Oil return problem

Hortons Norton said:

L.A.B. Could he be talking about the return from the head?

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Yes, it must be, but it wouldn't usually connect with the return side of the pump?

Pictures save a thousand words. :mrgreen:

I was just thinking if someone did at some point connect it to try drain the head quicker? Never know what people will try, LOL. And your right Dave a picture would tell the story better, I can't wait to see.

Or is it the "black" hole which can be seen in the (Dynodave atlanticgreen - "extra timing cover hole next to oil pump is mystery") photo at approximately 10 o'clock position to the upper pump stud, which I thought was a breather hole into the crankcase?

Didn't even remember seeing that one? :? That's gotta be what he's talking about. Thanks L.A.B.

According to various drawings in the factory manual and an Old Britts photo, it looks as if that hole is a timing chest oil drain and/or breather which connects to the gallery at the crankcase joint, so it is only applicable to the 750 models?

Could there be a "breakthrough" between this drilling and the return drilling?

Just happen to have a 72 case sitting next to me here.
Outside


Inside

The threaded hole nearest the top pump stud intersects the oil pump inlet channel. If he has the filter in the hose connected to this channel ,it is in the wrong hose. That hole is where the excess oil from the pressure regulator is directed back to the pump inlet on bikes with the timing cover drilled with a matching hole. The black hole above that hole is the oil drain for the timing chest and could not possibly be connected to an oil pump channel. It just dumps back into the crankcase. Jim

comnoz said:

The threaded hole nearest the top pump stud intersects the oil pump inlet channel. If he has the filter in the hose connected to this channel ,it is in the wrong hose. That hole is where the excess oil from the pressure regulator is directed back to the pump inlet on bikes with the timing cover drilled with a matching hole. The black hole above that hole is the oil drain for the timing chest and could not possibly be connected to an oil pump channel. It just dumps back into the crankcase. Jim

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This one.

Thankyou once again for the replies.

I am now having my first attempt at posting a photo. The upper hole above the oil pump is, as has been sugested, the gallery to the cast in gallery in the crankcase joint. It is the LOWER hole which is a mystery, which connects to the drilling between the oil pump return outlet port & the pipe on the rear of the crankcase for return to the tank (via filter).



I hope someone can throw some light on this.

Regards

Bob.

From the photos we've seen so far, it appears that from sometime around early 1972, the "upper" hole was deleted, and the "lower" hole was then used as the timing chest drain hole?

Although what the actual purpose of the lower hole was before then, I must admit have no idea, but perhaps others might, and it seems odd for it to be connected to the return side of the pump, as for one thing, it doesn't appear to be anywhere near where the return drilling is in the crankcase?

If the return oil from the pump is somehow able to vent into the timing case from that hole, then the majority of the scavenged oil would be continually circulating through the sump and pump and not actually be returned to the oil tank, so possibly it needs to be blanked off?

What goes through that hole is oil from the pressure regulator. Any oil that exceeds the setting of the regulator is fed back into the intake side of the pressure pump and pressurized again. Since the oil pressure on a warmed up bike seldom reaches the set relief point of the regulator, very little oil gets circulated. Jim

comnoz said:

What goes through that hole is oil from the pressure regulator. Any oil that exceeds the setting of the regulator is fed back into the intake side of the pressure pump and pressurized again. Since the oil pressure on a warmed up bike seldom reaches the set relief point of the regulator, very little oil gets circulated. Jim

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I think you could be looking at the wrong hole, Jim?

Apparently Bobolink doesn't mean the recirc. gallery in the gasket face, as I also thought it was what he was referring to originally?

Hole A is connected to hole B, excess oil from the relief valve [if the timing cover is drilled] flows into hole A and goes back into the pressure side of the oil pump through hole B to be re-pressurized. The hose connected to this channel goes straight to the banjo fitting on the oil tank. It cannot have a filter in that line other than the screen on the banjo.
Hole C is the scavenge return from the pump to the tank. The hose connected to this channel is the one the filter should be in. Jim

Jim, you are looking at the wrong holes.

From Bobolink's description, it's the two holes further back and higher up.

But the hole directly above hole A is the drain for the timing chest and it is a long way away from the scavenge return channel which is below the feed channel so I don't know how it could be connected without a curved drill bit. Jim [course I've seen a few of them]
The hole above that was another hole into the crackcase that I have seen once before. It didn't go anywhere.

L.A.B. said:

comnoz said:

What goes through that hole is oil from the pressure regulator. Any oil that exceeds the setting of the regulator is fed back into the intake side of the pressure pump and pressurized again. Since the oil pressure on a warmed up bike seldom reaches the set relief point of the regulator, very little oil gets circulated. Jim

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I think you could be looking at the wrong hole, Jim?

Apparently Bobolink doesn't mean the recirc. gallery in the gasket face, as I also thought it was what he was referring to originally?

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comnoz said:

But the hole directly above hole A is the drain for the timing chest and it is a long way away from the scavenge return channel which is below the feed channel so I don't know how it could be connected without a curved drill bit. Jim [course I've seen a few of them]

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Bobolink's engine is a 1971 model, and there seems to have been a change in the drain hole arrangements made between '71 and '72 cases if what Bobolink has described is correct? But I also do not understand how that lower hole could be connected to the return?

Bobolink said:

The upper hole above the oil pump is, as has been sugested, the gallery to the cast in gallery in the crankcase joint. It is the LOWER hole which is a mystery, which connects to the drilling between the oil pump return outlet port & the pipe on the rear of the crankcase for return to the tank (via filter).

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http://atlanticgreen.com/engcases.htm

"20M3S early" (Dynodave)

"20M3S late" (Dynodave)

"'73 Combat"(? = '73 750) (Dynodave)

Hey, Bobolink, what are the first 3 numbers of (of the last 6) by the base of the cyclinders on the driver(left) side?

LAB & Jim

Thankyou for your input. LAB, you are correct indicating the two holes with arrows (how do you do that?).

The upper of these holes is the one leading to the cast in chanel in the crankcase join. Thai drains the timing case does it?

The lower one does indeed link to the middle of the 3 oil pump ports & the return to the tank position on the rear of the crankcase.

Jim, from the relative positions of these holes it is difficult to see how this is achieved but by squirting oil into the oil pump port, it appears at both the oil tank return pipe & the mystery hole.

This would fully explain my original problem when I fitted a filter but what is the purpose of this hole? Is it supposed to be there or is it a PO's attempt at some devious modification?

I guess the only way to really know the answer is to strip the bottom end & have a look inside.

I do seen to recall when I last had the bottom end appart , probably 20 odd years ago, there was some evidence of some flak going round. Could have broken through somewhere perhaps?

Anyway, off to Spain & France on the bike in 3 weeks so shall leave my filter kit on the shelf & leave it as it has been for the last 32 years.

Any other input would still be most welcome though!

Regards

Bob.

Bobolink said:

LAB, you are correct indicating the two holes with arrows (how do you do that?).

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I borrowed your photo (downloaded a copy) then drew in the arrows using Paint.NET: http://www.getpaint.net/ (you may find you already have this on your computer?)

Bobolink said:

This would fully explain my original problem when I fitted a filter but what is the purpose of this hole? Is it supposed to be there or is it a PO's attempt at some devious modification?

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A PO has drilled out a blanking plug, possibly? I can see somebody has drilled an extra crankcase breather hole, and also what appears to be a hole for a punch to knock out the main bearing outer race?) :roll: