Blanking plate oil leak

Hi all, i have an oil leak from the timing case (rear) blanking plate area that i cant seem to cure..
I have replaced the joint several times with and without wellseal
The cover and securing set screws have also been replaced
But the leak continues
I did visually inspect the casing at the last strip to check for a crack, but none were visible
The next strip with have to include the use of a crack detector
Any thoughts?

I don't know that it would fit, but Jim Schmidt makes a silicone magneto gasket? It's a three bolt pattern.
I have found his gaskets great to use - and, from my experience, they don't leak.
I use rocker covers, spindle covers, timing cover and oil junction block.

robs ss said:

I don't know that it would fit, but Jim Schmidt makes a silicone magneto gasket? It's a three bolt pattern.

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The magneto bolt spacing differs from that of the starter motor blanking plate, so the gaskets are different.

There really shouldn’t be much oil there to cause a leak!

Is it perhaps caused by excess crankcase pressure?

What breathing arrangement do you have?

L.A.B. said:

The magneto bolt spacing differs from that of the starter motor blanking plate, so the gaskets are different.

Andover Norton - GASKET - MAGNETO/CRANKCASE (DOMMI & ATLAS) T2191 - 06.7568

GASKET - MAGNETO/CRANKCASE (DOMMI & ATLAS) T2191

andover-norton.co.uk

Andover Norton - GASKET-CRANKCASE BLANKING PLATE - 06.2548

GASKET-CRANKCASE BLANKING PLATE

andover-norton.co.uk

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Thanks Les - I've just checked Jim's site and he doesn't offer a blanking plate gasket.

olympus said:

The cover and securing set screws have also been replaced

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Although the gasket surrounds the front set screw hole there doesn't seem to be anything to stop oil from leaking along the thread.

Fast Eddie said:

There really shouldn’t be much oil there to cause a leak!

Is it perhaps caused by excess crankcase pressure?

What breathing arrangement do you have?

Click to expand...

The engine is sound and I have a PCV fitted when you remove the chain Inspection plug you can feel a vacumn being created
Good point on the quantity of oil in the case... I always replace the three seals as a matter of course, but when I last took the cover off a lot of oil came out
1. Is the oil pump seal passing oil directly into the case... I have questioned here before as to gauge the clearance between the case and pump??
2. Is the oil being restricted back to the crankcase allowing an excess to build
I just wish the blanking could be removed without a strip off of the timing cover.. has anyone modified the lower through bolt and threaded the case?

The timing chamber over fills on a Commando as the drain holes were never repositioned to take into account the forward tilt of the engine over the vertical Atlas etc. You can add a new drain hole but to ensure you leave no swarf its best one on a rebuild.

See hole C in this pdf

olympus said:

The engine is sound and I have a PCV fitted when you remove the chain Inspection plug you can feel a vacumn being created
Good point on the quantity of oil in the case... I always replace the three seals as a matter of course, but when I last took the cover off a lot of oil came out
1. Is the oil pump seal passing oil directly into the case... I have questioned here before as to gauge the clearance between the case and pump??
2. Is the oil being restricted back to the crankcase allowing an excess to build
I just wish the blanking could be removed without a strip off of the timing cover.. has anyone modified the lower through bolt and threaded the case?

Click to expand...

What kind of valve is a PCV? I've seen people use a valve that has a ball that seats and unseats to let air pass. IMO, that's no good. The only valve that is going to keep up with the engine RPM's is a reed valve type. I have a 70 commando with the timed disc camshaft port. My bike always leaked eventually somewhere. Whether it was at the tachometer port, valve cover, or magneto plate. I added the timing side modification with a Mikes XS reed valve and drilled an extra breathing hole from the timing chest into the crankcase between the casting of the ribs to aid air movement. I also drilled a drain hole for excess oil to drain back to the crankcase behind the oil pump boss. The leaking almost completely stopped, then eventually I added a Jim Schmidt reed valve to the camshaft port and my bike doesn't leak at all now because the dual reed valves can keep up with the pressure waves during high RPMS, which is what it's designed to do...



The yellow arrow points to where I drilled a very small diameter hole 3/16" to drain the oil level of the timing chest. The red arrows point to the original timing chest breather hole and the extra one I drilled behind the intermediate gear. The green arrow points to the reed valve mounted on a flat plate that replaces the dished shaped original one. HTH



With all this being said,.... Jim Schmidt now makes a sump plug reed breather than fits early bikes where the frame member blocks the use of the Comstock version.. so there is a simple solution...

I have no experience with Jim Schmidt's products and have long used a VW Golf/Rabbit power brake unit check valve. Has worked on both my MKIII and my G80 cs Matchless. While it didn't entirely stop the leaking, it greatly reduced it.

olympus said:

I just wish the blanking could be removed without a strip off of the timing cover.. has anyone modified the lower through bolt and threaded the case?

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Yes, the through bolt hole just happens to be the drill size hole for a 5/16 UNC tap.

L.A.B. said:

Although the gasket surrounds the front set screw hole there doesn't seem to be anything to stop oil from leaking along the thread.

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Good point Les, I'll bare this in mind to apply sealant or carry out the mod I alluded to earlier
Do you know why there are to set screws and a odd single bolt?

Mark Savage said:

Yes, the through bolt hole just happens to be the drill size hole for a 5/16 UNC tap.

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That's great news mark, thank you, I will certainly be modify this as its such a pain in the backside having to strip off the primary cover every time

As I recall, the material of the case isn't all that thick so it might do the put a jam nut on the back side with a little locTite.

olympus said:

Do you know why there are to set screws and a odd single bolt?

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No.

Thomasa said:

As I recall, the material of the case isn't all that thick so it might do the put a jam nut on the back side with a little locTite.

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Thick enough, about 5/16”. It’s not like it’s holding any weight.