agent laraby
XS400 Enthusiast
ok so rebuilt the motor a few months back and after 700ks head gasket failed and the bike reminded me of my old BSA with oil pissing everywhere. it had been blowing white/grey smoke for the left pot particularly so I was considering valve guides given the intermittent nature of things. I also used the old seal for the oil gallery which had failed up inspection. so replaced that and another new Head gasket.
put new head gasket on set timing did a few ks to tune it and it ran fine but was low on compression. (still blowing smoke intermittently. )
So off with her head again and discovered that there had still been oil getting into the cylinder chamber. I removed the cylinders and discovered that I had a broken oil ring in the left cylinder (there was small broken piece was in the the piston ring groove so the broken bit hadnt entered the oil circuit.).
Ithink I installed it incorrectly with overlap on the end pieces. The other oil ring s fine I also found a fair bit of wear/scoring around the rear of both pistons on the skirt and slight glazing in cylinder.
which after only 900ks total is of concern. see pics.
I am wondering if the piston marks could be cause by play in the con rod bearings, they seemed pretty tight when I put the bottom end back together so not sure this is the cause, the re bore was done professional and they are new .75 Os pistons. the scoring in the pistons does not have any groves
I am going to rebuilt the whole thing including new valve guides and seals, I have another head on its way which I will get checked and machined if required to make sure it is right .I am also thinking of pulling down the big end and replacing the conrod bearings. does any one know which colour is standard size and is there a guide for tolerances to move to the next shell bearing size? And has anyone had any scoring like this after rebuilding?
Cheers DG
put new head gasket on set timing did a few ks to tune it and it ran fine but was low on compression. (still blowing smoke intermittently. )
So off with her head again and discovered that there had still been oil getting into the cylinder chamber. I removed the cylinders and discovered that I had a broken oil ring in the left cylinder (there was small broken piece was in the the piston ring groove so the broken bit hadnt entered the oil circuit.).
Ithink I installed it incorrectly with overlap on the end pieces. The other oil ring s fine I also found a fair bit of wear/scoring around the rear of both pistons on the skirt and slight glazing in cylinder.
which after only 900ks total is of concern. see pics.
I am wondering if the piston marks could be cause by play in the con rod bearings, they seemed pretty tight when I put the bottom end back together so not sure this is the cause, the re bore was done professional and they are new .75 Os pistons. the scoring in the pistons does not have any groves
I am going to rebuilt the whole thing including new valve guides and seals, I have another head on its way which I will get checked and machined if required to make sure it is right .I am also thinking of pulling down the big end and replacing the conrod bearings. does any one know which colour is standard size and is there a guide for tolerances to move to the next shell bearing size? And has anyone had any scoring like this after rebuilding?
Cheers DG