Pistons! Help!

[cliokongen]

Im the lucky owner of a set of modified pistons. With modified I mean, skimmed on top and new valve pockets being made.

In my eager to get them made I forgot to check which way round in the cylinder bore they are supposed to sit. (remember to read the arrow you clown!!)

Soooo......

- These pistons have an offset wrist pin, pin not centered.

- They have different size skirts front/rear side.

Is there anywhre I can "read" these signs as to which way round in the cylinder bore they are to be fitted?????????????????????????

Michael (dooohhhh)

 

[turbo man]

Yer, If you have had the new valve cuts made in the top of the pistons, then you should notice that the two inlet valve cuts are bigger than the two exhaust, if done properly. The Larger cuts go towards the front of the engine for the inlet valves to hover over!

 

[Red16]

y do u need new valve pockets machining if u have the pistons skimmed? the valves wont be opening any further than they did before the pistons were skimmed, so they shouldnt be coming into contact with the piston!

 

[BenR]

are these std 16V pistons you have modified?

 

[JAY172]

there is normally reference arrows/markings on the piston crown to help you identify which way round they go. can you see any? tell me what you can see and i can find out which way they go.

 

[BenR]

he said he skimmed them so he cant see the arrows.

The larger skirt/cutout is on teh exhaust side so that would put the pin closer to inlet side IIRC.

 

[cliokongen]

They are Peugeot 206 GTI pistons 85mm...

And yes im a clown forgetting to notice the arrow on the crown!!!!

Cross pin hight of the pistons was to high, when connected to the Megane rods and crank.

@ BenR: Why is this. As i imagine the load on the engine/bore is on the inlet side as the engine rotates this way round!!!

Im sooooo confused....

I will newer forget to notice the arrow on the crown...

I will newer forget to notice the arrow on the crown...

I will newer forget to notice the arrow on the crown...

I will newer forget to notice the arrow on the crown...

I will newer forget to notice the arrow on the crown...

I will newer forget to notice the arrow on the crown...

I will newer forget to notice the arrow on the crown...

I will newer forget to notice the arrow on the crown...

Michael

 

[BenR]

During combustion you only really use the pressure rise for the first 25-30 deg or so and if the pin was offset to opposite side of the crank rotation then you get a loss of efficency and increased noise/wear and possibly failure from high rpm piston slap.

 

[BenR]

how thick was your casting and was there plenty of space to fit 85mil pistons?

 

[JAY172]

the pistons would fit in the way round that means the gudgeon pin is offset to the side of the direction of rotation.eg looking from the timing end the engine would go clockwise so the gudgeon pin would be offset to the right.if you cant visually see it then meassure it.the gudgeon pin is offset to eliminate piston slap

 

[cliokongen]

Thx all.....

I get it now....

@Ben: Cant remember how thick it was.... I would say that 85mm is the near the limit. There is still enough room between the bores. 86mm is pushing it a bit too much....

Will post pics of the project as it evolves.....

Michael

 

[BenR]

nice one!

 

[N.Hill]

A note of warning for 85mm piston dia. You are realy going to struggle to get a head gasket to seal between the bores when they become so close you will have to have a one off gasket made to a very high spec. Dont forget you are now going to be asking the gasket to seal at much higher combustion pressure as I presume you are not looking for std 150bhp. High comp forged std bore pistons may seem expensive but in the long run in problems and heart ache they are woth while.

 

[Red16]

hey cliokongen, heres a pic of my freshy modified pistons

http://erc.qmuc.ac.uk/cliosport/gallery/full/1069352389__SkimmedPistons.jpg

 

[StevieB]

Doesnt the offset go towards the max thrust side i.e. the bulkhead direction if the engine rotates clockwise when viewed from the offside of the car?!

.

 

[cliokongen]

@N.Hill

No need for a one off gasket..... They do exist!!!

Got a special headgasket from Mecaparts in france.... 85mm diameter, thicker and more durable rings around the bore....

Michael

 

[Red16]

cliokongen - any more info or pics of your progress so far?

 

[cliokongen]

Nope... Not really any progress yet... My head (thats the engine im talking about) is having a valve job done... The seating was not good enough!!

Having the piston pockets done as well.... Thx all for the info...

Im working on my inlet manifold... Doing the ports so they fit the head and special heat resistant (some kind of nylon) gasket....

Looking forward to getting all my stuff and starting the assembly...

Michael

(cant upload pics... sorry)

 

[Red16]

all sounds like good stuff, im just slowly making new flanges for my new manifold as and when i can be bothered its cold in the garage this weather!

if u email me the pics i will upload them for you.

By the way what are u actually doing to the engine apart from these new pistons?