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Cummins ISX Engines


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I recently read where a coach owners ISX 650 blew up. It was once again a dropped valve. I passed the story on to my son who is a certified Cummins tech asking what the issue is with these ISX engines. To help some of you I thought I would pass this on to you here. He taught me years ago to keep my RPM's at around 2000 whenever climbing grades. Now I see why. This is what he said:

" The ISXs had a lot of problems and they went on for years. This particular failure is a combination of weak valves combined with pushing too much HP/torque for an RV application. I know they came out with a new design for valves, heads and I’m pretty sure they have a newer “carbon scraper” / APR - Anti Polish Rings to help keep the liners in tact. They also revised the calibration to derate, I believe down to 600HP - it’s not a 650HP engine.

One problem is the torque demand. A lot of RVers are all about fuel economy and try to keep those Allisons in as high a gear as possible up grades. The torque curve peaks at around 1500 and many will try to keep the RPMs as low as possible, but you are placing the most stress on the internals at that RPM. Grabbing a lower gear and doing 1700-1800RPM is much more desirable. It’s the same reason you get more momentum in a lower gear, your temps are lower at higher RPMs, etc. For whatever reason, some people either don’t connect the dots or ignore it because they think lower RPMs are better for the engine / fuel economy. The ISX at those numbers are prone to snapping valves under stress. Happened to truckers too that ran ‘em hard under low RPMs in high gears up grades and such. "

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Yes John it does.

My son and an old trucker taught me years ago how to climb a grade.  Preparation  is the key. At the bottom of a grade and just before heading up I start downshifting.

They told me to downshift and get the RPM's around 2,000 and keep downshifting to keep it there. Not only does this reduce stress on the engine but also keeps the temp's down.

 

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  • 3 weeks later...

From my readings on irv2 forum, the ISX issues may be temp or acid related and not necessarily to weak valve springs.  And it could be a couple of the many thousands of ISX owners that have had an exceptional problem ($30K repairs) that gets the attention of others that "blows the issue out of proportion".

None of the occurrences have had definitive root cause identified.  So I would call it a forum click bait topic only at this point.

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  • 2 weeks later...

I learned of the ISX #6 intake valve issue a couple months after buying a 08 Navigator with a 06 ISX 525 engine 2 years ago. A higher % of MHs are having this problem than trucks and the higher HP (600-650) are dropping the valve more often. They are not snapping the valve off, the perimeter of the valve breaks off usually getting the piston and the turbo.
I know of two 525 HP, 06 or older, that have dropped #6. Hopefully the better valves and seats will stop the acid created by the EGR gasses from weakening the intake valves...$20K if you do it preimptpley and $30+K after it breaks. 

 

 

the EGR

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Just curious, what do you mean by "the perimeter of the valve" ? 

Is it the sealing portion of the valve. Wonder why/if anyone has not come up with a EGR delete kit for it, dirty but cheaper fix as on the smaller truck engines...

Edited by Ivan K
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Yes, the pictures of the broken #6 valves has chunks of the outside perimeter ( sealing surface) missing. I’ve been told a 1.25” metal freeze plug fits nicely into the EGR tube where it bolts to the engine intake tube.

Edited by Ivylog
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