Blown Seals

[dorourke]

Sorry to bring up a new thread, this might be a repete of another one I have not been able to find, I read as much as I could. The question is: Can a blown out seal on the crank (either the mag side or the clutch side) cause the engine to run only a little while then bog down from no compression? I have two engines that just stopped running. All electric is good, carb is good. One engine is barely running with the seal blown on the mag side (waiting for seal kit to arrive), the other w/bad seal on clutch side runs a little then dies out. Can it be dying from some fuel air mix in the case going to other than the cylinder?

 

[KCvale]

The mixed fuel from the carb goes in to the crankcase before it gets sucked up into the cylinder, if you have a bad seal you will get an air leak and yep, that will bog you down because it's too lean.
You might be able to compensate by enriching the fuel/air mixture with the barrel needle (pacman clip lower on the pin) but it will still run erratic as the leak will vary by temp and get worse.

 

[Al.Fisherman]

Bad seal, leaking seal = vacuum leaks. will cause a engine to run bad.

 

[dorourke]

Thanks for the help guys. I looking foreward to riding more than working some day. I am getting alot of experience in fixing these things and am patiently determined to making a reliable engine out of them, maintainence makes you better!

 

[KCvale]

Sort of on to topic...

I wonder if you took an intake manifold and bonded the stem of an innertube to it, then put your piston at TDC and pumped 10 pounds of air in you could check to see if the pressure dropped.
If it did that would seem to indicate a bad seal unless of course a perfectly good motor leaked too.

Just a thought for what might be a new motor test tool ;-}

As for breaking the case and replacing seals lets put it this way, I have 5 'problem motors' laying around and build well over 2 dozen bikes and I've never broken a case open yet.
Lets just say it's just not worth my time when the odds of just making it worse are pretty high and the motors are cheap.

 

[Al.Fisherman]

No, it will still leak out the exhaust. I was playing around with the same idea a while back, and I came up with this. Made 2 plates that bolted to the exhaust and intake ports, use a adapter to pressurized the engine through the spark plug hole. A better way would pull a vacuum on the case. As my hand pumped vacuum pump carped out, I'll now make a fitting that I can use my AC manifolds.
.....http://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-92474.html

 

[dorourke]

I did the old plumbing check on them and I got lots of bubbles out the crank seals when I turned over the shaft by hand. As expected the Mag side was like the Lawrence Welk show, the other on the clutch side only blew a few bubbles but the cover diden't seal as good as the mag side, There is even a seal for the wires that sealed pretty good. I think that's as good as any practical test I could think of without spending any money, just a little of my wifes dish soap.

 

[KCvale]

I did the old plumbing check on them ...

Great idea and an easy check!

Just one note about using dish soap, you are checking for a vacuum leak on the up stroke and the bubble test is on the down stroke.
That won't make any real difference other than if a seal IS blown it might suck whatever you are testing with into the crankcase on the up stroke as well so I wouldn't use a grease cutting dish soap hehehe ;-}

What about using just regular axle grease?
A thin coat would bubble and no biggie if it gets in, heck it might even fix it!

 

[dorourke]

Good idea about the grease. One note on the dish soap: I probably shoulden"t have used real dish soap, however a few drops in a standard windex bottle shoulden't hurt too much if any gets in the case. on that note most of the soapy water went on the out side of the seal and minimal would have been sucked into the break on the seal. reguardless, maybe regular kids bubbles (deluted) would be beter, after all it's supposed to be safe for the children.

 

[dorourke]

Better yet: When doubt, throw them out and replace them both, that way you know those seals are good and you can continue to diagnose the problem further if that isn't the cure.