Info needed: JXD versus JXLD

[Big D]

Hi all,

I’m looking for some advice on the Hercules engines for the M8/M20 armoured cars and whether the resident experts have experience with the JXLD engines as opposed to the JXD. I see some have fitted JXLD engines to M8/M20’s but I was wondering whether they were left in stock condition or whether they were ‘made to look’ like a JXD setup.

I need to put another Hercules engine together for an M20. I have several JXD blocks here but all require lots of work including removing stuck pistons and machining/sleeving the bores. Some blocks have holes in the bores so I don’t even know if they are viable options yet. I have plenty of pistons, rings, valves, bearings etc and providing one of the blocks is suitable, I could put something together. I have carburettors, fuel pumps, manifold etc but would need a timing cover, sump and a few other bits and pieces.

The other option I have is a Hercules JXLD engine which was in the M20 I have here. I’m guessing that this M20 was retrofitted with the JXLD when it was in the hands of the Greeks. I still need to investigate the internals of the engine but it is certainly in complete condition and has the required timing cover and mounts.

I understand the JXD and JXLD short blocks are similar, with the JXLD having a longer stroke and the external parts located differently on the block. There seems to be a lot of similarities and the timing cover, head and starter motor setup appear the same as the JXD. I understand the M8 manifold is a bolt on and the generator mount is the same as the M8.

The JXLD water pump and distributor/coil assembly is different to the M8/M20 JXD setup. The fuel pump is located on the other side of the block which pushes the oil filler/breather to a different location.

Subject what I find internally with the JXLD, what I have in mind is to make it look like a JXD as much as is possible and fit it to the vehicle. I can rebuild the other JXD blocks at a later time when finances allow it a bit more.

Has anyone tried to move the fuel pump on the JXLD to the other side, like the JXD? This would allow the breather/filler to be moved to the spot the fuel pump is currently located. Alternatively, I could just leave the fuel pump where it is without losing too much.

From what I can see I could fit a JXD water pump which would provide the right angle for the JXD distributor.

Has anyone tried to do this? What other hurdles are there?

[Ron King]

I looked at using parts or fitting a JXLD to a Studebaker US6.
From memory the block was slightly longer and the inlet manfold on the JXLD was slightly longer and would not inter change with a JXD one.
I think JXD series on motors the fuel pump could be fitted either side......one side used a push rod and the other side did not.

Also as you mention JXLD.internals slightly different and alot harder to find replacement parts if needed......JXD parts are much easier to find.
The timing case bolt up I think was the same.

[Big D]

Hi Ron,

Thanks for the reply. I was told that the M8 manifold was a straight fit to the JXLD block but perhaps I better check that. I don't have the M8 manifold here but I do have a White scour car one here so I could use that. The stud spacing is the same on them from what I recall.

Yes, I think the fuel pump could be transferred over to the other side without too many problems. I'm fairly sure the fuel pump runs off the camshaft on the JXD and so it probably runs off a pushrod on the JXLD. It would just be a matter of cutting the opening on the mount boss and getting the mounting holes tapped in the right place.

Another person has suggested using an electric fuel pump instead. I have a spare 12 volt electric fuel pump so I could simply put that in place and fit the JXD breather and oil filler to the vacant fuel pump hole, and remove the JXLD breather and blank that hole off. That could work...

[Lynn Eades]

Darryl, I have a book called Motors truck and tractor repair manual. It says the JXLD has a 1/4 inch longer stroke. and is a 339 cu. in. as opposed to a 320 cu. inch. JXLD is 131 h.p. while the JXD is only 84 h.p. Quite a difference. The big engine has a 6.9 to 1 cop ratio while the small one is only 6.5 to1.
The bores of both are 4 inch. The JXD is 4 1/4 stroke and the big engine is 4 1/2 stroke. this might mean that the pistons are not interchangeable (piston height) or the rods are different? Cranks are different? Look carefully. The JXD engine was used in many trucks not heard of now and seems to have originated in 1936.

[Lynn Eades]

Darryl, I have a book called Motors truck and tractor repair manual. It says the JXLD has a 1/4 inch longer stroke. and is a 339 cu. in. as opposed to a 320 cu. inch. JXLD is 131 h.p. while the JXD is only 84 h.p. Quite a difference. The big engine has a 6.9 to 1 comp. ratio while the small one is only 6.5 to1.
The bores of both are 4 inch. The JXD is 4 1/4 stroke and the big engine is 4 1/2 stroke. This might mean that the pistons are not interchangeable (piston height) or the rods are different? Cranks are different? Look carefully. The JXD engine was used in many trucks not heard of now and seems to have originated in 1936.

[Big D]

Hi Lynn,

Thanks for that. Very interesting. It confirms what I thought about the longer stroke but that is quite a power difference between them. I would have been better off with that engine in the M8!

Yes, that makes sense about the parts potentially not being interchangeable. My inclination at the moment is to not get too deep into messing with the internals of the engine. If the JXLD is a viable runner I am leaning toward fitting/sourcing the M8/M20 manifold, water pump, distributor and oil filler/breather, and then running an electric fuel pump for the moment. That would certainly make it look the part.

I was going to have to fit/source all those things anyway with rebuilding a JXD, so I really lose nothing with using the JXLD in the meantime and it would buy me some time to get some more money to get the JXD done.

[Lynn Eades]

There are plenty of options in electric pumps and an electric pump will never dilute your fuel and ruin an engine> Mostly they are pusher pumps and should be installed at the tank end. just be sure to match delivery pressure (and vol.) to the carb requirements or add a regulator as well. You can always turn off the pump if you think you've flooded it, and with the flick of a switch you'll have fuel to the carb.

[Big D]

Thanks Lynn,

Good advice.

[Big D]

Hi all,

I looked at the JXLD engine a bit more today.

I note that the water pump and distributor arrangement doesn't allow all three mounting bolts for the generator mount to be used. I'm not sure that is a good idea with the weight of that generator. The top lug which attaches to the support on the head had been broken off this mount and I wonder if the two bolt mounting instead of three had contributed to that.

The fuel pump is operated by a pushrod running horizontally from the camshaft across the block. I looked at the JXD blocks I have here and the fuel pump on the other side runs directly off the camshaft.

I've been told by someone else who has run a JXLD in their M8 that the M8/M20 manifold is a bolt on.

I have some JXD water pumps here and it looks like they will just bolt on and mate correctly with the JXLD oil filter holder assembly. What is the purpose of the box between the water pump and the oil filter? I'm looking at fitting a JXD oil filter canister.

Has anyone tried fitting a JXD water pump and M8/M20 distributor? Will the distributor timing 'work itself out' with this engine with it being fitted to the JXD water pump? I'm just wondering how compatible that distributor is with the JXLD engine and how the timing will be affected.

Does anyone have a spare water pump inlet for the M8/M20? The JXLD one is routed differently so I can't use the M8/M20 lower radiator pipe as it is.

[Grant Bowker]

Originally Posted by Big D

. What is the purpose of the box between the water pump and the oil filter?

With no actual exposure to theses engines to make intelligent guesses with, is it possible that it functions as an oil cooler?

[Paul Jones]

Originally Posted by Grant Bowker

With no actual exposure to theses engines to make intelligent guesses with, is it possible that it functions as an oil cooler?

Correct one of our guys over here has a JXLD in his WSC, by the way just like the JXD there is JXLD with different combinations of accessoires attached, for example orignally our guy had the starter motor on the drivers side (had to get WSC bellnousing) his petrol pump though is on the passenger side (no hole on the drivers side)

But the oil cooler might be a requirement as Hercules might of found it runs too hot.....

Regards
Paul