Yamaha QT50 crank seal replacement


Hey folks!

After asking about my QT50 having no power and blowing some white smoke yesterday, someone suggested a crank seal. After work today I took the top end off and the cylinder jug walls feel perfectly smooth and besides some carbon build up on the top of the piston it looks great.

While I had it running I decided to just change out the transmission oil. Turned her off. Opened her up and the oil was a tad frothy and full of super small air bubbles. I'm assuming that the right side crank seal needs to be replaced at this point.

Has anyone ever done one of these? If so. How easy is it to do?

Re: Yamaha QT50 crank seal replacement

Jack Rutherford /

special tools needed - piston stop, snap ring pliers, all copper penny or rag

see http://mopedriders.org/viewtopic.php?f=2&t=7361&start=60

scroll to bottom

Re: Yamaha QT50 crank seal replacement

Christopher Kimmel /

From the link to add this info to our site:

Should have done this FIRST. Any of you with an old moped or ANY 2-stroke change crank seals from the start. If it sucks on the left it will get air in and mess up your attempts at jetting. Sucks on the right you pull tranny oil in and burn it. Mine was doing this and steadily getting worse.

Doing crank seals on my 81 QT50 (60) I looked high and low on the internet. Couldn't find if this could be done in the frame without separating the crankcases......IT CAN.

Service manual has a complete disassembly of the engine but doesn't tell you it's not needed for crank seals. Left side you have to pull the flywheel.

If you don't have or get the right tool Use this: http://www.harborfreight.com/automotive ... 66868.html Automotive pulley puller. $13 from Harbor Freight.

Just also buy longer bolts and nuts to hold the jaws on (in one review on HF website). Be careful inserting the puller jaws in there are magnets and coils back there. If you're careful, no problems.

My flywheel (and crank seals) are original. Took some work to break that flywheel loose.

Remove the timing plate. BTW you'll need an impact screwdriver. Lots of JIS screws.

Take a small drill bit and slowly, carefully drill a hole in the crank seal. Crank seals are metal inside surrounded by rubber. The bearing is right behind so be careful. Run a wood screw in the hole and pull the seal out. There are videos online to watch how to do this.

For right side drain oil, remove cover, try to save gasket, if not order one.

Put an all copper penny between gears and break the crank gear loose.

Remove clutch, primary gear and all else in the way. This seal you can pry out carefully with a small screwdriver.

Drive the seals in squarely with a large washer and long socket. Or anything that will get the seals installed flush and straight.

Re: Yamaha QT50 crank seal replacement

Jack Rutherford /

This guy is basically doing the same thing:

Re: Yamaha QT50 crank seal replacement

Are you supposed to use yamabond or anything when installing new seals?

Re: Yamaha QT50 crank seal replacement

If you choose to, do so only on the outside diameter (steel) of the seal.

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