Sherman M4A2 Detroit Injectors

[Malcolm Towrie]

Originally Posted by Andrew Rowe

Hi Malcolm,
Are you running these N65's currently or are you using the older type injector?
It is a really good idea to have a fuel pressure gauge inline so you know exactly the fuel pressure going to the injectors and also what your by-pass cuts in at for the fuel pump. Also very critical to have your return line with the .080 thou,
(2mm ) restrictor hole on the end of the return line from the injectors as this holds the pressure for the injector, Cheers Andrew.

Hi, Andrew, yes, these engines both have the brown N65 tag on the injectors. I’m not sure what the “brown” signifies but it seems to be important.
I don’t have a pressure gauge installed on the engine but I did run the fuel pump on the bench and confirmed that the pressure regulator opened at 75 psi, which is in the spec range.
I pulled the elbow fitting on the return gallery and confirmed it does have a restriction orifice. Looks more like the 0.055” orifice listed as one of the options rather than the 0.080” one.
Malcolm

[Tony Smith]

Originally Posted by Malcolm Towrie

Hi, Andrew, yes, these engines both have the brown N65 tag on the injectors. I’m not sure what the “brown” signifies but it seems to be important.

Malcolm

Is an N65 a big enough injector size?

I have a few Injectors from Australian Grant Tanks, and these were the earlier type, but a Number 80. I realise that you can improve the performance, and efficiency (and emissions!) by upgrading to later versions of injectors and also the Cylinder liners, but would a N65 size Injector give equivalent power and performance to an earlier 80? I understand the earlier Injector has a different nozzle pattern that gave less efficient atomisation, but fuel volume per injection cycle is what makes power.

[Malcolm Towrie]

Originally Posted by Tony Smith

Is an N65 a big enough injector size?

I have a few Injectors from Australian Grant Tanks, and these were the earlier type, but a Number 80. I realise that you can improve the performance, and efficiency (and emissions!) by upgrading to later versions of injectors and also the Cylinder liners, but would a N65 size Injector give equivalent power and performance to an earlier 80? I understand the earlier Injector has a different nozzle pattern that gave less efficient atomisation, but fuel volume per injection cycle is what makes power.

Tony, neat photos!
I checked through the manuals I have but I couldn’t confirm what injectors these tanks came with originally. All I know is the Detroit manual for the 71 series of engines lists the N65 as an option.
I found out today that one of the injectors I removed from this engine was actually an N60. It was the only one with the ID tag on the body missing. Somebody must have installed it hoping it was close enough! The part numbers stamped on the injector tip and the plunger gave it away.

The engine is running much more smoothly, with easier starting and much less vibration, smoke, and eye-watering fumes after replacing these two injectors. #6 is the only one left to be replaced as it doesn’t cause any significant rpm drop when shorted.

Our other Sherman has N95 injectors in both engines. That size isn’t even listed as an option in the Detroit manual! The manual is a lot more modern than the tank so probably emission concerns left it off the option list. A previous member here must have decided, to hell with the smoke, let’s get some real power.
Ironically, it’s no more powerful than this tank, but of course there are a multitude of reasons why that may be so.
Malcolm

[Andrew Rowe]

From what I have discovered, it is not always that simple to just keep putting bigger injectors in. From the old HV series to N series, things like injector rack have to be changed and compression ratio and type of liners have to all have consideration , as there are several options available, Cheers Andrew.

[Malcolm Towrie]

Interesting, Andrew. Any idea why liners would have to be changed?

I would have thought blower output would be a factor too. Dumping more fuel in would require more air, at least at wide open throttle when the engine doesn’t have excess air. It’s gotta be able to burn all that extra fuel, not just belch it out as black smoke!

Each injector type doesn’t just squirt a controlled amount of fuel in over the throttle range, it controls the timing of the injection too by varying the shape of the helix cutout in the plunger.

Never worked on a diesel before. There’s a lot to learn!

Malcolm

[Andrew Rowe]

You are right in the fact that more diesel requires more air. There are the standard old liners that had a couple of rows of small holes all the around the liner and then for the bigger injectors there are liners with large e-elongated holes. You can view what type of liner you have by removing one of the little side covers on the side of the engine, and that will indicate whether the engine will appear to have been built matched to the injectors. There are quite a few different configurations that can interchange on these motors , from injectors to liners to different heads, 4 valve to the old "low block" 2 valve head. To get the power with bigger injectors the 4 valve head is needed. Cheers Andrew

[Tony Smith]

And don't forget, too, Malcolm, that despite the presence of the Exhaust Valves in the head, the 6-71 is still a 2 stroke engine and the liners (specifically the port shapes and heights) control the timing of the Intake Cycle and cylinder scavenging, in much the same way as a camshaft controls valve timing.

Over the many years of the GM/Detroit Diesel engines, a wide variety of liners were developed to give different operating parameters, just as many 4 stoke engines had a range of camshafts for differing applications. The 6-71 has been used in Trucks, Earthmoving Plant, Locomotives, Boats, Gensets, Waterpumps (and even Tanks!). Each application had a unique need for power, torque and rpm range. The port shape in the liner is modified to optimise engine output to application.

[Malcolm Towrie]

Originally Posted by Andrew Rowe

You are right in the fact that more diesel requires more air. There are the standard old liners that had a couple of rows of small holes all the around the liner and then for the bigger injectors there are liners with large e-elongated holes. You can view what type of liner you have by removing one of the little side covers on the side of the engine, and that will indicate whether the engine will appear to have been built matched to the injectors. There are quite a few different configurations that can interchange on these motors , from injectors to liners to different heads, 4 valve to the old "low block" 2 valve head. To get the power with bigger injectors the 4 valve head is needed. Cheers Andrew

We’ve got the liners with large holes. We had those airbox covers off to check out the pistons, ring, and bores. Pretty handy!

This tank has 4-valve heads on the original 2-valve blocks. Strangely enough, the other tank with the larger N95 injectors still has the original 2-valve heads.
Malcolm