Engine Rebuilding Project Questions

[MAYoung]

I'm in the process of rebuilding a 1998.5 24 valve engine that I found in a salvage yard. It is a non-53 block with 289,000 miles that was running upon salvage. Upon tear down, I discovered no major indications of failure; just normal wear patterns. I am currently working with a machine shop in preparation for a stock rebuild.

Here are my questions: First, the Dodge service manual states that if you are going to machine the head that you remove 0.0098 inches (9.8 thousandths) from the deck. That seems excessive to me in the event that 4 or 5 thousandths (or less) might clean up the head. The Cummins manual makes no mentions of minimum machining removals. Has anyone confronted this issue?

Second issue up is the reason for piston grading. Cummins has A, B and C grade pistons that appear to differ only in height by 0.004 each. The A piston is the "shortest." Upon tear down, I discovered that my engine had B pistons in all cylinders except for number six, which was a C grade piston. Does Cummins use these piston to accommodate tolerances in the manufacturing process?

It would seem to me that if you were thinking of future machining to the block deck that you would install the "tallest" piston (C grade) in every cylinder and then use the shorter pistons to accommodate the piston protrusion specs. Anyone exposed to these issues in the Forum?

Third is the head gasket. Cummins only offers one gasket thickness for the 24 valve engines. I believe that the 12 valve models had a range of head gaskets. Why is this and what have people done to address the piston protrusion issues after machining.

I'll post pictures of the project in a few days. It has been an interesting project with lots "words of wisdom" to offer.

Thanks in advance.

Mark Young
Fair Oaks, CA

 

[MAYoung]

 

[MAYoung]

Above is the rebuild project engine at salvage yard. A 1998 24-valve, non-53 block. Engine has 289,000 miles upon removal from a 3500, automatic transmission.

 

[MAYoung]

Bringing the engine home from the salvage yard.

 

[MAYoung]

Just a quick update: The engine is back at the machine shop to shave four thousandths off the deck. If my calculations are correct, I can use a set of A pistons and obtain the spec protrusion as I had with the original B pistons. On paper, the A piston is 0.004" shorter than the B piston. (I obtained the protrusion numbers for this crank by doing a mock-up of the piston with the crank installed and measuring one piston at a time, per Cummins instructions.)

I have found hints online that Cummins has these various height pistons to accommodate variances during manufacturing. If you have better information, I will listen to it.

I have found only one size thickness for the head gasket from Cummins. This still seems odd to me since decking a block is not an unusual event. Other postings have mentions 12-valve head gaskets coming in multiple thicknesses. I have read a number of postings where people have even machined the tops of pistons to obtain required protrusion clearances. All sorts of issues are raised in changing the geometry of the pistons.

I have many more photos to post but my computer is not talking to my iPhone right now. I'll post more pics later.

 

[GAmes]

With my rebuilt engine approaching 500k and burning a little oil I'm considering building another. A p-pumped 24 valve would be something I would consider. Where did you find your engine?

 

[MAYoung]

To GAmes: The engine was salvaged at All Dodge Truck, 11350 South Bridge Street, Gold River, CA 95670. 916-635-7602. Give them a call and tell them what you are looking for. They ship around the world.

If you have already built an engine then you know the effort and the economics involved. The 12-valve product seems to be an easier undertaking given the reduced electronics for the engine.

 

[MAYoung]

Home built gantry type lift that I fitted with a chain pulley hoist. It turns a miserable job of moving the engine into a two finger effort:

 

[MAYoung]

Side mounting plate to attach to Harbor Freight 2-Ton engine stand, gantry and stand, initial tear down.

 

[MAYoung]

More tear down. No signs of catastrophic damage.

 

[MAYoung]

Off to machine shop with componenets:

 

[Cummins12V98]

Keep the progress coming!!!

 

[MAYoung]

Block back from machine shop. Installed the crankshaft per Cummins manual and did a mock-up of piston protrusion on the deck. Also discovered that the engine was fitted with B grade pistons. Spec protrusion is 0.024" to 0.028" and all pistons were within that spec. I decided to machine the deck 0.004"

and install A grade pistons. The A grade pistons are four thousandths "shorter" than the original B grade pistons. If may math is correct, protrusion should be spot on.

 

[2Farr]

I rebuilt my 24v last year. Turned out very good. Some things to look at are Colt cams stage three cam. It will let more air flow and keep egt temps lower. Ceramic coat the piston tops, its cheeper than you think to have done. ARP head studs. I went a little stupid with my build but I do enjoy the results.[/ATTACH]

 

[MAYoung]

And yes, I almost forgot. A true non-53 block. Note "MEXICO" in casting.