True 79cc iron sleeve build

DieselTech

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Joined
Sep 18, 2021
Messages
2,089
Ok guys I finally got off my butt, & started to build a 79cc iron sleeve engine. My friend gave me his new engine that broke the magneto end of the crankshaft off. I had a really old 66cc with a bad case & good crankshaft, so I took the good case & the good crank & started to build. The crank has been balanced for my 49mm bore. I got the lower end built other than putting magneto magnet back on. Heres a few pics.I would like some of you pro builders to chime in when I get to the point of installing degree wheel & checking port timing. I'm wanting a low to mid range rpm grunt monster!!!
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Karl Snarl

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Sep 20, 2019
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Stock timing is pretty good for torque. Just need the ports widened a bit. You know what I did with mine, and I use the pipe to limit the rpms to around 7k. Just above 7k she just stops going anymore. From just off idle to redline, it's a bull. I raised my exhaust just that smidgen to get a little more duration before the transfer open. Since I'm staying at lower rpms, doing that helps to fill the cylinder a little cleaner and lets the wave have just a little more time to get back. Pretty sure that's where all the extra torque is coming from. Besides the nitro. I have ran it without nitro, nitro makes a difference, big difference.
 

DieselTech

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Sep 18, 2021
Messages
2,089
Thanks sir, yeah I've been wanting to try nitro, I think I'll use this engine for that. Yeah I book marked your pages on your nitro porting so I had it for a later date. I'm going to try & get degree wheel on there, so you guys can chime in on my port timing. Like make sure I'm getting the correct readings/reading degree wheel right. This crank I balanced must of been a older crank, the flyweights/cheeks were thicker than the one I removed. Also the diameter of flyweights was 1mm larger on this crank, it really fills the crankcase up.
 
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