im looking to buy some new pistons, how do i know if i need std. bore, 0.5mm, 1.0mm?

any help would be greatly appreciated

cheers, Theo

The current pistons should say on the crown what they are. If you need them due to a rebuild, it depends how big you want them.

thanks, so does that mean i could have any of the three if i wanted?

cheers, theo

NO if it's already bored +.5 then you can only rebore it to the next largest size (if the bore cleans up at that) i.e. +1mm. Are you rebuilding the engine yourself?????????

well i was looking to renovate slightly and was looking on the rally design website and saw a selection of pistons and was considering replacing them myself.
Is this a bad idea?

So what your saying is you can keep going up if you want to (obviously you cant go back down)

You can only fit pistons that the engine has been bored out to accept. Why do you want to replace them, does the engine burn oil, or just a whim. If its not using oil, then just de-coke, new rings, and refit. Spend the money on go faster bits. ATB Ray.

well i was looking to recon it but i am using a dohc so cant really tune it all that much, so thought i'd do my best to get it run at its best

Check out the price of parts before you strip the engine. You may decide it's not going to be "locost"

If you do decide to strip the bottom end you'll need to:

- measure the bores and check for wear and roundness (they can become oval with time) - you'll need at least an internal micrometer to do this

- if the sizes are within the tolerances (you'll find these in the Haynes book) you can just get new pistons of the correct size (i.e. to match the bore size)
you might find that the old pistons are fine too - in which case you'll only need rings

-important- If you don't get it re-bored you'll need to borrow a ridge reamer and remove any small lip around the top of the bores before fitting the new pistons

-if they are worn or oval you'll need a re-bore, a decent engine builder will charge about £50 for this and tell you what pistons you need (a reputable builder would also measure the bores and tell you what needed done - if anything)

btw - the same logic applies to the crank (which may need re-ground another £50) as you'll need new bearing for it as a minimum

also you'll need a complete set of gaskets and seals

-Robert

[Edited on 30/8/06 by mcerd1]

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Originally posted by rusty nuts
Check out the price of parts before you strip the engine. You may decide it's not going to be "locost"

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To give you an idea of DOHC parts prices, I fitted a new set of drybollick followers to my Misses's Granny, (four years ago), £12.50 + VAT EACH, and there are eight of the little b*****d's. Not a cheap motor to overhaul. Ray

quote:

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Originally posted by Chippy
To give you an idea of DOHC parts prices, I fitted a new set of drybollick followers to my Misses's Granny, (four years ago), £12.50 + VAT EACH, and there are eight of the little b*****d's. Not a cheap motor to overhaul. Ray

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quote:

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Originally posted by theohighland
well i was looking to renovate slightly and was looking on the rally design website and saw a selection of pistons and was considering replacing them myself.
Is this a bad idea?

So what your saying is you can keep going up if you want to (obviously you cant go back down)

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Have you seen "The Worlds Fastest Indian" (brilliant film btw)

Cast your own..... LOL

http://artfulbodger.2ya.com/
http://www.backyardmetalcasting.com/

Guess munro did go through a few before he got the technique right