leaking crank seal

Try this experiment:

Connect a long tube to your crankcase breather vent, and run it up to your handlebars with enough slack where you can pick it up and point it at your chest or face (if you dare)

Start the bike, drop it in gear and take off for a ride around the block at slow speeds, 1st & 2nd gear. When you get going, grab the hose end with your left hand and point it at your face.

THAT is the pressure your seals are holding back (minus a bit that makes it out your oil tank vent through the froth tower).

uh thanks for the advice grandpaul, however i don't think i'll be pointing a breather hose to my face when the engine is running, especially if i'm riding the bloody thing.

Dang! I can never seem to get any "takers" to try these neat tricks and report back with honest opinions...

October 30th I had an operation to repair my level 3 dislocated collarbone I had done three weeks earlier at Barber- they cut my shoulder open, re-located my collarbone and then cut my left leg open and used a tendon stripper to peel a big piece of ligament off of my hamstring- they then drilled holes in my collarbone and strung this new ligament through one hole around the back of the AC joint and into the other hole and then put screws in the holes to hold the ligament in place, thus 'making' me a new AC joint ligament to hold my collarbone in place since I had completely severed the original ligaments when I shoulder planted into the ground at 60 mph.
The cause? We had a completely new Norton race motor put together after I grenaded the old one at Daytona and it had a new metal type crank seal in the brand new Maney cases- I noticed right off that it had a slight leak when the motor got hot and we were keeping an eye on it- as I finally started to figure the unfamiliar track out, I had a long practice session where I started to push very hard and on the last lap of the session I cranked open the throttle coming out of turn 5- I didn't know the seal had failed in a big way oiling my rear tire along with the whole side of my bike- the rear end snapped out and I got high-sided over the handlebars into low orbit.
Wanting to know if it was a defective seal or not, Herb put another new metal type crank seal in the bike and put it on the dyno rolling road with the front belt pulley off so he could see the seal. Sure enough, when the motor got hot enough, you could see the seal start to fail. He tried it again with another new metal seal with the same results- hot=fail. Using the rubber surrounded seal like illf8ted suggested cured it- ran it hard on the dyno, no leak. Sometimes you have to learn things the hard way.

Doug, That finding surprises me. I have always run the steel cased seal in my racebikes and streetbikes and in all the motors I build. I do install them with a bit of epoxie so they don't get loose in the case.
It sounds like you may have a crankcase pressure problem. On my racebike I found using thick section rings [like stock] caused the rings to flutter at high rpm and the crankcase pressure would skyrocket. Thin section rings solved that problem. The motors I have built the last few years have had the reed breather on the rear of the case and that has been the best solution to oil leaks anywhere. And a couple free horses. Jim Comstock

Hey Jim; I did a few track sessions before heading down to Barber and we noticed a slight leak then at the seal- we assumed perhaps these new cases didn't breathe as well through the timing side where our breather is so we replaced the seal and put another breather on the back of the motor as well- so there were two large breather hoses on the motor, so that was not the issue. I think the problem was a combination of the Maney cases not liking the metal seal and perhaps this batch since we have used these before without major incident- I have had minor leaks there before in the past but nothing like this.

Doug MacRae said:

Hey Jim; I did a few track sessions before heading down to Barber and we noticed a slight leak then at the seal- we assumed perhaps these new cases didn't breathe as well through the timing side where our breather is so we replaced the seal and put another breather on the back of the motor as well- so there were two large breather hoses on the motor, so that was not the issue. I think the problem was a combination of the Maney cases not liking the metal seal and perhaps this batch since we have used these before without major incident- I have had minor leaks there before in the past but nothing like this.

Click to expand...

One way valve on your breathers or just hoses?

One way valves on the hoses.

Doug MacRae said:

October 30th I had an operation to repair my level 3 dislocated collarbone I had done three weeks earlier at Barber- they cut my shoulder open, re-located my collarbone and then cut my left leg open and used a tendon stripper to peel a big piece of ligament off of my hamstring- they then drilled holes in my collarbone and strung this new ligament through one hole around the back of the AC joint and into the other hole and then put screws in the holes to hold the ligament in place, thus 'making' me a new AC joint ligament to hold my collarbone in place since I had completely severed the original ligaments when I shoulder planted into the ground at 60 mph.

Click to expand...

Did Herb devise these personal repairs also?

Ha ha..... good one! It's amazing how much surgeons are like amateur carpenters.

Doug, I am building a race motor right now on maney cases with a reed breather on the rear of the case. I will keep an eye on it. Jim

I believe part of the issue in dealing with Maney cases is that they are made from a different alloy of course than the original Norton stuff and they expand more when hot, necessitating either an .005 larger metal seal or a rubber backed seal.

doug
really sorry to hear about your crash and subsequent injuries
hope you're on the mend and heal quickly
i was run over in brixton rd in london in november, busting 4 ribs and bruised and tore a few bits inside.
still a bit sore but recovering slowly and can walk and talk so i'm counting my blessings.
happy to say i was on my honda and not my commando.
anyway, thanks for the input from everyone. i have fitted the xs pcv valve and unfortunately have still got a leak.
this occurs as stated by doug only once the engine become hot
its not pissing out but a leak needs to be addressed as i don't want to perform the same stunt as you doug if i can help it.
sound like this rubber oversize seal might be the go
will keep you posted as to the results
thanks everyone for the feedback
chris

Hi Chris,

http://simplybearings.co.uk/shop/p32148 ... _info.html

try that one...works fine on my motors!

Regards

John

I just encountered the same problem on my 71 Roadster (Combat type breather system) yesterday. I have just finished a complete restoration and have so far put about 70 miles on the bike entirely with short shake-down runs of 5 miles or so
(I have had the XS breather valve fitted from the start), yesterday I went for a longer ride and the bike started leaking engine oil out of the primary case late in the run. When I took it apart the seal was still in position but I could rotate it freely with a small screwdriver pushed against the side. I only have the metal type seals in stock so I replaced it with a new one with some Loctite bearing fit. I will keep an eye on things and report back when I have a chance to go for another long run.

ok fellas
here's the word
with the xs 650 pcv valve fitted with new hoses fron the case and to the oil tank, when at low revs the engine feels choked and takes a good burst of throttle to get going. no good for me in my opinion. it did reduce the leak when not in use but i'm not too sure how effectively. i'm not sticking with it and have taken it off and put the original reducer back on. the result.....she is running beautifully 75mph at 4000 revs.
so back to the drawing board with the seal. i will try the seal posted by john (seely 920) and see how she goes.
results will be forthcoming
cheers
chris

15073jrmd said:

ok fellas
here's the word
with the xs 650 pcv valve fitted with new hoses fron the case and to the oil tank, when at low revs the engine feels choked and takes a good burst of throttle to get going. no good for me in my opinion. it did reduce the leak when not in use but i'm not too sure how effectively. i'm not sticking with it and have taken it off and put the original reducer back on. the result.....she is running beautifully 75mph at 4000 revs.
so back to the drawing board with the seal. i will try the seal posted by john (seely 920) and see how she goes.
results will be forthcoming
cheers
chris

Click to expand...

Did you ever say what year bike you have?

sorry dave
i've got a 74 850 but engine number is 319222 frame number 110961
so she's been around the block a few times
has definitely been down the road
and before i got her had been brutalised by someone trying to stiffen her up as a mobile vibrator
chris

Hi Chris,
What do you mean ?

it did reduce the leak when not in use

Click to expand...

.

I've never known a good valve like the XS cause any problems unless it was fitted the wrong way round. And it is worth checking the stator studs that screw into the crank cases

Chris,

Could you post a picture(s) of how you plumbed the PCV valve? I would say it's impossible for the valve, correctly installed, to cause the problem you indicated. Stranger things have happened, of course.