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ET: Engine (Twin) Persistent oil leak

998cc

Website 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

Well Known and Active Website User
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
 

Robert Watson

Well Known and Active Website User
VOC Member
Get it clean and dry... Then dust it with baby powder. then start it up. If no oil is seen, run it for a 100 yards and back, Still no oil, 500 yards and back etc etc. Got my A twin almost oil tight doing this for the best part of a day!
 

erik

Well Known and Active Website User
VOC Member
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

Website User
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website 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.

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

Well Known and Active Website User
VOC Member
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

Website 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
 

998cc

Website User
VOC Member
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.

View attachment 34550
That is amazing.
 

998cc

Website User
VOC Member
Get it clean and dry... Then dust it with baby powder. then start it up. If no oil is seen, run it for a 100 yards and back, Still no oil, 500 yards and back etc etc. Got my A twin almost oil tight doing this for the best part of a day!
Hello Robert.
Thanks for the response. That sounds like a reasonable approach. :) I'll try that in the next day or so, and it's a certainty the oil will appear while idling on the stand. :confused:

I have found and fixed a few leaks over the past week. One stubborn one left a few drips on the garage floor overnight. It turned out to come from the tiny screw in the end of the feed quill.

Best regards,
Russ
 

Marcus Bowden

Well Known and Active Website User
VOC Member
You can just imagine how Mr Vincent felt when sets of C/cases all machined up bolted together, blanks put on all the apertures, then submerged in water and an airline connected to pressurise the C/cases, then they revealed if they were porous or not before filling them up with parts, He had literally hundreds of them until they devised a way to seal them with shellac by putting them in a vat of it and pulling a vacuum sucking out the air then releasing it and the shellac was drawn into the cases. after cleaning and all threaded holes re-tapped yellow chromate was applied on the outside then stoved enamelled, he told me he didn't make much on shadows as the work involved was so much. Typical manufacturer, having a poor product which he had to sell, made in go faster adding a few choice distinctive components. It was certainly an experience meeting him so often as I did with the stem of bananas and an Ltr bottle of whisky, only ever taking a couple of hands of bananas but always kept the full bottle of whisky.
Never painting "D" cases as they didn't require it die-cast.
 

MartynG

Well Known and Active Website User
VOC Member
sketchy on detail - but a web search may fill in the blanks.

A few years back I had a Yamaha single with an ongoing oil leak. Local dealer identified the problem, Apparently there was a batch of YP250's all with this issue and it was traced to porosity in the heads. The fix was to remove and strip the heads then have them vacuum impregnated with some form of 3M product. My dealer arranged it. Never leaked after that.

I understand Ferrari still do this as part of normal manufacture for their alloy engine castings
 

Phil H

Website User
Non-VOC Member
Years ago there was a porosity problem with some Norton Commando heads. As I recall, the solution was to blast them with walnut shells to pein the surface.
 
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Cyborg

Well Known and Active Website User
VOC Member
I don’t know if die casting the cases completely put an end to porosity. I can’t say yet whether mine suffer from it, but there are a couple of voids. Thankfully in areas that don’t matter.

Not sure why Robert suggested baby powder, but best leave that one alone.
For something more manly, you could try something like this.

 

Bill Thomas

Well Known and Active Website User
VOC Member
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.

View attachment 34550
I would have thought , If the liner fitted right , It would not matter ?.
 

Albervin

Well Known and Active Website 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.
 

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