Oil loss from new engine

did you check for excessive bore wear and correct it, did you hone the bores, are the rings correctly gapped, are the rings in the right order and the right way up, were all the grooves perfect, were the rings the right oversize and matched the pistons?

if all the above are yes, then it should be ok. a rebuilt engine should make almost no smoke or blowby. check with a compressed air feed where the blowby is occurring, if the same on all cylinders then start the rebuild again. if only one cylinder then you know exactly where to start.

mrcheerful

Everything is brand new. Rebored 998cc. Even though pistons were new the rings were rigorously checked and carefully refitted after the dry build (see my OP). I have never taken so much care with an engine as this one.

No engine should do this whether the rings are yet bedded in or not. Either the breathers are blocked so it is building up crankcase pressure or there is a serious piston blowby problem. Do a compression test first. If one or more cylinders are very low then it needs to come apart again. If not then check the breathers.

-- Dave Baker - Puma Race Engines

I have done a compression check and the figures are 179, 188, 184 and 190 psi. This is on a 998 with 10:1 ratio, Piper Magnum 270 and 29mm inlet valves. But I can't find any reference data to tel me if these figs are OK.

Basically, something is *very* wrong. A properly reconditioned engine will not blow oil out of the filler cap, even while running in - even with the tolerances when it was current. And today's tighter tolerances make this even more impossible.

Those figures are fine, but they don't tell you if an oil control ring is snapped or seized, or there is excess side clearance on the rings giving an oil pumping effect.

mrcheerful

What's the oil level like?

There are only three routes that engine compression can get to the oil filler cap: past the piston rings through the valve guides or past a loose guide from a cylinder to an oilway through the head gasket

Try taking out three spark plugs, putting your hand above the oil filler neck and spinning the engine on the starter. Repeat, moving the one remaining spark plug to each cylinder in turn. Hopefully this will identify the cylinder that is providing compression to the crank case, by feeling a pulsed draught on your hand when the spark plug is in the faulty cylinder. Then, I'm afraid, it is a process of elimination to find out how it is getting there.

Jim

"Asolepius" wrote

that sounds high to me - or is it normal for a Sprite?

the relief valve operates at 50 psi

Normal running is 30/60 psi Idle 10/25 psi

If this is any help.

You live and learn. My Stag shows about 20 at idle and 50ish at 2000rpm. 45 at idle sounded high.

Thanks guys for all these replies. I have just been for a 120 mile run and the engine pumped a fair bit of oil out of the filler cap. But I think I have some idea of what's going on. For a start there was nothing in the catch tank apart from a few ml of water. The oil mist I was getting is now minimal or absent. I have realised that the filler cap doesn't seal - it's a rather rattly fit. This never mattered with the bog standard engine but I am using the latest competition rocker shaft with different and much better oil feed. I think it is not blowby but splashing that's causing the oil loss. I'll try the test Dave mentions above, but I will also fit an O-ring inside the cap to seal it. I don't think I have any problems with oil control rings as I am not burning oil - the plug tips are pristine. Also if blowby were the problem I would imagine there would be combustion products in the escaping oil , but it's crystal clear. I'll let you know the outcome of these actions.

I think we now have the answer. The O-ring in the cap has completely stopped any oil leaks of course, but more to the point there is still nothing coming out of the breathers into the catch tank. I should have realised - if it had been oil mist the whole engine bay would have been coated, but I just had clear oil running down the engine. All I have to do now is to clear up the mess on my beautiful engine. How easy it is to be misled......

Hmm. The oil return to the sump is via the space round the pushrods, etc. And should be more than adequate for that flow given it's gravity.

If the waste oil flow out of the rockers is so great to push out of an unsealed oil filler cap I'd be inclined to sort out the return path - rather than seal the filler. No engine is designed to have the valve seals and rockers submerged in oil.

Somewhere there was mention that it had a modified rocker shaft - is there a position that should have been fitted?

There is no option as the shaft is located by a tapered screw that only fits in one hole. I'm not suggesting the rocker box is filling up with oil - it it were I'd lose all my oil within a few miles. I just think there's a fair bit of spray off the rockers.

Is there any sort of restrictor anywhere on the oil feed to the rockers on this engine? Something deep in my memory tells me that there is, but I can't for the life of me remember where it should be - probably because there isn't one. Can someone please resolve this for us?

Ron Robinson