Thread: Piston ring warp & gaps?

According to the Autopress manual for this engine, the gap is 0.012-0.05mm for all rings.

My (non-expert) view is that that amount of warp on the ring should not matter, and is likely to come good after it gets hot anyway.

Ignore the warp, thats normal for old school manufactured rings.

4 thou per inch circ is a rough but workable rule, measure it by putting the ring in the bore and then pushing it down with the piston upside down. you want the gap set at the narrowest point.

the tolerance JDNSW provided sounds about right for the 2.25 and I'd be happy to go with it on a slow low comp donk like the 2L series.

dont forget to set the rings with the gaps offset equally and with no ring gaps on the thrust or return face of the bore when you do the assembly.

Originally Posted by Blknight.aus

Ignore the warp, thats normal for old school manufactured rings.

4 thou per inch circ is a rough but workable rule, measure it by putting the ring in the bore and then pushing it down with the piston upside down. you want the gap set at the narrowest point.

the tolerance JDNSW provided sounds about right for the 2.25 and I'd be happy to go with it on a slow low comp donk like the 2L series.

dont forget to set the rings with the gaps offset equally and with no ring gaps on the thrust or return face of the bore when you do the assembly.

Thanks Dave!
I take it that with 3 compression rings, you mean that the gaps should be spaced at 120 degrees around the piston?

Also, I assume the thrust side would be the right side as seen from the front of the block?

I have also read about inserting the pistons from the bottom of the bores to avoid wrestling with inserting into the slope decked top face?

Your wisdom is much appreciated.
Cheers, Chris.

Originally Posted by cjc_td5

Thanks Dave!
I take it that with 3 compression rings, you mean that the gaps should be spaced at 120 degrees around the piston?

Also, I assume the thrust side would be the right side as seen from the front of the block?

I have also read about inserting the pistons from the bottom of the bores to avoid wrestling with inserting into the slope decked top face?

Your wisdom is much appreciated.
Cheers, Chris.

That sounds about right, I just use the rule of thumb to put the rings in so that they dont line up arent perpendicular to the crank and have the largest angular separation I can manage.

But I'm not going to lie, Its been so long since I stuck new pistons and rings into a 2.0l that it escapes my memory as to if you can insert them from the bottom.

Generally no, because you have crank webs and bearing journals and crankshafts and things in the way from the bottom end of the engine.

I've never had any real difficultly inserting pistons through the top end of the engine except in the few cases where the big end of the rod was larger than the bore diameter, pushing them in through the angled deck of some engines just means clever use of ally shim plate and lubes to construct a ring guide to aid in compressing them into the piston during insertion (when I cant get them by walking them in with my fingernails)

If you use the warp and your ring land gap to your advantage you can start one edge of the ring in and then push down lightly on the piston as you squeze the ring in by the back of your thumb nail and it will insert cleanly.

Yes the big end of the conrod does not fit down the bore. There is a procedure in the manual to insert the rod from underneath and insert the gudgeon pin to connect the piston with it partly sitting in the top of the bore. The piston is turned through 90 degrees as it is drawn down the bore so the big end aligns with the crank, so who knows what gap orientation there would be then..... It would be much simpler the bench assemble everything and push everything in from the bottom in the correct orientation.

From memory (and its been a long time) you cannot get the big end down the bore, nor the piston through the crank throw, so if the crankshaft is in place, you need to do as cjc says. The exhaust port allows access to both sides of the piston.

The piston manufacturer got back to me eventually and recomended a .012" gap on all rings. I have been gapping them today and the bottom rings are good at 012", but some of the upper rings are out to around .014-015". I was going to install those with the larger gaps as the upper most ring on the basis that this ring gets hottest and expands the most?