piston photos - cracks, chips, etc

[CajunM35A2]

Please take a look at these photos and provide feedback:

This piston has a small chip or crack


This other piston has a small chip or crack as well


The radius going into the center hole on this piston is sharper than the radius of the piston shown in the photo below. I have two that look like this.


"softer" radius... - I have two that look like this.


Some might say go ahead and use all of them; others might advise to replace the two with the cracks or chips.

I would prefer to replace the two at least with the cracks/chips. Does anyone have a couple of take-out pistons that I can beg or buy to replace these?

 

[73m819]

I would think that ALL the pistons should be the SAME, if not there will be a slight inbalance

 

[deuceaid]

Sorry I dont have experience with this motor, but with any others,,, If I have broken it down that far, I would swap all for the "safe" peace of mind.....sorry thats all I have. Also thanks for posting pics of motor innards.

 

[gimpyrobb]

Wow, that second one looks the worst. Have you had the injectors tested? I wonder if clogged nozzles would do that?

 

[m139h2otruck]

It looks like this engine may have injector issues. Leaky injectors will "burn" pistons and it looks like this has started. I would change all pistons, rebuild/replace the injectors & check the fuel pump for delivery and timing.

 

[CajunM35A2]

injectors tested

Thanks for the comments.

Yes, I had the injectors tested. No. 6 was shot. The no. 6 piston is not one of these, but I did post a photo of it a few weeks back.

I have the 5 injectors that tested good and a new one to replace the bad one. The heads were all rebuilt at a diesel shop.

 

[CajunM35A2]

injectors; fuel ip

It looks like this engine may have injector issues. Leaky injectors will "burn" pistons and it looks like this has started. I would change all pistons, rebuild/replace the injectors & check the fuel pump for delivery and timing.

See my post above about injectors.

The fuel IP has been changed with a fresh rebuilt one at the start of this process.

 

[mhassett]

I would change out the pistons.
MHassett

 

[Bill W]

I would say that one time or another that the nozzles weren't atomizing the fuel correctly and instead they were spraying fuel directly on the (hot) piston., From what I've read in the past this was a common problem with single port/nozzle injectors and the military then went to the 2 port injector nozzle

 

[gimpyrobb]

AHH, good point!

 

[dodgedougak]

Bill W hit the nail on the head. Sure looks like fuel impingment to me.

 

[Capt.Marion]

Aren't Multifuel injectors supposed to spray a stream of fuel into the piston cup, using the heat of the piston to vaporize the fuel (whatever it may be), and thus cooling the piston?

It seems like these injectors would have to be magical to atomize all of the different fuels that we put in them--and these engines don't have the injector clatter that you hear on Cummins engines and other traditional diesels.

EDIT: more clarification here, from MAN, on the Multifuel design: http://www.steelsoldiers.com/deuce/31227-i-got-some-information-back-m-n-multifuel-engine.html.
It could be a leaky or dripping injector, though.

 

[dodgedougak]

Been doing diesel engines for 40 years and every injector I have seen and tested has been designed to "atomize" the fuel. That is to turn the liquid into a cloud of vapor. If it drips or sprays a stream, it is NG> The vapor is then ignited by the heat of compression. Some old hot-bulb semi-diesels used a blow torch to heat a hot-bulb area to assist in ignition but that bulb was in the head and cast iron. If you have a direct stream of liquid fuel impinging on an aluminum piston, it will destroy it. I am just learning about these multifuels, but don't see that aspect as different. The shape of the piston is designed for compression ratio and especially to set up air swirling to assist in complete air fuel mixing and scavenging. Just for info, we have marine diesels that burn residual oil and atomize that. This stuff is the consistancy of pudding until you heat it over 200F. Anyhow, hope some of this helps.

 

[kastein]

diesel and multifuel engines are two different beasts. My impression from reading everything I could about multifuels is the same as Capt. Marion's. The fuel is squirted into the piston head cup and burns from the surface down as the piston descends. This is one of the reasons we get crummy fuel mileage, but is the reason the motor can run on such a wide range of fuels.

EDIT: aren't these pistons steel, not aluminum, also?

 

[Bill W]

diesel and multifuel engines are two different beasts. My impression from reading everything I could about multifuels is the same as Capt. Marion's. The fuel is squirted into the piston head cup and burns from the surface down as the piston descends. This is one of the reasons we get crummy fuel mileage, but is the reason the motor can run on such a wide range of fuels.

Yes maybe they were set up that way originaly but after cronic problem with cracked piston the military went to the duel injector nozzles to better disperse the ( atomized) fuel to which it corrected the cracked piston problems.
A member here once posted a link to a article done by Army tank and automotive command outlining the problems that were occuring with muti-fuels in Vietnam and cracked pitons were cronic and the cure they came up with was redisgning the nozzles from single to duel port so as not spray directly on the piston head.
I have a original Multi-fuel trouble shooting manual put out by Continental Motors ( 1968 ) and its specificly states that if you find single ported nozzle in a engine that you are to replace them imediately with the updated duel port nozzles.

 

[Squirt-Truck]

But doesn't the Continental manual refer to the -1 engine? The -1A engine was (is?) produced with single hole nozzles as late as 1990. The C and D engines I think had the cracking issues due to excess fuel impingement on the top of the piston.

Look at this piston, does it look like it has a different geometry on the nozzle slot? This is a 1990 production piston in an engine with single hole injectors.

 

[cjtroutt]

I would pull the engine out major it and update it to to standers.
Here is the web site for New parts www.herculesengine.com/military.htm