Stubborn oil leak in Commando, need help.

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CptKelly

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I've had a 1975 ES Commando for many years. The engine has a Megacycle cam, and dual Mikuni's. Good runner. Unfortunately, I can't seem to get a very stubborn oil leak stopped. My latest effort was to remove all the primary items, and replace the crankshaft oil seal. I still have a major leak, but I just can't tell where its coming from. My engine does have the anti-wet sump piston valve in place. I hate to stop riding it, but this oil leak has got me stumped. Can anyone offer a suggestion?

Mike
 
Have you thoroughly washed the engine, then taken the bike for a short run to pinpoint the actual source of the leak?

Some people have mentioned sprinkling baby powder on the suspect areas just before the check ride; it's supposed to help identify the initial seepage point...

Problem being that often the leakage will migrate away from the source while "in the wind", and fool you as to where it's starting from.
 
The oil leak appears to be coming from the crank oil seal, and I just replaced it. The primary is getting the lions share of this leak. Unfortunately, I can't see where the leak is coming from. Does anybody know a really good Commando mechanic around Columbia, South Carolina? I am to the point where I'm thinking about building up another engine for my bike, as I have a spare.
This past year, I didn't ride the Commando at all, because of the mess it creates if you park it for a few minutes. I also have a Matchless G15 CS that I can ride, so its not like I actually need the commando, but I sure do like it.

Mike
 
Might it be in one or more of the 3 primary fixing bolts that surround the crank aperature?
 
The leak could also be coming from one of the 3 bolts that hold the inner primary on. I replaced the bolts with studs and nuts, using plenty of locktite on the crankcase after a thorough cleaning and blue locktite on the nuts. The lower one will need to be ground down to avoid the chain. Other thing is, do you have a proper breather on the bike? Comnoz has a new one that fits on the sump and is quite effective. There are other options, if you look up breather you will find plenty of reading and I'm not the expert. That said, I only have a tiny drip off the bottom of my flange after it wet sumps and this is a stock 69 with the timed breather.

When you replace the outer primary, put some silicone in the grove around the bottom of it. My primary does not leak. I also had to silicone the inner primary to the crank case gasket but DomiRacer sells a nice rubberized one too. Make sure the inner case is supported properly at the central mount with the proper shim.

Dave
69S
 
CptKelly said:
The oil leak appears to be coming from the crank oil seal, and I just replaced it. The primary is getting the lions share of this leak. Unfortunately, I can't see where the leak is coming from. Does anybody know a really good Commando mechanic around Columbia, South Carolina? I am to the point where I'm thinking about building up another engine for my bike, as I have a spare.
This past year, I didn't ride the Commando at all, because of the mess it creates if you park it for a few minutes. I also have a Matchless G15 CS that I can ride, so its not like I actually need the commando, but I sure do like it.

Mike
Click to expand...

Check the three chain case fixing bolts behind the alternator/front sprocket. If they are loose they can leak oil into the chain case.
 
grandpaul said:
Might it be in one or more of the 3 primary fixing bolts that surround the crank aperature?
Click to expand...

DogT said:
The leak could also be coming from one of the 3 bolts that hold the inner primary on. I replaced the bolts with studs and nuts, using plenty of locktite on the crankcase after a thorough cleaning and blue locktite on the nuts.
Click to expand...

"1975 ES" therefore it has four studs - not three bolts.



DogT said:
When you replace the outer primary, put some silicone in the grove around the bottom of it. My primary does not leak. I also had to silicone the inner primary to the crank case gasket but DomiRacer sells a nice rubberized one too.
Click to expand...

A standard gasket seals the joint between 850 Mk3 primary inner and outer cases, there is no groove/rubber band seal.



DogT said:
Make sure the inner case is supported properly at the central mount with the proper shim.
Click to expand...

The Mk3 inner primary case is secured by tightening inner and outer nuts against the case, and this arrangement does not require a shim.
 
CptKelly
sorry 7 replys yet it seems none except LAB have the faintest clue what you're talking about.
My only thought on leaking from the crank into the MKIII 4 stud primary is that I have seen on the crank surface when the main/superblend gets pressed on that it scratches the crank on the shaft ...very minor but ...it's where the seal runs. In short order the razor blade effect of the scratch deminishes the sealing ability of the seal and then the leaking begins.
Unfortunately the remedy is to polish the cranks after the main is pressed on and before it gets installed in the cases....i.e. the initial build up of the bottom end :x
repeated external replacement with only a new seal does not buy you much :|
 
Not clear exactly where the oil is being noticed that is leaking out. Dripping from under the primary case---behind the inner case---in the front of the case--in the rear of the case? If using Type F trans fluid---which is red color---is the drippy oil red? If the oil seal is leaking---engine oil will make it somewhat darker color and oil measured when drained from P case will be greater than what was added.
As strated in comment before---clean up well---blow baby powder on as much of the affected area as possible---then start the bike---dont ride it--just watch for oil leak to show up--darkening the b-powder--use a good light to illuminate the area of concern. Very slow leaks are usually discovered easily this way. If rapid oil loss is ocurring--this will be more easily seen. Also--remove the oil tank cap and see how much blow by there is---check routing of the breather hose---kinks--? any valve fitted inline?
 
I know some will disagree, but it's my opinion you're pissing into the wind chasing oil leaks on a Commando if you have not done something about the pressurized crankcase. I've changed those crankshaft seals until I was dizzy and they still leaked. I finally went with a XS 650 PCV valve and not only did my crankshaft seal quit leaking, all the other weepers are now dry. It was $16 at the time and it's an easy install, so what the hey. It sure beats changing crankshafts seals every month and oil dripping everywhere you park the bike.
 
I didn't realise it was such a new model. There I go, not reading the post, like I complain about every one else doing (to myself, usually).

I thought the late ones had the leaks and breather fixed, but what do I know?

Dave
69S
 
Don't have an ES but isn't the large keyway for the drive in the same place on the crank taper? If so some have a great sharp edge able to nick the seal. Best tape up the keyway before sliding seal over. Just a thought as I damaged two seals before I realised what was happening. It doesn't leak badly straight away but a few thousand miles later it shows up.
 
CptKelly said:
The oil leak appears to be coming from the crank oil seal, and I just replaced it.
Mike
Click to expand...
I had a leak from the crank seal on my pre-MkIII 850. I'm running a dry belt so it was obvious where the leak was coming from. I replaced the seal twice with no luck. They were the rubber coated type seals. Jim recommended using the steel bodied seal with a light coat of JB Weld. It worked.
 
Whilst you recon it's a crank seal leak, you may have oil escaping from the oil seal on the gearbox shaft/back of chain case. I believe the Mk3s have to have matching gear box and engine numbers (machined as a unit) to ensure the gearbox shaft is central in the oil seal. Fitting another gearbox may compromise this. Only way to see this is with the clutch and primary drive removed (major hassle) Run the bike stationary with a large mirror under it. saves jamming your head under the exhaust pipes.
 
Your crankcase is being pressurized by compression blowby, which is forcing oil through the main seal or around the too limited seating for the seal.
A leakdown test will confirm this diagnosis. See: http://www.harborfreight.com/catalogsea ... own+tester $39.95
Prior to the development of the molded lip seal, engines relied on a tight compression ring seal and gravity to retain crankcase oil.
And it worked.

Frank Forster
 
Your crankcase is being pressurized by compression blowby, which is forcing oil through the main seal or around the too limited seating for the seal.
Click to expand...

Not necessarily. A Commando without any check valve in the breather will have a pressurized crankcase. Although, piston ring blowby will create crankcase pressure, too. I've read here about a lot of work being done to stop oil leaks, special joint sealant, special seals, special "O" rings and the like. While these are all worthwhile, you may still end up with oil leaks if you have a pressurized crankcase. Guys, don't fight it. The Commando does definitely benefit from a reed type check valve in the breather circuit. They are cheap, the Mike's XS 650 PCV valve is $18. I see CNW is now selling the version that mounts directly to the crankcase. More better! I've tried the Motormite vacuum check valve. It's little more than a placebo. If it works at all it's for a very short time.
 
Donlon39 said:
Your crankcase is being pressurized by compression blowby, which is forcing oil through the main seal or around the too limited seating for the seal.
A leakdown test will confirm this diagnosis. See: http://www.harborfreight.com/catalogsea ... own+tester $39.95
Prior to the development of the molded lip seal, engines relied on a tight compression ring seal and gravity to retain crankcase oil.
And it worked.

Frank Forster
Click to expand...



Yeah, might be, simpler to just stick a reed valve on it, since you want one anyway, even on an engine that has zero blow by. I mean, we have 750 or 850 or even 900ish ccs of pumping pressure on every down stroke, the same on the up stroke of course, lets net a vacuum out of it. Lemonade from lemons.
 
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