Wormhole

I was wondering if a particular gap position on the first piston ring (closest to the combustion chamber) would make a better seal then say another position. Obviously the rest of the rings need to be clocked 120 degrees respectively. On a turbocharged car I can theoretically see this making a difference, but marginal at best.

Anyone got info?

badass951

I would go by factory specifications, and if this is not mentioned then just position them like you said, 120 degrees apart. I understand what you are thinking, but under the intake stroke everything should be evened out in the cylinder, and then under compression it would not matter where the ring gap was. I am 100% sure that if you just place them how you would like 120 degrees apart you will be doing the right thing.

Laust Pedersen

Here is my rationale for ring gap positioning:

All gaps should be pointing either forward of backward. The piston rocks on the piston pin, forcing the ring to slide on the ring-land in the transverse direction. The lengthwise orientation minimizes (eliminates?) the chance, that the edge of the ring makes a small wear groove in the ring land or cylinder.

Gaps should be alternating 180º. This provides the longest path for the escaping gasses to find the next groove.

In case of a 3-ring oil ring, treat the two scrapers as two individual rings, so for orientation purposes you now have a 4-ring system.

As a safety precaution against two rings “helping” each other making a gap-scratch in the cylinder, you could for example turn the top ring and (1-piece) oil ring 10º apart. However the ring manufacturers are very good at making the gap area the last part of the ring to seat, so a “cylinder gap-scratch” is very unlikely.

Laust

badass951

If you place them 180 degrees apart then there will be two rings on the piston facing the exact same direction. Ring end gaps should ALWAYS be scattered as evenly as possible.

Also, the ring puts pressure on the cylinder wall only, despite whether or not the piston is on the major or minor thrust side.

David Floyd

http://www.jepistons.com/pdf/piston_instrc4032.pdf

This is what I went by, stock ring positions my not be the same.

badass951

Laust, I just reread what you wrote and it makes sense now. However that would still leave gaps overtop of each other, even if they are separated by a ring in between. I am still confident in the fact that end gaps should never be facing the same direction.

Wormhole

I don’t have the factory manual with me at the moment, but I believe they call for the first ring to be positioned 45 degrees from the wrist pin, and the other 2 rings positioned 120 degrees from the first.

I see the point with spacing the rings parallel to the wrist pin, and then position the rest 180 degrees. The only reasons I can see for the factory recommended installation is for even wear, since the exhaust gases would be more evenly dispersed and no two gaps would be on the same plain.

Make sense?

adrial

How's the rebuild going?
Let me know if you need a hand.

I went with 180 deg apart, as Laust described. Engine hasn't blown up yet.

I dont imagine exhaust gas would wear at the alusil bores, but maybe I'm underestimating the power of the heat & pressure.

Sam Lin

180 apart, gaps at the ends of the wrist pins - what Laust said.

Sam

Wormhole

Hey Adrial, rebuild is going well. Block is completely broken down, tolerances within specs. Almost all parts have arrived, just a little more cleaning, and then I get to reassemble. The thing that has taken the longest is cleaning all of the gunk and old gasket material. I went through something like 30 cans of brake cleaner and degreasers already.

Thanks for the offer, but the car is way out on the Island in my father’s garage.

Any reason you went with the 180-degree method? Do you remember what the manual calls for? Did you use the factory ring set? Wish I had it in front of me.

adrial

I rented a pressure washer for the final clean up, I wish I had done that from the begining...made it so easy.

I went with the 180 degree method because it made sense to me (longest path for the gas to travel) and because I was told to do that by people that have been there, done that.

I did use factory rings. I almost used Total-Seal, but decided against it.

Chris White

Two basic issues –
Do not put the ring gaps on the thrust face and do not line up the ring gap ends.
I have always used the 120 degree method (the 180 degree method should work OK, I just prefer to not have any ring gaps aligned).
I did get to see a 911 motor that had the gaps aligned – the force of the channeled blow by eventually melted the piston and caused a serious engine failure.
I good engine builder will hone the end on the ring gap to prevent any cylinder scaring ,especially after gaping the rings (there will be a burr there).

Chris White

Wormhole

Thanks for your input Chris,
I think I will go with the 120 degree method for the same reason.

What are you considering the thrust face? Would that be perpendicular to the wrist pin?

Chris White

The thrust face is the side of the piston that is loaded during the power cycle – the drivers side of the block 90 degrees from the wrist pin.

Chris White

Laust Pedersen

Chris White: “The thrust face is the side of the piston that is loaded during the power cycle – the drivers side of the block 90 degrees from the wrist pin.”

Maybe in Great Brittan, New Zeeland or other odd places like that (sorry NZ951 couldn’t help it), but the power side is really on the exhaust side, since our engines are rotating clock-wise seen from the front (as most engines do).

Laust