500cc J-engine compression reduction

[sam2019]

To reduce the compression all we needed to do was take off a part of the head that made it smaller in the 350 stock configuration. This was done with a dremel and including washing the head it took under 40 minutes. I then decided because we had the head out and the engine has 20k km on it to also change the valve guides and the valves themselves - which are very cheap here, the entire package costs just little over 5 euros. After another 30 mins the head was re-assembled with new valve guides and valves and all of it did cost me 40 euros. Can't beat that! Compression now is 170 psi (down from 200) and knocking has disappeared. 170 was what we measured on the stock new classic bullet.

 

[sam2019]

Here you see the stock head - the red line shows to where we cut the material, head with new valves and re-designed chamber next.

 

[Dool]

Valve Seats or Valve Guides?

 

[sam2019]

guides - fixed!

 

[Dool]

If I do get around to modifying a J to larger displacement (have buy one first) I would be inclined to keep the Heart shape and just enlarge to the bore size retaining the "Squish" effect.
Whether this is any better I do not know.

 

[sam2019]

I would be inclined to keep the Heart shape and just enlarge to the bore size retaining the "Squish" effect.

only for half the circle then - the squishy part can not be enlarged. thats another reason I did do away with it.
And although I could feel a bit of an effect with the fuelx pro+, and quite some with the cam and of course a lot wit the BB kits I felt absolutely no difference after the reduction from 200 to 170 psi - although I expected some loss of power and technically there must have been some, just not enough to register on my behind.