Wossner Ring Gaps

[ashy_gtt]

Now then, just wondering what experiences people on here have had with gapping rings on Wossner Pistons?

I'm building an engine with over sized Wossner Pistons and the ring gaps aren't right, is it normal to get a large variation between the gap measured on the top and middle ring (I would of expected them to be the same).

I've dropped an e-mail to PEC and Wossner in Germany but thought I would ask on here too.

Cheers Ashy.

 

[sideways danny]

firstly you almost always have to adjust ring gaps. They are rarely if ever, correct out of the packet.

Secondly, it's important that the gaps on the 1st and 2nd rings are different, I normally work with a 0.002" larger gap on the 2nd ring

 

[ashy_gtt]

Danny, thanks for that.

I realise that they might not be right out of the packet but I just don’t understand why they would be so different. The middle rings measure 0.010” gap whilst the top rings are only 0.003” gap!! As I'm building this engine for fast road / race applications and looking at the Wossner instructions I should be looking at 0.004 x Bore Diameter which would be 0.33mm or 0.013".

Whilst I’m on what clearance do you recommend between piston and bore? The Wossner instructions say that the block should be machined to the size on the box, which in my case is 82.93mm +0.01 / -0.00 I’ve checked the bores and they measure 82.955mm – 82.96mm which is slightly over top tolerance. However, that being said I’ve measures a piston (not very accurately as I only had a vernier at home) and it came out at 82.86mm dia. Now I will take a 3” – 4” mic home tonight and check it more accurately but based on the above size and the fact that Wossner specify a 0.012mm coating thickness on the piston that only gives a total clearance of 0.125mm = 0.0625mm per side… Just sounds a little tight to me, even though the bores are slightly oversize?

 

[Andyrg@ ClioTurbo]

im lazy and always take mine to the machine shop and get them to sort it out LOL at least if they **** it up i get it fixed

 

[ashy_gtt]

Right, so heres the measurements.

Bore ID = 82.96mm
Piston OD = 82.93mm
Top Ring Gap = 0.003"
Middle Ring Gap = 0.010"

So not sure what wrong here, the instructions from Wossner clearly state that the block should be machined to the size on the box which is 82.93mm maybe it means you should add to that your required clearance...??

Anyway the fact is the bores are too tight and I'm going to have to strip it back down and send it for machining again!

Oh well, better to find out now I suppose!

 

[ashy_gtt]

im lazy and always take mine to the machine shop and get them to sort it out LOL at least if they **** it up i get it fixed

Who do you use Andy? Someone local?

 

[Andyrg@ ClioTurbo]

Yes mate I use Engine Services, in Dunton as for jon, tell him andy from Durham sent u

http://www.engineservicesltd.co.uk/

 

[ashy_gtt]

Nice one, I've dropped him an e-mail!

 

[ashy_gtt]

Reply from PEC / Wossner is

"Simple misunderstanding that we need to address in our literiture to make it clearer...

The size listed on the Wossner box is the piston size, not the bore size. The size listed on the Cosworth box is the bore size not the piston size...

Your bore size should be near as you can get, 83mm dead on as far as i can tell from here."

Simple missunderstanding that could of been very expensive for me!!

Just thought I'd post it up for anyone else doing this in the future!