924Board.org

[leadfoot]

After a lend of a ring gap filing tool, kind of annoying to have to purchase something I will only be using once. Doesn't seem to be any shops around in the part of the state that lend automotive tools...
can anyone help here?
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[924aussie]

What does it look like ?
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green 924 .. 1980 rego 924PSH
1998 Mopar Neon ... sick
2003 Challenger / Montery 4WD
1995 Hyundai Scoupe ... sold
1998 Nissan Silvia ... sons back from OS he has taken it
BIG BLOODY MOTORHOME 300zx Sold
1980 Fire truck Sold

[RC]

[leadfoot]

hmmm looks like a flat base with a 90 deg mounted disc shaped file.

bore has been honed, haven't got as far as checking end gap, figured I needed a file of some desription not having done this before.
Pistons are JE forged with JE rings.
going to set them up for bore x .050 gap top ring.

All going well so far, block cleaned and scrubbed, dried, painted and oiled.
basic assembly, crank scraper, oil pump...
Stu
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[RC]

Personally would not recommend the disc type tools, particularly the motorised ones, for a novice. So easy to remove too much material, more risk of chipping/fracture and they have to be set up accurately so the file/stone cuts square. You want the ends to butt together flush, not at an angle.

Am reasonably sure though that there will be no need to adjust gaps larger. Particularly if the block has just been honed on a std bore, it will be larger anyway, at least 0.0005", half a thou, and very likely more. Forged pistons run more clearance and if the machine shop was told they would have probably honed to the larger tolerance. Same thing if bored OS & honed for forged pistons. With a fresh overbore for stock/ cast pistons at minimum clearance there may be a need to file the ends for correct gap, but unlikely.

The recommended gap is often specified on the ring set packaging. Follow the manufacturers advice. As a general rule of thumb for conventional square cut rings allow 0.004" per inch of bore for stock or NA applications and 5 thou per inch for racing/ boosted applications. On a stock 86.5mm bore, 3.4", X 0.005" the gap should be 18 thou. More (within reason) is OK and will not drastically increase blow by, but too small a gap can lead to an expensive seizure. This applies to top and second ring. Often the second ring has a slightly larger gap, no that`s not arse about, even though the top ring is subject to more heat. Some particular rings may need different gaps. Follow the manufacturer`s specs.

Measure the gap at the bottom of the stroke (in the bore) for the tightest minimum gap. Use the piston to push the ring down square. In a used & honed bore the top gap will be larger due to the worn taper. Also check gap at upper position. There should be no ridge at all if the job was done properly, and a conventional stone hone used. So to confirm, also check at the very upper part of the bore, above the top ring land.

Sounds daunting, but really is no big deal. Feel sure you won`t need to file anything. Would guess that 3 out of 4 engines never get the end gap checked anyway, not only home rebuilds but in pro shops as well.
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World`s quickest 924 2L slushbox

[leadfoot]

RC, yes I meant 0.005 x bore for top ring
specs for the top rings are thus; bore x

high performance 1st 0045 - 2nd 0050
street moderate turbo/nitrous 1st 0050 - 0055
and get larger all the way down to blown race at 0060

setting mine up for street moderate.
be handy if the ring gaps were perfect out of the box....
Stu.
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[daniel]

I just use an ordinary file...
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

[bnoon]

With forged pistons, you were most likely sold file fit rings. Most likely not going to be the install and go type of street rings. You will need a small/fine grit file to finish them.

Make sure to check the ring gap at the top, middle, and bottom of the travel and average the three together to get your final number. I see that I disagree with RC on this.
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'80 924 Turbo - SOLD!
1986 Porsche 944 Turbo - SOLD!
Porscheless