E6 250 Piston failure

[Mcrafty1]

  I've discussed this here before to some degree but my 86 mack E6 250 has burned down around no five piston yet again (third time in 3700 hrs. ) my question to the mack gurus here is this: although I have the fuel turned up on this engine and drive it myself can anyone explain why the same number 5 piston is the only one that fails? the other 5 piston have been in the truck three times as long as the one that failed yet show no signs of over fueling or excessive heat. Some history...The first engine failure was 10,000hrs. broken ring which ended up on top of the piston (which now looks a lot like the same failure that I keep having) the engine was inframed, fuel turned up at this time and new heads were installed(all mack parts) same nozzles, 2000hrs later same piston failed replaced that piston and liner only and replaced the nozzle thinking that that was the culpert. Started to notice some blowby around 3600 hrs.and the pump failed at that point (governor issues) so I sent it (the pump) to a reputable diesel fuel systems shop and had it rebuilt and last week at 3740hrs. no 5 has failed again...I'm really at a loss as to why the same piston is the problem every time and I'm hoping some here has had the same issue and found out how to correct it. Thanks for any and all insight into this that you have. 

[fjh]

Are you sure that the no# 5 sealing washer came up with the injector and is not being left in the injector hole each time if the injector is too high (DOUBLED UP WASHERS ) it will be spraying to the outside of the piston! just a thought! 

[Mcrafty1]

Wow, that's a possibility I hadn't considered and it is doing it in the same spot each time...If that were the case wouldn't it be noticeable on the underside of the head? by that I mean wouldn't that injector protrude  a enough less below the head compared to the other two to be noticeable? or would it be such a small difference that one wouldn't notice it if they weren't looking for it?  If what you say is the case it would explain the whole sorted affair with this engine's problems. I'm for sure going to check it out, Thanks a lot! that might just be the answer.

[fjh]

Id Be interested to know! Post If you find out!

[Mcrafty1]

Will do

[theakerstwo]

Also have you changed the piston cooler nozzle?It could be stopped up or bent.I always pull them out before the piston comes out.The rod may miss it coming out but can hit it going back in.

[fjh]

Yup Good for a look as well Glenn

Let us know what you find!

[Mcrafty1]

2 hours ago, theakerstwo said:

Also have you changed the piston cooler nozzle?It could be stopped up or bent.I always pull them out before the piston comes out.The rod may miss it coming out but can hit it going back in.

Yes, nozzle has been check any clogging and has been checked for proper aim. Thanks

[theakerstwo]

It would sure be good to know if the pump  shop just repaired the governor and did not calibrate the pumpor or if they did all of the pump plus the calibration.If # 5 was over fueling due to bad calibration then this may follow you around for a longtime.years a go i saw a 711 do this for maybe 5 times before the pump was checked and repaired.

[fjh]

If a guy were to compare piston tops you would likely see if you have doubled up on washers by the spray pattern the spay usually hits right at the bowl corner. If it was fueling you would think you would have had pound (fuel knock) but ya never know!

Edited August 22, 2016 by fjh

[Mcrafty1]

2 hours ago, theakerstwo said:

It would sure be good to know if the pump  shop just repaired the governor and did not calibrate the pumpor or if they did all of the pump plus the calibration.If # 5 was over fueling due to bad calibration then this may follow you around for a longtime.years a go i saw a 711 do this for maybe 5 times before the pump was checked and repaired.

Thanks Glenn, The pump rack was overhauled and was re-calibrated the last time this happened,   and the governor was repaired this time and they said although it wasn't new by any means, it was right and would be fine for a while....or so they said, it is a very reputable diesel fuel specialty shop in Bangor, Maine that does many, many of the surrounding area truck shop and personal owner fuel work. I believe them when they say the pump is right.....however, I have no way of checking their work.

[Mcrafty1]

21 minutes ago, fjh said:

If a guy were to compare piston tops you would likely see if you have doubled up on washers by the spray pattern the spay usually hits right at the bowl corner. If it was fueling you would think you would have had pound (fuel knock) but ya never know!

The tops of the pistons look comparatively the same, what happens is it burns down by the side in a small area and melts the ring landings which are a different material (steel of some sort maybe? IDK) and then that tends to work around the piston within its own grove until finally pieces of it works it's way back up on top pf the piston and then the noises start, other than that the truck runs ok but develops blow-by. Last time I shut it down at the first signs of a problem and replaced that one piston and liner and this time it had done a lot more damage to the piston before any significant signs of trouble showed up other than the blow-by. The head on that end had to go to the machine shop and I decided I would do the other 5 holes and rods and mains this time so I'll be starting out with a new engine again....and I Will be cutting the fuel back a bit but I doubt it will be the answer to this specific problem.

 

  I'm still liking the two washer theory although I worked on that head yesterday myself. I was checking the valves and can specifically remember comparing that nozzle to the one on both sides of it and can't believe I wouldn't have noticed a difference in the protrusion of it in reference to the surface of the head since I was inspecting it for damage then.

[farmer52]

Have you checked the spray pattern of the nozzle?  If it is burning in a small area outside the piston bowl, that might indicate a poor spray pattern.

[Mcrafty1]

5 minutes ago, farmer52 said:

Have you checked the spray pattern of the nozzle?  If it is burning in a small area outside the piston bowl, that might indicate a poor spray pattern.

Thanks, Yes we checked that the first time and replaced the nozzle the second time just because that was all we could find to blame it on then but I guess that wasn't it because here we are today.

[fjh]

53 minutes ago, Mcrafty1 said:

The tops of the pistons look comparatively the same, what happens is it burns down by the side in a small area and melts the ring landings which are a different material (steel of some sort maybe? IDK) and then that tends to work around the piston within its own grove until finally pieces of it works it's way back up on top pf the piston and then the noises start, other than that the truck runs ok but develops blow-by. Last time I shut it down at the first signs of a problem and replaced that one piston and liner and this time it had done a lot more damage to the piston before any significant signs of trouble showed up other than the blow-by. The head on that end had to go to the machine shop and I decided I would do the other 5 holes and rods and mains this time so I'll be starting out with a new engine again....and I Will be cutting the fuel back a bit but I doubt it will be the answer to this specific problem.

 

  I'm still liking the two washer theory although I worked on that head yesterday myself. I was checking the valves and can specifically remember comparing that nozzle to the one on both sides of it and can't believe I wouldn't have noticed a difference in the protrusion of it in reference to the surface of the head since I was inspecting it for damage then.

 

[fjh]

54 minutes ago, Mcrafty1 said:

The tops of the pistons look comparatively the same, what happens is it burns down by the side in a small area and melts the ring landings which are a different material (steel of some sort maybe? IDK) and then that tends to work around the piston within its own grove until finally pieces of it works it's way back up on top pf the piston and then the noises start, other than that the truck runs ok but develops blow-by. Last time I shut it down at the first signs of a problem and replaced that one piston and liner and this time it had done a lot more damage to the piston before any significant signs of trouble showed up other than the blow-by. The head on that end had to go to the machine shop and I decided I would do the other 5 holes and rods and mains this time so I'll be starting out with a new engine again....and I Will be cutting the fuel back a bit but I doubt it will be the answer to this specific problem.

 

  I'm still liking the two washer theory although I worked on that head yesterday myself. I was checking the valves and can specifically remember comparing that nozzle to the one on both sides of it and can't believe I wouldn't have noticed a difference in the protrusion of it in reference to the surface of the head since I was inspecting it for damage then.

Obviously, Liking and proving are two different things ,Ya need to re install the injectors on the bench and see if they protrude differently on the failed hole! Sounds like you've tried everything else!The washer is the thickness of a dine you likely would have noticed but worth looking!

[Dirtymilkman]

I know this sounds stupid but I'd replace the injection lines. Or at least number  5. If a previous owner put a wrong line on that can throw off injection timing on that cylinder. They all gotta be the same length. 

[Mcrafty1]

On 8/22/2016 at 4:41 PM, fjh said:

Obviously, Liking and proving are two different things ,Ya need to re install the injectors on the bench and see if they protrude differently on the failed hole! Sounds like you've tried everything else!The washer is the thickness of a dine you likely would have noticed but worth looking!

The nozzles are out of the head now, when it comes back from the machine shop I'll check and make sure the sealing washers are not doubled up. Thanks, Allan

[Mcrafty1]

On 8/22/2016 at 10:13 PM, Dirtymilkman said:

I know this sounds stupid but I'd replace the injection lines. Or at least number  5. If a previous owner put a wrong line on that can throw off injection timing on that cylinder. They all gotta be the same length. 

Actually I believe that line has been replaced sometime during this whole ordeal....just when I can't say but I'm certainly going to look into it. I think when I do find the culprit it's going to be some stupid little thing like that. Thanks for suggesting that....you have me thinking about now.

[Mcrafty1]

Well, The head is done...and checked for double sealing washers, nothing there. The fuel line was changed on that cylinder the last time we replaced that piston so no smoking gun there either. Looks like I'll be putting it back together without having a fix for the ongoing problem....sigh, I suppose I'll just pull that head and replace no. 5 every spring before I start using the truck and minimize my losses do to down time. I don't have anywhere else to turn.

[fjh]

Bummer 

[Mcrafty1]

If, during re-installation of the head I find something that we've overlooked I'll be sure and post it up for all to see. Thanks to all for the help and suggestions. 

 

...It doesn't bother me so much that it is doing what it's doing, as it does that I can't figure it out. lol

[fjh]

It would be nice to have a smoking gun

[Mcrafty1]

For sure....but im out of ideas so back together she goes

[Dirtymilkman]

Liner protrusion good? Block deck is good? That'd be the center piston in the head so that is the "hot" one. It just really sounds like overfueling on that piston.