Athena 170 head volume
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The 170 kit journey continues.. I decided to check the head volume, and I'm glad I did.
It was 8,5cc in my quick and dirty measurement (might be less if measured thoroughly), and that would be ok for a 125cc, but I want more for 165cc -that is the actual capacity of the 170-kit. I put the dome insert in the lathe (again) to remove material from the combustion chamber. I made a FOS-shape since that was the easiest way to enlarge it without altering height or diameter (kept the same with of the squish band as before). All by hand, so no exact radius etc, but should work, and I should be safer from detonation.
I ended up with abt 12,5cc, and that seems ok. I'm planning to run a squish of 0,7-0,8mm. I would not dare to do that with the standard combustion chamber.I must say it seems like the Athena kit is a bit 'thrown together' with the odd port positions/timing, and now the small head volume.
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Well, I was too exited to test when I put it together. I had knocking at light loads with a hot engine (hard to hear what happens on high load/high revs), so it had to come apart again. I measured squish as it was, and it was close to 0,5mm.. Anyway, compression had to come down further, so I increased combustion chamber volume (diameter), and reduced squish area. It was almost 60%, and from memory 50% should be good for a wide band engine, so this is what I made it.
Also did some stuff to try to improve cooling of the head insert, since it seemed there was deposits of glycol on the insert where it was in contact with water. Like there was local boiling leaving glycol deposits on the insert. I sand blasted these areas to increase surface area a bit. I also blocked the holes in the head gasket closest to the thermostat, to force more flow through the head, and not going straight from the cylinder to the 'exit'. From what I have learned, exhaust side of cylinder and head is what needs most of cooling.
Need to do some jetting and driving in hot weather to see if this has solved the knocking. -
Sorry, but something sounds wrong to me. I’ve not heard of any Athena kits suffering from compression detonation problems, let alone if you’ve cut the compression by 50%!…
I had knocking/missing at low revs/throttle because my pilot jet was too small, was running at a weak mixture. As would an air leak on the inlet manifold or main seals. Are you sure you started with a healthy engine?….
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I have the 170kit but the factory head volume was 12.5ml,I went up to 13ml.
0.8-0.7 squish is way too low for the cc of the kit,on high rpm that may become 0.6-0.5.In my tune to be on the safe side the squish is 1.2mm
A good design gasket is that of the DT200R for the kit.
