We've been battling a bit with a strange (and frustrating) Norton problem, we've had the head off and on this bike about 6 times and still we're losing oil from the head and filling the combustion chamber. Alex made up a plate (shown in the pics) which has allowed us to pressurise the head to look for a potential leak, unfortunatley it showed no leak so we are now back to assuming that somehow the oil is being forced up past the rings into the combustion chamber. Today Alex and I will strip and hopefully rebuild the bottom end after hopefully having our Eureka moment!!!! Problem is I hurt my back taking the thing out so not only is this Norton challenging me mentally its also affecting my health!!!!!
Not saying this is the problem.But reminded me of something... Many years ago we had a Triumph in the shop that was smoking like crazy after a rebuild. Turned out the rings had been marked wrong, and we had installed them upside down. Only after checking them closely did we realize the taper was wrong. Always wondered how many sets they made wrong and released upon the world...
ReplyDeleteLarry I was just going to say the same, had a Zed motor burning oil on one cylinder after new pistons and rings, rings fitted up side down, refitted right way and problem sorted.... took many hours to get to the bottom of it.
ReplyDeleteThanks for the input guys, the rings on the 750 Commando are square edged there isn't "Top" side. Think we have found the issue (I bloody hope) a bit of silicon stuck in the scavenge side of the oil system, not big enough to block it but we think its been moving and acting as a valve, sump fills up with oil, backpressure increases due smaller free volume, oil forced up past rings. If its not this I give up, spent days working on this one and I've checked everything possible, found plenty issues and fixed them. Damned bikes eh!
ReplyDeleteAhhh, the dreaded silicone where it shouldn't be...hope that's it.
ReplyDeleteI think the guy who "built" it before (I use the build word loosely) must have had a job lot of it, smeared all over inside and OUTSIDE the crankcases, engine delivered back to its owner, this week should tell if its a good one or not!!
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