ET: Engine (Twin) Cam Wear

[davidd]

Stellite cams and followers seemed to be mandatory for racing. When I had Megacycle make my racing cams I had them harden them. I did this in place of the stellite. They harden them to 60-65 Rockwell. In the first racer I also had megacycle harden some stock followers. They have all been running in the racer for a decade and no wear yet.

John Healy, who has a hardness tester, tested the stock Club followers and found them to be 60 Rockwell. At that hardness I believed they were suitable for use with the hardened cam right from the Club. I am not sure what the stellite followers test out to.

I don't use old followers just to be safe.

David

 

[Nigel Spaxman]

I took the bike for a test ride last week. The timing chest is very quiet now. All the extra play has been removed by the addition of a few washers. One of the followers which was badly worn was replaced. The oiling mods didn't work. The oil doesn't return to tank enough. The addition of three extra holes only 1/16" diameter returning oil through the rocker feeds is too much and the engine gradually fills with oil from the tank. It is surprising to me that three 1/16" holes are to much, since the return pipe has a inside diameter of about 1/4". Today I am going to try first plugging one of the 1/16" holes, then two then maybe three. I am hoping the plugging just one of the holes will be enough so that I get sufficient return to tank. If it is I will plug a second hole and I will still have one hole giving me a bit of extra oiling. I won't be surprised though if I end up having to plug all three holes. I am pretty sure that I will still have cam wear problems. I think my seat pressure is to high. I will ride it for another season and see what happens.

 

[greg brillus]

Mind you, if you add the sizes of three x 1/16" holes together, that's probably not much smaller in area than the bore size of the return lines, which are in themselves quite small really. But that was an interesting test though just the same..........Perhaps the restrictions further towards the tank add to loosing the oil in between. It does show that you can't change too much before the system fails to function properly.

 

[BigEd]

Mind you, if you add the sizes of three x 1/16" holes together, that's probably not much smaller in area than the bore size of the return lines, which are in themselves quite small really. But that was an interesting test though just the same..........Perhaps the restrictions further towards the tank add to losing the oil in between. It does show that you can't change too much before the system fails to function properly.

The diameter of a 1/16" diameter may only be twice the diameter of a 1/32" diameter hole but the actual area is much greater so much more oil is going back into the sump rather than to the UFM. (My maths may be suspect but try 3.142 x r squared.) Also, although the return side of the pump has a larger capacity than the feed the oil in the sump is aerated so the effective amount of oil scavenged is less.

 

[timetraveller]

Double the diameter and you get four times the area. You can ignore Pi etc.

 

[vibrac]

Think of all those hours PCV and his team spent in a back shed in Stevenage all of us who wander from the path of Phil should do so with the knowlege we have got to go some to get better results

 

[Nigel Spaxman]

I quickly did some of the area calculations. It turns out the three holes I added are about 18% of the area of the cross section of the return pipe. (taking the return pipe ID as 1./4") There must be some areas in the return pipe though where it is restricted more than that, probably in the return banjo bolt for example. When I blow air through it doesn't seem like there is much restriction. I am hoping that when I am finished I can perhaps leave one of the 1/16" holes open to have a bit more oil going down the exhaust push rod tube on the rear cylinder. That might only allow an additional 6% more oil to go back into the engine. Maybe the existing system can't handle any extra flow back to the engine. The only way to find out is to try it. That is what I will do in the next few days. I already plugged one hole and that made no noticeable difference.

 

[oexing]

Nigel,
I ´d suspect your oil pump to be clapped out. At least that might be one cause for very poor scavenge action. That pump piston has to run with minimal clearance otherwise the suction will be very poor. Had this drama a while with the four valve Horex 600 that took ages to drain the sump after long times of no use. Finally I had a big session with the pump to get perfect fits in all places and Bingo !

Vic

 

[Simon Dinsdale]

Nigel
It's not just the hole sizes versus the pipe bore. After the rocker feed holes the oil pump has to carry on lifting the oil for another 8" approx in height (rough guess) as the open end of the oil return pipe is near the top of the oil tank filler neck. On a twin there is also 4 rocker feeds taking oil and in theory the first which is the rear cylinder inlet should get the best flow. The Vincent oil pump at its best produces very little pressure or flow. It's all to do with fluid dynamics.

 

[BigEd]

Nigel,
I ´d suspect your oil pump to be clapped out. At least that might be one cause for very poor scavenge action. That pump piston has to run with minimal clearance otherwise the suction will be very poor. Had this drama a while with the four valve Horex 600 that took ages to drain the sump after long times of no use. Finally I had a big session with the pump to get perfect fits in all places and Bingo !

Vic

Vic makes a good suggestion here to check the oil pump. Is there a simple way to check how good the pupm is other than removing the filler cap and looking at the oil coming out of the small hole in the pipe? That is simple but not very scientific.