Welding and remachining rotary pad?
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Style Maven
74 50s x3 78 P200 x2 84 Cosa PK50XL2 58 AllState 68 Sprint 80 50special '66(?) Super125
Joined: 22 Nov 2010
Posts: 8048
Location: seattle/athens
Mon Mar 02, 2015 11:58 pm quote
Ginch wrote:
I can't understand how this motor - it's a 200 right? - had a 150 crank in it, how did that work? Unless it had a 200 rod fitted to it to the 150 crank, otherwise the rod would be too short. And did you releive for the crank lip because it had weld in it from the repair?
It's convoluted, but it's all up there. The original crank's wrist pin bearing let go and the crank was destroyed along with the piston, cylinder, crank bearings & rotary pad. I had collected some random P200 motor parts from an abandoned project and the P150 crank was with this stuff along with my 'new' cylinder, piston & head. I thought it was a P200 but never checked before installing it in the repaired case. When the new wrist pin bearing wouldn't go in the rod I discovered the problem. Fortunately about this time I was helping Skot with his engine build and he gave me his old crank, certified P200.

Anybody need a P150 crank, let me know - I have a beauty

Yes, I had to remove the weld from the groove that runs along side the pad. Ideally it would be machined, but the shop matched up the port width to the crank I gave them .The rotary pad web on the crank of the 200 is a couple mm wider than the 150 because of the lip. My inlet port width is probably a bit narrower than stock to ensure I still have sealing surface on that inside edge. It all works, but I can now see that it's not the best job possible to optimize the opening.
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 8058
Location: Victoria, Australia
Tue Mar 03, 2015 2:48 am quote
Got it... watching this with interest.
GL, PK, PE200 with hack, Sears Rust Badge
Joined: 24 Apr 2012
Posts: 956
Location: Deep in the heart of Texas
Thu Feb 18, 2021 7:32 pm quote
Yeah I pulled up this old post.

I've had a problem with a P200 motor before Voodoo made this post. It never started cold easy, clutch and flywheel coming loose, a lot of blowback from the carb, and timing is off at high speeds. Just didn't sound as smooth as my other p200. Thought the crank was bad but problem continued after getting another crank. Saw one of FMP videos about rotary pads and decided to give it a check since I had the carb off chasing a fuel leak. Put a .1mm feeler gauge in the intake, turned the flywheel and it did not stop the crank from turning. Went all the way up to almost a .3mm feeler gauge before the cranked stopped. Split the cases and saw the rotary pad was bad. Doesn't look the worst but can't stop a .1mm feeler gauge. Should be from .005mm to .1mm.

Cases and crank are at an old time two stroke motor machinist who wields aluminum, and fix cranks. The cost was less then going to a reed valve setup but still expensive. After we thaw out, everyone lights are back on, water flowing as normal and temps are back up to 60-70 degrees I'll pick them up next week. I hope the problem is solved.

FMP rotary tolerance https://youtu.be/gnWy7WKmfKs

My rotary pad below. The clutch side edge of the intake is almost gone.

p200 intake.jpg

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