2 stroke rebuild

Just an update....... Bored the block today, I was a little worried I may have jumped the gun with the .020" pistons but with very careful setup I went from this...


To this.........



And finally this.....

 


Off to Mongoose tomorrow for the final piston fit honing. There is still .005" of meat left on the bore diameter for honing so .020" oversize pistons was the right choice. Setup was very important though and I also corrected some manufacturing sloppiness in regards to bore pitch and location. Now looking forward to painting and reassembly.

J
 
Thanks Dave, so far so good. The photos above we're taken at various stages of boring. I just wanted to show where these cylinders tend to wear the most typically. Everything cleaned up by the last pass with material still left for honing. Should get it back from Mongoose on Friday or early next week.
 
What did you bore the block on? Bridgeport set up? I am not familiar with what the bottom of the engine case looks like, was it a total pain getting it clocked in on table, or is there a nice flat surface to sit it on? Any pics of the set up for curious eyes?
Alan
 
I have a 200 Yami 2 stroke block sitting in my basement that I also bored out to fit 20 over Wisco forged pistons. I also took the block to a do it yourself sandblast outfit here in Victoria and sodium blasted all the old paint and any corrosion off, then primed and painted as new. I cut and fitted thin paneling type wood to seal off the places I didn't want the material to get to. It kept most out. Looks like a brand new motor. The intake and heads just needed to be scuffed up and repainted. I also had the heads and block planed flat just to eliminate any possible head gasket leaks down the road.
 
Did some painting while the powerhead/block is getting honed.... First coat after some zinc chromate....





This is the paint I'm using....



Hopefully it holds up. I went with the yellow zinc chromate instead of the usual gren because I thought it would be a better base colour for a white topcoat.
 
Last edited by a moderator:
I went to JB Auto parts on Oak St and had them make up a spray bomb matched to the colour of my block.
 
Some updates...... Got the case back from Mongoose. They did a great job with the final hone and chamfering the ports. Also had them polish the crank. Got through Christmas and finally received some parts I needed for assembly....









 
I haven't put together a 2 stroke engine myself, but I understand it can be quite a trick getting the main bearing caps matched up correctly. Does this engine use the cracked caps on the big end of the connecting rods? If they were, how did you ensure the caps were put back together perfectly?
Alan
 
Yes this engine uses cracked rods. I was a little worried about this step in the assembly process as i dont have the special tool and didnt want to spend a small fortune aquiring it. I was careful to label and keep each rod and cap pair together. So the day came to put the rods on the crank and it wasn't bad at all. A couple required some perseverance but in the end my fingernail and a sharpe pick was all that was needed. The two middle main bearings are cracked to but they are aligned by the case halves, easy. All in all it went together quite easy, I guess the test will be firing it up and it's longevity... 2 strokes are pretty basic machines though
 
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