pouakai
14th February 2013, 20:27
I have just somewhat got to the bottom of a problem but that itself raises new questions....
I few months back I brought an RG150 for my son to complete his 6L upon, not long after we had it it seized and spat him off. Problem was a smashed limiter collar on the power valve which subsequently crashed into the piston and ground out the piston bore clearance to 0.5mm!!
We rebored the cylinder to 0.75o/s fitted a new piston, reassembled the power valves (replacing the broken collar) and tried again. Within 100km near seizure was evident again. I pulled the top the top end and found the piston badly rubbed with the ring grooves nearly closed over.
I looked for an explanation, oilways are good, oilpump was working, jetting is standard.
I had the cylinder honed and ring end gap is good and clearance is generous. It was a puzzle until tonight.
I put the new engine together yesterday gave it a run - nice down low but wont pull past 10K so first suspect must be the power valves aren't opening. I pulled the cables and went for a run manually manipulating the power valve cam. Power valves open I re-found the power above 10K so obviously I assembled something wrong, BUT with power valves closed I could feel the piston hitting the power valves !! So the cause of failure is found !!
So the questions are:
When one rebores what is the procedure for ensuring that the power valves are trimmed to clear the larger piston ?
Should the engineer take care of this ?
Should I just trim up power valves with a Dremmel tool ?
Should create new limiter collars for the power valves with shallower decent ?
Is there an after market collar for this situation ?
Is this only ever a problem when one goes past the factory O/S of 0.50mm ?
Once I decide upon a resolution for the above are there any gotchyas when refitting the PV drive cables ? I've done it right before but not quite sure how I got it wrong yesterday.....
:scratch:
P
I few months back I brought an RG150 for my son to complete his 6L upon, not long after we had it it seized and spat him off. Problem was a smashed limiter collar on the power valve which subsequently crashed into the piston and ground out the piston bore clearance to 0.5mm!!
We rebored the cylinder to 0.75o/s fitted a new piston, reassembled the power valves (replacing the broken collar) and tried again. Within 100km near seizure was evident again. I pulled the top the top end and found the piston badly rubbed with the ring grooves nearly closed over.
I looked for an explanation, oilways are good, oilpump was working, jetting is standard.
I had the cylinder honed and ring end gap is good and clearance is generous. It was a puzzle until tonight.
I put the new engine together yesterday gave it a run - nice down low but wont pull past 10K so first suspect must be the power valves aren't opening. I pulled the cables and went for a run manually manipulating the power valve cam. Power valves open I re-found the power above 10K so obviously I assembled something wrong, BUT with power valves closed I could feel the piston hitting the power valves !! So the cause of failure is found !!
So the questions are:
When one rebores what is the procedure for ensuring that the power valves are trimmed to clear the larger piston ?
Should the engineer take care of this ?
Should I just trim up power valves with a Dremmel tool ?
Should create new limiter collars for the power valves with shallower decent ?
Is there an after market collar for this situation ?
Is this only ever a problem when one goes past the factory O/S of 0.50mm ?
Once I decide upon a resolution for the above are there any gotchyas when refitting the PV drive cables ? I've done it right before but not quite sure how I got it wrong yesterday.....
:scratch:
P