Just about to put together a 225 that has been bored to suit some used pistons and rods. I have 7 grams weight difference between the set of combined piston and conrod assemblies.
Laying the piston on the side, allowing the conrod to pivot, and weighing the big end end, i get a difference across the set of 4 grams, however the heaviest bigend is actually on the lightest combined weight one. Shaving a bit of weight off this one will mean that it will get even more lighter than the rest.

Whats the rule of thumb, is it close enough to just put together, or will I have vibration issues. It is a road car that will spend most of its time around 2500 - 3000 rpm, or less.

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1967 VC Valiant

Hi Nzpete,

From what I have read, about 10 gram variation over a whole set is acceptable. You are talking about 1100-1400 g total rod+piston+ring+bearing weight (depending on style, stock, race units), so 7g is only about 0.6% variation.

So, I would guess you should have no vibration issues, especially with mostly lower RPM street driving. That said, if it were me, and I had a way to measure these things (sounds like you do), then I might equalize the set to 2-5 g range, and try to equalize all the big ends and small ends (w/piston) too. I tend to run high RPM (5500-6000) on my 225 motors fairly regularly, though.

Hope this helps,

Lou

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