Piston Inside

 

[quote author=Don Ramer link=board=7;threadid=19857;start=0#msg187007 date=1064024993]
Piston
[/quote]


Don, This photo shows the "arrow" I was refering to earlier today in this thread. This arrow always points toward the front of the engine.

Looks like the RV piston there, BTW.

Don~

 

[quote author=Stamey link=board=7;threadid=19857;start=0#msg187022 date=1064026966]
So what's the procedure for measuring deck height? I never got into that with the gassers I built. I might need to know this if I have to replace my block myself. :


Chris


[/quote]

Deck height is measured with a dial indicator on oftentimes a magnetic base. You measure the protrusion the pistons sticks above the deck of the block or the "deck height"

Cummins uses three grades of pistons. The grading system has nothing to do with quality, but the pistons pin height it is drilled to.

Grade A is the higher of the three on an "A" "B" and "C" scale in terms of deck height.

Grade A is .024 - .028
Grade B is .020- .024
Grade C is .016-.020

The reason for the different deck height and grades of pistons is not from a block that is aligned bored incorrectly but from the crankshaft throws being turned off a few thou during production. Some cranks are actually measuring up to .010 thou off cylinder to cylinder.

Imagine a crankshaft bore that is off by .010 thou. By the time you torqued the main caps down the crank would not even turn. LOL!!

Don~

 

It is the 275hp. Not all of the 24 valves have this, my point was to support the stampings as to ref.

If no arrow is on the top it was to help be a guide. I will shrink down the side photo's to show each side as well. But yes Don your correct on the RV/Bus piston.

The stock pistons don't support this arrow though as to the norm. It's hard to miss an install on a 12 valve piston when you have the combustion bowl over to one side directed at the injector on the right side of the head.

With the 24 valve it's confusing with the bowl in the center with no marking as the norm with no tech support to back up asy. Cummins could have put better asy instructions out on this issue for people.

Don

P.S will include further photo's tonight working on them.

 

Don,

Did that RV piston have both compression rings with the NI-Resist inserts or just the top ring groove?

I was just wondering if they did that or not.

Also, I have a set of MAHLE pistons here that are drilled into the lower oil control ring area from the bottom. Is the RV piston you have done this way too?

TIA

Don~

 

Side View Piston

 

Side View Piston 180 Deg

 

Your photos answered both questions

Thanks

Don~

 

as far as deck ht goes it would best be said to look in the cummins manual ,there is a chart as to swap what for what.
in other words no mater what piston you have once the deck ht is known it shows what piston to order up, so you dont have to buy a fleet of pistons thnk goodness...
that said there are no options for o.s. pistons as far as deck ht. ..Make seince??? no. but thats the ans.
don and every one got my brain hooked up with thir exp.and came to my resque as far as which direction to drop them in.
mechanics choice . its hard to belive , but i am a beliver now. thanx everyone!!! this board is a life savor