Injector hole size

[Dirtscience]

I have just now started looking at first gens. I have been under the impression that first gens could not be pushed as hard on boost and cylinder pressure as the 2nd gens with the p-pump because the holes for the injectors are to large, not leaving enough metal around the injectors and the valves to keep from cracking. Is this ture? I just read several threads on guys running pretty high boost on first gen's. I guess my question is, do all the first gen heads have the same size injector hole or did they change at some time as with the introduction of the intercooler? I've got an awsome deal to me at least, a pristine 1'st gen owned by my uncle. Its only got 105,000 on it and he takes meticulous care of it. It has never had any mods done to it, just maintenance. I've been looking for a second gen to hotrod but may not be able to pass this up.



Thanks guys



Mark

 

[Philip]

When the change to intercooler came about. The injector tip size was droped. The nonIC trucks were the ones noted for head cracking. But there are some people here running high boost and lots of fuel on nonIC trucks and haven't had any problems yet.



As with any bombs. You take a chance.

 

[Dirtscience]

Thanks for the quick reply. I will probably buy this truck regardless, and not worry to much about the bombs for now. I am aware of the getrag weakness and the necessity for guages. Time to start digesting the 1st gen forum. I Love this web site.



Mark.

 

[Mel Fuelling]

Mark,

I believe many of us are finding out that there aren't any problems with the Getrag behind a CTD that an extra quart and a half of 5w30 won't solve. (Any one with contradictory experience please jump in. )



Since I put a SBC Con O (with the sealed roller or ball bearing in the flywheel) in my work truck, all of the low and mid range rattle that I have blamed on the Getrag is gone. Now it runs just as quiet as my automatic truck does. (I had an off brand replacement disc under a good Sachs pressure plate. The weak springs in the clutch hub were letting the splined center hit the limit pins in the hub. Now I can turn my delivery rate back up!

 

[BushWakr - RIP]

The 89 - 91. 5 model year trucks had larger injectors both in fueling and in overall size than the 91. 5 - 93's. .

The early trucks being non-intercooled AND having larger injector diameter meant that the heads are subjected to more stresses and have a greater likelyhood of cracking in and around the injector bore/valve seats area.

The early trucks used a 9mm inj. body and the later were 7mm... . that's all it seems to have taken to deal with this problem..... BUT !! virtually all of our heads ARE cracked to some degree... these things are pretty durable and they show it every day as we continue to beat on them and make them do stuff they were never intended to do...

Cummins actually has an "acceptable degree" of cracking that will permit the heads to be remanned out as fully servicable...



The worst thing we can do is to subject the heads/engine to high EGT's AND high boost together... . when bad enough all the heads WILL suffer some form/degree of cracking, it can't be avoided.



pb...

 

[Dirtscience]

Thanks for all the replies guys. Pastor Bob, the truck I am looking at is a 91. 5 factory intercooled. Did any of these early intercooled trucks come with the large hole or were they all switched at the time of intercooling?



Thanks again guys.



Mark

 

[JLEONARD]

virtually all of our heads ARE cracked to some degree

pb... I can't let this one pass by...

Yup and some of our heads are cracked more than others..... :-laf



In mid 91, the engines were intercooled and the heads were upgraded with the smaller 7 mm injector holes. That left more material in the head to combat the cracking issue.

 

[BushWakr - RIP]

Ooooooo... . that one singed a few hairs... .

 

[Dirtscience]

It's official, I bought the truck and will fly to Portland on 19th to pick it up and start the wallet emptying experience of driving it back home to AZ. Live and learn I suppose. Thanks for all the help guy's. Sorry for high jacking my own thread. I never thought I would buy a first gen, but not sorry I did.



Mark.