ET: Engine (Twin) Cam Wear

[oexing]

Hi Norman,
thanks, more to think about, I do not know how all these effects work out in real life. You may be right. I got twin start pumps at hand anyway and will fit them certainly, just am not quite clear about their behaviour in this discussion. Maybe your explanation should be a little tweaked as we have a piston oil pump here. You don´t get a steady oil flow from it that may show a higher pressure at higher flow rate from twice the speed. It is only twice the number of oil squirts per minute with pauses in between. If that provides a higher pressure I do not know, maybe only slightly higher.
At present I have run out of ideas about fault finding with wet sumping in this discussion, a night´s sleep may help hopefully .

Vic

 

[oexing]

Allright, got a new idea: Disconnect the return line and fit a clear hose for a test. Get the engine running for some time. As soon as the oil level in the sump rises high enough there cannot be any air bubbles in the return line , right ? That is at least a test for some possible air leaking into the scavenge side of the pump that reduces the returned volume a lot. At this time I still suspect some air leak due to poor fit somewhere around the oil pump. Just thinking . . .

Vic

 

[timetraveller]

Hi Vic, I'm not sure that I understand the test. When you say "disconnect the return line" do you really mean disconnect or block off. The way that I understand it is that however much the 'feed' side of the pump is circulating the 'return' side tries to take more. I don't think that one could do anything with the pipes to fill up the sump. It might work if one filled the sump up first before starting the engine so that for a while the return side only sucked oil and no air. When I've been involved with engines like that the amount of smoke produced means that one does not want to do it for too long. I've run two start pumps in all my engines for years and the speed at which the oil starts to return to the tank compared with a single start pump makes me very happy that I do. There are people who have trouble with oil or oil vapour escaping from the oil filler in the middle of the petrol tank and so do not like the twin start system. However, it is the simplest thing to stop that. I used a curved piece of 'baked bean can' (cans for other purposes are available). I fastened one end under the adjusting screw for the chain feed and then gently curved the piece of metal backwards and downwards. This ensures that the returning oil follows a nice smooth path downwards and completely stops any upwards spray.
If I'm right about the pressure building up due to restrictions in the return line when a two start pump is used then any air bubbles would also be slightly compressed and help to smooth out the feed to the various orifices. The air (gas) can be compressed while the oil cannot. (For pedants I know that is not exactly true but it is near enough for this problem.)

 

[oexing]

Norman,
my test should show up if there are any air bubbles in the return hose before the sump has been pumped to the low level. The actual problem seems to be that the scavenge side of the pump is not effective enough to drain the crank case, possibly because the extra oiling from the return line was increased above the amount the scavenge side can cope. I suspect an air leak in the scavenge side as cause of poor performance of the suction department. So I´d disconnect the return hose at the oil tank , extend it with a clear hose into some container to see if any bubbles show - that is , before the crank case is drained to the low level. Only then you´d expect to get air into the return line. And only when no air bubbles show at higher level than at low state we can assume the extra oiling to be excessive for the drain pump side. Or some other cause we did not yet think of . . .

Vic

 

[Nigel Spaxman]

Last night I plugged all the new holes in the rocker bushings. The oil return seems to be normal again now. I don't think there was every anything wrong with my oil pump. Before I started fooling around with the oil return holes everything worked normally. (except I wore out my cams) When I plugged the holes I used 1/16" wire to plug the them. On one of the wires I filed a flat so a slight bit of extra oil would drain down the rear cylinder exhaust push rod tube. It won't be much more than might pass through the rocker bearings though. Maybe down that push rod tube I will have twice as much oil as before. The normal holes in the rocker bearings that are either 1/32 or 1 mm have been replaced by three 1/16" holes, but since below that the only path into the bottom of the engine is past the rocker bearings, I don't think opening those holes out over 1mm makes any difference at all.

I think the double start pump must be a great idea as well because the oil circulation rate is very slow on the Vincent. With the bigger pump you are sure to get a lot more oil everywhere it is needed. My impression without taking any measurements is that on my Triumph or Norton the oil circulation rate is at least double that of the Vincent.

 

[vibrac]

But those parallel twins are plain bearing big ends they have to use a fair amount of power to pump buckets of black goo round their innards the Vincent doesn't have to it has roller big ends no more than it needs woven steel pipes to keep the oil in as it pipes it to the tanks
If a private detective can run 100000 miles with a sidecar without a strip down there is not much wrong for road use with the basic system

 

[Bill Thomas]

But those parallel twins are plain bearing big ends they have to use a fair amount of power to pump buckets of black goo round their innards the Vincent doesn't have to it has roller big ends no more than it needs woven steel pipes to keep the oil in as it pipes it to the tanks
If a private detective can run 100000 miles with a sidecar without a strip down there is not much wrong for road use with the basic system

And most of us have trouble keeping the oil IN !!. Cheers Bill

 

[macvette]

I'm not sure you are right about that Vic. A small gedanken experiment for you. Suppose that the two start pump gives twice as much oil flow, then restrict one of the apertures it flows through. What will happen. I guess that we have all done this with a hosepipe. Get the water flowing and then squeeze the end of the pipe with your fingers. You know what happens. The water goes further. There is no more water flowing but the pressure has gone up. One restriction with the Vincent oil return flow is the four small holes in the banjo bolt underneath the oil tank. More oil flowing through that, and other restrictions, will increase the pressure so that all those little holes further down the return will be subject to more pressure and hopefully pass more oil. I don't think that it has anything to do with the ratio of scavenge to feed side of the pumps. Provided that the scavenge is greater than the feed the sump will stay 'dry', which is part of what we are after. Tell me where I am wrong with this if I am.

Hi Norman,
We know that water and oil are, for all practical purposes, incompressible and fluid flow is governerned by the conservation of energy. When you squeeze the end of you hose pipe, reducing the size of the orifice, the fluid trades pressure for velocity hence the water goes further because it's velocity is increased and pressure reduced after the orifice. You don't need a hose pipe to convince yourself of this, a visit to the loo will do. The same thing happens in a piping system when the diameter reduces. When the liquid hits an increase in diameter, the liquid slows down and its pressure increases ( not fully to system pressure because of frictional and turbulence losses if the transitions are not gradual). Look up " Bernoulli Eqation".
It seems to me that in principle there are two possible causes, inadequate oil flow and/or poor metallurgy in that particular cam/ follower. The prime suspect for inadequate oil flow could be poor scavenging. On my single start pump, when the bike is started and run at tick over, the oil is pumped out in solid pulses which in a minute or so are reduced to the occasional spurts of mixed oil and air. I suspect if this does not happen, the issue is with the pump , air leaks on the suction side or oil leaks on the discharge side. I suppose it's worth checking that the rubber pipes connecting the rocker feed pipes are not restricted by being broached internally when the metal pipes were fitted.
Mac

 

[Bill Thomas]

We have had this before, With Vincents, And in the car world, Ford and Vauxhall, All types of oil feed mod's, In the end it was bad Cams/Followers. Cheers Bill.

 

[timetraveller]

Regarding Vibrac's posting, three above; it was not just the 100,000 mile bike but also Ron Vane's record breaking bike and many other Vincents. Ron told me that he had never felt the need for a twin start oil pump. I just like to see the oil getting round quickly. Regarding the cam wear; we all know that Stellite cams and followers do not wear out. Also I understand that those who have the French modification of fitting an extra high pressure pump to squirt oil at the cams also do not wear out their cams. I think that this demonstrates that there are two problems, material and lubrication and there are alternative solutions to both. Regarding the general subject of lubrication there is another problem. Over the years I have helped many people replace their bike's big ends. In every case the problem has been that the annular groove at the end of the crank pin is packed full of black and metallic particles. Carbon and wearing parts at a guess. The original oil filters clearly do not get rid of all this debris in the circulating oil and it centrifuges out to eventually block that oil way. Fitting crank pins which are oversized where they go into the flywheels (and thus do not have that annular groove) and circulating more oil with better filters is my suggestion.