lets talk a little more about a little therum to help quinch our therst for knowlage beyond a standard text book ans.
what have you pullers discovered works best..now i know you do not want to give up hard earned and paid for info...but maybe just a little ,so us poor folks can dream a little about the day when we could set up our little ctd maybe a little just for the long haul

 

thumper, not exactly sure what you are driving at here so will go with the title. For me I would place the ring gaps at 90 degrees to the wrist pin.(piston pin) Of course position each alternate ring gap at 180 degrees.
Is this what you are asking?

 

mexstan,
hey nice to hear from ya, hope you have checked out my pictures of pistons and oil cooling jets and stuff.
i was just snooping around to see if there was a better ans as to where the gaps "should go" compared to maybe a what works better in the real world.
most piston dont like the gap over the pin (siezes the ring from moving) yet thats what the book shows......just was wondering what the big gear heads do 8)

 

Got curious and checked my '03 service manual. It shows a picture of a piston with the rings at 120 degrees to one another but does not clearly show where to start. It sort of shows the bottom ring at 90 degrees to the wrist pin. !20 degrees spacing will work but for me, I prefer the 180 degrees.
Don't forget to check your ring gaps. Always try to go with the manufacturers specs. For those of you who don't have manuals a rough rule of thumb is .002" per inch of bore. For reasons that I do not understand, some manufacturers have a bigger gap on the secondary ring but the same gaps on the oil ring as the top ring.

 

have checked the ring gaps, some to big accordingto the book, talked with 2 diff cummins places w coast and east coast ,they booth said that they do not ever measure them!! thought that was weird ,glad thir not wking on my eng.!
well i can make them smaller but its hard to make them bigger .
as far as the starting pt [placment] its real vage. but these are not porsche pistons so mabe it dose not matter?

 

[quote author=thumper 549 link=board=7;threadid=20355;start=0#msg191038 date=1064950230]
well i can make them smaller but its hard to make them bigger .
as far as the starting pt [placment] its real vage. but these are not porsche pistons so mabe it dose not matter?
[/quote]


Don't you have this backwards? Think it should read "it is hard to make them smaller but is easy to make them bigger". A ring gap that is too small when heated can cause siezing or even pull the top off a piston. If this was my engine I would start with the oil ring gap at 90 degrees to the piston pin and then work up with alternate gaps at 180 degrees to one another.

 

yeah, visa-versa

 

It doesn't really matter because the rings rotate/oscillate and generally move around on the piston. The important thing is that they not start lined up so you don't start out with massive blowby. Mexstan's point about lining them up with the wristpin is valid. The idea there is to start out (when things are wearing in and edges are sharpest) not having any of the ring gaps on the thrust surfaces of the cylinder wall.

 

I have built a bunch of engines over the years. I always start with the bottom ring 90 deg from the wrist pin away from the thrust side, then stagger them 1/3 as they go up. Same for the oil ring pack.

 

Haulin, that will also work just fine. For some of the folks who may not understand, how would you explain how to identify the thrust side of a piston?

 

[quote author=Mexstan link=board=7;threadid=20355;start=0#msg191627 date=1065057961]
Haulin, that will also work just fine. For some of the folks who may not understand, how would you explain how to identify the thrust side of a piston?
[/quote]

Mexstan I am not good at this sometimes but on a four stroke engine the last stroke or firing stroke on the way down places the rod at an angle, the thrust side would be the side away from the head of the rod. Hmmm don't know if that is simple. The down ward force on the piston, with the rod at an angle forces the piston into the one side of the cylinder. The side of the cylinder that has the heavier pressure is the thrust side.

 

[quote author=Haulin in Dixie link=board=7;threadid=20355;start=0#msg191636 date=1065058498]
[quote author=Mexstan link=board=7;threadid=20355;start=0#msg191627 date=1065057961]
The down ward force on the piston, with the rod at an angle forces the piston into the one side of the cylinder. The side of the cylinder that has the heavier pressure is the thrust side.
[/quote]



Hey, you done good. Sounds like a good explanation to me and makes sense.[/quote]

 

I have built tons of engines, always have staggered the rings 90 degrees apart. Did not have any problems. As wanna said the rings do move around. Most important to us when we built was to idle the engine for half an hour to let the rings have a chat with the bore and get to know each other. (takes that long to burp the air outa the coolant sometimes.) Did take some apart that were oil consumption problems that had the ring gaps all lined up. We think it was a line grievance at the time. Ferd was very involved with these engines.

 

i strongly disagree with you that the rings move around after install... i dont have any proof of this but on 2 strokes they are actually pined in place so they cant shift.
its my understanding that 2 strokes set up a vibration that floats the rings there for a pin is put where the ring gap ought to be, stoping the rotation.
thats what i think i know.
and while were into this therum and looking at thrust angles seems to be a valid pt..
but i sugest you never idle a fresh eng. reson is this a good way to tear up a cam..most new cams come with a BIG warning to never ever do this. reason is, may be thats an other subject but you must surf or( hydro plane) so as to create a working surface. to slow ,-just grinds stuff up.

 

thumper, yes on a 2 stroke the rings are pinned in place for a reason. If they were not pinned they would rotate and could potentially rotate into a position that could cause physical damage. A four stroke engine is a different animal. The rings are free to rotate as they want to. Generally it will not cause a problem unless they by conincidence all line up. Then the worst that wil happen is high oil consumption and maybe a slight loss of compression due to excess blowby. It is possible to position the rings and they never rotate, but it is my experience that most rings rotate to some degree. Just start with the gaps in the right place and you will be OK.