Damage to 16v 82.5mm Wossner forged pistons (new photos)

All the 16v heads effectively have the same volume (45cc + or - 1).

The reason the wossner piston crowns hit the head was because the KR head has a smaller diameter chamber to suit the 81mm bore compared to the (9A)* and ABF and their 82.5mm bore.
NB. The chamber diameters are still not the same size as the bore though. They are smaller so the "intruder style" piston touched the head at the edges as they were 82.5mm and the head was designed for a 81mm bore.

The ABF head has a slope around the top between the inlet and exhaust valves that takes up chamber volume to compensate for the slightly larger diameter. 373D head has 27mm exhaust valves.

EDIT. Ignore (9A)* reference as incorrect. Meant 051 103 373D heads! doh

 

Standard pistons in an ABF Bottom end still foul the KR Head , its not just the Wossner High compression pistsons.

I've got a full set on pistons with the battle scares.

 

Not quite. pre 94 9A, 6A and KR use the same head and have pistons that are tapered at the outside edges. This 027103373 head that brooky had, was put on an ABF engine with high compression ABF pistons that would be matched to a 051103373D head, resulting in system fail!
The photos that I displayed in the thread used the head from a 9A to illustrate the point with an ABF ML gasket.

 

Not too sure about that either. vw_singh ran a KR head, as does steve_r albeit with ABF camshafts.

 

Yes they do as well as a 27mm valve seat. Less restriction for the expanding gases as they exit the combustion chamber.

 

They get more piston lift when you put 100bhp of nitrous through the engine

 

So the ONLY solution for using that specific wossner pistons and don't have this problem is to use the later casting heads with the 'D' at the end?

 

My point was more that the compression would not change depending on what head was fitted. If you look at the head between the combustion chambers you can see they are wider on the 027 and 051 103 373 heads though (may be slightly different depending on year but as I have 5 heads I have just checked the 3 051 103 373 ones were all the same. The 051 103 373D head is narrower at this point.

On that point as there is some opening up around the exhaust valves on the chamber wall in an attempt to presumably unshroud the exhaust valve a little, I wonder if the whole chamber were opened up to suit the bore any more benefit would be gained. Not a huge reduction in chamber volume to manage this either (approx 1cc)?
Absolutely agree on the reason the piston damage occurred though. If the correct head had been fitted to the ABF block there would not have been any problem. This is not Wossners fault.

Edit to correct wording - wider instead of narrower

 

Depends on what you want them for. 1.8 or 2.0?
If you get the correct type for your engine there is no issue. If you are going for a large overbore then you would have to check for clearance or use the 373D head.

 

I had the same problem with wossner 82.5mm pistons and were ordered for a 1.8 KR engine..

 

That is why I said this!

 

I know this thread is old and a lot of the stuff has been resolved but thought I would add this seeing it has come up again.

The above 82.5mm pistons have differing compression heights as one is fitted to the 9A short block with a 144mm rod with a 20mm pin. The other was fitted to the ABF with tall block and 159mm with 21mm pin. The difference in compression heights is down to the rod lengths not being the same as the difference between the short and tall blocks heights.
As the pins are different sizes it is not possible to fit them wrong (unless you did not notice the ABF piston rattling on the 20mm pin that is!)

But for anyone building a special engine you can now get a 159mm long rod with a 20mm pin allowing the use of the 9A piston in a tall block when a diesel 95.5mm crank is fitted. This setup will still need checked for clearance and volume checked too for compression but it does make the build a more viable option.

 

mike h had a set of pistons made with 20mm pin for a stroker engine project he was building .

 

two years ago seems like last week [:^(]