Hi All,
My 1954 ES2 is due for a rebore and I will ave to take it out to +60 at this point. Currently I am running a standard compression +40 piston and I was wondering if it would be a good idea to get the +60 piston with a bigger dome pushing the CR to say 7.5:1 or even 8:1. Would this ruin the characteristics of an otherwise soft torque easy starter motor?
Best regards,
Albert
sorry guys meant RATIO not…
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Hi Albert. I use a Heplex…
Hi Albert.
I use a Heplex 16H piston with valve cut-outs machined in (RGM did this for me). It may also be necessary to have the skirt machined to clear the flywheels. This gives a C.R. of 7.9:1. Iâve used these pistons in my 1960 ES2 with iron and now,alloy heads with no problems since 1982 (I couldnât get hold of ES2 pistons and16H onesused to be cheap). The bike has always been used hard. There is a distinct increase in âpepâ and I use an engine sprocket with an extra tooth (RGM). Flexibility doesnât seem to be affected. Ignition timing with the higher C.R. is 33 degrees BTDC fully advanced (38 with the standard 6.9:1). Balance factor should be checked. The original ES2 piston had a slot behind the oil control ring which, on my bike, closed up! The 16H piston does not have this slot (it also uses a thinner 1/8â ring as opposed to 3/16â) just a row of holes and seems to be stronger. Oil consumption on my bike with this piston is negligible.
Hope this helps.
Ian.
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sorry guys meant RATIO not RATION