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

[Big D]

Hi all,

I posted here some time ago about a Hercules JXLD engine that I wanted to get running and fit into an M20. I am rebuilding another JXD engine at the moment but my plan is to keep that engine as a spare, providing I could get this JXLD running reliably.

I’ve now made some good progress on getting the JXLD running. The engine was stuck (not seized) when I got it. I rebuilt the M20 gearbox and fitted it to the engine. Then over a period of months I kept pouring lubricant into the bores and gently worked the engine in top gear. It came free relatively quickly. Since then I have spent a fair bit of time adding accessories to the engine and testing the engine as I progressed.

I was wanting to make the JXLD look as much as possible as a wartime Hercules JXD engine, removing where possible, JXLD fittings and replacing them with JXD fittings. I removed the JXLD engine filler and oil filter canister and replaced them with the JXD parts. This meant I couldn’t use the JXLD fuel pump. As you can see I am relying on an electric fuel pump and I haven’t yet been tempted to go boring holes in the block for a JXD mechanical pump.

The engine starts almost first time every time and requires little if any choke. The compression is relatively even on all cylinders but not high at about 75-90 psi. I’m hoping this may improve as I get the engine running longer and up to proper temperatures. So far I haven’t found a working oil pressure sender and gauge combination so I have been using a plug in testing oil pressure gauge. I’m assuming that gauge is accurate and the oil pressure reads about 35-40psi.

I initially did short runs of the engine without the radiator connected and all appeared well. I’ve plumbed the radiator in now, filled the system with water (for starters) and dealt with the initial leak points. The plumbing seems water tight now so I am starting to run it a bit longer. I have noticed that the waterpump is leaking slightly but have put some more gland material into it so hopefully that settles down. If not, I am inclined to do the seal modification like SteveM8 did to prevent future problems. I haven’t been able to find the JXD cast outlet for the bottom of the water pump so I am using a JXLD outlet and a different shaped piece of pipe to the radiator.

The thermostat is working but again, I haven’t got what I’d call an accurate temperature sender and gauge combination. The one I have got working starts at maximum and then gradually works its way downwards to but what is displayed is not accurate. An IR thermometer is proving handy until I get that resolved.

I initially had problems with the engine flooding. I had fitted a rebuilt carburettor and I did the usual stuff like checking the float level, jets etc, and making sure everything was nice and clean. It was still doing the same thing though and the engine would run for a while, but stop and wouldn’t start again. Removing the carb showed a build up of fuel in the bottom of the manifold and I could see fuel was leaking out of the sides of the carburettor. I replaced the carburettor with a NOS one I had here. I had checked the float level on this one as well and ensured everything was clean. The problem remained though and I started to suspect the electric fuel pump might be delivering too much fuel. I put a test gauge on the pump and found the pump was delivering about 2.8psi so based on what I had read in the manuals I knew that was going to be okay.

I started to look at the ignition side then and found that the times the engine stopped running, spark was poor. I replaced the coil and that solved the problem. Clearly the other coil was breaking down and the engine was not getting a consistent spark. With the new coil fitted, the engine is much happier, even starting with two spark plugs out and sitting on the head while I was testing spark.

I have now got the engine running reasonably stable and it idles happily. I feel the mixture is still too rich though and the engine has a stumble just off idle when blipping the throttle. There is also some intermittent popping in the exhaust.

The engine prefers to have the idle mixture screw at the top of the carb screwed all the way in, and that gives it the best idle. It generally doesn’t require choke to get it started and it starts first time.

I was initially using 91 octane fuel but then went to 98 octane fuel and there was really no improvement.

I had set the ignition timing up manually and then set it again using a timing light. I have also tried adjusting the distributor by hand to give the best idle. It seems to idle best, both a little faster and smoother, when the timing is a little advanced.

Interestingly, I have a similar problem with my White Scout Car. This has a JXD setup and this engine also likes the idle mixture screw at the top of the carb screwed right in to get the best idle. It also has the odd popping in the exhaust and has a very slight stumble off idle when blipping the throttle (not as bad as the JXLD though).

In contrast, my M8 with the same setup starts first time (using the auto choke) and idles like a sewing machine. The idle mixture screw is about half a turn out. It is very smooth with no popping in the exhaust and no stumble when blipping the throttle off idle.

I’ve set all three engines up the same so I’m a bit curious as to what might be going on with the JXLD.

Here is a short video of the engine running:
https://youtu.be/eE_REYUwf34?si=9CbV8PQoW50mFfoV


Do any of the resident JXD experts have any bright ideas on the JXLD and what the problem might be?

I would have thought that it would have been something in the idle circuit that is the cause but with two different carburettors and one NOS, I’m starting to wonder.

Any thoughts would be appreciated.


Thanks
Darryl

[Mike Kelly]

Originally Posted by Big D

I have now got the engine running reasonably stable and it idles happily. I feel the mixture is still too rich though and the engine has a stumble just off idle when blipping the throttle. There is also some intermittent popping in the exhaust.
Do any of the resident JXD experts have any bright ideas on the JXLD and what the problem might be?
Any thoughts would be appreciated.

Have you looked at the spark plug colour ? If the engine is running slightly rich as you suspect, the plugs will be dark grey or a dark brown colour.

Old carbies ( even NOS ) can often suffer from leaky dried out gaskets, this can be a cause of air or fuel leaks within the carby passages.

As a experiment: If you have a Holden Stromberg carby around, give it a try and see if the engine runs better , you will then know if the problem is the original carby or something else.

[Big D]

Hi Mike

Thanks for the reply. Yes, I have checked the spark plugs and they are blackened (but not fouled) as you’d expect with a rich mixture.

I’ve gone back to 91 octane as I received advice saying these low compression engines don’t benefit from the higher octane anyway.

I connected a vacuum gauge to the engine yesterday and played around with the timing. The gauge showed a reading of about 17 1/2 (in the green) when I first fired the engine up today. I played around with the idle mixture screw but got no change in the vacuum. I then manually adjusted the distributor and got the vacuum reading up to 21. See the video here:

https://youtu.be/dlkhzon6CX0?si=wQJrhsXb42FoXoJ_

I think it is quite advanced at that point and I can't see the white mark I put on the flywheel at all with the timing light at that setting. That gives it the fastest idle but it hasn't changed the popping in the exhaust or the stumble as I blip the throttle.

I still suspect something isn't right in the idle circuit of the carburettor so I'll have another look at that.

Thanks for the assistance.

[Mike Kelly]

Hi Darryl

The popping in the exhaust, it might be that some unburnt fuel is being ignited in the exhaust manifold.

You could try fitting a smaller sized main jet in the carby. I don't think the rich running and black spark plugs will be caused by the idle circuit- it might be a high float level or a sticking float causing it to run rich.