Does anyone know if you have to have the pistons matched to the bores when buying these wiseco units with the part number: K598M995 std size with a 99.5mm figure????? On a brand new short block ???

 

You need to match the A / B fitment or get hone to fit.

however that part number gives too high compression ratio I believe..

Simon

 

Ok mate thankyou. Any chance you can get a price of oil pump and seals ie front main and oil pick up. A modine and set of piston's to match the motor i'm buying from you and if i've got enough cash ill take the lot from you on monday.1

 

Of course.

 

You may need honing to get the correct clearance in the bores, especially if the block is not new.

 

new block and pistons will be drop in, unless he changes his mind and wants to strip it and hone, then pistons would be hone to fit.. I can do either.

Simon

 

Having a brain fart moment, cant remember the make of my forged pistons but how does this A and B clearance thing work on a new 2.5L block? Is there two "sizes" to a brand new bore on these blocks and the forged pistons must be put in the correct locations?

 

the blocks and pistons come with A or B marks whcih indicate the clearance..
cannot remember what A and B represents in clearance.. however if you buy after market drop in pistons then you need to get the correct A / B sizings.. however if you buy hone to fit pistons then they are a tiny bit larger so you hone the block to get the correct clearance.
I only mentioned it as 170 was talking about buying drop in pistons when we spoke.

Simon

 

Nice one Simon...makes sense now as I saw the oe sti pistons that came out with A's and B's on them

 

The "clearances" for both "A, & "B" pistons should be the same. When the blocks are bored at the factory, there will be differences in the sizing, due to manufacturing tolerances.

The bores are graded as A, B, C, and then graded pistons are fitted to give a clearance within tolerance.

"B" pistons are smaller than "A''s", so the problem with a "one size" drop in, is that it has to be based on the larger size, so it isn't too tight in the smaller bores.

There can be nearly 1 thou' difference between an A, & B, and whilst it doesn't sound much, taken in the context that the target clearance is circa 3 thou', it's a big %.


Mark.

 

Blimey Mark you dont half know your stuff...

If i remember from my engineering days, 3 thou is about a hairs thickness..lol....My engine, although new, smokes just a fraction on starting which I guess is the difference in expansion during firing of forged and non forged parts (ie the block)?

 

Mark has forgotten more than I know with regard to pistons

I meant size of the piston rather than clearance as the clearance should be the same but hopefully you knew what I meant.

Simon

 

Eye, but whats a piston lol?

 

it's what happens to snails in alley ways near pubs on a Saturday night.

 

and thought that was just your shoes simon

 

snails is what I call my shoes..

 

Smoke on start up can be due to a few things. Worn valve stem seals can leak a little oil, worn turbo seal, and we ave found that some of the Garrett GT series turbo's need an extra restrictor in the oil feed, if the previous turbo was a TD04/TD05 based turbo.

Very unlikely to be piston clearance related.


Mark.

 

Hi Mark,

I'd hope I've not got worn stem seals as the heads have only done 30,000 with plenty of oil changes (every 5,000), it could be the Garrett I guess...dont think I'd worry about it as a little bit of oil on start up is a good thing anyway, cheers chap

 

I Need some help with this very issue !! Ive just put a post up as i want to get a new oem block but need the forged pistons to match cyl wall clearance as not wanting to split block.

 

the block requires stripped and honed to get the correct clearance due to not only differing tolerances but the likely hood of bore ovality even on new blocks!!