Forum

[ChrisD]

Jfw: I agree with our hosts in that changing piston shouldn’t have a dramatic impact on balance and vibration as there’s only ~50grammes difference between my lightest piston (500cc Accralite) and a 500cc JP piston at ~554.5gm (the Accralite 535cc piston is nearer 545gm) all weights inclusive of pin, rings, circlips. I didn't rebalance when I changed to 535cc and din't notice significantly more vibration.

But the difference between alloy and steel conrods is much more (my OEM alloy rod was ~326gm and the steel one was ~566grm) for a massive and destructive difference of ~9 ounces so if you change to the steel conrod you must rebalance. I know you didn’t say you considered changing the conrod, but for anyone else – beware. Accepting what I was told, that I didn’t need to rebalance after changing to a steel conrod, cost me dearly.
ChrisD

[Bullet Whisperer]

I stand by what I said in an earlier post, where on the numerous Bullet engines I have changed pistons in and also changed from alloy to steel conrods, I have not rebalanced any of them, except when I have removed a few pounds from the flywheels and every one has been fine, Get the flywheels' and mainshafts' alignments wrong, though and you will have a jack hammer on your hands. Incidentally, when I rebalance lightened flywheels, I use two mandrels of differing weights - one for 350 and one for 500 types, these mandrels fit the crankpin holes and when the flywheels stop spinning in random positions when suspended between centres, with the mandrels in place, they are 'balanced' enough for my needs. regards, Paul.

[jefrs]

I really like bizarre ideas even if they're totally unworkable. Piston rings being iron are usually magnetised, albeit weakly. These would be detectable were it not for the cylinder bore being in the way, the minimum distance for detection being about 4mm of air, not steel cylinder.



It might seem a daft idea sufficient to provoke spaying coffee into the keyboard but someone came up with the very similar idea of using a crank sensor.



Regarding the EFI-535 and the EFI-500, they do have balanced cranks. How well balanced is another matter but RE did improve the balance and the bearings on the new cranks. So unless you're going racing, best to leave well alone.




Here's another silly science experiment - it we were to wrap a suitable narrow coil of wire around the block just below the combustion chamber we should be able to detect the piston, con-rod and piston rings plunging up and down the cylinder from the induced current. Even aluminium has magnetic properties, just not as a permanent magnet. This uses a much larger 'sensor' than a hall-effect sensor, making it more sensitive, but much less precise. Being able to detect something, and being able to use it for anything useful being entirely different.