Hiya,
Since my 650 conversion engine rebuild, I've done a little over 1500kms. I've notice I've since developed a serious oil leak from the rear of the engine. At first I suspected the sump gasket, replaced it but still leaks. The only other places that I can think is Rear main "O" ring (main bearing loose??) or rear main seal. Both of which are supposed to be BRAND NEW. I'm going to pull the engine out either way, but does anyone have any other idea where the oil is dripping from.
Back of flywheel soak, (as is the flywheel cover - it has lots of oil). The back of sump is also wet. Not coming from top of engine as I checked and removed all the tinware. Puzzling.

124spiderman said:

Hiya,
Since my 650 conversion engine rebuild, I've done a little over 1500kms. I've notice I've since developed a serious oil leak from the rear of the engine. At first I suspected the sump gasket, replaced it but still leaks. The only other places that I can think is Rear main "O" ring (main bearing loose??) or rear main seal. Both of which are supposed to be BRAND NEW. I'm going to pull the engine out either way, but does anyone have any other idea where the oil is dripping from.
Back of flywheel soak, (as is the flywheel cover - it has lots of oil). The back of sump is also wet. Not coming from top of engine as I checked and removed all the tinware. Puzzling.

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Sounds like an engine out job unfortunately. It is most likely a faulty or incorrectly installed Rear main seal- it is possible to pinch or push the seal inside out when installing over the crankshaft which would explain your problem.
It is rare for leaks to occur between the rear main and crankcase- I don't use the gasket and simply use Loctite master gasket to seal the bearing carrier directly to the Crankcase with more Loctite thread lock on the bolts. 650 engines that have been run for a while with a loose rear main bearing can crack the crankcase in the area between the rear main and sump which will result in a sizeable oil leak (and engine rebuild) Inspect this carefully but I hope it is something much simpler...
Hope this is of some help- Merry Christmas!

Hope your Christmas was great.
Took the engine out today and as I guessed, it's dodgy rear main! Really annoying as it is new! Thanks again.