Does anyone know if there is a significant difference in weight between JP Pistons (from British Only) and EMGO pistons? Is there enough of a weight difference to throw off a crank balance job?
I began building a Triumph 650 engine a couple of years ago and am ready to resume the project. I had the crank balanced using a set of JP 0.040" over pistons that I now cannot locate. I priced a new set of pistons at my local parts house on Saturday, but they only have EMGO pistons.
The good news is the price of EMGO pistons using Harrison rings, at $120, is about half the price of a set of JP pistons and rings. I am happy to save $130, but not if using the EMGOs throws off my crank balancing. Should I cough up the money for another set of JPs or save the money and install the cheaper EMGOs? I do not intend on tearing the bottom end back down to have the crank rebalanced.
As information, I am building this engine in stock form for road use. It is for my 1971 Bonneville.
Thanks, Blapper. I am working under the assumption that a new set of JPs will weigh about the same as my original set. Who knows, maybe JP's production methods are not consistent and a new set of JP's might be farther off from my originals than the EMGOs.
I have to wonder just how sensitive the balance job is to a set of pistons. If it is that sensitive, it seems to me we would hear complaints about excess vibration every time oversize pistons are fit. Additionally, it seems the balance factor itself is a bit of a guess. Who knows, perhaps the balance factor I would get fitting the EMGOs with the original balance job may suit my particular bike better. Thoughts?
Not impossible, just unlikely. Worst problem is pistons that are a different weight left/right - both the same is not so bad.
Having said that, when you see the extent an expert goes to to get your crank/pistons/rods to the right factor, you'll understand that the difference in weight between one set of piston - esp EMGO's - is a lot.
I asked my balancer if I'd need to have a balanced engine tweaked as I was fitting heavier pistons due to a rebore. He said that in an ideal world it should, but in the real world most times people don't notice much difference, as long as the same type of pistons were used (eg cast Heps, JCC, etc, & not some heavy forged jobs). The crucial thing is to make sure that each piston assembly weighs the same, otherwise a rocking effect will be set up (which causes vibes all the way up the rev range). Heavier pistons will drop the factor slightly & vice versa. Biggest weight change I ever did was 20g/piston & if there were any vibe differences due to it then they weren't anything to worry about (normal road use). hth