Rate of oil return to the oil tank on twins

[Roderick]

I've just rebuilt a 1960 G12 and at the same time a 1955 AJS Springtwin with a 1957 600 twin engine in it. I started up both engines yesterday and noticed that the 600 engine is returning oil to the oil in a very strong, steady stream with occasional breaks, almost like your kitchen sink tap whilst oil from the 650 engine returns in sort of slobbering pulses & much less strongly than the 600 engine. Both engines' sumps were drained before the test and then primed with a 1/2 pint of oil and run long enough before the test to be sure all of that oil returned to the tank. Neither engine's exhaust is smoking.

I rebuilt a 1961 31CSR some time ago and the rate of oil return to the tank on it was somewhere in between these two.

Over the years I have had experience of twins of other makes (BSA Golden Flash & Ariel KH) and been surprised at how low the rate of oil return can be.

How strongly or how much oil should you see returning to the oil tank on AMC twins? Is there cause for concern in either case or both?

Rod?

[ChrisTheChippy]

My 650 csr seems to return in a steady pulse on tick over if that helps. As long as I see the oil returning I'm a happy man. I think no two bikes would be the same because of factors like build quality of the engine and differing wear on the oil pump over the years . I think a steady pulse should be fine. Mine gets used and not blown up yet so I guess that oil rate is fine .

[Duncan]

Just a thought, could it be that as there is no oil pressure relief valve on the 600 engine all the oil is going straight to the sump whereas the 650 engine is throwing some into the timing chest, so it is taking longer to find its way to the sump?

[Roderick]

The 600 does have an oil pressure relief valve fitted. I'll have to check that it isn't stuck open for some reason. I've ordered an oil pressure gauge to test oil pressure in both bikes too. Do I take it that it's "slobbering pulses" rather a long steady jet of oil is what most people would expect to see at tick over or slightly above when looking into the oil tank?

[ajscomboman]

I'd be interested in finding out where you've got the pressure relief valve fitted on the 600. Don't quite like the sound of a slobbering pulse but it should be a steady flow rate rising and falling with revs. A video would be a better indication rather than words.

[Roderick]

Sorry, Rob, I can't remember off-hand where the oil pressure release valve is fitted on the 600. Next opportunity I have to look in the filter chamber or the timing case I will report. A video of the flow is a good idea but I will have to wait until my son visits because he will know how to uplift a video onto this forum. I'm afraid I don't.

[MalcW]

I'd be interested in finding out where you've got the pressure relief valve fitted on the 600. Don't quite like the sound of a slobbering pulse but it should be a steady flow rate rising and falling with revs. A video would be a better indication rather than words.

I thought that since the return pump is larger than the feed pump, it potentially returns oil quicker that it's provided. So oil returning in pulses is the norm, since the sump should predominantly be empty? But I could very well be entirely wrong.

Malc

[Mollbhan]

Have to agree with Malc, I have a 61 G12, the oil returns in pulses as I would expect, if the oil returns in a constant steady stream it may be building up in the sump.

[clive]

Before I fitted an anti-sumping tap on my twin (with linked mag cutout could not trust myself without) it always seemed to return oil in a constant stream when I checked it before riding off. It was only after I fitted the tap I realised it was simply emptying the sump (and it now pulses after a bit after starting).

[1608]

My 1960 G12 oil return pulses, as I believed 'they all did that Sir'. Perhaps a general consensus of any or all owners of the late twins on here could clear this matter up. As it happens, I noticed that the AMC bikes have a 1/2" flow and return pipe. My Ariel and likewise BSA twins only use a 1/8" bore piping. So, 1/2" bore pipe emptying the sump will initially gush and then simply pulse thereafter. Its to do with flow rate as opposed to preasure.
Nice bit of waffle, eh!