Anyone recall late oil level mod to timingcase?

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Keith.owen
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Re: Anyone recall late oil level mod to timingcase?

Postby Keith.owen » Fri Apr 24, 2015 9:31 am

Hi all,
I fully intend to investigate this mod. It sounds promising and since my NH project is not intended to be entirely original (no silk covered wire and lodge spark plugs for me) I don't see it as a problem. My only concern is not to butcher my cases needlessly.

I have posted separately on my search for a donor timing side crank case.

Keith
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Re: Anyone recall late oil level mod to timingcase?

Postby david.anderson » Fri Apr 24, 2015 10:11 am

I have a slightly different opinion. Oil mist lubrication with overhead valve models is the minor part of the lubrication. When the rockers are pressure fed there is a lot of oil to the top end which must drain down inside the pushrod covers and it should liberally lubricate the cam. The oil pressure to the rockers is very quick and the cam should be lubricated well virtually at start up.
When the rockers are fed from the return line, there is a lot less oil flowing to the rockers so less oil flows down the pushrod tubes to lubricate the cam. But more of a problem is that on start up it takes a fair while to have an oil supply to the rockers. The oil completely drains back out of the rocker oil line to the oil tank. Undo one of the rocker banjo nuts and see how long it takes after start up for the oil to start flowing. For that reason I never rev a cold engine.
The raised oil level mod clearly provides a lot more lubrication to the cam and followers, but after the engine is stopped, the oil slowly drains out through the timing side main bearing, so unfortunately it does not provide lubrication to the cam immediately after start up.
The side valve cams are only lubricated by mist. I have carried out the raised oil level mod to my side valve but I do wonder how long it takes for the oil level to be raised sufficiently. Fortunately the side valve cam is much bigger so the lobe will be dipping in oil sooner than the later ohv cams would. I do think that direct oiling by a small pipe as mentioned would be beneficial to the sv.
With an ohv the crankcase tapping and extra (pressure fed) oil pipe to the cam would not reduce the oil pressure or amount of oil to the pressure fed rockers. The oil pressure valve is located in the oilway to the bigend. As such the rockers and cam pressure feed would receive all the oil until such time as the pre- set oil pressure is reached, then the oil pressure valve opens and the bigend would receive the remaining oil. So it is the bigend and oil flung from it up the cylinder wall that would be reduced.
One final point is that with the raised timing case oil level mod, there would be more lubrication to the timing side main bearing. A bearing that is flooded in oil will fail rapidly. The mains are normally fed only by mist. It is fortunate that the crankcase is a fairly tight fit around the timing side mainshaft, so that the bearing is not flooded but it would be receiving a lot and possibly too much lubrication.
David

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Re: Anyone recall late oil level mod to timingcase?

Postby Vincent.vanGinneke » Fri Apr 24, 2015 10:37 am

If I now understand it correctly, the best would be to have a cup beneath the cam to lubricate it, but at the same time keep the rest of the camshaft department as empty as possible ?
Would that be a combination of this ill fated gasket and the 'HS' copper tube ?

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Re: Anyone recall late oil level mod to timingcase?

Postby Keith.owen » Fri Apr 24, 2015 11:32 am

So,
Really the question is 'is the lubrication of the cam adequate as originally designed and should one therefore not touch it'?

It is interesting to note that the later singles got their rocker feed from the oil return. The amount of oil received must be little based on:

the oil return pipe is much larger bore than the pipe taken from the T piece to the rockers - the rocker feed will therefore offer much more resistance to the flow of oil than the patch to the tank hence most oil will flow there

The oil flow from the return pump is sometimes no more than bubbles at low revs and after the sump has been scavenged

This raises an interesting question concerning lubrication of the later versions of engine. Perhaps the earlier ones provided better lubrication of the rockers and cams?

Keith
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Re: Anyone recall late oil level mod to timingcase?

Postby keith.hodgenia » Fri Apr 24, 2015 2:03 pm

David, I am interested to know more about "A bearing that is flooded in oil will fail rapidly." Keith.

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Re: Anyone recall late oil level mod to timingcase?

Postby nevhunter » Sat Apr 25, 2015 1:51 am

It certainly applies to aircraft Jet engines and woodworking machinery that turn at high revs. Nev

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Re: Anyone recall late oil level mod to timingcase?

Postby david.anderson » Sat Apr 25, 2015 10:22 am

It would be hard to have too much oil to the camshaft. The raised oil modification to the timing case was not invented for no reason, and it is not taking oil supply from elsewhere. But I do think that there would be enough oil to the cams when pressure fed rocker oiling is used. The reduced oil supply to the rockers when fed from the return line was a fad that was common in the era that Ariel did it. The main reason for reducing oil to the rockers was to help prevent over oiling of valve guides. Today, valve guide oil seals are used universally and top end oiling is always under pressure. I have the raised timing case oil level on all my singles except a 49VH.
At low revs there is no problem with a flooded bearing. However, as the speeds increase, oil whirl becomes a problem. Oil whirl is very undesirable because it introduces cyclic rhythms and vibrations. The cyclic stresses are imposed on the shaft, bearings and machine. Hydraulic pressure within the bearing cage due to increasing revs can split the brass cage that hold the balls in position, the balls move together, the outer ring moves in relation to the inner and the balls fall out of the tracks. There are however bearings that are designed for flooded applications, but they are a specialist bearing.
If you look inside your Burman gearbox you will see that the casing is very tight around the bearings so as to exclude too much oil or grease from the bearing and prevent flooded application. In the BA, the ks end mainshaft bearing even has a metal shield to the outer face so as to minimise the grease in the bearing. And the mainshaft bearings are not flooded unless the gearbox is over full. But I can imagine the gears would really flick the oil/grease about.I do however always pack the bearing with grease initially as it may run dry for a while otherwise.
David

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Re: Anyone recall late oil level mod to timingcase?

Postby BryanLambert » Sun May 03, 2015 10:46 pm

This is all very interesting. My recently acquired NG sprinter was described as having an ill-conceived oiling modification which severely over-oiled the cam chest. A pipe fitting can be seen mounted on the upper front of the timing chest which isn't a breather, because there IS a breather elsewhere. I do know that the previous owner, who made this reference, removed the outer cover (because he inspected the cams) but did not strip the engine further; so it sounds as though the mod in question was a direct feed to the cam area. I can well believe that this did more harm than good!

Digressing a little, I know from experience of racing BSA single cylinder engines in grasstrack that the C15 in particular has its rockers fed by a small pipe fed from a tee on the return line. I've never known this give any particular trouble, and given the extensive modifications often found in these engines, I'm sure that any required modification would be common knowledge.

Jawa track racing engines feed surprising amounts of oil to the rockers, as a direct feed from a Pilgrim pump. JAP engines are prone to over-oiling of the top end and consequent running problems caused by oil being drawn through the valve guides, but Jawas don't seem to mind and it all goes down the push rod tubes to lubricate the cams before draining into the crankcase and vent valves. These are 500cc singles capable of 8000rpm which have a solid reputation in various types of classic racing.

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Re: Anyone recall late oil level mod to timingcase?

Postby Mike Nash » Mon May 04, 2015 8:47 am

David, I'm very interested in your thoughts on risks of over lubrication of the timing side bearing as I'm keen to try this cam oiling modification on my VB. But will it really be a problem? Surely the nearest to a flooded bearing we have is the big end which although it may fail for many reasons never shows signs (as far as I'm aware) of distress due to over lubrication. And of course, on the VB at least, it receives all the pump can supply into a uncaged crowded roller bearing which probably has more bearing limitations than most.
Regards, MikeN.

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Re: Anyone recall late oil level mod to timingcase?

Postby david.anderson » Mon May 04, 2015 10:57 am

Mike
I have carried out the raised oil level modification to all my bikes except for those where oil is pressure fed to the rockers. I have done thousands of miles on my 57VH which has the raised cam oil level, with no problems. I was just pointing out that a bearing can be over oiled. In the case of a bigend it is a roller bearing and I was actually referring to ball races being over oiled. That is why I spoke about the cage splitting and allowing the balls to move together. I also said that the timing side mains would not be flooded but would be receiving a lot and possibly too much lubrication. I should have been more specific and referred to ball bearings. The gap around the timing side mains and the crankcase is minimal. When the cam oil level is raised oil clearly leaks through the gap and into the mains, providing a lot more oil to the bearing.
Norton Commandos have a steel disc fitted to the outside of the timing side mains to prevent the main bearing from operating in a flooded state. The oil level in a commando timing case is high and the oil pressure relief valve dumps all excess oil into the timing case. If the steel disc is left out the timing side ball race fails rapidly if the engine is operated at high speed. But in that case the oil does flood through the bearing and there is a lot more of it. The tight fit of the Ariel single crankcase around the timing mainshaft does limit the amount of oil to the bearing to what is probably an acceptable amount. As stated I have not had a problem but it is something that I have thought about but probably should not have mentioned.
David


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