71' 750 Cdo........leaks !

I didn't ride my 71' much last year because of all the oil leaks that have progressively gotten worse. So for the last day & half I've spent some quality time with her. First I noticed my primary case likes to take on extra oil so the crank seal was replaced. Next was the base gasket for the barrel. There has always been some silicone around it for the longest time from previous owner. I cheated a bit by just raising the barrel up enough to slide the gasket over the studs by cutting the front stud hole of the gasket in half. Next was the head gasket, old one was a composite dried out and crumbly. A new copper gasket with copper coat sealant was used. New valve cover gaskets too. De-carbonized the piston tops and cleaned up the outside of the barrel while I had the room. Tach drive mod w/oil seal, CR #2450 seal.
This bike has the breather hose on the left front of the engine case w/hose to oil tank. Put gas tank back on and head for gas station 2 miles away. I pull up to pump and find a pool of oil in the corner of the right front engine case behind the tach drive and I can see oil bubbling out that side of the base gasket. WTF ! I get back home and see lots of oil returning through the breather hose. My oil level is just between H-L marks. It leaks more now than ever...
Oh, and it hit 100 degrees here again today for the third straight day... :evil:
Why is there so much pressure coming from the breather now? Is this possibly causing the new gasket to leak?
I don't want to take it all apart again................
Tim_S

Hm, sounds too dam familiar to me when I was in a state of denial about ring gap blow by over coming everything else.

Does it have a breather valve? It's a PVC (Positive Crankcase Ventilation) valve between the case and the oil tank. There is enough posts on this forum to fill a book on the subject, and I can double dog dare you, scores of members will gladly pipe in with comments.

You need one.

That said, Hobot may be right. I don't think a PVC valve will solve a ring problem.

Best of luck, keep us posted on your progress.

I think you may have the timed breather in wrong. The little tab fits inward and engages the cam. The old timed breather from the lh cam usually works pretty well. Oil level is too high if it's between H-L. It should be on the low side.

Are you certain you haven't over filled the oil tank after wet sumping? My 71 doesn't leak a drop, and in my experience the 71 and earlier machines need no modifications to be oil tight apart from the tach drive seal, which you have already done.

best of luck.

There is no breather valve of any type in-line of the hose to oil tank, never has. The hose connects to a 90 degree elbow on the outside of the case and goes straight up to the oil tank. The rings haven't been touched in who knows how long? No smoking either. Instead of a mist coming out of the hose I get a stream of oil pumping back into the tank. In a matter of a minute I can see oil bubble out of the seam where the new gasket is just on the right side.
Before I started all the work I drained the old oil. I added new oil upon completion ........

Tim_S

My ring gap problem took over 6000 miles to show up, in stages of thing leaking and intermittent smoking, till too smokey to go out in public. So no smoke tends to imply rings-bores still ok, but if breather functional then must remain blow by suspicious. My buddy Wes discouraged me to take time to lay in real cotton thread as I'd done in past, so my Combat still weeps a bit on 70 mph rides but covers cases and side covers if I throttle it up over 5000 to feel 2S cam kick in. At least the exhaust smoke solved so far. Those who claim oil tight get my respects but wonder how hard they grantee it too?

I feel your pain about tearing it all down but oil leaks are a bitch to live with. I just hate them.
Bite the bullet dude. We'll walk you thru it.

Mikes XS will sell you the reed valve.

Well those answers were helpful :wink: Since you only changed the base and head gasket and decarbonized the head and pistons could you have dropped a piece of gasket in the case and blocked the return pickup. Check you have oil returning to the tank via the pipe as well as the breather pipe. The large filter should prevent blockages but just in case something is actually blocking the main hole at the top of the filter, in the gauze retainer plate. The add on breather comments are valid but that aint going to get to yr root cause.

The timed breather will return a lot of oil to the tank if you have wet sumped, but it should stop after about 30 seconds. Take your breather tube off and start the bike and see what it's doing. If you get continuous oil out of it, you're getting too much oil in the engine for some reason. I have a catch bottle on my oil tank breather and I have less than an ounce in it after the summer. You could try the comstock(?) breather that goes into the sump plug. You may have to get it from CNW now, not sure. Then you could just block off that fitting at the timed breather. I stopped a lot of leaking, but I didn't have much, after I put a ball valve in the oil feed line from the tank and no more wet sumping it got even better. I hardly see a drip any more.

Dave
69S

Ok,,,here we go again. This was really bugging me so late last night so eye looked through the two Haynes manuals and the shop manual...again. Funny thing I mentioned my dilemma to the INOA group too and no one ever mentioned the pressure relief valve?? I have too much pressure and I need relief :roll: I didn't mess with any breather parts at all because there are none visible from the outside of the motor. Just an elbow fitting and a hose to the oil tank. This is just a gasket fixer upper project. The motor wasn't apart. Except for the head to replace the head gasket. I cheated on the base gasket by cutting the gasket in one place only by the front center stud hole right down the middle of that hole, no other place. Raised the barrel up just enough to clear the studs and put gasket on. One dab of sealant on the cut hole part around the front stud. The new base gaskets are made of the same material as the valve cover gaskets, not paper and you don't have to soak them in water to stretch them to fit.
I checked the parts book for a look at what to expect to find when I take the valve off. You need two wrench's one is 15/16 for the dome nut and 1 1/8 for the valve body. Unless yours comes off in one piece like mine did. I found that under the dome cap was a glob of black goo, jelly like. Then I pulled the spring out, then with my tiny magnet I tried to get the metal cup or piston the spring sits in to come out. But only the two tiny round flat shims came out. Tried again, no go, pushed in a little with a tiny screwdriver and felt a little resistance as it was being stubburn. Tried again with the magnet then it popped out on it's own. It's supposed to work like a plunger but something was restricting it. I took the valve body out of the case and found that the screen on the inside end was clogged with more goo. Restricting the oil flow and movement. The metal cup or piston was stuck from the oil suction and not allowing the timed part of the pumping process to function and allowing the oil to blast a stream of oil back into the tank via the breather hose.
Reassembled and went to bed,,,,,,,This morning I started the bike and magically the oil stream has turned into the oil mist it's supposed to be. After running the bike for 5 minutes no leak at the base gasket either. I will test run the bike tomorrow under more extreme conditions and report back.

On another note,,,, I checked two of my other Cdo's norton relief valves and they vary with the shims. One bike has two shims, another has no shims and this 71' had one shim as pictured above. The black wet spot is the black goo stuck inside everything. Water & oil make for an interesting mix even when stored in the house where my shop is. From now on checking my relief valves on all the bikes will be included as part of the maintenance package......


Tim_S

Tim_S said:

Funny thing I mentioned my dilemma to the INOA group too and no one ever mentioned the pressure relief valve?? I have too much pressure and I need relief

Click to expand...

A stuck OPRV could result in slightly more oil reaching the sump when the engine was cold, but the scavenge pump should be able to cope with that, however excess crankcase pressure and excess oil pressure are two completely separate issues and I wouldn't necessarily expect anyone to mention the oil pressure relief valve when debating an excess crankcase pressure problem.

Tim_S said:

The metal cup or piston was stuck from the oil suction and not allowing the timed part of the pumping process to function and allowing the oil to blast a stream of oil back into the tank via the breather hose.

Click to expand...

I must admit I don't quite understand your thinking on this, as the breather and OPRV are not connected, the OPRV merely regulates the pressure of the oil going to the crankshaft and valve gear so the OPRV has no direct influence on the breather. I do agree that it is certainly a good idea to periodically service the OPRV and also check the OPRV operation with an oil pressure gauge.

You mention the breather hose to the oil tank, but is the tank free to breathe to atmosphere or to the air filter?
I had bad leakage problems with the 750 I bought off a plumber ages ago and after seeing the oil tank puff out like a balloon on start up, on closer inspection, yes the breather hose went to the tank but the brain surgeon had soldered shut the top tank breather to atmosphere. :roll:

What are the odds the OPRV being relieved of it's blockage and the little piston not being stuck and the fact that the steady flow of oil back to the tank from the breather is now back to just a mist as it should be? No other action has taken place. The other hose that used to go to the stock air filter just hangs down where it usually drips on the ground.
So I went for a test ride today stopping every so often to check things. About 20 miles into the ride my right leg got wet when the plastic rocker feed line slide off one of the fittings on the top right double banjo. I didn't realize it until I wiped up most of the oil on the right side. You can never carry enough rags with you when you own a Brit bike. I do believe my breather issue has been corrected for now,,,,, :roll:
Time will tell.....thanks to one & all for your moral support.

Tim_S

There's no reason for that head feeder line to come off the banjo fitting. Get some new Nylon 11 or air brake hose and replace it. If you need a link, I'll find it. Or go for the expensive SS lines.

Dave
69S