The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: stev60 on 28.04. 2017 01:53

Title: Excess Oil
Post by: stev60 on 28.04. 2017 01:53
I have a problem with what appears to be excess oil to rockers, Engine starts and runs well until oil finds its way into combustion chamber and eventually actually runs out tail pipe, along with the smoke when oil feed to rockers is disconnected no problem, the banjos are correct  and ive even put a reducer in the line. I assume oil is running down guides, next move is to remove inspection plates on rocker cover and see whats happening, has anyone experienced this before.
Title: Re: Excess Oil
Post by: TT John on 28.04. 2017 08:56
Not wanting to teach you to suck eggs etc but have you connected the oil feed to the rockers on the return pipe at the oil tank, as there should not be a great deal of pressure at the rocker feed, I thought that perhaps you may have connected it up wrong, the only other thing it could be is that the banjo nuts with the small feed holes in them are wrong, I think one is smaller than the other.

Regards TTJohn
Title: Re: Excess Oil
Post by: JulianS on 28.04. 2017 09:14
Oil in combustion chambers could be worn bores and/or rings, leaking head gasket , as well as worn guides. Or too much oil in sump due to problem with oil return or wet sumping.

When my A10 has, in the past had oily combustion chambers, then it was one or more of these.

Oil from the tail pipe would indicate to me the need to check all the above because it is quite rare in an engine in reasonable condition.

Any blockage in the rigid return pipe in the oil tank causing too much oil to be diverted to rockers?
Title: Re: Excess Oil
Post by: muskrat on 28.04. 2017 10:41
Oil to that extent in the pipe would to me be a worn or broken ex guide if it's not smoking like a 14 year old.
Title: Re: Excess Oil
Post by: chaterlea25 on 28.04. 2017 22:01
Hi Steve,
the banjos are correct
Do you mean the banjo bolts?
If the wrong ones are fitted then you will have the problems you describe
Another thing could be a partial blockage in the return pipe in the tank?
Is there an oil filter fitted in the return line? is it connected the correct way?

Title: Re: Excess Oil
Post by: Rgs-Bill on 29.04. 2017 21:29
    I have been told, than when you rebuild the head to use Norton valve guides which are designed to use a valve guide seal, also been told .001 thousands too large of guide clearance can cause the problem being discussed here, with rocker oil running down inside the guide, a making bike smoke.  I do not know if this would be a good test or not, so correct me if wrong.  When my exhaust guides were too sloppy, if I held my finger over the oil return hole in the oil tank, the cylinder which had the sloppy guide would smoke even at idle, proving that excess oil was going down the worn valve guide.  I love BSA`s but they were too cheap to make some of these design modifications in the later models, because they new that the unit construction engines were all ready to come out, I do not think they even published a service bulletin addressing this situation.
   You  just have to talk to an old timer, like the one who told me to use the Norton valve guides which uses a seal, when re-building your BSA heads.  This also may be all wet as a theory, because only one old timer told me this, so it was his own opinion that this would solve the problem for ever.


Title: Re: Excess Oil
Post by: JulianS on 30.04. 2017 13:48
A10 guides can be converted to take Norton type seals on the inlet.

Not an uncommon mod.

Works very well.
Title: Re: Excess Oil
Post by: edboy on 30.04. 2017 22:53
i think rgs bill is suggesting a loose guide may be the culprit. if the norton guide is larger diameter it could be turned down to make an oversize guide?
Title: Re: Excess Oil
Post by: coater87 on 01.05. 2017 02:41
 This tool will cut cast iron and bronze guides down for installing seals. This is just an example so you can see how it does its thing.

 The local bike shop uses a large pillar drill and a home built driver, they hold the head by hand and let the guide pin and tool do the work.

 I believe harley sporster valve seals work on damn near any bike, unless you have a super hot cam with huge lift and are running out of clearance fast. But a seal will not fix a worn out guide.

 The tool is about $150 for a good one, or if your head is bare any shop able should charge less than $40.00 to cut your intakes down to except seals.


Title: Re: Excess Oil
Post by: Black Sheep on 14.05. 2017 07:06
Interesting that we have moved to fitting valve guide seals. Do BSA twins actually need them? If fitted, would they in fact be disguising a problem? I appreciate that Norton Commandos have them however Dominators do not. Could it be that the canted forward Commando engine creates the requirement? In 45 years of A10 riding (still the same original A10) I have never felt the need to fit seals. Have I missed something?
Moving on, with alloy heads, it's not uncommon for oil to make its way between the outside of the valve guide and the head. The guide may appear to be a good fit when cold off the bike, but when hot can become slack and that's when the oil burning starts. I've come across this a couple of times over the years.
Title: Re: Excess Oil
Post by: Triton Thrasher on 14.05. 2017 08:26
Whatever the problem is, it is not the non-existent seals.

If oil is running down the valve stem, or the outside of the guides, you may see evidence of that, by looking into exhaust ports and looking into the spark plug holes and turning the engine to open the valves.

I don't suppose you get much of a view of the valves and guides down the inlet manifold, do you?

As for over-feeding the rockers, have you done something to the oil tank or scavenge line or rocker feed system?

If it's worn valve guides or rings, it shouldn't have happened suddenly.  A loose guide can happen suddenly, as can an oil ring stuck after a partial piston seizure, as can a displaced piston circlip, usually not all that long after fitting.
Title: Re: Excess Oil
Post by: Colsbeeza on 08.08. 2018 07:04
Did Stev60 solve his problem.? It sounds very similar to my problem.
I have been out on the newly-restored engine of my 1961 GF, and the smoking has not decreased much. It is occurring only on the left cylinder.
I will describe what is going on, and see if anybody could suggest my next steps:-
 The bike has now done two x 20 mile runs, so I think if it was just seating of rings the smoke should be bugger-all by now. The first run was with an 18-tooth engine sprocket (too revvy) and the second with a 21-tooth (much better). It seems to have great power - not that I have tested it much.!
After starting cold- wait about 30secs to 1 minute and the smoking starts. A little at first, then after another minute it gets fairly heavy white smoke - therefore presumably oil. Then it starts to drip from the pipe-muffler clamp, and smoke comes from there also. On my first outing, a mate followed (on a 1954 Norton Model 7 Dominator) in case I needed transport. He told me that once I get riding, the smoke decreases such that after about 10 miles it was fairly light, and by the time I got home it was hardly visible, only after throttling back and then re-accelerating.
On the second outing, the smoke started he same, but rode on my own so cannot say how visible it was.
This morning, I started it for a mate, and the smoke started exactly the same as described.
I drained the sump both times, and got about 150mls so wet-sumping does not seem to be an issue.
There does not seem to be any oil loss from the breather. The rear of the crankcase is clean. I am running it in with Penrite HPR 30 20W-60 and I have fitted a Norton-type oil filter. The oil has high zinc and no friction-modifying additives according to the blurb. The oil pump seems to be working OK. Oil pressure is 60psi cold and drops to 40psi when hot, and the return oil flow looks great, with typical entrained air bubbles.
The head was not restored. I remember removing the valves about 25 years ago to lap them in and to check the guides and I was able to get a little movement. To assess the guides, I got Robertson Brothers in Newcastle NSW motor repairers to dismantle and give me a second opinion. They knew their stuff, but said the guides were OK. However, two years ago and still not being confident, I asked a bloke to dismantle and check the motor and also the valves and guides, and his opinion was also that the valves and guides were OK. Clearly they are not new, but it doesn't seem that they are worn enough to blow clouds of smoke.
The oil is getting a bit dark with carbon but still quite green, and the SRM-style magnetic sump plug is also layered in carbon - no gritty stuff though. Nothing to be alarmed at yet.?
The plugs are sooty, but I thought I would put a few miles on it before trying to tune it.
I think my next step is to check the rocker banjos to see if the orifice sizes are OK. But does anyone know what I should look for here.? How big are the orifices for a standard GF.??
If the orifices are OK, my next step is to pull off the head and cylinders and check for cracked oil ring on LHS and re-check the valve guides.????
Title: Re: Excess Oil
Post by: stev60 on 08.08. 2018 09:07
The problem I had, is now almost non existant, with more use, the bike had been in storage for 25 years, and threw up a lot of problems, a little oil finds its way down one side on warm up sometimes and drops out the muffler connection but not out tailpipe , once run its gone. Plugs are right color and no smoke. All Ive done is a valve grind. There is something special about the parallel twin motor. I can understand the enthusiasm for it in this forum  Star twins are few and far between in NZ. 
Title: Re: Excess Oil
Post by: chaterlea25 on 08.08. 2018 21:10
Hi Colin,
Before you dismantle the engine
Have a look in the inlet and exhaust ports, if oil is traveling down the guides it can be easily seen, also if oil is leaking between the guides and head
It might be worth doing a leak down test which should show up if there's a ring or bore issue

Title: Re: Excess Oil
Post by: Colsbeeza on 08.08. 2018 22:40
Thanks for the update Stev60. It does not seem that you had a real problem.
John, I will check the banjo bolts first. I did find 3 Forum posts on the banjo bolts and it seems that the correct orifice size is 3/64" for the GF. That will be an obvious thing to do first, and rectify if needed - I can always try Richard L's cheapskate method to reduce the hole size!!. *yeah*   See (
If that does not fix it, then I should examine the ports on the way to head removal.
Title: Re: Excess Oil
Post by: berger on 09.08. 2018 00:36
steve60 don't be afraid to block the rocker feed off and run it for a while to see if it stops smoking,,  I unknowingly rode mine with oil pipes on wrong way round and no oil going to the rockers ,{carnt do that again modified feed line} long story short no damage done and that was 80 odd miles , valve gear was ok. camshaft and followers flat, shells took loads of hammer threw a circlip and ground bore up, engine was running on mist by way of me filling tank above return feed hole and it was just surviving but rockers were starved and everything up there ok.  I ran it other day without rocker feed for test purposes on some modified return lines on the oil filter , if you do it might tell you what your trying to find out, after all they didn't allways have oil to valve gear. Or even better don't take any notice of this because ive just read the first post you did. DUM BERGER!!!!!!!get to the pub you need a fix!! too much workshop time makes berger a loon ,,, or maybe DELIBERATE mistake just to make you laugh..... or even think THICK c--t shut up and go the pub
Title: Re: Excess Oil
Post by: TT John on 09.08. 2018 09:20
I found another thing which causes oil to leak all over, that is the pressure releaf valve, I just had an occasion where I had to check this and found the ball was not sealing on the seat, the ball also had a ridge running around it, so it's worth checking this to try and eliminate oil leaks.

Title: Re: Excess Oil
Post by: stev60 on 09.08. 2018 21:31
I think guides may have been a bit of my problem, when I had the head off last noticed a crack running across one exhaust port, dosent seem to effect the running, but have a fully reconditioned head to go on  when I get into the mood to face the pushrod lining up drama *conf*