The International CBX Owners Association

I need to remove between 6 and 8 grams from the big end of 3 of my con rods.
Could somebody suggest which areas of the big ends could be ground off without weakening the rods in the first place?
BTW, 8 grams is not a trivial amount of metal and most probably more than one suitable areas will need to be ground .. Best, Aris

Aris: Look for excess material from the casting process. Other than that, I would start at the bottom of the rods.
I may be wrong, but the little bosses on the top end may be balance pads.

Mike thanks

The tops are already balanced to a few tenths of a gram.

It is the bottom (big) ends which I need to lighten.
The obvious place is where you indicate. BUT wouldn't this weaken the rods? Surely these 'ridges' are there for a purpose (reinforcement?).

Cheers, Aris

The weight of the big ends (and the rest of the rods and pistons too) is offset by the rotating mass of the crankshaft counterbalance weights and since you cannot measure those individually down to a few grams, I wouldn't mess with the rods at all if they were mine. Lightening your heaviest rod might actually be going the wrong direction . . . . maybe your lighter rods actually need to be heavier to improve the balance of the reciprocating masses? Add a pair of 2 or 3 gram washers under the nuts? I wouldn't bother

Improving on the overall balance might be necessary when you're trying to add to the max engine RPM, but realistically, how much time are you going to spend above 10,000 RPM? If I recall correctly, I think I read somethere that Honda tested a few of these engines to destruction at 12,000 RPM and they lasted for an hour or more?

I'm not saying it's *perfect* as Honda built it . . . . but do we really know enough to make changes here? Maybe, but we're nearly splitting hairs here IMO

If you're determined to mess with them, taking the weight from where Mike suggested is as good as any place. I suppose you could make an argument that removing metal from anywhere weakens the rod, but then having the bottom of a rod cap open up is a pretty unusual failure, and those sorts of failures usually happen when someone beats the death out of of an engine and/or fails to check or change the oil. That's not how I picture you at all Aris

Don

Don
I can assure you that in a straight six cylinder engine, the crank is balanced on its own, without weights to compensate for rods as in some 'V' engines.
In my own case, after checking my crank for everything, including run out (very little, way below Honda'a spec), I had it balanced down to a very fine point. So now is the turn of the con rods!
I have done the small ends which I have matched to within a few tenths of a gram. All that's left now is the big ends of the con rods.
And I think you are right that removing metal from the bottom cap 'ridges' is probably OK.
And yes, I am not a conscious engine destroyer (I have inadvertently done my bit .. few times ..). I get my highs from precision and smoothness.
So unless anyone else chips in, it will be the bottom of the caps ...
Thanks, Aris

Aris, any possibility of titanium bolts? (No, I do not know a source.) Even at that, consider thermal and stress expansion rates compared to the steel bolts. I don't remember how titanium compares with steel in those properties. At 8 grams, max, I tend to concur with Don.