robbo9006

Had the machine shop who were going to bore out for these saying they had been machined and were incorrect .
To low a compression.

So i contacted my source and his reply was

iam afraid your machine shop hasnt got a clue about cosworth engines then,the piston were machined to Colins performance data,decked 1mm to avoid piston to valve contact and the sides bowled out to lower the comp,the piostoms are perfectly fine to use i have used loads to the exact same spec.

Are there any qualified thought as i don't no the supplier or the machine shop well.
I do have a sneaky suspision the machine shop is used to oval bored out pistons standard n have not come across any Mahle ones before,so have not met the spec.
What do you think?

TiB

iTrader: (1)

Which machine shop?

tabetha

Just looked a piccies of my pistons, and they are much deeper chambers in mine, going by that the piccie appears to show yours are higher, but impossible to say with out crown to pin measurements etc as the whole crown on yours could be lower for example.
I no longer have any of my old ones to measure for you though.
If when installed they come about 20-30 thou proud of the block as mine do yours will be lower than mine as my std chamber is much smaller diametre, as the outside edge is much wider.
tabetha

robbo9006

http://i51.tinypic.com/fz6veb.jpg

robbo9006

http://i55.tinypic.com/i3fi2t.jpg

robbo9006

These are some other pics

cosy trav

iTrader: (1)

Here is a pic of mine Mahle low comp 7.2:1 collins did the engine build against standard pistons .

Paul_RS

iTrader: (4)

The OPs pistons are machined. Mine have been done the same to lower the comp.

robbo9006

Right i still have two conflicting stories.
What do i do .
I wonder if i could send one to this collins place to see if they are usuable.
I noticed the pistons in the pic are smotthed on the edges .
The lad at the machine shop mentioned edges cause crack points.
so i could just have the edges rounded.
Detonation was mentioned.
also the machined out part was to much.
I still do not no what to do.
The machine shop has a high reputation.
Still at loggerheads.
The pistons have also been said to be fine and the design/spec have been used on there cars.

o and am i the OP's

Paul_RS

iTrader: (4)

They have been in my car to that spec for 10 years. Have a look on my resto thread to see how they still look today

https://passionford.com/forum/restor...bay-resto.html

Apparantly they are 7.2:1 on a 2wd car and 7.5:1 ish on a 4x4? Plus they've given enough clearance for me to run a BD14 inlet cam.

robbo9006

Any more on this the machine shop say it will work but will require a massive turbo.
What turboes are on the spec you have

bad boy rs

iTrader: (7)

Is it normal for the pistons to stand 20 though above block ? The 200 block I'm going to use next had standard 4x4 pistons and they are 20 thou proud I was a little worried about valve clearance

Paul_RS

iTrader: (4)

The standard pistons do stick out of the block, can't give you an accurate measurement though lol.

I'm on a t34, think its some weird .48 housing'd hybrid lol

robbo9006

Is there any more on this.
I don't think i will be using the pistons at this rate as i have not enough to persuade the engineer that all is ok and he is having the last word.

Danny @ Enhanced Performance

iTrader: (3)

A 20 thou proud of block is at the limit i normally wont go any more than 15 thou specially on a high revving engine but then it depends what h/g you are going to run??



cheers danny

Paul_RS

iTrader: (4)

He's knows better than all the tuners that have used them for 20 years?

robbo9006

The last reply works for me and i tend to agree.
Just i like the guy so need him to agree before i put the engine together.
If he does not agree there is a problem .
He has 30 years experience.
Is it the fact he has a broad experience and has only come across standard cosworth pistons.
surely he has met collins spec pistons.mahle forged before.
If not how does the lads who are pushing 450bhp that uses him get bye.
maybe they should have a set n push 500bhp.lol

Paul_RS

iTrader: (4)

Just one thing - I assume they have mahle stamp on the underside of the piston? Just checked they do so you know you have genuine mahles

robbo9006

Yep mahle.
I think as they have are clean on the top they have been re machined since they came from Mahle.I am going to a rally shop to see if i can put one at the side of a new one.
I think there is one in Blackpool Road n Rally.
I want this sorting this weekend as the garage who is building it all will be wanting there space back lol.
I need a st220 engine building the block has let me down again.
Any good value for money engine builders in lancashire that would do a V6

TiB

iTrader: (1)

i offered you a piston to check yours against?

robbo9006

Did you,i totally missed that.
What do i do meet up sat morn or what.
Cheers Lee
I am of work all day Friday as well

TiB

iTrader: (1)

Give me a call in the morning say 10ish.. 07973744159

robbo9006

Like to thank Lee for good info at the mahle piston confrence.
I will have another go to pass muster at the engineers ,but some how i am thinking it might be just best to buy some more.
If i was to radius them n take the block down.
The machining cost will be alot more than another purchase.lol.
What a good lad ,totally focused on the Cossie,my mondy didn't get a mention.lol

robbo9006

I had the pistons machined.
Then realized they were std.
So am sourcing 4 ,1mm over sized ones.

robbo9006

Sourced new cp pistons ,forged with valve cutouts.
Very nice back on track.
Have all but a crank now.
Hopefully will have the car back together soon.
Then sort things out whilst she is running.

janvanv

Just curious, what did you pay for the CPs?
PM me if you'd prefer.

robbo9006

Just procured the full spec.
Its my first cossi so here goes.
CP forged pistons with a 4x4 head.
Cossi rods,crank n block.
Arp everything.
T3 turbo,going to T35.
Ecu with collins chip.
Larger intercooler.
Live mapping to do as advized by Lee.
Been a trek but have an excellent diff n gearbox.
Going to have diff ,gearbox n 3" exhaust fitted soon.
Waiting for the engine to come out of rebore.
Has any one used V6 pistons on the cossi to take up to 2.1.
I heard the essex ones work but i have 4 spare duratec 3.0 of a st220/jag.
would these work