I mentioned in an earlier post that I was rebuilding my Honda PA50II engine as it was showing signs of a bad seal: no idle, overheating, and other inconsistencies. While your replacing a seal it's usually a good idea to replace the bearings, especially if your running a kit. Honda cranks are pretty tough and I don't think performance versions are readily available, so I'm sticking with the stock crank. I ordered new bearings and bought a set of seals off a friend who also has a kitted PA50II. When I opened the cases (for which I had to make a special clutch-puller out of a Honda axle nut welded to a pipe with a M14 nut a bolt at the other end), I found the magneto side seal had completely worn through and that the seal spring was in contact with the crank. This was definitely the problem. 

Here is the bad magneto-side seal:

The split cases with existing bearings and seals:

I removed the old bearings, cleaned the cases inside and out and installed new bearings by heating the cases in a toaster and placing the crank (with bearings installed in a freezer) and then lightly hammering them together with an added layer of Yamabond.


After I had installed the new bearings and seals and almost reassembled the entire engine I realized that the stator plate has a little lip which requires that the magneto side seal be recessed in the cases about 1/4 inch. I hadn't realized this when I installed the seal, so I tried pressing the seal further into the cases. 

Well, I pushed it too far... Needless to say, I had a much worse case leak on my hands.

This was all in October.  I took a break... and about three weeks ago I cracked the cases again to reposition the seal only to find that the seal had been destroyed by the inexplicable PA50I worm gear on the crank (don't ask me why I have a PA50I crank in PA50II cases because I don't know).

The destroyed seal: 
 Regardless, the seal was done, so not wanting to leave my cases open for too long, I put the old seal that I thought wasn't bad back in. 

Apparently that seal was bad too...

So, I ordered another seal, and fresh cases gaskets from Treats along with a Malossi 21mm intake so I can run my 21mm PHBG carburator (off the Puchavus) as soon as I find it... I cracked the cases again, replaced the seal at the correct depth and reassembled the engine.
Variated cases are beautifully simple:

While I had the cylinder head off I noticed the piston was wearing around the edge, probably only at quite high RPM's because the damage was very light. I took a Dremel and cut a deeper squish band into the head.

Here's the damage, I'll try posting pictures of the modified squish band later:
The new engine runs very well, with some minor overheating that I think is a result of poor timing... I'll get to that later. In the meantime the carb is leaking... Ah, mopeds!

My current setup is a 70cc Polini cylinder with stock 12mm carburator and stock exhaust with notched stock variator. If I can get the overheating issues cleared up I expect to see 45mph at The Bourbon Bandit's Whiskey Business.

Next up 21mm PHBG carb and Motion Left exhaust.

Replacing the Replaced Crank Seal, Again

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Monday, March 29, 2010

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