r5 ds7 piston help

[bosslock]

Hey guys. im New here.

I bought a 72? ds7 250 and swapped the cylinders to r5 350cc

pistons slide fine in barrels but when i do up heads its very hard to kick over? and the pistons sort of jump once one each stroke.??

havent started it yet as motorr is out of the fram.

any advice is helpful as this is my first build.

[gman]

welcome Bosslock. my stock yr1 350 has allot of compression and needs a real good boot to turn it over. Would be next to impossible to kick it out of the frame. I'd definately do a squish test to find out your piston to head clearance, Your piston may be be hitting the head. May be worth the expence of a few gaskets to remove the heads and barrells to see if there is any evedence of something astray. check rings, piston circlips and barrell for scratch marks. Does the engine turn over freely without the spark plugs in? what heads are you using?

[bosslock]

Hey G man. i am using R5 head and R5 barrels. turns over freely when i remove the spark plugs.
cant hear any slapping of piston on the head.

How can i check piston to head clearance.

Thanks for your help

[gman]

G'day bosslock. to check the squish (piston to head clearance) first remove the head. You should be able to reuse the head gasket if its the copper type. Find 2 pieces of solder ( Needs to be soft solder about 1.5-2mm thick or 2 smaller pices twisted together) and make a cross, the width of the piston. lay the solder on top of the piston with 1 peice of solder aligned over the piston pin, the other from the exhaust to inlet manifold direction. make sure your solder reaches to the edge of the piston. Leave the piston positioned in the bore a few mm before top dead centre. Now replace the head and slowly turn over the engine untill it reaches, then passes top dead centre, this is when the solder will be squished to the clearance between the piston and the head. Now remove the head and measure the solder with some verniers, Standard factory clearance can be between 1.2-2mm. When chasing some more hp some tuners will shave the heads to bring there sqiush down to as low as .8mm which raises compression.
I have done a simpler less accurate test by using 1 piece of bent solder fed down the spark plug hole to get a measurement, this won't be as accurate as the piston can rock in the bore. I have heard of people use plasticine instead of solder but this wil;l spring back after it is squished. Another note, I found it hard to find soft solder. i ended up using a thin gauge solder twisted together which was soft enough to leave an indentation between finger nails. Anyway good luck, if you have any questions pm me with your phone number.