270° 953cc Sidecarcross engine build

Thinking about running a mini bike PMA on this motor like off a CRF70 or a Chinese knockoff. Should be enough to power the probe ignition and a pair of Dyna coils. Would love to use a HHB one (they are a sweet looking bit of gear) but I'm trying not to add any more rotating weight, plus I don't really need that sort of power output (no lights or elec start etc)

The rotor is only 88mm OD and weighs just 520g
Obviously I'll have to make up an adaptor plate and machine the correct taper inside the rotor.

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I've been working on the top end lately, dialing in the cam and checking clearances etc.
I was pretty happy when I first put it together and it rotated a full 720° without anything hitting!
The exhaust valves came pretty close to the pistons, I measured .008".
Some machining was required to get the .065" that I'm after on the exhaust valves.

Before machining:
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After machining:
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Pair of pistons bolted to the mill table:
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I had to adjust the angle of the dome on top of the pistons, as it was it would 'trap' gas around the edge at TDC. Now there is a 5° difference between the piston dome and the inside of the combustion chamber which will help push the charge to the center of the chamber.
This should keep Jack happy! :D

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Before and after- the one on the left has been machined.
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What angle did you end up with in reference to the piston top? I see that you mention jack in your thread, is the chamber design stock or welded up? I am in the middle of my piston design and this would be useful information, thanks!
 
GGJosh, I am using a Lillie CNC replica head, the chambers are standard other than the work that has been done to improve flow around the edges of the valve seats. From what I can see 'squish band' angle around the outside is mostly untouched.
I measured it at 45°, so I machined the angle on the piston crown to 40° allowing a 5° wedge to push gas to the center of the chamber.

Cheers
 
Wow, super bad ass build. I wish I had access to some of the machinery you have. I am stuck with a old lathe LOL. Looking forward to the finished bike. AWESOME.
 
Wow, super bad ass build. I wish I had access to some of the machinery you have. I am stuck with a old lathe LOL. Looking forward to the finished bike. AWESOME.

Yes I'm very lucky to be able to use all this equipment, it's in my dad's home workshop.
It's an old lathe as well, but you can do anything with a bit of patience if you put your mind to it!
 
I had to pull the bottom end apart again, the dummy 1st gear was bugging me because it was meshing too tight. I was going to turn a blind eye to it but it got the better of me. The best solution to fixing was to make a new gear because the faulty gear is too hard to machine.
I tested a stock Yamaha countershaft and 1st gear meshing with the new 4sp clutch shaft and it meshes nicely.
This made the job a bit easier as all I had to do was machine out the centre of the Yamaha gear and trim 4mm off the side, then make up a new centre and weld it in.

New gear next to stock 1st gear
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