RING END GAP

[GARRICK.CLARK]

Hi Guys happy new year to all.
I have been reading up on pistons and what the ring gaps should be for turbo use.

I am rebuilding my top end of my 1911 turbo motor to give it a lower comp. that's done.
So I'm prepping the piston and cylinders for refit, I have had the AA cylinders honed to get rid of some score marks.
I read last night that a tight ring gap can cause score marks on the cylinders, which mine did have. So got the feelers out and checked what my gaps are. So on a fresh hone job the 1st and 2nd ring gaps are 6 thou. this seams very tight to me. Was this the cause of the scuffed cylinders.
I also went on the wiesco piston site and it said that for street turbo ring gaps should be 6 thou per inch of piston ,so 96mm pistons being 3.78 inch the gaps should be 23 thou.

The hone job took at least 1 thou off the bores so NEW they would have had 5 thou gap.
Surely that gap would have closed up once the motor was up to temp.

[craigvwdude]

.006 is a really tight ring gap.
My last turbo motor I built I set them at .020".
And yes, a tight ring gap can cause cylinder scoring.

[GARRICK.CLARK]

Nice 1 Craig. I'll get em set at 20. Hopefully it will stop the cylinder scoring.

[Piledriver]

Err a little large on a turbo motor.

Some like the second ring gap a tad larger still, as it is primarily an oil scraper, and the larger gap gives top ring blow by a path out, allowing better sealing of the top ring.

This is also why "full circle" second rings are a really bad idea.
The top ring cannot seal as designed.

[dave t]

I thought "total seal" rings would be good in a turbo engine? HHHMMM more to think about.

[Piledriver]

I thought "total seal" rings would be good in a turbo engine? HHHMMM more to think about.

For the top ring perhaps, some folks swear by them, some at.

Basic physics is against them for the second ring location.

[GARRICK.CLARK]

Ok. I have adjusted the ring gaps, hopefully its ok this time.

I was wondering if I was to add some 1.48 rockers to this engine will it give an improvement over the standard 1.3 rockers.
I've got .430 lift which is 10.92 mm lift using an 86a cam.

With the extra lift from the ratio rockers what would the lift in MM be, and is it worth doing.

[Piledriver]

You will end up with an 86b, effectively.

requires dual springs, carefully check valve clearances vs piston and head-wise, spring bind, keeper etc.

[GARRICK.CLARK]

Hi guys. Thanks for all the replies .
I did a test today . I put a cylinder and piston in the oven and got them up to 200. The skirt clearance was 2 thou. Is this too tight.

[Piledriver]

What piston alloy/type?

2 thou is not too tight for the skirt at running temp, that about right actually, perhaps a teeny bit loose.

The piston is going to get a LOT hotter than the jug in a normally running engine.

[GARRICK.CLARK]

Hi Pile. I'm not sure what alloy the pistons are really It didn't say. And no instructions. I got them in 2013. the skirts didn't have any coating on either

[Piledriver]

Where they from, made by?? forged?
Any marking inside (cast in logos etc?)

[GARRICK.CLARK]

I'll have a look. There defo an AA set.
I'll be back.

[Piledriver]

AA 96s are std cast pistons, fairly high silicon, they expand more or less like stock.
2 thou would be ~fine at room temp.