Crank seals?

ran49

ran49

New Member
Well I guess I have a blown crank seal.Engine's been behaving strangely,reving up at idle and
running a little jerky at cruising speed.After ruling out most of the usual culprits I began looking for air leaks.While it was idling without clutch cover I directed an unlit
propane torch at the small gear.Wow! I just about blew my engine.It went straight to red line and the kill switch wouldn't stop it for some reason.Had to drop it off the kick stand to stall it.
Strange thing is,aside from a few quirks the engine runs strong and there is no visual evidence
of a leak at the seal,although I haven't removed the gear for a close look.I do have an extra set
of seals and if I can ask a stupid question,is it possible to replace the seal without taking the
case apart? Thanks,Ron
Sorry,I should have stated the engine is a Dax 70cc.
 
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http://motorbicycling.com/f39/bicycle-engine-total-tear-down-391.html look here in link #5 I have the seals info listed off of the seal.
You shouldn't need to split the cases to replace the seals they will pry out drill a small hole in the seal and hook it to pry it out be very careful not to nick the crank or the housing. Take your time on this. To install the seal lube the seals lip with grease and use a seal driver if you don't have the driver a deep socket the same size as the o.d. of the seal will work drive it flush with the case or just a little more than flush with the case. Make sure you don't ding the crankshaft if you use a socket.
If you take the numbers to (Advance Auto this is a parts store you might have something else where you live ) they should be able to cross ref. the sizes to get you the seal/seals, see if you can't get a double lip seal better than a single lip seal for these engines.
The screws are not soft you need to use the correct fitting screw driver on the screws head.
Normandnut
 
Thanks for the replies.
Finally pulled the small gear and the seal was trashed.When this engine was new it had a flaw.The hole for the large head screw that holds the small gear was not tapped deep enough for the screw to tighten against the gear.The gear would drift out enough to allow the key to slip out.
I fixed that problem and it ran great for many miles.I can only guess that when the key fell out it became stuck between the gear and the seal.Probably didn't help that I was revving the engine trying to figure out why clutch wasn't engaging,lol.Took awhile for the seal to finally fail.
Anyway it was easy to remove as it was pretty much in pieces.A spark plug socket was a good fit for pressing in the new one.(which I just happened to have,That's a first)
Couple things I learned.If your engine want to rev up it idle everyone will tell you your carb slide is sticking.It just might be a air leak.
If you check for an air leak with propane make sure you have means to quickly kill your engine.Mine was close to melt down,although the piston and cylinder checked out fine. Thanks again all,Ron
 
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