...since it's apart...refresh it???

["Mad Max"]

Okay - Since I'm going to be swapping the head and cam, and since the short block will be on a stand, and since it has 245,000 miles on the clock, and even though it has good oil pressure and temps, I want to go ahead and freshen up the bottom end - mainly because I can.



I know many of y'all are correct in saying 'if it ain't broke... ', but I can't think of any reason not to go ahead and put in fresh bearings and rings, seals, freeze plugs, everything like that. I don't want to bore it or have the crank cut . 010/. 010 if it doesn't need it, but my questions become these:



- Rings/Pistons: If there is still a nice crosshatch, can you install new rings? How do you determine if the crosshatch is good enough? Regardless, can a block be rehoned for new rings without a rebore and new pistons, or can fresh rings just be installed on the pistons as is - no machine work, and would that help at all?



- Bearings: No-brainer in my mind, but, the local Cummins dealer/service shop in Denver said they don't service/cut cranks - they replace them with new standard cranks, but HUGE $$$ for a crank.

If the crank is not damaged, and not undersized, I figure the crank could be polished and a fresh set of standard bearings installed, yes?



I just did a nice warm 440 gasser for my Ramcharger, and I had no problem cutting the crank . 010/. 010, boring it . 030 for new pistons/rings, using all new valvetrain, and calling that engine good to go. But it isn't intended to have 50 psi of boost or to go 300,000 miles without blinking - it isn't a Cummins block, crank, pistons I was dealing with, and I need to know..... is a Cummins that picky and should I be as well? I need y'all's Cummins-building experience and savy on this one. It'll be months before I even get the engine torn down to see what I have, but I'm trying to get a feel for the 'what if' scenario.

My '93 Cummins runs strong, and while 245,000 miles is a happy amount, it's still a lot of miles, and if I can put in new bearings and rings, without any block or crank machine work, I'd like to do that - just because it's down that far and doable. I would hate to reassemble the engine with the fresh cam, head, twins, etc, and feel I was being cheap by skimping on some of the vital parts of the reciprocating mass. Bearings and rings are cheap, but I don't think I need new pistons or a crank.



Lastly, the guys at the Cummins service shop seemed to indicate that if there were anything wrong with my engine they would not fix the old parts and would only replace them with new parts (specifically the crank), and (with my gasser perspective) I thought that was a bit, well, narrow minded, but it may have been the correct response for servicing Cummins parts, IAW broken/damaged parts cannot be ressurected. I have no problem believeing that, but I'd be happier to hear that a Cummins crank can be cut and the block bored (if necessary) without any long-term detrimental effects.



You're thoughts about this, either way, are very much appreciated and will be considered with complete unbiased thanks.



- Sam

 

[TKingsbury]

I would say bearings would be no biggie. People roll in new bearings everyday while the engine is still in the vehicle, so there's no machine work being done there. I would probably check the clearances before and after each bearing is installed just to ensure no surprises. Now for the rings, that I do not know.

Travis. .

 

[HFletcher]

Once my cummins dropped a valve seat. When I pulled the head the cylinders still showed crosshatching as others have also reported. However when I removed the two pistons to have those cylinders rebored it was discovered that the rings and groove tolerances were way out of spec. The reboring guy pointed this out to me and popped my bubble. I originally thought the engine was barely broken in at 170,000 miles (not abused) - but the pistons are aluminum and the block isn't. So, based on my experience, I think you'd be wise to check the piston ring grooves - you may decide to replace the pistons and then . . . you might as well do some bearings too - you're already there. jmho Hank

 

[Forrest Nearing]

you can slide new bearings in it... but if you're going to have it out on a stand, I'd kiss it w/ a hone and put new rings in it too...



you can install new rings without honing the cylinders if the crosshatch looks good, but if you're that far into it, just kiss it w/ a hone to put a new surface on it.



as you're well aware, you could probably expect another 200k+ miles out of it if you didn't do a thing, but it's not very often that you're presented with a "convenient" time to to a refresh/rebuild.



I'm a big fan of preventative maintanence... I'd rather do things on MY TIME and have piece of mind than wonder how far from home and rushed for time I'm going to be when something lets go!



Forrest

 

[Forrest Nearing]

oh yeah, and I don't know how much power you're lookin' to make, but I'd definately check the deck for straightness... lotsa boost needs good head gasket retention... and that needs a flat deck!



really stinks to find a warped deck when you're on your 4th head gasket and the engine is in the truck! LOL!



Forrest

 

[JLEONARD]

I agree to score up the cylinder walls with a hone and put in new rings.

Also as long as the crank looks good just put in the new bearings.

Lots can go wrong with a crank re-grind... I've seen good and bad (bad even from supposedly good shops) and a bad job won't stay together long in a diesel.

JMHO

Good luck.

Jay

 

[1stgen4evr]

Crank grinding

THE critical point (aside from correct deminsions) on a regrind is to maintain the radius in the flanks of the journals to match factory specs. Too many regrind shops will not duplicate that since it is harder to keep the grind wheel to spec. (Some shops don't even have the tool to radius the wheel. ) If that is done right, you can expect to run the regrind without ANY problems. I would also have the crank magnafluxed to check for possible cracks. As mentioned, it is a long way down to the crank if something goes wrong. I would never use a crank past . 010- . 010 but have seen some done that were greater than that.



Consider very carefully the condition of the cylinders right at the top of ring travel. That is the point of most wear. The cylinders can look very good and show plenty of crosshatch in the major portion of the bore but have more wear than you would think without careful measuring. Now this is just a heads up. The bore may be fine.



If you put new rings or new pistons and rings, you are going to push the new rings against a ledge (all-be-it very small) at the top of the original ring travel. If all checks in spec, I would run it like it is or bore first over for new pistons and rings. I would never spend the money for a new set of pistons without boreing first over size.



If it were a power unit that didn't take two days to have it out and on the stand, some things could be overlooked, but in the truck you are lavishing all this TLC on. Nope.



My two cents worth.



James

 

[JLEONARD]

Too many regrind shops will not duplicate that since it is harder to keep the grind wheel to spec. (Some shops don't even have the tool to radius the wheel.

Ahh James... a man after my own heart.

I was going to get into this, but decided not too... glad you mentioned it though and opened the door.

I addition to the wheel radius, there is another issue that has to do with hardness depths and "typical" heat treat patterns on journals. Often times the grinding crosses thru the heat treat zone at the end of the journal and creates a stress riser... even if the wheel is properly dressed (I don't mean with a tuxedo).

(Our company used to make assembled camshafts for Ford and I got into this issue)

Sorry for the geekiness

Jay

 

["Mad Max"]

good stuff

I very much appreciate your inputs fellas, and I'm glad to see that what I'm wanting to do isn't out of the realm of possibilities. I'm 100% sure I'll do bearings, and when it's all apart I'll have the block checked out for any signs of cylinder wear/straightness, get the block decked for good measure, and at a minimum replace the rings. If it needs more then it'll get it. This rig is going to be my RV and I'm planning a lot of cross country trips, not to mention the show seasons.

It's going to be a fun build, and it'll take at least a year to do, but it aught to be a fantastic long-trip hauler.

Any other inputs on a basic engine 'touch-up' are greatly appreciated. I like this discussion because it gives me some great insight into just why these engines last as long as they do, and I think that, speaking for myself, that is good to know as it motivates me even further to do this build, and to know how best to maintain it to keep on lasting. I've been a fabricator for half my life, but I'm still a rookie in Cummins engine knowledge. I'm looking forward to the teardown almost as much as I am the build-up, just to learn more.

- Sam

 

[MMiller]

I myself would never grind a crank unless it was gouged. I have had many diesel cranks out, and polished them up and put them back in standard. I have done several rebearings, and watched many done in chassis. None of those were polished. Polishing the crank really isn't necessary IMHO on a simple rebearing. Rebearing it, plastiguage it if it makes you feel better and run it.



As far as the rings, that is entirely up to you. Was the truck using oil? Was there an excess of blowby? Did it run strong? Has it been maintained well? Did it start nice a crisp? I myself have a hard time screwing with something that is working fine, with little oil consumption. I really would not bore the block either unless a hole is scored. If it is what you want to do, hone it, inspect ring grooves, and ring it.



Heck my 440 was stock bore high mileage engine. It measured . 004" oblong in the bottom. I took a hone and worked each cylinder over until they were . 004" over stock and round. I put some stock bore, forged, 6 pack pistons in it and have had 400 miles of good service. No oil consumption. Now before you jump my 400 miles, its a pulling truck and off road truck. It gets miles in 300' intervals, and spends hours running to go a couple miles off road. I have been very happy with its service. The crank I had polished and put it in with stock bearings. Now that was my 440. Like you said Sam, diesels are a little differnt beast.



All these statements were my humble opinions. Good luck with your project Sam. Gonna have to stop in Iowa and let me ride in it!!



Michael

 

[JApplegate]

i hate to be the black sheep in a herd of white sheep..... but look at what i drive... . i already am... bearings/seals, yes (replace), pistons, cylinders, rings, cam, ect. (messure, then decided what clearence you want. if your racing her then no room for error, driving back and forth to work and no towing i would go to max allowed. but you can even begin to talk about these untill you messure and it's up to what you want. Also make sure they are round. . and not an oval)

also from what i've heard from professionals around here... . on diesels like cummins, detroit, john deere 1,000,000* miles. Ford's 200,000 miles*. gmc (duramax (not detroit)) 500,000* miles i think??) now i agree we don't drive are's like tractor-trailers who run at one speed most of the day. BUT cummins don't like doing that.

*running at stock settings