc. Did you find any crap in the oil when you drained it? Looks like you found it early.
Question: what does a spun rod wrist pin bushing generally indicate?
Lack of oil lubrication to the wrist pin. Blockage of the oil passage through the rod to the bushing causing the wrist pin to seize on the bushing thereby spinning the bushing. Check the oil passage in the rod down to the crankcase, there may be debris in there from the cam chest etc. Did you find any crap in the oil when you drained it? Looks like you found it early.
Bushing in these tapered end rods are splash lubed, no oil passage.
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Spun rod bushing ?
