Ever wondered how the timing chains and gears get lubricated, or more to the point where does the oil come from? Well I did, and realised the only way is from the oil pressure relief blow-off valve. This vents surplus oil into the timing case and fills it to the over flow level hole at the rear of the crankcase where it drains into the crankcase sump. The timing case holds abouta cup of oil before the overflow level is reached (the height is aboutlevel with the crank mainshafts) which lead me to think of a couple of thoughts worth mentioning.
When, the timing cover is replaced it will be empty of oil. This can often be after a complete enginerebuild. The temptation after you start for the first time is to hardly rev the engine for quitea time, maybe keeping the revs down for even longer even when riding it.
As the oil pressure relief valve only opens at around 50 PSI maybe as high as 60 PSI, there is quite a good chance thatthe oil pressure does not rise to the blow off point. You can see then that the timing case will remain dry, or couldtake a very long time, before oil fills the case. Remember the oilblowing off is only the surplus and not the full amount from the pump, just enough to stabilize the pressure, so it might be quite a small amount.
The only way to safe guard this is to make sure you rev the engine to at least medium revs for at least a minute or two, but better still would be to fit a temporary pressure gauge and rev the motor to a point that a blow off pressure has been met. This will be when the pressure stabilises and does not rise past the blow off pressure. You can then have a good idea that some oil has filled the timing case.
It also crosses my mind that a worn engine might have trouble ever reaching the blow off pressure at all, which will mean the oil in the timing case tends not to be replaced that often, even after an oil change as it just is the same oil sitting there.
You can see then that an occassional bit of high revving with cool oil on a high mileage engine might have some benefit. Only pressure monitoring will tell you what is really happening though.
With a new rebuild, for machines with rev counter drive holes, it could be possible to top up the oil with a funnel before the very first start, otherwise make sure you have the chains gear and spindles well oiled up.
Just a thought, but it might be worth taking note after that very expensive rebuild? Every little thing helps.
Les H
Hi les, I agree, Les Emery…
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Hi Eugene. Thanks for that…
Hi Eugene. Thanks for that, Les Emery's article is very informative and interesting. He could have suggested blocking the oil feed back into the oil tank with a finger to really deluge the head with oil (only appropriate for scavenge oil lubed heads). I guess this could be done quite often at intervals forthe first few tens of miles after a rebuild.
His figure of 70 PSI blow-off pressure is higher than I had said. I know Lesrecommends a straight grade oil, which will develop higher oil pressures with cool oil rather than the more commonly usedmultigrades which will be thinner at lower temperatures (but still thicker than hot oil) The use of multigrades will mean higher revs will be required at lower temperatures to initially fill the timing case, but once filled this aspect has no real concern when normal riding style is adopted. It was only the initial rebuild start up that I was writing about.
Interestingly though, the thinner multigrades will have more chance of wetting the cams at colder oil temperatures and lower revs than his recommended straight grade oils as thequantity and flingwill be greater from the big ends. You may ask why a greater quantity? Well the pump at any revs always pumps aspecific amount or volumeof oil. But cold straight oil will create a higher oil pressure as the big ends are more restrictive to thicker oil than thinner oil which will mean the blow off relief valve will more likely to vent off thick oil to keep the pressure down. The more oil you blow-off, the less will actually get to the big ends (the pressure at the big ends will be the same though)so the quantity being flung off from them and hitting the camshaft will be less.
Regards
Les H
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Hi les,
I agree, Les Emery has a very good tsch service note on his website about running in a new cam & its initial start up & lubrication. He alsorecommendskeeping the rev up & checking the pressure release valve setting. Here is the article:
As the maker, there are three things that we can do to help prevent camshaft wear.:-
The engineer fitting the camshaft has the greatest responsibility for proper running in of the camshaft.Following the steps described below will insure a long and trouble free life from the camshaft and component parts.
If the engine is dismantled for repair or maintenance, it is important that the tappets are kept in the correct order.Each tappet is paired with a camshaft lobe and swapping the tappets around can lead to a camshaft failure.
Research indicates that most camshafts that wear out start to fail during the first few moments of operation.Many camshafts are irreparably damaged before the engine is started, because the basic rules of camshaft running-in have not been followed.
The cause of premature camshaft and tappet failure is metal to metal contact between the tappet and camshaft lobe.Should this contact occur due to lack of proper lubrication or excessively high pressure due to valve train interference shearing oil film, galling will take place.When galling takes place, metal is transferred from the camshaft to the tappet or from the tappet to the camshaft in a process similar to welding.Small areas (microscopic high spots present on all machined parts) become overheated due to friction and pressure and bond together, tearing sections loose from the tappet or the camshaft lobe.These pieces of metal remain welded to the face of the tappet or the camshaft lobe and create further local overheating during the following revolutions of the camshaft and lead to ultimate failure of the affected camshaft and tappet.
There are a number of things that can lead to the ultimate camshaft failure:-
Make sure that the pressure release valve is set to open at the minimum oil pressure of 70 P.S.I.
CAMSHAFT WARRANTY
New tappets (camfollowers 067820) must be fitted before assembling the engine or the warranty will be void.
Camshafts returned for inspection must be accompanied by tappets and valve springs.
Tappets returned for inspection must be accompanied by camshaft and valve springs.
Removing and Fitting the Tappets
The tappets are located in the lower part of the cylinder barrel retained by four 2BA Screws (two to each plate) passing through a separating plate for each tappet.
To remove the tappet cut and remove the securing wire for the plate retaining screws.The tappets are machined in pairs, THEY DO NOT INTERCHANGE.
It is most important when fitting new tappets, to apply camshaft lube (part number 067128) and ensure the chamfered edges are SIDE BY SIDE FACING THE FRONT OF THE ENGINE.Inadvertent reversal will prevent correct lubrication of the camshaft and tappets.
Firmly tighten the plate retaining screws and secure with steel wire linking the two screws.
Les Emery
Service Release 19/06/01
Copyright â Norvil Motorcycle Company 1982
Page last updated 27/11/02