Wossner Pistons

[petert 586]

I finally got around to doing something with some Wossner GTi6 K9182D050 pistons I picked up cheap. They're going into an XU10J4 block with an XU9J4 head, fitted with 36.5/30.0mm valves and some lairy cams. I had to take a bit off the dome, otherwise they would have been 14:1. The other issue is the radial clearance required for the larger valves. I had to go 0.5mm deeper as well, to get the lift @ TDC clearance correct. They really are cheap and nasty pistons. The deck isn't even parallel to the pin.

[welshpug 1,657]

at least they'll be a bit lighter now!

[Andy 105 1 Cars]

Peter. I do not like the sound of ‘cheap and nasty’ given that I have a set of 85mm ones that I got because they were cheap. If you needed to modify to get clearance for the 36.5mm valve , I will almost certainly run in to the same problem, unless your ‘lairy’ Cams have more lift than my stage 2 solids at tdc . 

On a separate note, if you are using your machinery, I take it that your shoulder is improving . Looks like good news. 

Regards.

 Andy

[petert 586]

To be fair, they're probably not that bad but their reputation proceeds them. You'll soon see if they're parallel when you trial fit them. If you purchased Mi16 spec pistons they'll probably be fine. As mine were GTi6 pistons, the pockets would be spec'd for smaller valves. As supplied, they would have supported approx. 0.170" lift @ TDC. My inlet is approx. 0.190" @ TDC. Shoulder is slowly improving but no bike just yet.

[Andy 105 1 Cars]

Ah. That explains the pockets. Mine are for the XU9J4 and , to be fair, they have deep pockets ( which partially explains the raised crown to compensate ) . Glad to learn that you need to shave the crown to get the c.r down to sensible levels . 

Sorry that the shoulder is still preventing cycling. I did an hour on a turbo this afternoon , as it was blowing a gale here . I had quite forgotten just how hard the turbo can be !  

[opticaltrigger 52]

Wossner pistons,

There really are some issues with those guy's and accuracy. I mean it really is a case of Monday morning pistons or Friday afternoon ones. You just do the lottery with them...

I remember all the trouble with the ones we used. I knew I would have to take a bit off the top, but I ended up removing a mill from under the pin boss area, as they were hitting the crank webs at TDC, terrible........

 

Personally, I will never ever, ever, use Wossner pistons again. Peter you couldn't have put it better. Really, really nasty. (imo)

If I was to buy again, I would probably just pay the little bit more and go JE or similar.

 

All the best

O.T.

[petert 586]

It gets worse. I started cutting the exhaust pockets today, with a program I've used many times before. It seems the centres for the exhaust valves aren't anyway near where they're supposed to be. From the picture, you can see there is approximately a 4mm gap on the periphery. At least it's in a safe direction. There's no chance of ever hitting an exhaust valve radially. But what about the lost compression? I'll have to make a special program to clean it up.

[Andy 105 1 Cars]

It looks as if Wossner have machined very large valve  pockets for both inlet and exhaust as some kind of generic solution and then put a significant intruder dome to compensate . Shame that they could not centre up the pockets . I am feeling worse by the minute . If I take my Wossners any where near Guy Croft he will throw them in the bin 

Andy

[allanallen 528 2 Cars]

Certainly looking like they’re just a generic 16v piston with the pin size and height machined in to sort of suit the application, rubbish. 

 

Nice jig pete

[petert 586]

I ended up running the program as is, leaving that step to a depth of 1.2mm. I'll blend it in with the dremel so there isn't a hot spot. CR finishes at 12.1:1 with a 0.7mm gasket or 12.4:1 with a 0.5mm gasket. I'll run the later and it will be fine.

[Sandy 191]

The TU ones have the same issues and the TU 8v ones don't appear to have any sympathy with the head/chamber they're intended for. I've been trying to educate people on this for years, but they're so widely sold and there's a lack of quality off the shelf alternatives, that people convince themselves they must be ok. It's less work to make SBD C20XE Omegas or some Honda K20 CPs fit, they are barely any dearer retail and the quality is light years ahead. Retailers will favour the Wossners, because the margin is good and supply regular; but they're not cheap enough to end users, to even say you get what you pay for.

[opticaltrigger 52]

On 10/7/2018 at 9:50 AM, Sandy said:

The TU ones have the same issues and the TU 8v ones don't appear to have any sympathy with the head/chamber they're intended for. I've been trying to educate people on this for years, but they're so widely sold and there's a lack of quality off the shelf alternatives, that people convince themselves they must be ok. It's less work to make SBD C20XE Omegas or some Honda K20 CPs fit, they are barely any dearer retail and the quality is light years ahead. Retailers will favour the Wossners, because the margin is good and supply regular; but they're not cheap enough to end users, to even say you get what you pay for.

Fantastic !!!...... Absolutely nothing more needs to be said about these.

A totally definitive comment on them. Excellent............ 

[Sandy 191]

If you were to act on my suggestions above, custom rods will most likely be needed. Outline dimensions are as follows:

 

C20XE Omega "pot", crown height 30.5mm (pin centreline to deck), pin diamater 21mm

 

K20 CP etc, crown height 30mm, pin diameter 22mm. Note some K20 pistons are produced with alternative CH and pin size, for long rod or "frankenstein" builds.