starting my 12v build after cylinder 6 ring failure - Dodge Cummins Diesel Forum
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post #1 of 35 (permalink) Old 12-19-2017, 12:39 AM Thread Starter
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starting my 12v build after cylinder 6 ring failure

Hey guys! new to the forum, been on diesel bombers hoping for more activity here lol!
So long story short my ole' reliable 96 12v developed a significant tick/knock while pulling my not so heavy boat up a grade. coolant at 170 20psi boost 1100 egt and out of the blue a small noise became loud by the top of the hill . When I stopped, the engine stalled and felt as though it was trying to seize. hopped out checked the fluids, all looked well, and then she reluctantly started up again, when i hopped back out my 180k engine now had a lot of blowby that was not present before. ffrom this point on the motor had a consistant knock that fluctuated with rpm and did not change much with load. I limped her home about 30 miles, parked for about 6 months, drove her another 10 miles to my shop. dropped the NV hoping my clutch pack had busted somthing and was making the noise but no luck. Then I pulled the engine. Made a side mount out of some 3/8 plate, got it on the stand, pulled the head and my suspicion was verified. cylinder six was the issue, the piston skirt has scraped away my beautiful crosshatching from the sides perpendicular to the crank. dropped the pan and pulled the piston today. The lower compression ring is seized in its groove and seems to be the root of the problem. the piston took more damage than the cylinder luckily. So far I have only taken some quick measurements but its looking like I could get away with a new piston, rings and a good hone. all the bores are near 4.016 and the wear on cylinder 6 is less than .001 out of round. you can barely feel the scratches. I had already planned on pulling the engine to reseal and build her up for a hopefully reliable 500hp daily driver, So my current dilemma is how far I should go on the short block. I'm leaning towards just honing and replacing one piston and mains/rod bearings and oil pump, I considered replacing all the rings but i'm not sure it would be worth the risk of them not seating. Im definitely going to get the block and head checked at the machine shop for bore, out of round, taper, warpage etc, but assuming everything is within spec i'm leaning towards saving the money and not doing a full rebuild. I'd appreciate any advice or thoughts you guys have at this point, there is certainly more to come but I plan on getting the bottom end squared away first.
will have some good pics up soon apparently i need to have more posts first

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post #2 of 35 (permalink) Old 12-19-2017, 02:17 AM Thread Starter
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post #3 of 35 (permalink) Old 12-19-2017, 02:18 AM Thread Starter
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96' 12v 180k, nv4500, EMS CAD delete,38x15.5r20 Fass 125gph, 1/2" lines, Certified injection 300hp benched ppump,16* timing, DAP 7x.010, hx35
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post #4 of 35 (permalink) Old 12-19-2017, 02:22 AM Thread Starter
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post #5 of 35 (permalink) Old 12-19-2017, 11:37 AM
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Honestly at 180k on the odometer I seriously doubt the other 5 cylinders have bad rings. The rear cylinder gets the coolant flow last so #6 has a tendency to swell and seize long before the rest do. Typically a performance build has a few thousandths more piston to wall clearance on #6 to compensate for the fact that it runs hotter. So basically honing that cylinder and running it looser will result in a more equal piston to wall clearance among all six cylinders under heavy load than the factory setup would anyways. So if you are trying to keep the cost down I truly don't see leaving the other cylinders alone as a mistake. I would feel more comfortable with that than doing a rebuild with cheaper non OEM parts trying to keep your budget in line.

I am a fan of a coolant bypass at the rear of the block to help move the coolant and relieve pressure at the back of the block at higher rpms.
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post #6 of 35 (permalink) Old 12-19-2017, 03:17 PM
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There's 1 types of coolant bypass 1 for pressure for high RPM and the other for temperature which is for towing maybe???

Not sure how this works because the coolant temperature sender is right there how would it get hot unnoticed ?

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post #7 of 35 (permalink) Old 12-19-2017, 03:42 PM
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#6 gets hot far quicker than the gauge is able to respond.

I think the issues on #6 not only have to do with poor coolant flow but also it's a cylinder that runs at the hottest piston temp due to poor airflow compared to the other 5.

Piston temp is probably why the ring failed I suspect?

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post #8 of 35 (permalink) Old 12-19-2017, 05:07 PM
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How "turned up" was your engine, OP? How do some guys have a million miles before a rebuild, and some fail under 200k miles?
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post #9 of 35 (permalink) Old 12-19-2017, 08:31 PM Thread Starter
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The bypass sounds like a good idea, although i was under the impression that it was more of an egt issue is cylinder 6 along with coolant temp. crazy part is my truck has always ran cool like 170-180 unless i was towing really heavy. What do you guys think about whether or not to replace rings and hone the other 5? I plan on getting oem rod and main bearings and oil pump. Another thought is I could get number 6 bored out just a hair if it will help my odds in the future lol. I do plan on pushing her a lot harfer after this is all taken care of. And Spawn, all mods are in my sig, truck was close to stock and it wasnt pushed hard at all as my clutch would slip at about 25psi boost

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post #10 of 35 (permalink) Old 12-19-2017, 09:35 PM
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I would agree to just give it a home and clean up the other cylinders. See what your machinst says.

You can address the air flow issues on #1 and #6 in the head if you want that will help mitigate the problem.

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post #11 of 35 (permalink) Old 12-19-2017, 10:00 PM
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Number 6 runs hot due to it being the last cylinder to get coolant and the other 5 have already heated the coolant up, it's the nature of a inline engine. It's normally not noticed until more fueling is added and their loaded for extended periods.
Years ago we had the same issue with the 401 engine on 8000 Ford tractors.
They ran fine from the factory, but if you turned the fuel up a little for more power it would score #6 piston.
The simple fix was to hone that cylinder .003 over giving more room for piston expansion.
When I rebuilt my present engine I had an extra .003 honed into #6 cylinder.
Towing heavy with my fueling mods I knew #6 was going to heat up.

OP make sure to check the piston cooling nozzles, their a big part of keeping the pistons cooled on these engines.

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post #12 of 35 (permalink) Old 12-19-2017, 10:49 PM Thread Starter
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Hemirunner, aderss the airflow would be a more spread out dual intake? I will definitely get the machinist's opinion. Destroked, I will be sure to check the cooling nozzles as well, the loose bore idea for cylinder might just save my a** haha. Any thought on whether or not to put new rings in all the cylinders?

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