Yura

Hi. I have in spare engine block with pictons, crankshaft etc. I want to prepare it for installation. How can I know, need to put a new pistons or just new rings is enough? What I need to measure for this? Sorry, In manual I can't find an answer for this question. What is the limit of cylinder wear, how to check it?

Chip

iTrader: (3)

you need to examine the ring grooves, 5 thou max clearance, you need to measure the piston to bore clearance, 5 thou max again.

Any more than that, and IMHO the pistons arent useable.


Im sure there must be a manual somewhere with exact figures, but those are the ones I used as a ballpark.


I suspect the "proper" piston to bore clearance is probably nearer 2 thou, but at 5 they wont rattle badly, especially if they are the 4wd ones as the pin is offset differently.

Yura

sorry, 5 thou you mean 0.5mm?
But at wich position to measure the piston to bore clearance? in different position in engine block it has different clearance to bore in used engine.

Chip

iTrader: (3)

No I dont mean .5mm

I mean 5 thousands of an inch.

40thou = 1mm
5 thou = 0.125mm

I tend to ignore the top inch or so with worn engines, if its oversize any further down than that though, it will be noisey.


Bottom line is, if you want it right, its new pistsons and a rebore.

anything else is just making do

daviddunlop83

iTrader: (7)

5 thou as in 5 thousands of an inch which is .125mm

pa_sjo

It's actually .127mm

To some people, that's a lot

Chip

iTrader: (3)

Not on this sort of measurement it isnt, the 5 thou in the first place was only an off the cuff figure anyway.

You are correct though, if he even has a way to measure quite that accurately

Yura

thanks, another question plz - what do you mean "ring grooves", fitted ring gaps?

Chip

iTrader: (3)

The grooves in the pistons that the piston rings sit into.

Yura

you mean clearence between ring and top part of piston groove?

Chip

iTrader: (3)

Yes mate

You put the ring into the groove, and see what size feeler gauge you can fit in there with it.

Yura

as I know 4x4 bottom end + 2wd head will reduce c/r. can I put just 2wd pistons into 4x4 bottom end, or I need something else from 2wd versions?
Thanks.

Chip

iTrader: (3)

Other than the CR issue, 2wd and 4wd pistons are interchangable.
(check valve clearances though, like you should always do if changing pistons)

Yura

What do you mean? How to check it?

Chip

iTrader: (3)

Not easy with hydraulic lifters!

But you need to make sure the valves arent going to hit the pistons one way or another.


The easiest way is that if you have both sets of pistons to hand and it didnt hit on the old set, simply check the existing ones have equally deep cutouts

Stu @ Claims Care Centre

iTrader: (1)

put playdow ontop of the piston and put head on and turn it you will know how close it is then. thats how burtons say to test lol

Chip

iTrader: (3)

With hydraulic lifters?

Stu @ Claims Care Centre

iTrader: (1)

good point its at home ill have to look what they ment!

Chip

iTrader: (3)

If the lifters arent pumped up (which on a rebuilt engine they wont be) then it will give the wrong reading.

Yura

can I use with 200 block 4x4 oil pump and 2wd sump, or need I put 2wd one?

Chip

iTrader: (3)

Ive got a 200 block on a 2wd sump on my engine mate so thats definately not a problem

Yura

So, you use 4x4 oil pump(assembly) with 2wd sump? The differense in shape of sump is not critical?
Thanks!

Chip

iTrader: (3)

Im afraid I cant remember now if I used a 4wd pump or a 2wd pump, my comment was just that you can definately use a 200 block with a 2wd sump.
Stu or Tony will know the interchangability for certain, PM them and ask them to have a look at this thread.

Yura

ok!
Have find mahle pistons on ebay from Woodford Garage Motorsport.
http://cgi.ebay.com/RS-COSWORTH-GENU...em310128686594
I need +0.5mm pistons. Asked them about pistons for 2wd version and received answer "we have 0.5 pistons in stock and there all the same now for 2wd and 4x4". Why now they are the same??? help please.

Chip

iTrader: (3)

Because they are all the superior offset guedgeon pin design now I would imagine. no reason for them to carry on making the early rubbish anymore.

Bart

You can only get 4x4 pistons so you have to keep this in mind for youre c/r. To lower the c/r you have to machine the pistons.

Yura

If I put 4x4 pistons with 2wd head as I know my CR will be 7.8, but I need standart CR.
so, I need to buy new pistons and machine it for standart cr(8)?

Chip

iTrader: (3)

7.8 would be fine, but I bet yours wont be that anyway as no doubt the head will have been skimmed.
And realistically the block probably needs a reface anyway.

You'll need to measure it all to know your actual CR, not make guesses

Bart

I agree with chip.

TiB

iTrader: (1)

I can say from experience that this is NOT the case.. at 5 thou even 4x4 pistons sound like they want to leave the engine, granted once they are warm its not bad but the warm up cycle is soul distroying.


Lee

TiB

iTrader: (1)

To measure the clearence successfully you must measure toe bore and measure the piston seperately and subtract one from the other.

(just in case your trying to fit a feeler gauge down there)

Yura

Head thickness is about 138.4mm.
7.8(or about 7.85 according head thickness) will be fine with chip(MSD t34, siemens'55) for std engine??
TiB, your advice also to change pistons at 5thou clearence piston-cylinder?
Thanks.

TiB

iTrader: (1)

2thou is the reccomended size but i have run at 3 thou with no problems.

Yura

What do you think about cylinder liners? to put it into 200 block, machine it to std size, put old 4x4 pistons(in case of normal condition), new rings etc? may be stupid question, but it can save alot of money

davidreader5

I have sent you a PM.

Regards Dave R.

TiB

iTrader: (1)

I personally think liners are fine.. if you have them fitted and give your pistons to the machine shop and tell them you want 2 thou clearence they will sort it for you.