A10 SR Serious Smoking

[KiwiGF]

Hi KiwiGF,
Thanks for your ideas, appreciated.
The test I did by doing a quick engine run with the sump plate off (see earlier post) confirmed that a serious amount of oil was ending up in the crank case. Certainly more than was being pumped back to the tank. As you say the end feed has to be a suspect as well as the scavenge/return side. So I will be replacing the end feed seal and checking the return path carefully pre rebuild.
Its very evident that the SRM high capacity pump is capable of flowing as much oil as the clearences around the engine will allow.
Agree that debris bigger than clearences won't get through but as the clearences wear bigger more crud will find its way past, slowly increasing the clearances, - a vicious circle. Given my findings of debris during the parts cleaning process, it was definitely getting past the big end shells. (Yes, they are completely shot and were adding to the crud).
I did find some crud in the sludge trap but not much, probably the detergents in the oil carrying most of it onwards and back to the oil fiter on the return side.
Also agree that barrel wear is one of the main causes for the smoking, exacerbated by the abnormal amount of oil in the crank cases from end feed seal and/or the big ends.
As I said in an earlier post, this looks like a 'perfect storm' of several contributing factors.
One thing is for sure, as a direct result of this experience, I am going to know a heck of a lot more about the A10 engine, what does and doesn't suit it and how it really works than I thought I did.
Cheers,
Dan.

I did read the earlier post about the oil return test you did and I am still wondering if you MIGHT have drawn the wrong conclusion (probably not so please forgive me if so).

All the oil from the supply side of the pump ends up in the crankcase, either by passing through the big ends or pressure release valve. The volume of oil going into the sump CANNOT exceed the volume pumped through the supply side. “In theory” the geared pump is pretty much a constant volume pump at any given speed, in that the gears will drive a given volume at a given speed regardless of the pressure in the supply side, some oil will “bypass” or leak past the pumps gears but not much.

I very much doubt the volume of oil pumped through the supply side is affected much by the big end clearance, but I do not have facts to back that statement up. The oil pressure drops right down when the oil is hot and the PRV then has no job to do, it basically is a safety valve that only operates when the oil is cold (from what I have read elsewhere, I don’t have a gauge ).

The pump is if course in effect two pumps, one pair of gears for the supply and one pair for the scavenge, both driven at the same speed, the scavenge gears are wider than the supply gears so they pump more oil at a given speed.

[BeezaDan]

Hi again KiwiGF and All,
Yes, agree with your statement KiwiGF that the whole flow from the oil pump ends up in the crank case.
Following my forensic investigation of the stripped engine and thoughts from knowledgeable forum members, it might help general understanding on why my engine (and maybe others) is smoking badly if try to put my thoughts another way.

For a crank end feed oil system on an engine operating perfectly and fed with whatever type/ grade oil you choose to use -

The initial high pressure flow from the oil pump goes only to the crank, which means that the crank end feed oil seal has to deal with a potential momentary pressure of up to 100psi.
(Just for info - The SRM crank end feed seal is rated at 100psi, any pressure above this risks popping the seal. Reference article in Classic Motorcycle Mechanics mag by Brian Woolley of CMM and Steve McFarlane of SRM).

There is a little back pressure on the pump at that point so the oil flow won't be to the full capability of the oil pump.

So lets call that initial full high pressure oil flow 'X'.

Then very quickly the PRV operates to reduce pressure going to the crank end feed and then to the big end shell bearings, it opens to take part of the oil flow from the pump through a bypass route that feeds the timing gears and ends up delivering the excess oil to the camshaft trough where it is thrown around the crank and timing cases by the cam shaft and the timing gears.
Lets call that flow 'X2'.
The main flow from the oil pump runs through the crankshaft end feed route to the big end shell bearings. That oil is thrown vigorously around in the crank case and into the lower cylinder bores. (No problem if the piston and piston ring clearances are to specification and operating correctly).
Lets call that flow 'X1'.

So flows X1 + X2 =  X (the whole output from the pump less a small amount of back pressure caused by keeping the PRV open and the main bearing shell clearances). All of the oil flow ends up in the crank case as you rightly said.

Now lets consider the same scenario in an engine suffering worn cylinder bores, excessive main bearing wear resulting in large main bearing shell clearances, and a possibly a part blocked return line back to the oil tank -

Total oil pump output of high pressure oil flow 'X' happens as above.
The PRV operates to reduce pressure via flow X2 as above.
Flow X1 to the crank end feed and then the big end shell bearings operates as above.

Now the X1 flow is dramatically increased due to the excessively worn big end shell bearing clearances, (which in respect of oil flow are not operating correctly due to excessive wear).
The X1 flow ends up venting out of the big end shell bearings at an increased rate dictated by the capability of the oil pump, and in the case of a high capacity SRM pump at a significantly higher rate. The big end shell bearings are being rotated at high speed, throwing a much increased volume of oil around the crank case and into the bottom of the worn cylinder bores,
The X2 flow is decreased proportionally and still ends up in the crank case and being thrown around by the cam shaft and timing gears.
So we still have oil pump total flow 'X' as before but subject to modified conditions.
If the oil scavenge return to the oil tank is also part blocked the amount of oil ending up in the crank case and being thrown up into the worn bores would very quickly overwhelm the ability of the pistons and piston rings to control it from ending up in the combustion chambers resulting in a badly smoking engine.

So in my view, fixing the worn big end bearing shells and checking the scavenge/return oil flow path to the oil tank are the two main objectives for sorting the problem. Of course, if the bores, pistons and piston rings are excessively worn the engine will still smoke a bit but a lot less oil being thrown into the lower bores means potentially a lot less oil getting past the piston rings and into the combustion chambers.

Oils thinner by grade or made thinner by heating would also exacerbate the problem.

I am fixing it all, so unless I have missed something I expect to achieve a smokeless A10 once its rebuilt and run-in.

Sorry for the novel but it might help someone else with a badly smoking A10 to stay sane, or even prevent them from setting fire to the thing.

Of course, if I end up with a still smoking A10 I'll be cremating it for posterity as soon as
I get out of the funny farm.

Cheers All,
Dan.

[RDfella]

If pistons / bores are in good nick, extra oil flung to the bores from the big ends shouldn't make much difference.
A certain model of engine I used to frequently work on in the 70's / 80's had three variants as regards this issue. Early ones had no con-rod drilling to lubricate the cylinder walls. Later models did, whilst the high-horsepower ones had a 2nd oil pump delivering 10galls / min at 60psi to the piston undersides via a spray rail. None smoked more than the other in this regard. Some did, but for other reasons - eg .005" over-bore to prevent seizure on uprated engines, white smoke when idling due to low compression ratio, etc.

[berger]

well i'll just have another gulp of gravy and a big drag of me fag. when you say you had 18thou piston to bore clearance and 20thou ring gap it wouldn't matter if you only had drip feed or shell and BP were pumping oil in off a rig. those bores are gunna smoke like an ageing hippy. I know I am one

[ironhead]

Unless the PRV is totally seized shut, the crank seal will never see 100 psi momentarily or otherwise.

[Jules]

No discussion (yet) about the cartridge oil filter, I agree that the scavenge side needs a good hard look, particularly as you mentioned that the filter is on the return (low pressure) side - with the amount of crud that you talk about its quite possible that the filter was blocked and quite quickly too, I'm sure its capacity is quite small....

[Swarfcut]

Anyone remember the original BMC Mini? A gearbox full of engine oil directly under a longstroke engine.  Can't remember a baffle plate above the gears, but when new I never remember constantly topping the oil or much blue smoke until the valve guides wore.

 interesting thoughts there by Dan, in essence a difference of where the majority of the oil ends up, but as RD notes, the bore and rings in good condition would cope with this liberal volume, as in the Mini.

 My guess is it's a combination of almost all the lubrication and wear problems these engines can suffer all mixed, jumbled and stirred, but I can see Sherlock Dan is very firmly on the case.  Once cleaned out, I'd ditch the filter short term as like Jules I reckon the scavenge side is a major factor in this problem.

 Swarfy.

 Additional. Nice to see Bergs sticking to a healthy lifestyle........

[KiwiGF]

I have not bought an SRM pump but from what I have been told is that the gears are 35% wider so it pumps 35% more oil, so, at a given resistance to flow, the pressure will be a bit higher.

The A65 pumps also have the 35% wider gears, and I have one fitted to my A10.

Just my opinion but I don’t see how having a greater flow from a pump could make an engine smoke, and I don’t see it having worn big ends causing it to smoke either, the oil flow past the shells won’t change much with larger than service limit clearances. The big ends will knock when they have just a few thou clearance. From memory the big end ovality service limit is 002”?

A leak in the scavenge system could cause a build up of oil level in the cases, but I have heard of engines missing the scavenge pipe, that worked perfectly ok  (the oil just rises to to the hole where the scavenge pipe fits, maybe a safety feature).

[JulianS]

Shows the SRM pump internals below. Also has dowled body and O ring seal between the worm and body.

With the end feed it is very important that the seal and quil are not damaged. My experience with a (unknown at the time) damaged seal was that after draining the sump and within a short time of starting a lot oil was blown from the breather then a few miles after that the blow stopped. Careful examination of the seal revealed a split. Replaced the seal and the blow from breather had stopped and things back to normal. So it seems that the scavemge side was temporarily overwhelmed due to seal damage.

[chaterlea25]

Hi Julian and All,
Recently myself and another member on here were chasing round and round for a reason why his newly built engine was blowing oil out the breather
Eventually I discovered that oil was leaking at the crank end feed  in the timing cover
I reasoned that it's the gear train up to the breather is carrying the oil up to the top hat and then out the breather outlet
We had gone through everything else several times including bypassing the return filter and removing the sump magnet to no avail,   I had an endfeed cover from a project to hand,  fitted that and problem solved

John

[berger]

before I re seated the little ball in the crankcase and fitted the srm pump mine wet itself to the point where it ended up all over the floor and blew past the mag seal, while it was doing this it never chucked any smoke out  {an example of swarfy's mini mention } and pretty quickly there were bubbles in the return flow, that with a 60 year old bsa pump. I still say dans problem was the pistons , rings and bores.       

[KiwiGF]

before I re seated the little ball in the crankcase and fitted the srm pump mine wet itself to the point where it ended up all over the floor and blew past the mag seal, while it was doing this it never chucked any smoke out  {an example of swarfy's mini mention } and pretty quickly there were bubbles in the return flow, that with a 60 year old bsa pump. I still say dans problem was the pistons , rings and bores.     

Yep, I don’t use my GF that often, after a month of non-use the level in the tank will have gone down 2”, maybe 4”, I don’t get smoke, or oil leaking from the breather on starting. It’s done 9000 miles since the bores were honed to remove scores and new JP pistons and rings fitted so you can’t say the bores are new!

The big ends being worn on Beezerdan’s bike is a concern if it has not done many miles (do we know how many?), and if the big ends are worn but it’s got good oil pressure when hot that would be a puzzle.

A mate took down his GF engine at 30k miles after a rebuild with std main bearing bush, no discernible wear anywhere except the cams and followers which he hadn’t replaced during the rebuild.

Another mate has an A65 hornet with roller conversion, might not be by SRM he bought it like that, he stripped it down after he had done 100k miles and is replacing shells and mains and rings as a precaution, no discernible wear seen in the bottom end. He is not gentle with the hornets engine either!