6.9 Blowby...Rebuild or new rings?

[Rusgo]

1986 turbocharged 6.9 with head studs installed.

Have 190k miles on it. Runs great, starts with just a touch of the key, starts on cold mornings, but I'm losing oil everywhere and have high crankcase pressure.

Compression seems solid, idles perfect, and no weak cylinders.

I've heard these engines had a piston ring design flaw from the factory the leads to excessive blowby around this time.

I wouldn't mind timewise tearing the engine apart to re-ring it if I knew it would help.

Anybody ever get good results from new rings on these engines?

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[frankenwrench]

Realistically u may just need valve seals. And as far as high crank case pressure how are you sure of this? Not saying you are wrong, just curious as to how you checked this. And if so make sure your cdrv is in good shape and if you have a rdt make sure you don't have any blockage or kinks in the hose. If it starts easy and compression is good I wouldn't see a need for new rings.

 

[Therkhan7_3Turbo]

Coming from a 12v Cummins to this I thought the motor was shot in mine... Looks like a lot of blow by but also have to consider the inherently high compression ratio of what 22:1? On the 6.9? A lot for rings to try and seal, plus all the old internal rubber ( valve stem seals ) I'm willing to bet your motor is fine just needs some new valve steam seals.

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[Rusgo]

Yeah that compression sounds about right. And I should probably clarify, I'm not burning or losing a ton of oil, just losing it out seals and sucking it into the intake through the CDR.

Have a good amount of pressure coming out the oil fill and things like a hose clamp on the cdr hose has oil leaking passed what should be a solid seal.

I'll double check CDR is working okay. Most of the leaks get worse under heavier boost. If I just baby it, it's not so bad.



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[IDIBRONCO]

Did you install the head studs? If so, did you look at the amount of wear in the cylinders? In the past, without all of the knowledge that is around today, there was an issue with running a turbo on these engines. Wes and I have talked about it and we think alike on this. The issue was that a lot of trucks with turbos didn't have a pyrometer installed. Also, I changed these engines out for a living for just over 6 years, from August 1995-September 2001. Not one IDI powered vehicle (Ford or Chevy) had an intercooler. I think people just put their foot to the floor and went like heck. They probably ran with too high of EGTs. The rear two cylinders (#7 and #8) would be completely wore out in toughly 150,000-200,000 miles. I'm talking about .020-.030 wear. The next two forward would have around .015-.020 wear. The front 4 would all be starndard with just a few thousandths wear. I don't want you to panic, but be aware that this is a possibility although these engines would usually have some knocking from piston slap. Our engines didn't have defective rings, the ring gaps were all large by design (for some reason) so these engines all have a lot of blowby compared to most others.

 

[Rusgo]

The head studs and turbo were installed maybe 10k miles ago. Not that long ago. Oil leaks and blowby have been getting progressively worse since I owned the truck, so long term wear may not be the same as those earlier setups.

But yeah, I cheated on the head stud install. Heads never came off so no chance to look at the cylinder condition. Incremental in order bolt removal and install.

Crazy the walls can wear that much though. Still have to verify a couple things before tearing into it. Hoping my walls are nice and pretty.

If the bores and pistons look good I might buy oversized 2nd rings and file them down to a normal gap

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[rustygold]

If the bores and pistons look good I might buy oversized 2nd rings and file them down to a normal gap

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If you get oversized ring will hurt more than help. The ring will bust at some point in time on first start up or down the road. And on top of it all you will have piston slab like crazy making it nosie and wear wrong.

Im tearing my mine down here soon to fix mine and im going with new pistons and gapless second rings to hold more compression.

I would only to the ring like you if im getting rid of it maybe not even then because time is money with me.

I am the guy that doesn't half it because its faster or cheaper if it will not work in the long run.

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[Rusgo]

Yeah I might go gapless too. Bit spendy.

So if a standard diesel ring gap was achieved with the 2nd ring as opposed to the oversized factory gap, it would eventually take out the engine?

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[rustygold]

Yes because its all about expansion rates. I know in race motor you can go with a .1 over and file it down or get file ring for A cheap gapless ring but they rebuild the motor so often they can do that. I would check piston clearance first you could have glazed cylinder walls.

And gapless are not to pricey might see about R&D.

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[Rusgo]

I have read about guys going much smaller on the 2nd ring gap. Down below .020 even.

Spec for Cummins 12v 2nd ring is approx .035 Not sure if it affects things long term though. Spec for IDI is around .065

Primary reason for the gap is stated as oil control and pressure control. They dont want pressure getting trapped between the rings when tight gaps exist. Causes piston ring flutter.

The large 2nd ring gap spec doesn't appear to be related to possible ring end contact, especially since the top ring gets hotter and expands more, but still has a much tighter spec.

A gapless 2nd ring would also impact the the pressure differential characteristics in the same manner, so design wise, you'd still be telling the factory engineers to ****** off.

Looks like in the piston ring world, there is a large debate about the benefits and drawbacks between engineer, builders, racers, etc.

I'm kind of leaning toward the possibity of something working better than a design that allows excessive blowby for much of the service life of a vehicle.

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[rustygold]

A gapless 2nd ring would also impact the the pressure differential characteristics in the same manner, so design wise, you'd still be telling the factory engineers to ****** off.
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The gapless ring in talking about is 2 two ring on the 2nd ring land.

And as for gapless ring have you tore down a tractor motor they have up to 5 ring on the 3 third landing and 4th still and oil ring.

So there's lots of debates everywhere but the whole thing is less blow by more thermal energy energy made into mechanical energy. That why ford is putting a opposing piston motor 3 cylinder in the f150. Works like a two strokes, no valves ,6 piston, two crankshaft, no spark plug its off of compression and put out more than 50% more thermal energy into mechanical energy.

Now most diesel will run hundreds of thousands of miles with blow by for years and so just fine. I just like a tight motor.

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[Rusgo]

Tested out the blowby by checking oil fill port when hitting the throttle. Good stream of fog at idle that gets a bit worse with RPM. Under higher boost is when the oil leaks are the worst, and also when oil is pushing through the cdr valve.

CDR seems to be doing its job. Disconnect it from the intake with engine running and it's open under various conditions.

Couple crazy things happened. Installed a new facet lift pump, and I kid you not, the truck ran smoother with a touch more power. Especially at low rpms. There was a weak spot on my return lines that burst after installing it and running it for 30 mins. Thinking my mechanical pump wasn't doing much.

Other thing was a wire under the dash sagged down to the top of the throttle pedal cable. I was smelling burning rubber for 20 minutes while driving and couldn't figure out where it was coming from.

The wire was worn through and turned the throttle cable into a heater element. The cable melted the inside of the throttle cable sleeve and seized itself up! Found out trying to put the brakes on at 50mph. Scary stuff. Hitting the clutch made the rpm spike. Had to turn off the engine and coast to a stop.

So yeah, the engine is coming out soon.

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[rustygold]

Thats scary stuff. Im pulling my for blow by and oil leaks. I hate dripping oil.

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[bbjordan]

Well, not exactly new rings...https://www.oilburners.net/threads/redneck-6-9-rebuild-dont-try-this-at-home.60592/

It's still running great.

 

[Rusgo]

Well, not exactly new rings...https://www.oilburners.net/threads/redneck-6-9-rebuild-dont-try-this-at-home.60592/

It's still running great.

Nice shade tree skills for sure. Maybe I missed it. Did you check how worn or out of round the cylinders were before assembling everything?

Remind me of the stories of the Cuban mechanics keeping all their american cars from the 50s and 60s going for decades.

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