Race Engine Forum UK

Hi,

today I've checked the piston ring end gaps for my Uno turbo engine (80,5 bore) and the top rings are all 0,35mm/0,014".
The second ring gaps are all 0,25mm/0,010". In my understanding this is slightly too narrow, so I called Woessner (the supplier of pistons and rings). The technician said that this is alright for the second rings because they don't get so much heat. He highlighted that they've checked everything and I may install them. I must say that everything is as it should be, except for the second ring gap, where I still have doubts.

What do you think:
- install them or enlarge the gap before installing them?
- what's with the statement of the technician?

Greatings Christoph

P.S. Rings are for a downstroked race engine which will see 9000 rpm and 28 psi.

This is one where you have to trust experience.

The reality is that it is beyond all the most advanced facilities to compute the behaviour of rings expanding under the influence of heat during the various engine start, warm-up, hot transient & steady state conditions because mapping of ring land temps and cylinder expansion depends on the thermal inertia of those components. As an illustration of what's involved, if the bores did not expand at all, the rings butt together and seize solid at even 260 deg C second ring temperature even if build with about 30 thou end gap.

I am sorry that I cannot present a more qualitative answer at this time and I will not state that 10 thou second ring is too tight, ie: wrong - because the guy you spoke too may know 10 thou is safe for sure, but on your 80.5mm bore unit I myself would be building with 2nd ring 12-14 thou". That is proven safe by me on that unit. There will certainly be no penalty whatever in terms of oil consumption or compression.

If you refer to an OE manual for that engine you will be on safe ground. Unfortunately I do not have one, but I have always found the OE spec for ring end gaps to be absolutely fine for race engines too. It may well be that the spec for this engine is as low as Wossner state.

GC

Hi Guy,

thanks a lot for your reply. So I prefer to build with 12-14 thou". It's just a little bit more work and then I'm on the safe side.

Best regards
Christoph