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

Posted on

Monday, March 29, 2010

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