ET: Engine (Twin) Persistent oil leak

998cc

Active Forum User
VOC Member
Good day all.
After this last build (2017-2018), I have a great running Black Shadow that has a persistent oil leak. Prior to today, it seemed to be coming from the front exhaust port, so I just finished installing sealed lower valve guides, re-cut the valve seats and installed a PCV breather at the front exhaust valve spring cap. I took the bike out for about 20 miles this morning, and it is a pleasure to ride. However the leak is still there and is so bad, it covered the front of the engine with oil which also made its way to the rear tire (tyre).

After this morning's ride, I parked the bike on the driveway and observed the engine for about 15 minutes while idling. The oil just seems to appear under the front exhaust port on the cylinder muff about three fins down from the head joint. It also appears on the next three fins down and then drips onto the front of the engine.

Pressurizing the case to a few psi yielded no leaks while applying soapy water from a spray bottle to the entire engine. That was a last ditch effort! :confused:

In KTB, E. M. G. Stevens advises to apply Wellseal to the right rear head bolt of each cylinder where these thread into the case. I did seal these some 40 years ago and have had no trouble. Could this now be the culprit? Hoping there is other wisdom here as I'd rather avoid pulling the top end again.

Thanks.
Regards,
Russ
998cc
 

LoneStar

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VOC Member
I find it's impossible to identify the source of an oil leak after riding, as air currents send the oil in unpredictable directions, including forward and upward.

I clean the bike with degreaser, then run it on the stand for a while and inspect joints with an ultraviolet flashlight. This causes most oils to glow, making the source of the leak obvious. If your oil doesn't glow, you can add UV dye.

Here is one source for UV flashlights; there are surely others too: https://www.banggood.com/Convoy-S2-Nichia-365nm-UV-LED-1Mode-OP-Reflector-Flashlight-p-1024097.html
 

erik

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I have the same problem but not so strong on my comet in the same place.On my engine it is only a few drops and not a real leak and I decided to leave the engine unopend .I think the casting of the muff is with small porousitys (in German : Lunker) from the casting process.Maybe one way to cure this problem is to close the oilway to the cylider wall.I did that on my rapide without any negative effects.Next time I open the timing cover of my comet i will do the same.Erik
 

Phil H

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Non-VOC Member
Russ, since your bike is a Shadow I presume that the cylinder head is painted. Years ago I went nuts trying to fix an oil leak on the cylinder base of my Triumph. It turned out that the leak was in a different place to where the oil was appearing, and the oil was creeping along under the new black paint before it surfaced elsewhere. The leak was from an incorrectly plugged oilway drilling in a new set of barrels. Perhaps this might be worth investigating in the effort to locate the source of your leak.
 

Bill Thomas

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I think if you could find a pin hole in the muff,
You could just close it off by knocking around it, Being Alloy, Do they call it Peining ?.
Good Luck, Bill.
 

Oldhaven

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VOC Member
Is the Shadow with the leak an early one? My '48 Rapide has the same problem in the same place, though not nearly that bad. I believe it is from porous castings, and though I have blanked off the cylinder wall oil feed gallery I am sure some creeps up there anyway. That was a serious complaint about early Vincents here in the US.

By the way, in the picture of Nero on the home page is that stain in the gravel on the rear of the stand from an oil leak? If so, now there is some serious incontinence.
 

Cyborg

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48 Rapide oozing oil? I’ve posted this photo a couple of times, but think it does a reasonably good job of illustrating the porosity that occurs.

This went through the parts washing tank (with solvent), then through 4 sessions of 50 minutes each in a heated ultrasonic cleaner, and then a fairly long session with a high power pressure washer. It appeared to be absolutely spotless until I put it in the oven to heat up for the liner. It was oozing out of the fins as well.

48230B72-5995-437D-AF44-38ED0431A6F0.jpeg
 

998cc

Active Forum User
VOC Member
Is the Shadow with the leak an early one? My '48 Rapide has the same problem in the same place, though not nearly that bad. I believe it is from porous castings, and though I have blanked off the cylinder wall oil feed gallery I am sure some creeps up there anyway. That was a serious complaint about early Vincents here in the US.
<snip>

Thanks, Oldhaven.

It's a '53 engine. However, the front head is an early one which lacks the cast-in vertical ribs, and it does have a few areas of porosity. It has remained more or less dry over the decades, so I don't think that is the culprit in this case. The muffs are new components sourced from Coventry Spares. Interesting point regarding blocking the oil supply to the cylinder wall. It seems others have one this as well with success, so I will do it if need be.

Best regards,
Russ
 
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