Mills Replica - Cylindar Position

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Mills Replica - Cylindar Position

Postby w6vfo » Fri Feb 17, 2012 1:13 pm

I have a replica mills .75cc. They cylinder head was loose when I received it so it looks like the previous owner had messed with it. I noticed the cylinder sleeve insert has two holes in the front and two holes in the back, one set of holes slightly higher than the other set. Does anyone know which way the cylinder is supposed to be fitted - the upper set of holes to the front or the back?

Thanks - Bob
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Postby SteveM » Sat Feb 18, 2012 2:38 pm

Can you post a picture of the issue?
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Postby gossie » Sat Feb 18, 2012 5:23 pm

There is a right and wrong way.
Why not assemble the engine, mount it, add 1/3 of each fuel, an 8X4 prop. and see if it runs.
If not, off with the head, turn the cylinder 180 degrees and try again.
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Postby Frank Klenk » Sat Feb 18, 2012 9:30 pm

I took my Mills apart a couple months ago and here are the notes I wrote up.
Piston slot points forward
Liner intake slot points rearward and 2 intake holes point forward
Carb small hole to rear and large hole forward, both at idle

Frank
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Postby ffkiwi » Sat Feb 25, 2012 5:43 pm

A 75-unlike the 1.3, has two pairs of diametrically opposed oval slots for the exhausts and two pairs of small diameter holes side by side (like a figure '8' on its side) for both intake and transfer. The highest pair of holes are the transfer ports in the liner-and these should go to the front on assembly. The other pair of course are the intake. If in doubt by eye, measure the distance up to the pair of holes from the bottom of the liner with a decent engineers rule or calipers. Ensure the exhaust ports line up fully with the openings in the crankcase casting when you reassemble, otherwise the rod can scuff against the bottom of the liner-which is why there are cutouts there for clearance.

'ffkiwi'
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Postby thomas-oliver » Thu Nov 15, 2012 4:34 pm

The exhaust scavenging on a two stroke begins by the top of the descending piston beginning to crack open the exhaust port, allowing the gases to begin to flow out, then as it moves down further, it begins to open the transfer port allowing the incoming fresh charge to help push out the exhaust gases. Therefor the exhaust port is always higher than the transfer port. The bottom edge of the piston controls the opening and closing of the inlet port.[/url]
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Postby Gluehand » Sat Nov 17, 2012 11:37 am

Yes, the intake & transfer ports are different height.
The higher port should be pointing "forwards", as should also the cut-out of the piston top.
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