Internal Sump Blockage

Well I "THINK" I have found the root case to my problems. After removing the head and barrels do to excessive smoking I also removed the timing cover and serviced the oil pump.
This resulted in discovering the internal sump passage to the pump is blocked. Can not pass any air through the hole no matter what. So my suspicion of all the oil being returned to the tank via breather has been confirmed.

I didn't want to hijack the oil pump service thread so thought I would start a new one to try and get some information to deal with this issue.
I have read lots of information on here about the oil pickup mod and at some point would like to do this, just not right now. I would really like to clear the passage without taking the cases apart.

Below is a reply from hobot posted in the oil pump service thread which probable explains my blocked passage.

hobot said:

Combat's don't need an oil pump to return oil to the tank via the factory breather hose. Combats have long thin internal sump passage that can get blocked by Combat shedding its cam thrust washer tabs. Thrust washer tabs get beaten by crank till size-shape to get stucked into return side of pump which can damage pump gears. Oil pumps have twice the sump size gears & out flow than pressure side. The TS cover gasket and the oil pump nipple seal come in 2 combo's of thicknesses that are supposed to match to give correct crush to seal w/o damage or significant pressure leaks. Call or search Old Brits for the correct combo of seals to buy. Easy enough [if messy] to top off oil tank and pull its return hose into a jug and start up and rev a bit to see if it blasts out mixed oil/air adequately.

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I have soaked the passage with solvent which would very easily remove any hydrocarbon sludge and still can't pass air through using and air compressor. I can get a piece of wire back through the timing case side to about 7 cm thats it.

Has anyone successfully cleared this passage with the cases still together? If so please tell me how?

The bike is a 72 Combat but the cases have been replaced at some point. I will post another reply with pics so you know what I am working with and hopefully can offer some suggestions.

The breather is on the lower left backside of the case.



This is the backside of the timing case.



Some shots showing the inside of the timing cover.

There is one hole in the front section, you can see it where the screwdriver is poking through.


There are two holes in the back section above the gear. Approximately 11 and 12 o'clock positions.


Where the oil pump mounts. I can get air to pass in the pump intake ( hole on the left, air to pass in the pump return ( hole in the middle). But no air into the one on the right (internal sump passage).SORRY THIS PIC IS UPSIDE DOWN


Here is a pic of the case insides taken of the web


Since I can only get back 7 cm it appears I have quite a ways remaining to go according to the above pic.

Ugh, what ever got trapped in the passage got stuck in there while the Al channel was swollen by heat so by time you can handle it its contracted to trap firmly. I think this is part of Trixie's oil leaking problem, trapped swarf from a number of blow ups, so only solution I know is bypass the long forward passage by drilling into TS passage at rear. Don't have to mill out the DS as NOC Tech book showed and repeated by vendors and others since. A screen over the sump hole like comnoz has would be tricky but wise.

I have been trying to think of a way to use steam to heat things up and see if that helps dislodge things.
Fill cases with boiling H2O or something??? :mrgreen:

Boy do these Cdo's open our minds to a wide scope of possible processes. If its steel/iron piece then nitric acid would dissolve enough of it to mushy rust so could spit out and not hurt the Al. Simpleton solution is JBW plug the front and drill/mill down into TS to expose more direct drain to pump.

hobot said:

Boy do these Cdo's open our minds to a wide scope of possible processes. If its steel/iron piece then nitric acid would dissolve enough of it to mushy rust so could spit out and not hurt the Al. Simpleton solution is JBW plug the front and drill/mill down into TS to expose more direct drain to pump.

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Nitric acid is certainly an option and I have some. Remember I would like to do things with the cases still together. Is it possible to JBW plug the front and drill into TS with them together. I wouldn't know where exactly to drill.

If I get the passage free I may just leave it as is for the time being as I don't intend to rider her that hard.

I would bet that some of that red "silicone/gasket" material has dislodged and blocked your oilways..... Then there is the thought of how long were they blocked and what damage, if any has occured....

DPO sure did a hell of a job sealing the TS cover. It took the better part of a day to get it off. If its the red silicone/gasket I would think a piece of wire would poke it out. No luck there though.
I have been thinking about what damage has been done and get that awful feeling in the pit of my stomach. Only saving grace is it initially didn't smoke when I got the bike and I have only road it a few minutes around the block so far so hopefully no major damage.

The (excessive use of) RTV has ruined many engines. Like you said, sick feeling ... a complete teardown is the easy answer. But I understand the time/cost issue. Thing with it is, may run fine until wailing down the freeway for 10 miles and rod bearings could starve

you cant fix this with out splitting the crankcase. some one has mismatched a 72-73 750 drive side with an 850 timing side. this combination will block the pick up, as the 72-73 750 pick up is in the timing side and the 850 is in the drive side

Dirt2Oil said:

The breather is on the lower left backside of the case.

This is the backside of the timing case.

Click to expand...

Bill when you say pickup are you talking about the holes circled here in red?

no those holes are for the drain plug.

Dirt2Oil said:

Bill when you say pickup are you talking about the holes circled here in red?

Click to expand...

OOOOOOk then, I thought that was where the oil started its journey toward the the oil pump. Now looking at it I can clearly see its for the drain.
So what your telling me is when I poke a piece of wire in the pump pickup hole I am actually hitting a dead end about 6.5 to 7 cm's in because of the cases being mismatched? Oh boy that changes everything. :cry:
I was actually getting excited that the HNO3 would do the trick.
Are there any photos showing this pickup in the 750/850 cases floating around someone could post?

One more thing to try at this point if you haven't already:
Looking at the timing side oil pump mount, the hole on the left is the oil supply from the oil tank line.

The hole on the right is the scavenge side and connects to the crankcase sump through a complex drilled passage.
Directly down from the right side hole on the exterior of the case you will see a slot head grub screw.
Remove this screw and you find the drilled passage up to the right side hole. The problem is that the connecting passage that goes down to the sump pick up point can only be accessed from the inside of the cases.

Try removing that grub screw, see if you have a clear passage up to the oil pump mount.
If you try to pressure force some solvent into the scavenge side hole on the oil pump mount with the crankcase drain plug removed you could see if there is a clear path.

Good luck.

Good Luck? :roll:

In following pix you can see normal combat case pickup at left end of passage that is shown plugged with brown/gray epoxy.
http://atlanticgreen.com/images/cmbtscvgT.jpg

In following pix I have created a hole with a drill in a drive side combat case, that hole normally does not exist and will seal off the 850 timing side case pick up.
http://atlanticgreen.com/images/cmbtscvgD.jpg

Like Bill said, 850 timing side mated against a normal unmodified combat drive side will not EVER work....due to a competely blocked pick up hole

This case set is from my combat that "ate" a piece of broken valve spring. It is now modified in a MUCH better way than (IMO) the INOA/ole brit method

Ha sounds like you've used up any short cut effort saving solutions After a day just to open the TS cover and not run into sheared off cover screw with buggered threads - parting cases for direct access should be a relaxing straight forward task now. About only bad that can happen with a blocked Combat sump passage is over filling enough for leaks every where but still supplying good oil pressure and still forcing oil back to tank as fast or faster than pumped out. Best wishes blowing your mind blowing passages away from blown engine.

Thanks for posting those 2 photos of creating new oil scavenge pickup points on those cases.
I'm going to do the modification on mine this winter.

I like that second photo of drilling the drive side into the weir area.
Now I understand that the Old Britts mod totally removes the weir instead of just making the hole.

Here is a picture of my cases, it helps me with the abstract view of the internal oil passages.
The orange dot is where the drilling your photo shows goes.

In hindsight, why did Norton do it that inefficient way back then?

the INOA/old britts mod IMHO is the wrong way to do this. the best thing is doing it the way dyno dave or I show and leave the weir THAN switch to the comstoc/CNW reed breather # 0500-09 in the original breather location. as dave pointed out the INOA mod will not give you any kind of protection. this way you will at least have some sort of a strainer before the pump.

Bob Z. said:

Thanks for posting those 2 photos of creating new oil scavenge pickup points on those cases.
I'm going to do the modification on mine this winter.

I like that second photo of drilling the drive side into the weir area.
Now I understand that the Old Britts mod totally removes the weir instead of just making the hole.

Click to expand...

dirt2oil

PM sent

This is a real philosophical quandary to me trying to keep Triixe as factory as practical, so want to keep the Combat 2ndary oil return intact and now see I could stuff some filter screen in the DS recess after milling out TS to create a rear drain filter while bypassing the front drain internal passage. I would also drill out a few holes in the cast in baffle to help prevent much crank windage oil pile up there and still have effective breather hose return on wet sump start ups. The low down breather fitting prevents easy tranny removal w/o tipping engine forward or removing to get tranny out.