ET: Engine (Twin) Persistent oil leak

Cyborg

Well Known and Active Forum User
VOC Member
I would have thought , If the liner fitted right , It would not matter ?.

No doesn’t matter. This one was ok and I ended up using it on my Mongrel Comet project. I popped the liner out to see what sort of crap was built up in there ( check fit) and also deal with the oil feed hole in the liner which like every other one I’ve measured was too high. The muff seems to be darker since I installed it, so suspect it is still oozing slightly. Would be nice if it waited until it at least until it go some engine heat! Originally the plan was to paint that engine black, but the cylinder muff kind of put me off that track.

I’m a little concerned Robert hasn’t responded to my wisecrack about baby powder. He’s about twice my size, which is what I would normally worry about, but with social distancing rules he’s likely loading a projectile.

DB315F6D-3E97-4D44-B619-7DA51A6724A0.jpeg
 

998cc

Active Forum User
VOC Member
Check your rocker oil feed bolts. I have a leak from the front exhaust rocker oil feed that ends up in the places you describe. The new Neal Videan washers have an undersize ID causing a light burr on the washer. This leads to a slight weep which becomes ugly after the oil gets hot.

Albervin.
Good thoughts there. I used to have problems in these locations. For this build, I bored the VOCS copper sealing washers oversize to accept a small O-ring which is also snug on the bolt shank. It is essentially a home made Dowty washer that seals the underside of the bolt head to the top face of the banjo.. So far, no leaks there.

One leak at a time. :)
 

Robert Watson

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VOC Member
I have dispensed my very little wisdom on chasing oil leaks so here are two things come to mind with the little "comments" in this thread.

No1 When John Andrews rode his Shadow from Nova Scotia to Toronto, he stopped at one point to fill with fuel. The young attendant (we used to have them in those days) inquired about the large quantity of oil that it had deposited on the ground underneath the engine and what he intended to do about it. "At the appropriate moment I shall put some more in the top!" was his reply.


No2 A not so unknown member of the Club resident at the US at the time, wondered which of his armament should be used to take out the large and noisy dog next door (at some distance mind you) to make it cease its incessant barking. I think at the next Section Christmas dinner he was presented with a mortar round to be used on the neighbour - not the dog. Cyborg beware!
 

998cc

Active Forum User
VOC Member
All.
From the responses here, porosity or ducting of oil under paint or between metal surfaces are legitimate concerns. So let's assume the oil is oozing out through porosity of the muff. How does it get into the muff in the first place?

Though possible, it seems unlikely that oil from the head could migrate into the muff casting from above since the contact with the head is largely limited to the top of the liner spigot. Oil weeping from the head should therefore appear at the head joint.​
From the crankcase, oil migration seems to be more plausible due to oil under pressure being present at one head bolt (stud) for each cylinder. Also, crankcase pressure must have some influence on forcing oil up in between the muff and the liner unless the liner is a perfect fit in the muff.​
Assuming the oil comes up from the crankcase, I am thinking of cleaning and sealing the muff gasket face including along the line of contact with the liner with Three Bond sealer and letting it dry. Then assemble as usual. Next, pull the timing cover and block off the oil supply to the bores.

Your opinions (both pro and con) are invited.

Thanks.
Russ
 

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
No oil to my liners for last 200k plus miles, what I would like is an oil jet at the bottom of each liner to under the piston for cooling, if I was competitive but never really have been, and as everyone knows "Speedisexpencive" ! I believe Mr Vincent told Marty Dickenson that.
bananaman.
 

Monkeypants

Well Known and Active Forum User
Non-VOC Member
All.
From the responses here, porosity or ducting of oil under paint or between metal surfaces are legitimate concerns. So let's assume the oil is oozing out through porosity of the muff. How does it get into the muff in the first place?

Though possible, it seems unlikely that oil from the head could migrate into the muff casting from above since the contact with the head is largely limited to the top of the liner spigot. Oil weeping from the head should therefore appear at the head joint.​
From the crankcase, oil migration seems to be more plausible due to oil under pressure being present at one head bolt (stud) for each cylinder. Also, crankcase pressure must have some influence on forcing oil up in between the muff and the liner unless the liner is a perfect fit in the muff.​
Assuming the oil comes up from the crankcase, I am thinking of cleaning and sealing the muff gasket face including along the line of contact with the liner with Three Bond sealer and letting it dry. Then assemble as usual. Next, pull the timing cover and block off the oil supply to the bores.

Your opinions (both pro and con) are invited.

Thanks.
Russ


Russ, is the bottom side of the oil tank wet with oil?
I ask that because I chased what I thought was a multitude of engine leaks only to find that the problem was one big leak up top.
The eyes see oil on a fin and the brain says it must be coming from around here somewhere.
Not necessarily!


Glen
 

Oldhaven

Well Known and Active Forum User
VOC Member
Oops, meant to do a thumbnail image, but the picture above is what my muff porosity looks like, assuming it does not use a transporter beam.
 

kettlrj

Well Known and Active Forum User
VOC Member
Hi 998,
Some time ago a section member had a similar problem with his Comet. Following all sorts of solutions put forward by other members such as piston ring broken, loose vale guide and all other weird ideas. I went to see the bike and when it was running there was a lot of oil dripping from around the exhaust port. I asked him what had he been doing to the bike lately and he It seemed that he had not fully tightened the pipe nut securing the return pipe to the cylinder head rocker feed pipe. The oil was then running down the head fins, totally unseen, and then running out next to the exhaust port. Therefore my advise would be to look at the link pipe between the two heads to see if it is leaking from where the flex pipe joins the rigid pipe.
Regards Richard.
 

kettlrj

Well Known and Active Forum User
VOC Member
As a matter of interest, the joint between the rocker feed pipes and the cylinder head often leaks because after all these years the pipes do not always sit square and load up the fibre washers on one side which overloads the washer and squeezes the washer out from under the pipe fitting. I have started using 16mm Enots bonded washers under these pipes. The beauty of these seals is that they clamp down on the metal outer ring which pulls the pipe into line and lets the seal do what it should do. The other benefit is that you end up with what is classed as a hard joint instead of a soft joint which means that the clamp load from the screw is maintained, which is not the case with the soft joint determined by the fibre washer. I also use 1/4" BSP Enots washers on all the other oil pipe fittings. The long oil feed and return pipes can come loose with when fitted with the fibre washers due to vibration and being moved to enable the gearbox cover or timing cover to be removed. Making the joint to the oil pump a hard joint prevents this loosening action.
Regards Richard.
 
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