Av8tor - I read a post from a couple years ago where you were going to make thrust washers for a 21cc Mac blower engine that had needle bearings. I have the same engine that was on a weedeater - Mac 60sx that I was beginning to convert when I noticed the roller bearings and found your post in a search. Was your project successful and did you use the McmasterCarr thrust washers? Anybody else successfully convert this engine. The one I have is extremely clean with almost no sign of wear. It is so light and compact it seems perfect for gas/glow conversion except for no ball bearing mains.
Keith

Hi,

I put this project on hold, just because I had lots of other more pressing things to do. I will get back to it one day. I just made thrust washers out of bronze washers, and made slots in them to admit oil. I am sure they will work fine. Part of the reason the engine is so light is because it has the roller bearings instead of the much bigger and heaver ball bearings and their larger seating areas. I'll finish that one up some day, and put it on a 60 to 90 size plane I imagine...

AV8TOR

Thanks for the reply Av8tor. I will blunder ahead - I found a thrust washer that should work. I was going to get a Frank Bowman ring but this looks so good and I may try it as is first. I had it started on gas/glow before I disassembled and it ran extremely well. Hope it does when I get it back together and on plane. Does anyone else have experience with this engine?

At least on mine, the ports are quite small. I haven't checked the port timing yet. I will definitely check the port timing and enlarge the ports if/when I get around to finishing it up and using it. I was attracted to it because of its compactness and light weight. Let me know how yours turns out, and good luck with it.

AV8TOR

I have 6 of the mac's. only converted one so far and had it on a 70" Exciter scratch built low wing plane. It performed quite well but never did any mods to it other than CDI ignition added. It had always had serious endplay on the crank, making it very noisy at idle speeds. I am about to take it apart and see how much of a thrust washer I need inside the case to stop it. Brass thrust washers would be my choice also. It does have roller bearings on the crank, but since it was never meant to have any end force against it as built, I think it wears the inside of the front half of the case. Is this what you had with yours?

John

Gr8flyer55 - Sorry for my slow response - I have not been checking post - will watch more closely.

I found 4 oilite washers (2 different sizes) from McMasterCarr for <$2.00 plus $4.00 shipping for thrust washers. I am in the process of fitting them now. Pushed the needle bearings further back into the case to make up for the 1/16" thickness - I am going to try to put one on each end if there is room to keep piston rod centered. I was going to cut off the crank shaft on the back of the engine just long enough to go through the needle bearing then replace the oil seal with a plug as suggested by Av8tor. Before I cut it off I got to thinking - will blocking the end completely - interfere with how much oil goes into the bearing. If the seal is still on the shaft it seems like there would be some pressure movement out along the shaft carrying oil into the bearing that is stopped by the oil seal. Will enough oil get into the bearing with it completely stopped up. Probably silly but I was hoping someone would read this and comment.

Gotrain.. what is the link to McMasters ? I've heard mention of it alot but can't seem to find it...

John

Gr8flyer55 - I forgot to comment on the crank endplay. Probably what happened is the crank, knocking back and forth from prop thrust, pushed the needle bearings back into the race making the endplay. I doubt it ground the case down. Mine had almost no slop in it when I disassembled it because the bearings were out slightly to keep the crank centered with little/no endplay. I pushed them back into the case to make room for the thrust bearing. I have been gone and have not gotten back to finishing the assembly. I am going to run it as is (hopefully) then order a Bowman ring to note the difference before I mount it on the plane. At least that's the plan.

I googled McMasterCarr - they are an industrial supplier but were very reasonable in shipping and handling for such a piddly order.

http://www.mcmaster.com/#

Thanks for the link.. good place to look for stuff, I agree!

John