Thanks for all your replies. I already checked about the 1/4 BSF bolts not being too long, and also that the rocker feed bolt aren't too long. It was when I was examining that that I realized the restriction to the oil is not the hole in the rocker feed anyway. It is true that there is a lot of oil mist and spray in the timing chest already. There is always plenty of oil in the head whenever I look in there too. But many other motorcycles have problems with cam wear and often it does seem that the oil just doesn't get to the right place. It is hard to keep the oil inside. It only goes where we don't want it to go. Oil is unlikely to rush towards a rotating shaft! I had to put an additional spring on the decompressor to stop it leaking there, and that is right behind the cam where I don't seem to have enough oil! I know that many people are happy with the 1mm holes in the feed bolts and some other people find that the original 1/32 holes were OK, but with the wires there may not be enough oil. Terry Prince told me the 1/32 holes are too small, and that I should go to 1mm. I am going to try a lot more oil and see if that helps. As long as the pump can still clear the sump I think it will be an improvement. I think it will as there will only be two extra 1/16" holes going back into the engine. I don't think it makes much difference what size the holes are with the standard arrangement or the locking rocker bolt system, as when you look at it the restriction is really in the rocker bushing rocker pin clearance. It think there were quite a few things wrong on the Vincent twin engine even though Phil Irving was a genius and there is hardly anyone else I admire more, except for the Wright brothers. I am sure that I will still have the same supply to the rocker pins as I have put three holes in the top of the rocker feed bolt, but just one hole at the bottom. The same small pressure that is in the return line will still be present at the inlets to the rocker pin holes. From the wear problem I have it does seem as though the two exhaust lobes are doing better than the intake lobes. There does seem to be a lot of discussion about this topic for many years in MPH, I am not the only one who has had problems. Some people even add an extra oil pump!!! I think maybe there is a problem but I am hoping I can solve it a bit more simply. The stuff that came with my basket case was horribly worn, and had been bastardized in Argentina to keep it running. I just looked in a box of parts from that; the MKI cams that came with it weren't to bad only a little wear on one lobe. Maybe I should try them out with some new followers. The cam followers I got were horrible. They must not have been the ones that went with the cams.
ET: Engine (Twin) Cam Wear
- Thread starter Nigel Spaxman
- Start date
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- cam wear
Hi Nigel
What are your valve seat pressures like??
What are your valve seat pressures like??
Robert
I have never checked that. I was wondering if that could be the problem. I am using R&D springs and all the stuff from Terry Prince that goes with them. I guess if I hooked a spring scale onto a rocker arm and pulled up on it I could get a pretty good approximation.
I have never checked that. I was wondering if that could be the problem. I am using R&D springs and all the stuff from Terry Prince that goes with them. I guess if I hooked a spring scale onto a rocker arm and pulled up on it I could get a pretty good approximation.
On the engine I am building I measured the height when seated and then just put them on a bathroom scale under the head of the drill press and closed them down to the height. Seat pressure about 95 and if I recall about 140+ (approx reading) over the lobes. I remember John McD saying 100 seat and no more than 150 over the lumps and that was on Mk2 cams.
Last fall I was tidying up the timing chest on the Comet and noticed wear on the cam. I am not sure if it was new when installed (I bought it as a runner) and had VERY few miles on it, maybe 1000. It came out and stellited Robinson cam and followers went in. My Woolly Rapide probably has 70K miles on the cams and I haven't needed to adjust them in years. I have checked a couple of times but nothing to do.
Last fall I was tidying up the timing chest on the Comet and noticed wear on the cam. I am not sure if it was new when installed (I bought it as a runner) and had VERY few miles on it, maybe 1000. It came out and stellited Robinson cam and followers went in. My Woolly Rapide probably has 70K miles on the cams and I haven't needed to adjust them in years. I have checked a couple of times but nothing to do.
I made a tool to measure the seat pressure. Cyborg mentioned that Dan Smith had one. I figured I could make one faster than going and borrowing Dan's. I had an old rocker arm that someone had ground in the wrong place so I never want to use it and I had some old bronze rocker bushings that someone had made in Argentina. The tool uses a fish scale and the hole for the scale is four times further away from the valve than the rocker pin so the measure on the scale is 1/4th of the pressure on the spring. The spring opens at about 28 lbs on the scale which is around 112 lbs which is not bad. When the valve is near wide open it measures 44 lbs so that is 176 lbs. I guess this is only a little higher than it needs to be, according to Robert. Is this to much pressure? This is with some new springs, top collars and upper valve guides from Terry Prince. I think they are R&D springs. When I wore out the first cam lobe last year I was using standard valve springs top collars and upper valve guides, this was some stuff that came with my basket case. I don't know what pressure those had but the wear happened a lot more quickly and it was worse. I think it is likely that those springs were weaker than the ones I have now though. Those ones were larger in diameter.
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sent you an email with some information. To your gmail account.
Eugene, thanks for that information. According to that info and Robert's advice my valve seat pressure it too high (about 25%) and this is likely the reason for a lot of the wear problem I have. I didn't have this wear problem when I was still using standard vavle springs. (I had wear on one lobe and none on the other three) I am going to try it for another season though with the oiling mods I have already completed. If that reduces the wear then before I put any new cams in I think I will reduce the seat pressure to about 100 lbs. Has anyone tried the stelite followers with hardened cams? That is the combination that works well in Triumphs, BSAs, and Nortons.
I believe Robert is running that combination. He would know better than I.
Hope it works out and look forward to seeing you at some point soon.
Hope it works out and look forward to seeing you at some point soon.
Stellite cams and followers, a little harder on the cams than the followers. Gary Robinson stuff.
I am using the Gary Robinson stellited cams and followers, no wear yet.