Engine/Transmission (1994 - 1998) '98 12 valve, ISB block and what else?

[CumminsPower98]

I have known for quite some time that my '98 12 valve block was a little different on the outside as compared to '97 and older. Well tonight I was looking through some Cummins brochures I have here, one for the ISB and one for 12 valve 3. 9 and 5. 9. I noticed that the ISB block in the pictures looks exactly like mine (both sides) and that the block in the other brochure looks just like the '97 and older ones. Maybe this is why my '98 sounds different then all the older ones I have heard. My uncle just bought a '98 12 valve 3500 and it sounds just about like mine also. It seems obvious to me that the block is at least the same as the ISB but what else? Does anyone know if the pistons might be the new design also hence the more rattly ISB sound I get as compared to the older ones? Some of my friends think it sounds more like a 24 valve. I feel that it sounds somewhere between the older 12 valve and 24 valve. Any thoughts??? I'm really curious now if the only differences are the head and the fuel system in the 1998 year models. One nice feature I plan to take advantage of in the future (bypass filters) is the second oil return boss in the driver side of the block that now has a freeze plug in it. The older engines do not have this.



Mark

 

[Jim Fulmer]

Don't forget High Nickel content and extra webbing in the bottom end for more strength.



Jim

 

[A Johnson]

Definately not the same pistons as the ISB. The older 12 valve had offset piston bowls and the ISB has a centered injector and thus a centered piston bowls. It is my understanding the extra ribbing was for noise reduction, whether it is actually quieter may be debatable, I suppose it depends on how the noise level is measured. The bad news is I would assume you would have the series of block that may be suceptable to cracking below the freeze plugs. My . 02 for what its worth -- A Johnson