Oil on fins

[Phil C]

Hello everyone,

Very rainy afternoon down here in Devon, so I was just sitting here, mulling over what to do next on my old bike (1965 B40F.)

When I've been out on it, the cylinder fins are a bit oily.i don't know how common that is. I don't think the oil is coming from the rocker pipe banjos, but I'm not sure where it's coming from. Where's the most likely source of the leak, would you say? Cylinder head gasket?

Phil

[spaceman]

Problem is you can get leaks on the cylinder head which can cause oil to flow down on to the cylinders. Best approach is probably to clean the top of the engine of oil and, after a ride out, to see if the source of the leak can be seen. If it's not the cylinder head leaking, it may be from the cylinder head gasket around the pushrod tunnel which is where oil returns to the sump from the rocker box.

Unfortunately, I know from experience that identifying the source of these types of oil leak is surprisingly difficult.

[chaz]

one lesson I learnt from a 1990's Royal Enfield that I serviced was I had cleaned off the head and cylinder but there was a strange drip assumed it came from the gasket face. A wipe around did not show anything. after another run around it was back. a leak was found between the fins due to porosity. on contacting Hiscox I asked if it was common, they didnt think so only a handful a month!!
the cost of impregnation wasnt far off the price of a replacement head complete with valves, yes, it had dropped a valve guide as well.

A lesson learnt that porosity or cracks can open up with heat then close themselves when cold, which was then evident on a compression test.

[spaceman]

I once suffered a persistent small leak on the cylinder head on another non-BSA bike. I tried everything to identify where the leak was coming from, even talcum powder, but all to no avail. The problem was that by the time you got back from a test run, the oil had been blown everywhere. I took the head off to inspect it but could never work out where it was leaking from and it could well have been porosity or a crack. In the end, I replaced the engine to solve the problem!!

[cdsdorset]

Get yourself some oil dye and a uv lamp.

[Phil C]

Thanks but I'm not sure dye and a uv lamp would identify the source, as after a run the oil is quite widespread on the fins, although not very much in terms of quantity. There's not loads of oil splashing or blowing around everywhere, but after a run if I run a finger along the fins it picks up some oil. It's liveable-with, but I'd like to sort it if it's fairly straighforward.  Would the cylinder head gasket not be the most likely cause? I kind of assumed it might be.    Phil

[spaceman]

I would have thought that if it was the cylinder head gasket leaking oil (especially around the push rod tunnel), the oil would remain confined to the cylinder fins rather than spreading to the fins on the cylinder head. If this is the case here then the gasket would seem to be the most likely culprit.

That said, providing it's only a thin smear of oil on the fins, I'm not sure I would worry too much about it!

[cdsdorset]

Thanks but I'm not sure dye and a uv lamp would identify the source, as after a run the oil is quite widespread on the fins, although not very much in terms of quantity. There's not loads of oil splashing or blowing around everywhere, but after a run if I run a finger along the fins it picks up some oil. It's liveable-with, but I'd like to sort it if it's fairly straighforward.  Would the cylinder head gasket not be the most likely cause? I kind of assumed it might be.    Phil

You don't need to do a long run. Just enough to start the leak. You would be surprised how accurately dye can pinpoint a leak, I use it a lot.

[JulianS]

My B40 would dribble from the exhaust lifter in the rocker box.

[MGI]

In respect of Chaz's post commenting that Hiscox did not come across many porous barrels, only a handful a month. I assume that there is an element of humour therein on the grounds that a handful a month is a considerable number.

[chaz]

that was the words from them, apparently the have a crude impregnation in India , basically puts a thin skim of brown glue in the base of the fins. over time and vibration/heat cycles, this breaks off. result, a leak. They didnt seem overly worried that they get so many requests for new heads.
the Bullet 500 I worked on was still running but leaking, on removal and a good look around I saw the dropped guide, £100 for impreg, £40 for o/s guide and fitting, recut seat and grind in. the complete new head was around £130 inc guides, valves, springs, basically ready to fit.

my company use Loctite in Reading, Ultraseal Coventry for faulty castings now we dont have our own plant. its a vacuum process which sucks the fluid into the casting before setting it. The Indian style is more or less a paint on process.
A handfull amount is probably a small quantity when you look at the quantity they produce and sell compared to the numbers from the big 4 Japanese.
I used to get the trade mag, the production figures were printed monthly The Indian market is massive so spares can be made in bigger quantities and cheaper so not really a concern for them. The bike in question was turned around in two days, would have been at least a week to repair.

[Phil C]

I'm quite tempted by the uv light and dye, as suggested by cdsdorset. I think it would be interesting. Might try it.