The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: nigeldtr on 25.09. 2009 17:52

Title: Oill pressure and camshaft lubrication
Post by: nigeldtr on 25.09. 2009 17:52
Perhaps someone can help.

1.As I understand it, the camshaft gets its oil supply when the pressure release valve opens.
2.If the engine is cold, oil is thick and pressure release valve opens ? everything gets plenty of oil
3.Engine gets hot, viscosity falls and the oil pressure drops down to say 30 psi or less.
4.Pressure release valve now stays closed for the rest of the run as it only opens at above 50 psi.
5.Park the bike things cool down, viscosity goes up valve opens, start all over again - fine.

So, to keep your camshaft well lubricated don't drive for hours on end without letting things cool down ????

My GF has a tired main bearing and I have fitted an external pressure gauge to see what is going on. I pick up the pressure before the release valve. When cold, pressure shots up and stays around 50 psi where the valve opens. Once the engine gets hot this falls away and I am running around on about 15/20 psi oil temp 70C (don't worry I am about to change out the main). Surely, anyone who has a less than perfect timing side main is possibly going to have problems on a longer run with lubrication of the camshaft and followers unless the oil supply from the rocker box is sufficient to lubricate the cam when the engine is hot ????

Sorry If this all seems a bit daft but I am really struggling to believe that the oil pressure release valve on most bikes opens again once the engine is up to running temperature.

PS I fitted a new SRM release valve and found this opened around 70 psi so this baby will shut off oil even earlier *eek*

Title: Re: Oill pressure and camshaft lubrication
Post by: bsa-bill on 25.09. 2009 18:33
I think that given there are not A10s lying at the side of the road all over the world with oil starved cams there is more to thier lubrication than that provided by the pressure relief valve.

Some thought would be

1. the cams live in a little sea of oil in a through, this should negate a need for constant replenishment to some degree
2. how does this little sea get replenished?
3. from the rocker box ?, well oil from the rockers has to go somwhere probably does come down from the intake valve side
4.Owners who put breathers into rocker box maybe doing their cams no favours as possible any pressure in there should help oil down to the cams.
5 Slpash from the crank - not sure about this one as the cams may also splash a bit about throw oil out of the through

And finaly how can a desiqn that's been around for so long still raise question like this, perhaps this is why they still hold our interest

All the best - Bill
Title: Re: Oill pressure and camshaft lubrication
Post by: Dynamo Regulators Mike on 25.09. 2009 20:18
Yes, the oil to the big ends gets thrown around as well. The cams do not need a lot of volume for protection.
I found the SRM pressure regulator gave about 70 psi as it came. But mine had a couple of washers preloading the spring. I removed these with SRM's blessing to get just about the 50 psi the lubrication system was designed for. One side benefit is that presumably the pump drive gets an easier life as well as reducing leaks.
cheers Mike
Title: Re: Oill pressure and camshaft lubrication
Post by: A10Boy on 25.09. 2009 20:28
I agree, there's a significant amount of oil pumped through and thrown off the big ends, it goes all over the internals of the crankcase, plenty to keep the cams wet.
Title: Re: Oill pressure and camshaft lubrication
Post by: Rusty nuts on 25.09. 2009 20:41
Oil trough? How lucky you are!!!
Spare a thought for those of us with longstroke engines that rely on oil fling from crank webs & whatever (if anything) that trickles down the pushrods to lube the camshaft. Keep those rockerboxes pressurised!
Wet sumping (in moderation) ensures at least the camshaft gets some good lubrication on startup before a run, and for that reason I love it!

Title: Re: Oill pressure and camshaft lubrication
Post by: nigeldtr on 25.09. 2009 21:22
Well seems we have a good consensus here! I agree with the, drip splash and throw it off theory!! As said earlier, it can't all hang on oil pressure, when I consider what me and the lads all road around on 30 years ago we would never have got anywhere. I find it amasing that they every ran at all considering how badly they were maintained after the pub on Sunday afternoon - all credit to BSA.

Hmmm perhaps it was the wet sumping that kept them all alive - now there is a interesting and dangerous theory *smile*
Title: Re: Oill pressure and camshaft lubrication
Post by: rocket man on 25.09. 2009 21:56
i will stand back your right theres a lot to be said for wet sumping
it keeps your crank oily  *smile*