No.4 Inlet valve bucket oil starvation??????

[Mr Bump]

If there was a restriction at the barrel base it would affect both 3 and 4 inlet equally and also 3 and 4 exhaust UNLESS #4 cam journal clearance was subtantially tighter than the rest in which case the oil will take the path of least resistance and favour the other journals until the oil pressure and volume over came the restriction on 4.

This makes sense. Sounds like you've checked everything else. Have you looked at this idea? You could try swapping the cam bearings on no. 4 with the bearings off another position and see what happens, or possibly sand some material off of the lower shell (obviously the shell will then be scrap afterwards) and briefly run the motor to see if you get improved oil flow.

Thinking on, is it possible that number three cam journal has worn undersize, so the oil is finding the path of least resistance because no. 3 is slack, rather than no.4 being tight?

Only other thing that occurs to me is actually measuring the oil pressure to see if the pump is tired.

Must be very frustrating. Good luck.

Olly

[kev edwards]

If you cut the bumpy bits off an old cam you can test to se if you are getting a slight twist in the head when torqued down, a slight twist (this is just conjecture though) may stop the oil going across the bearing surface and onto the inlet 4 bucket, and also the possibility the cap on that one may be tight.

[z1bman]

what is the oil flow like without the camshafts fitted ?

[dougie1]

I think I’ve bored everyone enough with this on this site and the Butchered Classics forum, had some really good responses but I think I will try Kev Edwards idea.
Was opposed to trying that at first as I felt it was a bit like putting a bigger fuse in (not the best analogy) as I don’t think the problem was there when I bought the motor due to the cam lobe having no score marks. I will just do some final checks on the cams and shells before committing.
Kev, what sort of width and depth was the groove you put in and which direction was the groove from the oil hole, forward or backward.
Cheers all, Stephen.

[kev edwards]

My cams weren't scored either, i used a dremmel and round diamond bit, took to about .25 mm deep and a bout a 1 mm wide, 45 degrees going toward the outer end of the cam and back, I done all the lower ones, remember left and right will have to be mirrored, I got this idea from another club member, mine also had a cam cap that probably come from another bike and was binding, I resolved this by packing the offending cap corner by 200 microns, the joys of having a 40 year old bike that's had many hands through it's motor, I am happy with the results, it's far from stock and a ltd so the rivet counters don't care or scream heathen.