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Originally Posted by Old Fart
I never checked clearance on my engine when it's hot. Will the clearances tighten or open up when hot? Dunno but I'll check next time I'm it as it's easy to pop the rear cover on a stretta. If the clearances diminish significantly I'll have my answer as to why .004" is the lower limit.
Perhaps a seasoned guru can weigh in on this and splain why we shouldn't run tighter on these engines.
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I've done some testing with the desmoquattro's in this arena. What I've learned is; everything tightens up when hot. I've seen .001" on average and in some cases, even slightly more. Also, the desmoquattro's cam's flex much more then the testastretta's do this means, the clearances on the desmoquattro's need to be a bit looser to help compensate for that bending effect. Also, tighter clearances, really don't have any benefit. I've done tests with .002" closing/opening clearance and it didn't change anything vs .005" opening/closing clearance. I've recently done leak-down tests and compression tests on good heads trying to determine if it really makes a difference and in all honesty, my testing concluded; proper belt tensioning makes MORE of a difference then clearances.
Needless to say the testastretta with its center cam holding position, helps greatly with cam flex, throw some MBP's in there and you should theoretically be able to run pretty tight clearances to help avoid the rattling around effect.
Quote:
Originally Posted by 916duc
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Pretty kool, though I don't think its "new" per-se, just a re-hash of an older design.