SOHC.co.uk Forums > CB750
bore to piston clearance k2 advise please
K2-K6:
I learnt engineering in metric, so have to convert into thou to understand it if necessary.
This may be right :- 1st 0 after decimal place is tenths, 2nd 0 is hundredths, 3rd 0 is thousandth and so 0.001 should be one whole thou ;D
Honda manual says minimum of 0.0004 inch ... which should be 4 tenths of 1 thou ... effectively just under a 1/2 thou, that's if I understand it correctly ;D
It's weird as it's a decimal division of finest English inches .... all seems a bit cock eyed to me.
If it's definitely bored in that spec, with correct materials, then it should be fine to run it.
McCabe-Thiele (Ted):
It's 4 ten thousandth's of an inch
Not helped when they changed the definition of a million. It's not generally 10 to the power of six as it was, the yanks call 10 to the power of five.
roverboy:
hi roverboy here thanks for all you replies will have to study the information from you all thanks again ps were the engine when new painted or untreated as would like to keep the bike original again thanks for your help
K2-K6:
I'm unsure of your knowledge here roverboy, but don't want to teach anyone's granny to succeed eggs ;D
These are notably tight in that tolerance and characteristics of their design, an important part of why they sound so smooth when all to spec and assembled correctly. There's no real risk in running them at the stated tolerance, but many opinions out in the great wide web as to what should or shouldn't be done.
As comparison, and linked to your title, the rover V8 (if that's in your interest) has, for the same dimension of skirt to bore clearance listed as 0.0003~0.0017 inch specification. Honda 0.0004~0.0016 for comparison.
This engine quite similar in metallurgical design intent, cast aluminium block and piston with ferrous bore liner to arrive at similar clearance, even with larger diameter piston.
Your measurements need to be noted with all the components at same temperature .... barrels, pistons, measuring equipment etc which usually means individually measured pistons and bore matched to that, letting the barrels cool after machining to the same as pistons for comparison validity. This is sandardl inspection procedure though and will validate the existing specifications you have ready to assemble.
Engine oil condition being another significant component in how they run. Whichever oil used, condition of oil is paramount in these to avoid compromise.
roverboy:
many thank for you help by the way the rover name is my other love rover 90 p4 kind regards
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