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Three Ring Pistons v. Four Ring Pistons?

WildernessJeep

WildernessJeep

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Working on putting this M936 together after a sleeve came apart. The parts house says they can only find three ring pistons to go back in. Four ring pistons came out. The guy says there will be no difference and the three ring piston will work just fine (if not better) than the other five pistons with the old four ring pistons. Opinions?
 
simp5782

simp5782

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I've always had 4 ring pistons on the few 855 motors I've been in. Those were complete in frame kits though

What is your ESN or CPL number for the motor and i can give you the 4 ring piston number. Also will tell me what compression ratio you have. Wether is be a 15 or 15.5

Or the # off the old piston

The 3 ring i see listed for my old 250 is a 15.5 and my engine actually had a 15.0.
 
WillWagner

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It the original p/n crossed to the p/n of the 3 ring, you should be fine. When those parts are crossed, there is a related service parts topic referenced. That SPT will tell you if you can intermix the new and old pistons, it is a weight thing. Go back to where you got your parts and ask them to look for the SPT on the supercession to see if the new piston will be OK with the 5 old ones.
 
WildernessJeep

WildernessJeep

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simp5782 said:
I've always had 4 ring pistons on the few 855 motors I've been in. Those were complete in frame kits though

What is your ESN or CPL number for the motor and i can give you the 4 ring piston number. Also will tell me what compression ratio you have. Wether is be a 15 or 15.5

Or the # off the old piston

The 3 ring i see listed for my old 250 is a 15.5 and my engine actually had a 15.0.
Click to expand...

ESN 11647977

IMG_20200610_160605590.jpgIMG_20200610_160547517.jpg
 
WildernessJeep

WildernessJeep

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So here's the piston number of what came out of the engine. Decidedly a 3-ring piston. I've ordered the new piston already, but it's a 4 ring piston.

IMG_5075.jpg


I found this piston on the ebay. Are the rings the same?


IMG_1484.jpg
 
M35A2-AZ

M35A2-AZ

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I have piston and sleeve kits, if you need six. Not sure if they are 3 or 4 ring, I can look if your interested.
 
WillWagner

WillWagner

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WildernessJeep said:
So here's the piston number of what came out of the engine. Decidedly a 3-ring piston. I've ordered the new piston already, but it's a 4 ring piston.

View attachment 803300


I found this piston on the ebay. Are the rings the same?


View attachment 803299
Click to expand...
Yes, the pistons are the same. Rings are the same, but you shouldn't re use rings. I won't say it can't be done, because I have done it to get stuff up and running to finish jobs out in a dirt field or on an oil platform, but 90% of the time if reused, it turns into an oil pump/blow-by queen. Reuse is a get out of the woods thing, unless you don't care.
 
WildernessJeep

WildernessJeep

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I ordered new rings, new piston, and a new connecting rod with bearings just to be safe. The question is about which piston is correct. At this point, I've ordered both, and we'll see when the boxes arrive which one fits.
 
Mullaney

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WildernessJeep said:
I only need a single piston. I've ordered the 4 ring kit, but it won't be here until later this week. Trying to figure out what I need to put the engine back together "right".
Click to expand...
Hi WildernessJeep,

I definitely don't claim to be a Diesel Mechanic and I have ZERO certifications from any organization. On the other hand, you mentioned "put the engine back together right" in your post a little over a month ago. It seems to me that if you were far enough into the block to replace one piston that a complete in-frame rebuild would be a fix it and forget it way to go. Maybe at least removing another piston and looking at it as well? If one "bucket" died - what is to say that the last guy didn't do exactly what you are doing now?

Believe me, I know it isn't cheap. I have fixed and found more to fix and fixed that and found even more that needs fixing on my truck. I read this entire post and couldn't figure out why a sleeve came apart - and heck - even if you explained it I might not understand. But what I keep thinking is that you are already deep into the guts of this thing... Seems like going back with a set of 6 matched pistons would be the way to go. Balance is important when you wind it up.

I just had to ask.
 
WildernessJeep

WildernessJeep

Active member
187
88
28
Location
Huntsville, Texas
Mullaney said:
Hi WildernessJeep,

I definitely don't claim to be a Diesel Mechanic and I have ZERO certifications from any organization. On the other hand, you mentioned "put the engine back together right" in your post a little over a month ago. It seems to me that if you were far enough into the block to replace one piston that a complete in-frame rebuild would be a fix it and forget it way to go. Maybe at least removing another piston and looking at it as well? If one "bucket" died - what is to say that the last guy didn't do exactly what you are doing now?

Believe me, I know it isn't cheap. I have fixed and found more to fix and fixed that and found even more that needs fixing on my truck. I read this entire post and couldn't figure out why a sleeve came apart - and heck - even if you explained it I might not understand. But what I keep thinking is that you are already deep into the guts of this thing... Seems like going back with a set of 6 matched pistons would be the way to go. Balance is important when you wind it up.

I just had to ask.
Click to expand...

I actually did a full rebuild and got the truck back yesterday from the shop. It still has some bugs, but it drove home!!!

R
 
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