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

Standard KR Cams , Piston crown is 4mm , valve clearance is fine i think it is the combination of ABF & KR. Would have been better on reflection with the 9A Pistons 30.2mm comp height.

I got the Head ported and gasflowed at Stealth Racing ten years ago, don't think they skimmed it, what should the depth be of the two indicator holes below the water outlet ?

 

personally, i`d whip out all of the pistons and use a very fine file to radius the edge that has been catching, making sure the surface finish is very good to prevent hotspots. failing that, use a die grinder to carefully remove material from the head itself.

 

On a standard KR, this is +1.2mm +/- 0.15mm

From this thread

...& compression height nos are less than I'd expect. OEM KR I have at 34 +/- 0.1mm

 

For me, from the pictures (and please correct me if I have interpreted this wrong), it looks like the bore is bigger than the size of the chamber in the head, hence the marks around the outside of the piston and head. Would it not be an idea to put a gasket on the head and match the size of the chamber to the size of the gasket? Admittedly this will reduce the CR a little, but on the flip side will provide a smoother flame path.

 

might be worth whipping out the pistons just incase the ring gaps have nipped up.

 

If the head was from Stealth, that means it was done by The Man In The Shed. It will have had a light skim, at the very least, to remove any machining marks, and bring the chamber volume back to where it should be (as the porting increases the chamber volume).

I'm not sure what the dimension should be. I'll PM you the details of his shedness, and you can ask him. He could probably do some grinding on it to relieve the piston contact, or advise you what to do.

 

Dont fit two gaskets bud, you'll increase the squish band to about 95 thou and will induce detonation. Remove the pistons and have the edges machined at an increased angle to clear the head.. "dont" have the squish band touched, thats the flat part near the valve cutouts, only have material removed from the compression intruder.

I would also remove for the reason mentioned elsewhere, to inspect the pistons for any other damage, such as ring lands. I did'nt want to mention it at the time as you'd already fitted the pistons, but I'm told Wossners can suffer with cracking due to the forgings they're used on. Fingers crossed though that they'll be fine in your application, but now is the time to check.

Best of luck with it all.

 

Brookster, I think that I may have found why you encountered your present problem.
I recreated you engine albeit in a STD form used the many spares I had out in the shed. This which I found out.
Your engine is a combination of ABF block, KR 051 clyinder head and high compression pistons that protrude the block much more than std items.

Here we see that the STD ABF short block has flat pistons with inlet valve cut outs. These slugs protrude the block deck by around 1 mm static



This is a KR short block where your head would have come from.
Pistons have rounded edges and protrude as Chris said around 1.2mm static.


Another ABF deck view showing pistons at TDC.


KR engine with pistons at TDC



Typical 2.0 head gasket will allow for piston protrusion.


Uncompressed metal gasket is 1.9mm thick.



ABFs 051103373D cylinder head combustion bowl seems to have a greater taper angle to unshourd valves. Shown here with typical 2.0 head gasket.


Notice factory cut outs in combustion chamber to partly unshrould valves on this KR 051103373 head casting.


Closer view of the KR combustion chamber NB same as 9A pre 94.


Closer view of the later casting '373D' - ACE, ABF, ADL and post 94 9A


Study this picture. It shows a STD ABF short engine with the piston at TDC...

...then ask yourself.... what if we removed these pistons and replaced with units that stuck out 3mm more above the cylinder deck ( this length will increase slightly with rpm) and fitted the 373 head casting that had more valve shrouding and possibly piston interference...
Hope these pictures help.

 

yet again very good info ed

 

Thanks for that Toyotec , very good information , i will get the head machined on boths sides to get rid of the flat edges.

is the ABF Head totally round, except the squish area ? must be.



it will be interesting to see what the compression is afterwards.

 

Well dropped the cylinder head off at Hinles Bradford for the Spark Plugs thread repair and also for the KR Head modifying to clear the 31.6mm combustion height pistons.

http://www.hindle.co.uk/

i will keep you posted on the results

 

Feck me Toyotec, tha's still fecking brilliant!

 

Fantastic

this was two years ago Sheeeeesh how time flies.

 

Completely over my head! Can you explain slower Dave?

 

KR Modified Head on a ABF Bottom end = more power

http://www.clubgti.com/forum/showthread.php?t=186028

 

Ah, gotcha.

More here:

http://www.clubgti.com/forum/showthread.php?t=146656

 

Brookster: i had the same problem with 82.5mm Wossner pistons but for the kr engine.At the end i machined the chambers to allow for clearance as you did but was a bit **** job ;p because i used a dremel and not a machine shop.

The Toyotec's thought though was very interesting and things i didn't ever notice(about different types of head and valve shroudings) Great info there Toyo

 

Toyotec : so if he used a head of later casting he wouldn't have this problem?

 

If an ABF Casting had been used it wouldn't have been an issue, The KR Casting was used for higher compression and also the KR has 28mm exhaust valves.

 

ABF castings have 27mm exhaust valves?