luke81

I'm vastly unqualified to be answering, but take it for what it's worth....I've been around heavy trucks my whole life with my family owning a trucking company and doing almost all of our own service work in house. We've battled injector issues on certain engines for years and as far as I'm aware we have never once experienced piston failure from an injector leaning out like you would in a gasser. By nature of how a diesel operates if lean could cook pistons you'd blow up every time you were at 0 throttle.....at least as I understand it. Now I'm very interested to hear the results of this. Thanks for the updates!

turbom700

Been thinking about this more, what do the piston that melted look like and what do the others look like? Cummins blocks like to squish the piston in high HP engines on long runs. That's why places like DJ machine do bed plates to strength the cylinders at TDC, along with add longer rods to help with the rod angle issues that the ISX have.

hotrodford

high temps , high higher or extremely high boost may change , operating characteristics / these motors are super severe service / we have Kid Turbo , Havana Joe , and Buzzi Fabio Tommy Monza and Tyson , all of whom have been there done that , as in run diesel marine / these aint no 2 second 2000 hp dyno queen

HabanaJoe

A diesel can not "lean out" and here is why - a diesel ONLY compresses air and fuel is injected evenly into compressed Hot air, the amount of fuel in the compressed air will burn, if there is too much air the flame will not get hotter since there is no ignition source, it ignites by compress not by artificial means. Too much fuel and it will puddle either in the concave of the piston or down the sides and things will melt.

In a gas engine no matter what type of fuel deliver you have the cylinder compresses both gas and air and there is an ignition source, the air fuel mixture is not even in the cylinder and ignition can occur at the wrong moment compared to there being more or less fuel in an area causing it to lean out.

In your case from my past experiences you may not have melted pistons (I have not seen what you have so I can only make assumptions), you need to look in the cylinder and see where contact between piston and cylinder wall is. Many cases the piston expands too far on the top and drags at the top of the cylinder on the way down, once that happens everything goes bad and pistons look to be melted around the edges then move inward looking like a "lean" burn, the cause was piston expansion not A/F ratio.

Just my 2 cents?

Unlimited jd

Excellent explanation Joe.

PigNaPoke

just a thought, no o-ring to keep oil out of cylinder... they were running away on the extra oil they were ingesting and they torched themselves on the rich condition with extra oil?

Baja Rooster

An amazing project and incredible undertaking. Thanks for keeping us in the loop!

kidturbo

I once argued that same case, and lost...

Joe explained it best, but simple answer is as you lean out, only your power level drops. No throttle body, so fuel is your only speed controller. That said, adding more fuel than can be burned has been used to help cool the pistons in certain setups. But mostly it comes down to timing, timing, and timing.

Normally in stock diesel setups most of the fuel pulse is injected after TDC. In peak power that might equal 60/40 mix, cruise 30/70 range. When you push that number to like 80/20 or even 100% BTDC, cylinder pressures spike, and EGT's are lower, torque is much better. Vs same fueling at 20/80 would yields you lower power and higher EGT because the fuel is burning on the down stroke, and most of the heat going out the pipes.

So to make big power in small cubes you need that extra timing advance. But that also causes the pistons to absorb heat a pressures higher than they would with same fueling and less timing. Pistons are being cooled by oil spraying on the bottom, which wicks it away pretty good, and should keep them from expanding. BUT, if you can't cool em quick enough, or cylinder pressures are too high, then aluminum piston fails. Monotherm "steel" pistons have a much higher tolerance to pressure and heat. One big issue with Cummins, no glow plug holes to stick a pressure sensor in and monitor cylinder pressure when tuning on dyno. So its a best guess what cyld pressures are hitting at XX deg BTDC.

I have a customer with a location you could use an hour north of Salt Lake. But ya might need an ice breaker to cut a path down the river.

outonsafari

i almost want to bet a bottle of jameson the new gear box / overdrive transmissions are finished and on a shelf waiting for installation

class6

Your fuel delivery timing is probably the reason. And you did the pistons in while getting on plane not when they spun. The most and only damage I've done to diesels is while trying to start. Starting ether and or too much fuel at start can do damage.