I now have all four deck hights skimmed to 1.25 and the heads come out at 55 cc's , 90.5 mm barrels with 69mm crank so the CR works out at 8-1 , dose the CR sound about right or could this be a little high. Good quality CB heads and Mahrle forged barrels and pistons used . i would appreciate any advice on the subject of CR,s ,cheers.
On our type 4, we have 1.53mm deck height (average over 4 cylinders) 96 bore, 66 stroke & we have 57cc on the heads Works out at 8.1:1 CR Did you use the John Maher calculator? http://johnmaherracing.com/calculators/engine-calculator/
Yeh Mark , its a very handy piece of kit , dead easy to use. mine's a type one , not sure if that makes a difference.
How can i make sure the valves wont foul the pistons , without firing it up and waiting for the bang "again"
Ive not got the Tom Wilson book here, tizz at work! I think & could be wrong that he states deck height to be 1mm minimum, 2mm maximum. I cant be sure though but I do recall, when we measured ours, we was more/less bob on in the middle! I know what you mean about waiting for the bang..I have that to come (1st engine build in years)
Are ye tellin me you havent got that engine runnin yet , what ye been doing all this time , at this rate para will have his van running before you !!
Its almost built, set back with the pushrod tubes! It should be ready for the fan shroud and tins tomorrow night now, the replacement tubes came yesterday! Ive got a 6 rib box to pop on too Ill fit over autumn, if all goes well! Para has his motor in a zillion pieces at the moment
Fingers crossed, this one will (hopefully) run sweet as a nut! I would like to build a 2276 for the westy..one day!
I mistakenly built mine with 9:1 ratio. For that I get approx 1 extra HP compared to 8:1, but I believe it runs hotter than neccessary. Next rebuild will see the ratio come down a bit, I'll be aiming for 8:1.
8: 1 will have to do , to get any more i would have to skim all four barrels , and i think that would bring the valves dangerously close to the pistons . the heat is my biggest worry , two adults ,three dogs and in a fully loaded camper chuggin up a long hill will put a lot of strain on the heads and pistons , I might keep the old melted piston as a dash decoration to remind myself to take it easy with the loud peddle .
the valves won't hit the pistons unless you're using a cam with hi lift and the indexing is off....or you've flycut the heads way more than necessary
You simply stretch the tin ones . You are supposed to stretch them to the correct length before fitting anyway. The springs on the spring ones are feeble compared with a well stretched stock tube.
