Removing pistons from conrods

spetz · Post by **spetz** » Sun Jun 18, 2006 6:09 pm

Rebuilding the engine and decided to get the conrods shotpeened
Talking to the engine builder and he said there is a chance the pistons may not be able to be removed from the rods as it may break something?

My question is, can they be safely removed?
And , as far as balancing goes, is it ok to balance the engine with rods and pistons as one?
I asked the builder and he told me the engine was balanced as one whole recorporating mass

Post by **Bennoz** » Sun Jun 18, 2006 8:24 pm

Hey Spetz, unless there has been bad wear or seize in the piston pin, they should be able to be removed safely (as long as he's careful - as pistons aren't real strong when it comes to impact force)

The piston pins are a press fit & you will need a 10 tonne or similar press to remove them. Of course Mitsubishi 'recommend' their own special tools...

Here is an extract from the engine tech guide:

Engine balancing should always be done with the pistons attached as a complete assembly. As you mention 'reciprocating mass' - the pistons are a part of this mass.

spetz · Post by **spetz** » Sun Jun 18, 2006 10:54 pm

Do you think it is worth shotpeening the rods?

And, does it need rebalancing after doing so??

Thanks for the help!

Post by **Bennoz** » Mon Jun 19, 2006 6:21 pm

What sorta dollars are you looking at to have it done?

Shot peening is good if you are going to spend lots of time in high rpms... which by the sounds of it you do!

It sort of toughens the outer surface of the rod & remove any stress points that could be crack starters. I've had it done to a number of my old cars - and generally always had them balanced afterwards.

dannyboyau · Post by **dannyboyau** » Tue Jun 20, 2006 12:34 am

The 6A12 is a highly tuned engine from the factory and is balanced by mitsubishi when the engine was built. If you read there workshop manual there is certain referances to this. When they balance at the factory they do so with all the reciprocating mass. This is the flywheel assembly, piston, conrods, crankshaft, harmonic balancer and bolts and pins required to hold this all togeather. That is why you will find drill holes in certain places on the crankshaft, harmonic balancer and flywheel assembly. This is to remove wieght so as to balance the reciprocating mass. You would only need to rebalance if you change any of these parts. Shotpeening the rods would only really be needed if you are dramatically increasing horsepower and then i would suggest forged rods. I ran 400Hp through my 6A13 rods for over a year and no problem with the rods. Pistons not so good but the rods on the 6A12 look virtually identical to the 6A13. Of course Shotpeening wouldnt hurt.