Engine/Transmission (1994 - 1998) boring .040 or sleeving a 95 12v block

[tcrawford]

I have a 95 12v and my choices are to bore 40 over on all 6 --- sleeve 2 cylinders and then i could bore 20 over. I would have to sleve them all to stay std bore and thats too much $ i could find a new block for that. I havnt been able to find anything where anyone has gone 40 over on these to see if they have any issues with it running hot or even cracking a block i plan to get about 800 hp outta it when it goes back together and will be just a fun daily driver with some ocasional toy hauling nothing to serious. Any help would be great at i have to give the machine shop an answer on monday thanks

 

[Joseph Donnelly]

I would bore the block . 040” (1 mm). Cummins offers oversize pistons in this size and the cylinder walls are thick. To sleeve the block, the cast iron walls would end up thinner to make room for the sleeve. If you are going to make that much HP, you should get higher strength main cap bolts or studs, and consider using the Cummins bed plate between the block and the oil pan.

 

[tcrawford]

There will be alot of supporting mods made to make the power. I am just worried about it running hot, mainly. I have built several gassers and i know they tend to get warm somtimes when you bore them and the last thing I want is a 12v with a ton of $ wraped up in drivetrain and truck to be undrivable or not be able to tow my other toys

 

[Dieseldemon]

I have had a lot of 1MM over and have had no trouble with any of them you can mix and match all pistons from Cummins 1/2mm and 1MM with 5 4 3 2 or 1 Std bore as they all weigh the same.

 

[JMcCoy]

800 HP!!! WOW. The cost of your block is the least of your worries. LOL. GOOD LUCK

 

[CharlieFoxtrot]

Previous owner had the engine rebuilt in my truck about ~60K ago due to loss of piston oil spray on one cylinder. It's bored . 040 and has new Cummins pistons. He lives in TX and towed ~5k lb with it fairly regularly and didn't report any problems. I live in FL and don't haul or tow often. Running empty I will see 190-195 on my stock gage at times during the summer, and then the fan cools it back down. This is my first Cummins, but it seems to behave as I'd expect, from what I read here. I don't worry about it.



I wouldn't sleeve a block. I've done it on gassers and think replacing with a good used block would have been wiser. If you don't want to bore . 040, get another block. With the money you're going to spend on mods, you want to be 100% confident in whatever you decide.



HTH



kevin