How much oil should come through timed breather?

On the '69 S which uses the timed breather coming off the cam I have always gotten a fair bit of oil through the breather hose back to the oil tank. If the oil level in the tank is a little high there is always a dribble out of the oil tank breather in front of the tank. On other threads we've talked about the "top hat" on this central oil tank and the fact that a lot of turbulence there can cause oil to come out the oil tank breather which starts in this "top hat", where the breather hose from the crank also ends. I have about 6k miles on the bike since a total rebuild and it has suddenly started spewing a lot more oil out of the oil tank breather. When the bike's hot you can see droplets of oil coming out of this breather when you rev it. It's going all over the gearbox and making quite a mess, not to mention losing a lot of oil. Tonight after riding about 20 miles I left it idling in the shop as a puddle formed underneath and then pulled the hose off the crankcase breather and there was a pretty steady stream of oil coming out. I can't figure out why it has started spewing so much oil. In the past I could expect a few drops to come out of the oil tank breather after a hard run, but now it's a puddle after a short run. I changed the oil last week and initially thought maybe I had put a bad filter on, figuring that since it's in the return line if it had a partial blockage it might prevent oil being returned from the sump causing more oil through the breather. I changed the filter and no difference. The oil pump was NOS and was put on only about 2-3k miles ago. I pulled the timing cover tonight to check the seals, pump, etc. and can't find anything out of the ordinary. I've been getting good oil return to the tank even at idle, but when revved you can tell there is a fair bit of oil coming through the breather hose into the tank as well. At this point I'm pretty baffled as to how much oil should be coming through the timed breather (I suspect a decent amount because it picks up pretty low in the crankcase) and how it could possibly start spewing so much more oil suddenly through the oil tank breather. Any insight or suggestions would be greatly appreciated.

Thanks,

That doesn't sound right. My '70 Roadster will use a quart of oil in about 2000 miles (40,000+ miles on this speedo...). Most of it seems to drip out of the air filter. Is your timed breather working right ?

Greg

As far as I can tell the timed breather is operating properly. It worked fine until last week and when I took the connection at the breather off and kicked it over I could see the inner disk turning.

Very little oil should come out of the timed breather. It sounds to me like the oil is not being scavenged from the cases by the oil pump effectively.

Possibilities would be a plugged passage on the inlet side of the scavenge pump or a damaged oil pump. The engine was not assembled with the tab style thrust washers on the cam was it? Jim

I did not use the tab-style thrust washer on the cam. My thoughts were also that it wasn't scavenging the cranks properly. I am getting good return to the oil tank. I drained the sump after riding a couple of days ago and got about 1/3 cup oil out, which seemed a bit more than usual, but not a huge amount more. Could the timed breather, because of its location, be more susceptible to a small change in sump oil level? The pump is pretty new and when I pulled it off I could feel suction through each inlet when turning it by hand. I replaced the pump last year with a NOS one because the original pump had years ago had a piece of stellite from a cam follower go through it and chipped one of the gears so that it wet sumped quickly.

On the couple bikes I have owned with a timed breather I would get a mist of oil from it but no real liquid. I have seen what happens when the oil pump gets damage from a broken thrust washer. Major amounts of oil come out from the breather and also the crank seal.

1/3 cup of oil from the cases sounds like a reasonable amount. You might want to re-check that after a short highway run and a quick shutdown to see if it is scavenging well at speed. If the suction passage were restricted it could cause oil to build up in the cases at speed. Jim

Thanks Jim. I pulled the breather hose off the oil tank before I rode it last time and got maybe a teaspoon of oil through it in 4 or 5 minutes of running. After a 20+ mile ride I pulled it off again and it was pretty much gushing. Before I pulled the hose off, I could rev it an see a spew of oil out the tank breather. This is the earlier style central oil tank where the breather hose comes into the "top cap" rather than ahead of it like the later central tank.

This is a long shot, but when I had my engine apart, the timed breather (rotary breather valve item 46 here http://www.oldbritts.com/1971_g1.html) had a stress fracture in it so I bought a new one. I'll look around and see if I still have it and make a picture. Not sure that would be the problem though? I don't remember where the crack was, but it was quite visible when I had it apart.

Here it is, but I really can't imagine that would be the issue.


Dave
69S

I have a similar problem on my early commando too. After a long run I find a tiny stream of oil has come from the base of the air filter and migrated down under the gear box. Talking to a fellow commando owner who had a similar problem he solved it by installing a check valve in the breather near the breather elbow. Apparently this stops air that is being pushed out by the falling piston being sucked back in through the breather. Air inside the engine has a lot of oil suspended in it and this air cant be pumped by the oil pump but can be pushed out by the breather.

Mark.

have you changed the brand or type of oil that you are running?

Haven't changed type of oil other than going back to 50w for the summer. I've not been able to find any blockage in the scavenging, but lost power early last night and still waiting for it to come back on so didn't have enough light to check much. The INOA tech manual suggests a possible cause could be an air leak behind the oil pump. The gasket sure looked good, but I believe I put it on dry last time. May try a little sealant this time - Mick Hemmings says this is one of the very few places he sometimes uses a sealant on a gasket.

OK, I pulled the timing cover and oil pump to check the oil scavenge. The oil drilling from the sump plug to the oil pump is clear. Used a little sealant on the oil pump gasket in case there was air leaking behind the pump. Went for a short (10 mile) ride this evening and there' still a lot of oil coming through the breather and out the front of the tank. Pulled the sump plug and got less than 1/4 cup of oil out of the sump. I just don't see how this much oil can be coming from the cam when there's no more than this in the sump. If the breather disk were cracked like Dog T's, could it cause this? I can see it turning when I kick the engine over, but maybe it's getting weird at speed?

I guess I would do a leakdown test to see if you have a ring leakage problem. Jim

Please let me know your findings as I have the same problem with lots of oil coming out the air filter - been the same since I bought it last year (1970 model). Interestingly I disconnected the breather and ran it to a bottle for a while, used to get about 50mls per 100 mile, but still got oil dripping from the filter. I also installed a check valve but this made no difference to the breather.
I have tried running the oil tank low (off the dipstick) and this is the only thing that improves matters but I don't like this as a fix, especially with no oil pressure indicator. Also if I try to stick below 2000 rpm I get no oil leaking.

Nelson, is this with your 'new' oil tank, the one where the breather goes in beside the top hat instead of into the top hat? So far I haven't seen any oil out of my air box yet, but if I do, I still may cut off the top of the top hat and put an inverted P trap in the top of that line that runs into the air box. I'll bet it's just oil and vapor splashing around in the tank and getting in that line, unless a crack develops in it somehow, but then I would think it would leak all the time, at least if there was oil in the tank.

Dave
69S

No, this is still the stock '69 oil tank. There's always been the inevitable dribble out of the tank breather, but this has turned into a gusher. I'll try a leakdown test like Jim suggested, but I've checked the compression and it's between 140 and 150 in both cylinders and there's no smoking or plug fouling. I studied the oil flow chart in the MKIII manual last night and it seems to me that since the sump was nearly empty after a short run that everything is scavenging properly and for this much oil to be coming out of the timed breather that maybe all the oil from the head is going down the push rod tunnels to the cam rather than any other path. Make sense? I did pull the head off recently to replace the studs since I couldn't get rid of a slight weeping around the head gasket. I'm starting to wonder if there could be a restriction in the oil way from the head through the cylinder.

Whether the oil is returning down the pushrod tubes or the drainback passage would make no difference, the oil still ends up in the same place and shouldn't change what is going out the breather.
One other thought. A head gasket that is leaking from the chamber to the pushrod tubes will dramatically increase the crankcase pressure and could cause excess oil from the breather. Have you retorqued the head gasket? Is the head flat? If the head gets cleaned with a wire brush or abrasive disk it is easy to end up with low spots between the chamber and the pushrod tubes. Jim

The head has been retorqued several times since the gasket was replaced and before I replaced the studs I lapped the head on a surface late to be sure it was flat. It's a flame ring gasket with some copper spray for a sealant.

Nelson, did you ever get this sorted out? I have a 70 roadster that does the same thing.

Wco, this thread is 2 years old. I haven't seen Nelson around for a while. I'm sure he'd respond if you email him.

That said, since I put a ball valve in the oil feed line and turn it off while not riding, it stops the wet sumping and leaking while sitting. It has also stopped nearly all oil from coming out of the timed breather and I have a catch bottle off my oil tank breather so I know how much is coming out. Mostly it's just oil vapor that condenses. Now it's also said that not letting the bike wet sump reduces the lube to the cam during start up, so you may want to take that into consideration.

Before I put the catch bottle and valve in, I started the bike with a catch bottle off the timed breather after it sat for a few days and I got maybe an ounce or 2 out of the breather on start up, then it quit. If you let is sit for a month not started you may get quite a bit out of it. The timed breather is supposed to go into the oil tank and there is a sort of separator there that should remove most if it, but some always comes out of the oil tank breather into the air filter, at least mine did. I've heard of people with the early timed breathers and central oil tank that work just fine without leaking out the air filter and all over the gearbox, but mine leaked a lot. Maybe they start it every day, I didn't.

Dave
69S