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