Cylinder Head Squish Band Machining

[Todd Rovello]

I could use some advice from you engine guys.

Just rebuilt a 1973 1256b top end with the sunburst head. I suspected the head may be warped. After torquing it down I was only getting 90 psi compression. Installed a spare head and the compression jumped up to 120.  The bike is stripped to the frame so it was difficult getting a solid kick thus the compression readings may be a little low. What is the normal compression for these engines?

As for the spare cylinder head I have two of them and and the squish band is a little nicked  up on each one.  Can these be reconditioned by machining or possibly polishing with #400 then #600 grit sandpaper?   Any advice appreciated.

Todd Rovello

[wfopete]

For starters, for an accurate test you need to be able to give that motor 10 fast, solid kicks with the throttle open. Also is the top end "dry"? Might want to try it with a dash of oil down the sparkplug hole to help minimize blow by on the rings. I don't know much about 125's but ROT I'd say you should get a minimum of 150 psi for a happy 2 stroke.

Pete Petrick
175 Jackpiner
Slow but Good

[Todd Rovello]

Thanks Pete!

Anyone have experience with machining the Sachs cylinder heads? I put a straight edge on the stock head and the mating surface is definitely not straight. How much material can be machined away and is any further machining then required of the squish band or combustion chamber?

Also the pitted squish bands on the spares can't be good for performance. Any ideas on smoothing these out? Thanks.

Todd Rovello

[checkcrew]

Todd,

contact Jerry Birky at PVL "Penton Imports"
he does the head mod for the 400 motor,
he should be able to help,

let us know how you make out,

regards,

Mike Gallagher, NJ.
[email protected]

[gooddirt]

 have some good heads $40.00 each

[Todd Rovello]

Thanks guys for the replies. GoodDirt, I am most definitely interested.  Do you have any pics? The part number on the underside of the head is 06 13 106 096. It has the cutaway fins for the up pipe. Thanks.

Todd Rovello
[email protected]

[gooddirt]

Will send photos sunday.

[242]

Redneck Head resurfacing. Find a good flat surface, like a cement sidewalk or porch. Use valve grinding compound and grind head in a figure 8 pattern. I heard once that mud was used on a blacktop road. Guess what ISDE rider did this? When head surface is all shiny your done. You woun't believe what we did in the old Penton days to keep a bike running.

[Todd Rovello]

I checked with Jerry Birky about machining the head. He said I shouldn't be too concerned with the squish band pitting so long as there were no sharp edges on the pits that would create hot spots for preignition to occur. I may be able smooth them out by hand. I would still like to find another good cylinder head. Needs the head with left side fins cut away for up pipe.

[gooddirt]

todd, some head pics in 'sachs head questions "   post.