I have just had my block re sleeved to match a set of Wossner 88mm pistons .... After putting the head back on the crank won't rotate, does the combustion chamber in the head need to be "bored" to 88mm to?

 

or should the pistons not protrude above the deck, I can't see anything in the manual about that ...

 

put a level across the head and measure the gap between the level and the deck.

 

That piston looks pretty high.

Even a stock s2k with a spun bearing will allow the stock piston to contact the cylinder head.

 

Yeah, I'll get the feeler gagues out and measure it ... I've ordered a mag dial gauge to get a more accurate reading

Have spoken via email to Wossner with the same picture and their reply was to send the pistons back for them to check

All 4 pistons are that high (from my eye view anyway) so I don't *think* it's a spun bearing ..... will have to strip the block anyway so can make sure of that

 

Not particularly accurate but a rough measurement from a piece of square bar and feeler gauges

Number one is 1.06 mm
Number two is 1.36 mm
Number three is 1.06 mm
Number four is 1.19mm

Hopefully the dial gauge will turn up tomorrow and I can be more accurate

Do those initial numbers look high? I've found a few references on forums to about 40 thou which is about my measurements

 

I'm not saying you have a spun bearing.

I'm saying in a stock motor, the piston is very close to touching the head already.

And if it spins a bearing (bearing gets thinner) the piston will hit the head. Just giving you an idea of how close it is.

So with that logic, any piston the extends above the block will not fit.

 

Mahle pistons had a similar problem. They advised putting a 45 degree chamfer on the edge of the crown that extended 1mm from the top of the crown. Seems the extra bore is enough for the edge of the piston to contact the head.

You will need to make up a holding fixture to put the pistons in a lathe. I turn up a bit of round bar with a step that engages tightly on the inner edge of the skirt and use a alloy cross bar through the pin to bolt the piston down to this fixture.

 

The stock pistons extend above the deck by abit. I know becuse I was trying to cc a build I did, and it was not possible using traditonal methods. but yes the perimeter may need a chamfer since the picture show no chamfer at all. By the way where did you get you Wossner pistons from? I also thought Wossner offered frm compatable pistons?

 

@billman Ahh, I see

@chris Hmmm, that's interesting ... Wossner don't say anything

@alloy I'm not 100% sure which dealer my machine shop used, they got a better price than I could online so I didn't actually ask. Wossner list them as being an exact fit (obviously after sleeving and boring the block)