Cb250 Pistons for CB72

[DrMowl]

Hey Brian,

seems like a lot of you guys have made their own spacers/gaskets. How do you make them fit well? It's not that hard to get make a gasket out of paper, but to apply it on aluminium and cut the aluminium exactly is quite hard without the proper tools.
What kind of spacers on the cylinder studs do you mean? Do you have any pictures of these?

Maybe I can find somebody with a CNC machine.

This also would be the cheapest way.

[OldScrambler]

On single-cylinder motor I traced the inside cut-out from the base-gasket..............and cut with a band-saw. I then traced the outer shape of the base on the upper-case, and cut with the band-saw. I buffed the edges to make them smooth. I double-drilled the stud-holes.

You could also take the components to a water-jet cutter. A local shop made me a custom copper head-gasket for my Triumph Cub with a water-jet and they work real well.............no failure to date with compression at 13 to 1.

[GORDON BROWN]

Hello

Dr.Mowl Just noticed the post and realised that no one had mentioned the valve angles being different on the two engines. I have seen the CB250 pistons used but I am sure they had the valve pockets machined to suit, as well as sides of the crown. I suppose spacing the head away from the pistons would eventually stop anything from touching but you might end up with very low compression etc. as well as the cam chain problems.


Gordon

SAFOJ

[honda brian]

Hi Doc, sorry this reply has taken so long. I got the spacer cut at my local metal shop. I'm not sure what they used but it was only about $20 if I remember. They copied a base gasket which I supplied.
Brian.

[honda brian]

Hi Doc, sorry this reply has taken so long. I got the spacer cut at my local metal shop. I'm not sure what they used but it was only about $20 if I remember. They copied a base gasket which I supplied.
Brian.

[davebern]

I have actually made CB250 pistons fit in the 1980's when I first got the bike. I bought the bike and someone had tried fitting the pistons and gave up. I did machine the sides of the piston crown on a lathe untill the crank could turn without the head gasket in place. I didn't take anything off the top. I ended up with 9.5:1 compression. The bike ran like this happily for years until it was worn out and needed a rebuild a few years ago. I then rebored it and put in Hap Jones S12 pistons, which it has now. These are lower compression (about 8.5:1) so the bike has less top end, but seems to pull nicer....

Dave in Australia.