valve size

[Farmer DaveParticipant @farmerdave]

Hello all Can anyone help. I have built a 2 cyl boxer horizontal 4 stroke with atmospheric intake valve and mechanical exhaust, I cant get it to run very well,I suspect the valves and air ways are to small for the size of the cylinders (28mm bore x 30mm stroke) the valves are only 8mm dia what would be the optimum size for the valves. Thank you all in advance Dave

[Farmer DaveParticipant @farmerdave]

[Ian S CParticipant @iansc]

Dave, have you tried lighter springs on the intake valves.

Ian S C

[JasonBModerator @jasonb]

Nearest I've done would be the IHC that had 1" borex 1.5" stroke, valves had 0.328" heads on 3/32" shafts ports were 0.312"

I also have a hired man 1.25" bore x 1.625" stroke that has 1/2" valve heads, 1/8" stems, ports 0.339"

As Ian says a very light spring on the inlet valves, if you have compression you should be able to hear the valves sucking in air and see movement, like this

[Farmer DaveParticipant @farmerdave]

Thank you for your suggestions guys. Intake valves are bobbing up and down nicely, the springs are very soft, I don't think that is the problem.Jason the engines you use as a comparison would confirm my valves are to small and I've started to make larger ones and I think I'll raise the compression a little.

Regards Farmer Dave

Edited By Farmer Dave on 10/04/2015 21:35:59

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