I'm having a local machine shop work over the bottom end of a motor for my IT car. This motor was overrev'd, but continued to run until it dropped a cylinder about 2 hours into an enduro. The head was pretty well beat up, but we've gotten that back into shape with a bucket of new parts and a bit of machining. The machine shop's evaluation of the bottom end is more surprising.
Appparently the crank is within spec, but the mains come out with only 0.0005" clearance -- apparently *smaller* than the spec range. The machinst says he'd much rather see 0.0015" to 0.0020" clearance for an enduro motor. He's recommending align honing the mains to open up the clearance. I suppose an equivalent move would be to turn down the crank, but I haven't asked him about that.
I'm puzzled by the tight (but consistent) clearances on the mains. I'm surprised the clearances would be that far under spec on a used motor that was running well and didn't seem to have any oiling issues (at least that were apparent in the teardown).
Any insight would be appreciated. I thought the head would be the costly part and the bottom end would be a routine cleanup, measure, and reassembly with new bearings. Figures I'd be 180 deg off on that!
tom
Appparently the crank is within spec, but the mains come out with only 0.0005" clearance -- apparently *smaller* than the spec range. The machinst says he'd much rather see 0.0015" to 0.0020" clearance for an enduro motor. He's recommending align honing the mains to open up the clearance. I suppose an equivalent move would be to turn down the crank, but I haven't asked him about that.
I'm puzzled by the tight (but consistent) clearances on the mains. I'm surprised the clearances would be that far under spec on a used motor that was running well and didn't seem to have any oiling issues (at least that were apparent in the teardown).
Any insight would be appreciated. I thought the head would be the costly part and the bottom end would be a routine cleanup, measure, and reassembly with new bearings. Figures I'd be 180 deg off on that!
tom