I experienced a knocking noise out riding yesterday from my 1993 CR250R. I'll explain the bike history and what happened. I'd appreciate any comments to help me narrow down this knocking.
Bought used Feb 05, I rebuilt top end immediately using Wiseco piston kit. Bore is over sized to 265cc. Replaced reeds with Boysen.
Rode bike all last year, even through this winter. At rebuild compression was about 180 psi. After break in, compression 200 psi.
I rejet for whatever the elevation and air temp. I maintain the bike cleaning the air filter, plug and change the oil almost every other ride. Engine has been super strong and performing great until yesterday.
I always allow the bike to warm up fully before riding. Yesterday after a regular warm up we hit the trail, 30 seconds into the ride I hear a knocking noise from the engine, changes with engine speed. I stop and idle the bike, still hearing the knocking at idle, I rev it a little, still knocking. I shut it down immediately and walked the bike back to the truck. I thought at least I'd check the variable rate exhaust to see if the knocking was coming from there. I removed the exhaust valve inspection cover, fired up the bike, just to see if it was going to rotate to align the marks. It all was good. However the knocking was gone. I rev'd the bike up several times, help it at high RPM, no more knocking. I was reluctant to ride, but went anyway as everything seemed perfectly normal.
Went for a 2 1/2 hr ride, in the beginning I took it easy expecting to have the knocking sound come back. I began riding normal, on the pipe a lot, all seemed normal. 2 times during the ride, the knocking came back, only temporarily. When the knocking started, I let off the throttle and it stopped right away. Then I began riding normal again all seemed well.
When I got home, cleaned up the bike, decided to perform some tests:
Spark Plug: normal nice mocha colour
Compression: 190 lbs
Took off pipe, exhaust port and piston appear normal, no cylinder wall scoring, no visual signs of any abnormal wear.
Took off intake and reed cage. Intake side of piston appears normal. Lower cylinder wall in excellent condition. Crank looks normal, no signs of any abnormal wear. I doubt it's the timing, as when the knocking stopped, the bike ran perfect. Maybe I had better pull off the flywheel and check the timing.
Then I started thinking about maybe the transmission. Everything appears to be turning as normal. No chunks in the oil, oil looks normal.
Took off the variable exh valve cover, all looks to be working properly. Nothing out of the ordinary there.
What could be causing this knocking? :bang: :bang: Can't be detonation, I have been running the same oil and gas all year, mixed at 32:1. My only worry now is the crank pin or piston pin. I guess I am going to have to pull off the jug and check for bearing play. I was hoping something obvious would show up before I took off the cylinder.
Anyone have any other suggestions what might be causing this mysterious knocking?
Sorry for the long winded post. :blah: :blah:
Keith
Bought used Feb 05, I rebuilt top end immediately using Wiseco piston kit. Bore is over sized to 265cc. Replaced reeds with Boysen.
Rode bike all last year, even through this winter. At rebuild compression was about 180 psi. After break in, compression 200 psi.
I rejet for whatever the elevation and air temp. I maintain the bike cleaning the air filter, plug and change the oil almost every other ride. Engine has been super strong and performing great until yesterday.
I always allow the bike to warm up fully before riding. Yesterday after a regular warm up we hit the trail, 30 seconds into the ride I hear a knocking noise from the engine, changes with engine speed. I stop and idle the bike, still hearing the knocking at idle, I rev it a little, still knocking. I shut it down immediately and walked the bike back to the truck. I thought at least I'd check the variable rate exhaust to see if the knocking was coming from there. I removed the exhaust valve inspection cover, fired up the bike, just to see if it was going to rotate to align the marks. It all was good. However the knocking was gone. I rev'd the bike up several times, help it at high RPM, no more knocking. I was reluctant to ride, but went anyway as everything seemed perfectly normal.
Went for a 2 1/2 hr ride, in the beginning I took it easy expecting to have the knocking sound come back. I began riding normal, on the pipe a lot, all seemed normal. 2 times during the ride, the knocking came back, only temporarily. When the knocking started, I let off the throttle and it stopped right away. Then I began riding normal again all seemed well.
When I got home, cleaned up the bike, decided to perform some tests:
Spark Plug: normal nice mocha colour
Compression: 190 lbs
Took off pipe, exhaust port and piston appear normal, no cylinder wall scoring, no visual signs of any abnormal wear.
Took off intake and reed cage. Intake side of piston appears normal. Lower cylinder wall in excellent condition. Crank looks normal, no signs of any abnormal wear. I doubt it's the timing, as when the knocking stopped, the bike ran perfect. Maybe I had better pull off the flywheel and check the timing.
Then I started thinking about maybe the transmission. Everything appears to be turning as normal. No chunks in the oil, oil looks normal.
Took off the variable exh valve cover, all looks to be working properly. Nothing out of the ordinary there.
What could be causing this knocking? :bang: :bang: Can't be detonation, I have been running the same oil and gas all year, mixed at 32:1. My only worry now is the crank pin or piston pin. I guess I am going to have to pull off the jug and check for bearing play. I was hoping something obvious would show up before I took off the cylinder.
Anyone have any other suggestions what might be causing this mysterious knocking?
Sorry for the long winded post. :blah: :blah:
Keith
