16 replies to this topic

[mini93]

iv been to southam mini and metro centre earlier, speaking among other things the plans for my clubman engine

currently its a 1098 but i want to over bore, iv been looking at the small bore +80 thou pistons but speaking to rod at southam he says that with the 1100 pistons the gudgion pin was moved so if i try fitting the +80 pistons which were designed for a 998cc engine the pistons will not fit because they will protrude the top of the block...obviously isnt good, and so will not work how i like
but i thought what about machining the top of the piston, which is where my question come in...how much is the piston likly to protrude out the top of the block?
ill need to consider how much space i have between the crown of the piston and the 1st piston ring, because i cant remove too much because that will be unreliable and might become damaged

if anyone has any sujestions/help would be much apeciated

Thanks David.

[JetBLICK]

1098 stroke minus 998 stroke... i.e. 83.72mm-76.2mm=7.52mm

[Bungle]

could a way around the problem be running a decompression plate like the supercharger boys do ?

this would lift the head further away from the pistons

[mini93]

im not bloody running de-comp plate!

drats...means i wont be able to over bore and hope the block is still fine 7.52mm is far too much

[Ethel]

1098 stroke minus 998 stroke... i.e. 83.72mm-76.2mm=7.52mm

Divided by 2 because the stroke is the crank throw x 2 - from 6 o'clock to 12 o'clock of crank revolution.

Been said many times... a lot of work and expense to get similar results as a standard 1275.

[JetBLICK]

1098 stroke minus 998 stroke... i.e. 83.72mm-76.2mm=7.52mm

Divided by 2 because the stroke is the crank throw x 2 - from 6 o'clock to 12 o'clock of crank revolution.

Been said many times... a lot of work and expense to get similar results as a standard 1275.

[mini93]

iv already got a worked engine in my rally car, and gona have another very worked in my project car...i think its time for a little tinkering with a smallbore

the amount it stick out by compaired also depends if the piston was previously flush to the top of the block

how much shorter are cooper s rods?

[mini93]

does no one know the difference in the rod length between standard "A" small bore and the cooper s ones?

[JetBLICK]

consult vizard i'm sure it'll be in there... think they're the same tho?

[mini93]

just read the book 2 secs ago

"all series 'A' connecting rods, with the exception of the 970 'S' rods, are 5.75 between centres."

if its just the 970 its gone be a job getting the rods

[nmt_oli]

I was looking into this a while ago. and the general concensus was "it can't be done safely".

Someone was helpful and said they had a similar setup running in the 70's, but they couldn't remember many of the details.

If its under 4mm, as it seems to be, it may well be doable. As long as the existing pistons are not flush, that gives you some leway there (hopefully 1-2mm), the pistons should be able to be machined my 1mm, although it obviously depends on the piston.

When i get time and get my 1098 block in pieces i may buy a +80 998 piston, bolt it up and see what happens.

[alexcrosse]

the top of my omega pistons are skimmed in the 1430. 3mm off yours should be fine. As for trying to get hold of 970 rods, give up, theres probably 3 left in the world! lol. Or you could always think about short stroking the crank and running normal 's' rods.

[mini93]

miiight not matter anymore......because

link 1098 +60 jobbies

if alls well n good ill be geting them from aus for about £75

[JetBLICK]

I'll ave you know, you can still buy 970 rods... £100 each.. but they wont help the situation considering they're longer than standard rods

[mini93]

ha oh right, s-rods woudlnt have been good anyway 100 a rod is quite expensive for somthing which hasnt been worked