20 replies to this topic

[Apdiliars250]

Hi I'm I'm looking at buying some pistons for my 1380 turbo build the only option really piston wise is omega 11cc I'm sure they use to do them in 18cc.

Anyway is it worth going for floating pins? I can't really see much advantage apart from when the pistons need removing again.

[whistler]

If you want 18cc then contact AC Dodd. He modifies the dish to suit.

[Spider]

I never build any performance engine with press fit pins. 99% of the time, you'll be fine, but that 1% of the time,,, the pin will walk. Most engine shops don't fit the Press Fits - for these engines - the right way in any case, they do them by heating the Rods and slipping the pins in. The Factory expressly does not recommend this method of fitting. By doing so, you have no idea in the world just how tight the Pin is. Yes, you can check the fits and interferences but that in no way indicates just how tight the Pin is. Also, with your engine, being on such a large bore size, if the Pin walks, there's no fix there, it'll be another block. Even checking the Pin Fit (by doing them as the factory recommends) is no guarantee that the Pin won't walk, especially in such applications as yours.
 

I build these type of engines with Floating Pins and Teflon Buttons. Never had an issue.

[Apdiliars250]

If you want 18cc then contact AC Dodd. He modifies the dish to suit.

I don't quite need 18cc just they are only available in 11cc but I didn't think about getting the dish modified. AC Dodd is not far from me.

[Apdiliars250]

I never build any performance engine with press fit pins. 99% of the time, you'll be fine, but that 1% of the time,,, the pin will walk. Most engine shops don;t fit the Press Fits - for these engines - the right way in any case, they do them by heating the Rods and slipping the pins in. The Factory expressly does not recommend this method of fitting. By doing so, you have no idea in the world just how tight the Pin is. Yes, you can check the fits and interferences but that in no way indicates just how tight the Pin is. Also, with your engine, being on such a large bore size, if the Pin walks, there's no fix there, it'll be another block. Even checking the Pin Fit (by doing them as the factory recommends) is no guarantee that the Pin won't walk, especially in such applications as yours.

I build these type of engines with Floating Pins and Teflon Buttons. Never had an issue.

I am starting to think floating pins are probably the better option now. Do you know if the MED do the little end bushes for the rods? I can only find them for the forged pistons

[Spider]

I am starting to think floating pins are probably the better option now. Do you know if the MED do the little end bushes for the rods? I can only find them for the forged pistons

 

I don't bother fitting bushes. From an engineering viewpoint, yes, that's the right way to go, but all I've ever done is hone out the little ends of the rods until I get 0.0005 to 0.0008" clearance to the Pin.

[mini13]

as per spider i hone the little end and fit ptfe buttons ( or use rods that are already floating eg h beam rods), the buttons normally need to be made to suit as the pins vary in dimensions  between manufacturers. Also, if your making your own, get the PTFE form somwhere reputable Ive heard of people running into issues with the ptfe not actually being ptfe (nylon? acetal?) ( although this should be obvious if your use to working with it)

 

another benifit is you can swap parts around while building easier, to match deck heights, although the pistons are pretty uniform so really its rods that you would be swapping out, bit say you crack a ring land or similar then it makes swapping out much easier.

[mini13]

Ive also dished my own pistons out in a lath when i had access to one, a fairly easy process, but you have to be carefull that your not going too thin.

[Steve220]

If you've got 11cc pistons, take meat out of the chambers. It means you can shape them to benefit combustion too.

[Apdiliars250]

Thanks for all the replies this has helped a lot.

[mini13]

Meat out of the chambers is a good call, although theres an upper limit to this before you start compromising the chamber shape, about 28cc is as far as I would go in the chambers. that would bet you to 9:1 with 11cc pistons which is a decent figure unless your running lots of boost.
 

 

calculator for reference below

https://www.classicm...al/compression/

 

[Steve220]

With a single skim, most decks will give around 30 thou clearance to piston crown, so there's loads of flex there.

[Apdiliars250]

Meat out of the chambers is a good call, although theres an upper limit to this before you start compromising the chamber shape, about 28cc is as far as I would go in the chambers. that would bet you to 9:1 with 11cc pistons which is a decent figure unless your running lots of boost.
 

 

calculator for reference below

https://www.classicm...al/compression/

I think my engine at the moment is 9:75 with 9cc dish pistons. I cant remember all the other measurements it was some years ago.  

[mini13]

that suggests that either the chambers have been taken out a bit already, or the pistons were a fair distance from the deck. ( or a mix of both)

 

Personally i don't like running pistons down  the bore for squish reason,s I always have the block skimmed to bring them up to about 5 thou down, leaving enough for a clean up skim if its ever needed. also Im not a fan of de comp plates for the same reason.

[Steve220]

that suggests that either the chambers have been taken out a bit already, or the pistons were a fair distance from the deck. ( or a mix of both)

 

Personally i don't like running pistons down  the bore for squish reason,s I always have the block skimmed to bring them up to about 5 thou down, leaving enough for a clean up skim if its ever needed. also Im not a fan of de comp plates for the same reason.

 

And Quench area.