Mystery oil leak

fastback · Jun 12, 2007

Ok - I know it's British but this one has me a bit stumped. :?

I am getting oil coming out from between the cylinders at the lowest fins in the front. It runs out and around the front center nut/stud. It appears to come out from between the cylinders at the base in the rough area of the casting.

The head gasket is dry and tight where I can see it (just replaced and re-torqued ). There was alot of oil coming out before the rebuild and I assumed it was leaking from the case/cylinder joint, but that is not what is happening (sealed tight now).

If anyone recognizes this let me know!
Thanks,

gordon russell · Jun 12, 2007

Fastback,I had a similar oil leak and did a search on past posts,yes it was the intake rocker box cover,a new gasket and a little sealer on one side fixed the problem.

gordo

79x100 · Jun 12, 2007

Inlet rocker cover is the favourite for this leak three fins up at the front as it's where the cooling ducts through the head run.

Another possibility is rocker spindle covers (especially new stainless ones as they're not always as flat as they should be). Surprisingly, the weep of oil running downwards is barely visible on a clean head and once again forms drips at the front.

fastback · Jun 12, 2007

I'll quadruple check and keep watching.
I did install new rocker gaskets, annealed copper washers on the rocker spindles, tightened the clamps on the oil lines, so I can't see any oil dripping down from above, yet the evidence is pooling at the bottom of the cylinder. :x

I have nightmares that someone will say - "oh that clearly indicates you have a cracked barrel" or something like that...

79x100 · Jun 12, 2007

A light dusting with chalk powder or talc can help with locating.

750 barrels don't usually crack at the top. At the base flange is another matter altogther

It could be a porous head, they're not unheard of.

In my experience, leaking spindle retaining plates are more likely to be from behind the plates than from the washers.

I know that there are people here who hate silicone but I think that a very thin smear on the gaskets here is a good idea. Likewise the inlet rocker cover. Even if you have flatted it, it does have quite a narrow mating surface and is only clamped from the centre so over-tightening is counter productive. I find that mine need goo to be 100% oil tight.

norbsa48503 · Jun 12, 2007

To quote:
I know that there are people here who hate silicone but I think that a very thin smear on the gaskets here is a good idea.

No need to use silicone when Hylomar is around. It doesn't dry into the balls of goo that give silicone a bad reputation.

79x100 · Jun 13, 2007

norbsa48503 said:
To quote:

No need to use silicone when Hylomar is around. It doesn't dry into the balls of goo that give silicone a bad reputation.

I don't like Hylomar, it really does seem to form little rubbery balls and they don't stay on the joint either.

Don't get me wrong, I do traditional as well, never without a tube of Wellseal in the garage but on these low clamping force joints with thick gaskets, I do find a smear of silicone ideal. (By "smear", I do just mean a wipe with a siliconey finger, not the sort of bead that plumbers put round a bath

)

By the way, if gasket goo does detatch, assuming it's not on the feed side then I can't see that it could do much worse than find its way into the sump strainer on a Commando.

Ron L · Jun 14, 2007

By the way, if gasket goo does detatch, assuming it's not on the feed side then I can't see that it could do much worse than find its way into the sump strainer on a Commando.

I think you might like to see some connecting rods I removed from an engine sealed with silicone and a half teaspoon of little "balls" of silicone I took from the sludge trap. It plugged the oil passages in the crank starved the big ends and cracked the rods vertically. I will never use silicone where there circulating engine oil.

As far as head gaskets, I have never needed more than gasket shellac or Copper Kote, even with the flame ring gaskets with the thick rings from Domiracer. That being said, I agree that a thin smear of silcone or Hylomar around the oil drain back hole and the pushrod tunnel hole on the gasket is safe if you are very careful.

norbsa48503 · Jun 14, 2007

Note that Hylomar is anaerobic. So if any extra flows into a high flow oil area it slowly is sloughed away , it doesn't dry unless it under pressure so no little balls. As you all point out most people use too much.
On the rocker covers I use the soft,red,synthetic gaskets they don't leak but still require the trimming needed for oil drainage needed on all gaskets. Because they are soft they also need to be torqued evenly and because the bolts won't hold any reading this torquing is a bit tricky as the reading only appears for a moment. A fish weight scale and a box end are the tools needed for this.

fastback · Jun 14, 2007

I used Loctite 518, actually permatex 51813 - anarobic red goo on the case cylinder joint - seems to the trick. Put a light smear on the head gasket around the pushrod tunnels for good measure too. All is tight at the moment. There is no leakage from the rockers, spindles. So I am still baffled. I will take the bike for a good ride this morning, change the oil and continue to observe and wipe with a white glove. It kind of reminds me of a kid with a runny nose, won't talk about the bottom end...
:roll:

Ron L · Jun 14, 2007

Norbsa,
The original universal blue Hylomar is not anaerobic, but a polyester urethane non-setting sealer. Hylomar does make anaerobic (methacrylate) sealants as well, under the names of Gasket 2000, 3000, etc., but most people think of the blue Hylomar.

I don't know how oil soluble the blue Hylomar is, so I am careful when using it around oil galleries.

norbsa48503 · Jun 14, 2007

Ron, I stand corrected.

kommando · Jun 14, 2007

Too much Blue Hylomar can block oil return pipes, don't ask me how I know :shock:

79x100 · Jun 14, 2007

I didn't know that there was any Hylomar other than "Blue". I used it on two-strokes in the 1970s because it seemed such an improvement on Red Hermetite (didn't smell as nice though !) and found that even when used moderately, it didn't stay as a bead on the inside but released in the oil.

I've never found silicone loose and am a bit puzzled as to how it enters a crankshaft. The only possible places would be from the oil junction block gasket or from the oil way at the rear of the timing chest, but a half teaspoonful ? :shock:

Whatever, I do understand that not everybody likes RTV and I don't have a mission to convert others

If you do try it at home children, be careful :lol:

scim77 · Jun 14, 2007

Just on the subject of sealants, I too have used RTV sealants, Blue Hylomar and Wellseal, but regard the Stag Wellseal as my absolute favourite. It never sets, is very user tolerant in application, sticks like the proverbial, seems to be impervious to all fluids and always works. A truly excellent product.

Mystery oil leak

Similar threads