Possible head/valve problem

[Downthehaul]

I have a prostar with an isx, model number says 435st, is that an 871? I can’t find that distinction any damn where.

I did an overhead set according to rawze’s video and the cummins manual. When I read in the cummins book about the detent on the jake brake I measured it, and was alarmed. Here are the figures on the detent as measured with a feeler guage.

Cylinder 1: .040-.041
Cylinder. 2: .047-.048
Cylinder 3: .035-.036
Cylinder 4: .030-.031
Cylinder 5: .032-.033
Cylinder 6: .027-.028

The way I got these was setting the jake rocker to .276, then putting the guage in at detent position at increasing thickness until I felt greater than zero resistance.

I’m concerned that they are in such a wide range. The book says .025- .110, but should they all be similar? Anyone have experience with this? I read a rawze post that says if they get lower than .028-.030 the head is shot and needs to be replaced. This engine was rebuilt before I bought it at 503,000 but the head was NOT replaced. It now has 707,000.

It’s at cummins right now and they’re doing the overhead, I’m waiting to hear back. Hope I’m mistaken somehow.

And if anyone knows where to find a list of spn codes, specifically 1747 and 502807, that would be great. Can’t find those two anywhere.

[Unilevers]

oooh those are getting really low. The extended valve stem heights need to be measured and the head checked. Its looking pretty wore out and the valves are sitting high in the head.

[Hammerhead]

That's not a very accurate way to measure clearance.
If the head is original with that many miles, it's time to measure them properly and be prepared to replace the head.
Use a dial gague, they don't work well with the standard radiused needle end, so see if your supplier has a "lever" to attach to it for more accurate measurements. The radiused ends don't sit well, as there are no smooth surfaces on the rockers, and the they rock, not straight line, so they don't stay uniform.
I don't have a pic with me, but I have a small "bar" with a small hole on one end. I unthread the radiused tip and the threaded part of the tip goes through the small hole and tightens back up. This makes a nice large surface that isn't affected by the lack of smooth surfaces and measure the stroke well.
I hope I explained that well enough to get an idea of what I'm talking about.

[Waterloo]

If they did not replace the head when they in framed it, odds are it is toast. These heads are one time use only and throw away. I would be more concerned about the liner heights, did they cut the block for the new liners and properly measure them? Odds are, the motor will need an in frame in short order. Like 99% odds...

[Downthehaul]

Well hot dog! That’s some good info thanks y’all.

I see what you mean with a dial guage. I got a cheap one but it was useless and got returned. Cummins is going to measure the clearance and let me know.

I would bet they did not cut the block. Reading the receipt from the shop that did the rebuild it sounds like they did the minimum; liners and gaskets, bearings and such. The previous owner was burning through oil and it had carbon packing. I think everything was just cleaned. It’s been running good so far but I know how fast that can change.

If the head is bad, how big of a risk do I run by driving on it? And if I replace it, can they fix the liner issue you’re talking about at the same time? I’m trying to weigh the cost of another inframe vs. replacing the head or potentially blowing the motor.

[Waterloo]

Only way to properly repair is to in frame, purchase new head and if nothing has cut lose, you may be able to re use the liners and properly cut the block. But, having been through this myself, when you actually get inside the motor, you may just have to order the entire kit and replace everything, especially the lower end. Odds are, this motor was just thrown together and dry started, just like mine... $38,000

I went to GA, and rebuilt mine the second time in Rawze's driveway. We got it apart, and it was ugly, they installed all of the wrong parts, skipped many steps, etc. 50,000 or so miles, the motor would have destroyed itself, the block would have been destroyed if what we found had cut loose.

[Downthehaul]

Holy moly, that’s more than I paid for the truck. What does the whole kit include? Surely the crank and the block don’t get replaced?

[tree98]

Hey Downthehaul, you mentioned that Cummins was doing your overhead and was gonna check your head to see if it needs replaced. I can tell you without a shadow of a doubt that they are not the people you want to stake your livelihood on! And if you decide on an inframe they are the LAST people you want doing it, unless you like literally throwing money away.

[Downthehaul]

Indeed? That’s intriguing, why do they have such a reputation in your book? I don’t have trouble believing it, these repair shops always seem to have only one thing in mind, and it’s not even money, it’s just getting rid of you.

They are putting it on a dyno now, hopefully that tells me something.

Do you recommend any individual or shop who does a rebuild right? I’d be willing to do any work myself that I possibly could, or help out in any way.