pcv valves and oil leaks

Not open for further replies.
Jan 2, 2009
I have just got an 1973 850 MK2a back on the road and would like some advice if possible from more knowledgable Norton folk than me.
I appear to have some oil leaks from my engine. This does not suprise me, as I seem to be quite adept at putting engines together that leak.
No 1 leak deposits oil on the leading edge of the primary drive cover, but is coming from somewhere close to the L.H. exhaust manifold. I can't really see any more than that...maybe the head gasket just under the exhaust?
No 2 leak seems to be coming from the small rocker shaft covers, with their multiple gasket/dodgy bits of tin.
No 3 leak seems to be coming from the the rear rocker adjusting cover, with its sigle nut fixing onto a cover that must act as a large diaphram spring?

So any tips would be greatly received. I am not about to strip the bugger down right now though...it runs OK.
I am however interested in PCV valves. I am interested in any PCV valve I can install in line in the large breather pipe which comes from the timing cover, where the mag used to live on an Atlas...Again I am not about to strip the motor down to use a CNW job.
I am figuring that reducing crankcase pressure may reduce oil leaks...
Thanks, Stu.
There are loads of threads concerning oil leaks, but I think my experience is similar to yours, so it might be of some help. My MK3 leaked like a sieve, wet sumped the entire oil tank overnight, and lost engine oil to the primary, causing clutch problems. I did three things suggested on this board and now have a bike I can ride w/o 30min of dithering with each time out. I sent the timing cover and oil pump to AMR for their valve and pump mod and the wet sumping disappeared ($70 + shipping). I installed DynoDave's clutch rod seal ($20). Finally, I took JimC's advice and installed a Yamaha XS650 breather valve ($16 + shipping). For $100 or thereabouts and a bit of time, my bike was transformed. This board is easily the best resource available, and although opinions differ, all of the advice is good.
1 and 2 may well be the same. Try a little Yamabond (or equivalent grey gasket sealer) on the gaskets under the spindle covers. I'd also recommend silicone rocker cover gaskets (from RealGaskets.com or Rocky Point Cycle), as those tend to leak and could be the source of some of your problem also.

Suggestion about a PCV valve or equivalent is also worth pursuing.
Lots of threads on the forum about different breather check valves. I opted for the cheapo route and used the Motormite power brake check valve (p/n 80190) available from any auto parts store. I figured if it works I'll just renew it with each oil change as part of routine maintenance. I'm impressed so far in that my valve cover gaskets don't leak now even without the RTV that I normally used on them.

Your #1 leak sounds like oil from the head gasket around the front studs (head nuts 7 and 8). Treatment requires removing the head, but a breather valve might help a lot.

Leak #2 is easy to fix with gasket sealer on all those parts. I use Permatex spray High Tack (red stuff) and also blue Loctite on the bolt threads (my Stainless bolts want to come loose otherwise).

The intake rocker cover has a funky nut that should have an aluminum sealing washer under it. Again, a breather valve might cure that one.
JimC said:
Yamaha XS650 breather valve

Reed type PCV valve. $16. Very effective. Easy to install. Put it anywhere in the breather line.

You'll probably find that the closer to the engine you can put the valve the better.
I, too, tried the Motormite vacuum check valve. It not very effective and doesn't last very long. In my case it lasted for a few hundred miles. That is, after a few hundred miles the oil leaks started reappearing.
Thanks Gents.
XS650 valve looks good.
Will look at the sealant issues and silicon gaskets too.
Does anyone know the Yamaha xs 650 breather valve part number or is it only available as an after market item
Just easier to buy from a yamaha dealer for me .
JimC said:
Yamaha XS 650 reed type PVC valve, Part #15-0677

I ordered mine from:http://www.mikesxs.net/products-40.html#products

I think he's asking for a Yamaha part number, I I think that's Mike's part number. I haven't seen anyone else offer that part yet. At that price it's hard not to just get it (unless you are looking at heavy overseas costs: shipping, VAT, etc.). kanaka didn't specify a location so I'm guessing.

I little more poking around and I'm pretty sure the Mike's XS Valve is not a Yamaha stock part. I believe it's a "proprietary part" he's sourced from somewhere.

You can read up on the similar issues the XS folks are having here:

Thanks all Just ordered one from Micks cost of fraight was same as part but such is life
I was going to order one too , but got too annoyed at paying $20 shipping for a domestic order a $17 part. Call me cheap - but it is more the principle of the matter. I told Mike that I so to. I have no problem paying for a part - just don't pretend it's "shipping"
fastback said:
I was going to order one too , but got too annoyed at paying $20 shipping for a domestic order a $17 part. Call me cheap - but it is more the principle of the matter. I told Mike that I so to. I have no problem paying for a part - just don't pretend it's "shipping"

Free shipping for orders over $150! :roll:

My guess is that that unit goes to something else, non-motorcycle even. Some research might turn it up.
My name is Bob Patton, this is my first post to this list. I've owned my Commando for about thirty years and riden it quite a bit. There is some good info on the web about crankcase breathers. Michael Moore at Eurospares has some posts at http://www.eurospares.com/sucker.htm. They are old but useful still. The NOC site also has some stuff on the subject. The Motormite valve has never really panned out because, I think, it isn't designed to handle really the drastic fluctulations in crankcase pressures found in a 360deg twin. Ducati and a few other manufacturers have used reed valves. I didn't know that the XS650 used an external valve like them.

Phil Radford at Fairspare America gave me a tip regarding valvecover leaks. The gasquet in its original form creates a valley between itself and the cover, it collects oil. If you use some Yamabond to stick the gasquet to the cover, let it set, then trim the gasquet to the cover along the inside. Difficult to describe, but if you have the parts in front of you it's obvious. Every little bit helps.

Bob Patton
Good info.

Ducati breather valves, but they are more like $80 or so, depending. Ironically the "trick" think for the Duc folks is to move the reed valve away from the engine and to the airbox. Unfortunately this works better for race motors but the posers don't care.

pcv valves and oil leaks

And as mentioned, BMW has something similar (and cheaper). I found one place with the valve for approx. $10.
pcv valves and oil leaks

I'm sure someone will find this or a similar part elsewhere.
BMW Parts (England)

I'll do some more research.

Here's another vendor for the BMW valve:
Beemer Shop $16

pcv valves and oil leaks

I see the BMW valve has been discussed before on the BritBike forum, heck my brother even found the part number at one point... two years ago. Sigh.
Well my XS650 valve arrived today and was planing on fitting it tonight but I have a silly question first
I plan on mounting the valve near the battery on anj 850 mk2
I will run the crancase breather pipe from rear of timing cover to the intake side of valve
but what have others done as far as outlet side of valve do you plumb in back to the oil tank just below filler neck as per normal or do you let the outlet just go to atmosphere via a pipe and block of the oil tank whole below the filler
hope this is not to confusing
What Bob said about the exhaust rocker cover is certainly true, the gasket protrudes upwards and lets oil puddle behind it, and it can't escape. As for the breather, I fitted a tube to the inlet rocker box when I was having a lot of oil leaks early in ownership, and ran a tube to a catch bottle. But it was always filled with emulsified oil, as it was effectively breathing straight to atmosphere. So I fitted a cheap parts store PCV valve to that line, still running to the catch bottle. Now all I get in the catch bottle is a little water. It is quite interesting to extend the tube from the valve into a bottle of water while the engine is running, and see the volume expelled from that top end.
Those Duc and BMW valves look perfect. They are such an improvement over the rubber diaphram automotive PCV valve I've had coming off the timing cover on my 850.
There could be a problem in venting a Commando motor from the head because there's really no way for the head and the crankcase to breathe back and forth. Especially when blowby, the source of the pressure, is going into the case and has to migrate past the tappets or through the little gallery drain in the head to vent out the top. I tried something like it with a PCV valve at the timing cover and a check valve at the intake valve cover leading to the intake tract. I haven't seen any change in idle or rich/lean issues if it's shut or open. Acutually, if anything it would probably make it run richer.
Anyone tried a valve from ET Performance?
My Harley friend has ET valves on all his street and race bikes and I plan to test one on my 850 Commando.
Expensive valves but seems to last forever.

Not open for further replies.