How To: Restoration of Ford M8 armoured car US Ordnance number 7373

[David Dunlop]

Darryl.

Do you have a bare splined shaft available the gen pulley will fit on?

If so, you could centre the pulley on the shaft and place the assembly between two hard level surfaces (steel or glass is best) and see if the assembly stays where you placed it or rolls to a different point and stops. If the latter, the assembly is out of balance and has stopped where the most weight is at the bottom.

Seems odd that somebody milled out some metal between the fins on that pulley on the ‘short side’ of the shaft hole. I would have thought that would have made the ‘long side’ even heavier.

David

[lynx42]

Hi Darryl, any reason that you have put the generator pully on back to front? The fins should be up against the generator face not out there where you can get caught on them. The fins are to push cooling air through the genny.

Doing a great job. I'll have to pressure feed my Lynx hydraulics to find the leaks.

Cheers Rick.

[Big D]

Hi Rick

Good spotting. I had been playing around with the pulley and its alignment at the time. I have put it on the correct way since then and it seems to spin evenly enough.

Yes, I was impressed with the pressure bleeder option and ordered one of these from the US. It seemed to have pretty favourable reviews from what I had seen and really the only drawback with it was the lack of a release switch on the output. The hydrovac should be done this week so I will hopefully have this bleeder by then and will use it to bleed the brakes.

[Big D]

Hi David

Not a spare one, I’m afraid. I did play with the pulley on the generator spline both ways and I actually think it will spin okay. I will keep an eye on it when we hopefully fire up the engine next week.

[lynx42]

Originally Posted by Big D

Hi Rick

........

Yes, I was impressed with the pressure bleeder option and ordered one of these from the US. It seemed to have pretty favourable reviews from what I had seen and really the only drawback with it was the lack of a release switch on the output. ......

I reckon I could make one of them up with a garden weed sprayer. Let you know.
Cheers Rick

[Big D]

Hi all,

This weekend, a friend and I fired up the M8 engine for the first time. Ed is a good engine man and he worked on British Army military vehicles in his younger days. He did most of the internal assembly and set up on the block.

I had completed the assembly of all the accessories on the engine on a tubular steel stand and I set up a wooden platform in front for the radiator so I could run that at the same time and make sure that was working okay as well. I don’t have an original upper radiator pipe so I cut a bit of pipe to temporarily use. This bit of tube is a bit longer than what the parts manual specifies but I needed the extra length so I could give the fans enough clearance from the makeshift radiator platform.

I remote wired the engine into the hull of the M8. I thought this was a good idea initially but upon reflection introducing a whole lot of other variables into the start-up equation was maybe not the best move, when all the wiring in the hull was untested. It worked out alright in the end though.

The first switch on produced nothing and we found the starter solenoid wasn’t engaging. As I learnt on another forum, the M8 is wired as such that when the ignition is switched on, 12 volts is supplied to the control terminal on the starter solenoid. When the starter button is pushed, it grounds that 12 volts which activates the solenoid and sends 12 volts to the starter motor post. I wasn’t completely sure the solenoid I had needed the 12 volts on that post grounded, or needed 12 volts sent to that post, to actually activate the solenoid.

After checking with another M8 expert (thanks Willy) I confirmed the solenoid I had fitted was the correct type. After a bit more tracing I found that the cause of that issue was a bad earth on the instrument panel, so the grounding through the starter button was not taking place. After working through the circuit diagram again I couldn’t see how the instrument panel was actually grounded, as it is mounted on rubber insulating blocks. Anyway, I ran an extra length of wire from the instrument panel body to the panel mounting bracket on the hull. This gave the ground required.

Once I had the 12 volts coming off the solenoid to the starter motor, I found the starter motor wasn’t working. After a look at that I found that one of the brush springs was shorting out against one of the nuts holding the brush pigtails to the starter casing. Those wee springs don’t like high current through them and it damaged the spring. I had to search a bit to find a spring locally but a retired auto electrician I know managed to find one in his box of spares that would do the job. We put it all together and it worked but the nut on the little screw holding the brush pigtail to the case was still very close to the brush springs. I have wrapped the nut with a strip of insulation tape in the meantime but both of us agreed that the nuts are probably not standard. I have a new set of brush springs coming from the US and when I fit those I will find a nut with a lower profile.

I rigged up a fuel supply to the newly built fuel pump and first touch of the starter button on the instrument panel, the engine ran. It sounded very nice and seemed very responsive. The NOS fuel pump which I had put new neoprene diaphragms into worked well.

There were a couple of minor issues during our various tests, like one of the water pipes coming off and spilling water everywhere. I have been advised that I will receive the ‘Golden Screwdriver Award’ for not tightening the screw on the clamp enough. There was also a slight leak in the gasket in the thermostat housing, which I’ll sort out when I actually fit the thermostat.

After a number of starts we found the battery was starting to slow. I did a few voltage checks and it didn’t look like the generator was feeding the battery enough so I will check that and the regulator out.

I have a new calcium type N150 battery but I don’t have a compatible battery charger here and I wasn’t super confident it was being charged fully prior to us starting the engine. It certainly looks like that is the case now so I will order a new calcium compatible battery charger tomorrow.

It’s a great feeling seeing and hearing the engine run and knowing most of what is attached is operating correctly.

I will fit the clutch assembly and gearbox next and then fit the correct ignition lead terminals now that they have arrived (thanks Brian). They need a little ferrule at the end to stop the wire coming out which I have not seen available so but I might have to come up with an alternative for that.

After that, my next step is to fit the newly rebuilt brake hydrovac into the hull and complete all the plumbing on that. I will then pressure bleed the brake system and that should get the hull pretty much prepared for fitting the engine and gearbox assembly.

Here are a few videos of us running the engine, testing the generator and regulator etc:

https://youtu.be/sOCfMGhI3mU

https://youtu.be/VUlI76GAZBE

https://youtu.be/If3TuDe7TIQ

https://youtu.be/dMuRJgVTYV0

[Big D]

More photos.

[Big D]

Hi all,

I managed to get a week off work and I’ve had a busy seven long days straight working on the M8, so this will be a lengthy post. I am aiming to get the M8 rolling for an airshow next month so the pressure is on…

I spent the best part of 3 days fitting the hydrovac, sorting out the correct fittings, putting in the last of the plumbing and with the help of my retired mechanic friend, bleeding the brake system. It was an education working on the brake system of this vehicle. I think my rough count was over 100 individual hydraulic connections for the brakes on this thing, and of course over 100 sources of potential leaks! I spent a fair bit of time going around each wheel and each axle checking all the connections before filling the master cylinder and starting the bleeding process.

I used the new power bleeder this time and it worked very well. However, its operation on the brake master cylinder was not straightforward. M8 and M20 owners will know that the brake master cylinder sits quite close to the sloped front of the hull. So close in fact, that I couldn’t get the cap for the pressure bleeder to screw onto the reservoir with the standard NPT straight fitting. I tried removing that and replacing it with a brass NPT elbow. Even then, I found it was still too close to the sloped part of the hull to screw the cap on. There wasn’t much in it so I got the grinder out and shaved a few millimetres off the top and top edges of the brass fitting to see if that would give me the clearance to get the cap on the reservoir. Alas, it was not, so I finally had to undo the six bolts that hold the large bracket that the brake and clutch master cylinders are bolted to and drop the whole assembly by about 2-3 mm. A bit of a pain in the butt, but that got me the clearance to get the pressure bleeder cap and elbow onto the brake master cylinder. I flared a bit of 3/8” tube and fitted it to the elbow and then used a hose clamp to attach it to the pipe on the pressure bleeder.

The manual on these things recommends 15 psi to bleed the brake system. We didn’t need anywhere near that much and did the whole system while at about 7 psi. The 7 psi was enough to get fluid spewing out of one of the joining connections that I had obviously completely missed when tightening everything! Note that the photo shows the pressure bleeder connected to the clutch master cylinder in preparation for that.

We bled from the top junction block that I made and then the three bleed points on the hydrovac from rear to front. The pedal was still spongey at that point so we went around the wheels after that. The pressure bleeder was very handy as it meant two of us could be outside the vehicle moving the equipment around and cleaning up any mess coming from any of the bleed nipples. All that was required was to keep a couple of litres of brake fluid in the pressure bleeder and to keep an eye on the gauge on the bleeder to make sure the pressure hadn’t dropped. I only had a problem with two connections; the flaring I had done on the tube from the bleed junction to the hydrovac was not good enough and that connection was seeping. That required pulling the section of tube out and redoing it, along with fitting a better quality tube nut. The brass tee connection on the front axle is also seeping a bit so I will need to find another one of these. I can recall being suspicious of this connector when I fitted it but it was the only one I could find at the time.

The brakes now feel good at the pedal with the required ¾” play. I just need to go around all the wheels and adjust the shoes now.

I also tidied up the ignition system with the new connectors. I couldn’t source the wee ferrules that hold the end of the wire in the plug but thanks to Brian for his suggestion about a blob of solder at the end. This stops the wire pulling out but still allows the plug to rotate on the wire for fitting.

Bolting the ignition lead tubing down requires getting the thermostat housing fitted at the same time, as one of the housing studs secures the ignition lead tubing. I made a thick gasket for the housing so that it would help align the thermostat in the housing. My retired mechanic friend tells me this thick gasket material is similar to the Vellumoid material specified in the parts manual. The gasket needs to be the thickness of the lip that goes around the body of the thermostat. The material is not easy to cut neatly but it helps to centre the thermostat in the housing when you bolt it together. I had read a forum post about these thermostats just ‘floating’ in the housing, and I suspect that was because the gasket material wasn’t thick enough and the hole in it was too big and it didn’t centre the thermostat.

I got the new battery charger for the calcium N150 battery. This is a seven stage smart charger and automatically works out the chemistry and voltage of the battery that is being charged. This brought the battery up to a fully charged state.

Ed and I ran the engine again and it started very quickly. We let the engine warm up and tested the operation of the thermostat. Ed also checked all the tappet clearances. It’s interesting that the M8 tappet clearance is 0.010” for both intake and exhaust whereas the Scout Car is 0.06” and 0.08”. I wonder why the difference….

There are still a couple of wee issues. The temperature gauge I have is a French one and doesn’t work with either sender I have. I have the correct US temperature sender in the head now so I will have to find the correct matching gauge. Thanks to Brian for sending me the details on that.

The voltmeter doesn’t work and I believe it is faulty. The ammeter also doesn’t appear to work but I need to do a bit more work on that to see if it is the gauge or something else. The fuel gauge now appears to be working which is good news.

The oil pressure on this engine goes to 30psi almost straight away and seems to hold there. Whether I have the gauge and sender matched correctly, I’m not sure, but we tested the oil pressure using a standalone gauge and it shows a similar figure. Out of interest, the scout car engine I recently rebuilt also sits on 30psi and it gets to that reading within a few seconds of start-up, unlike the experiences of others that I had read about of waiting 40 seconds for the oil pressure to show on the gauge.

There is still a question mark over the generator output/operation. I’m pretty sure I just haven’t got it earthed well enough on the block so I will remove that and remove the paint off the mounting surfaces and try it again once in the hull.

I’m also not sure that the starter motor is functioning at 100%. It rotates and starts the engine but it doesn’t appear to spin at the speed it did initially. I suspect the brush spring but the new ones I sourced should be here this week.

After the testing of the engine I removed all the wiring I had temporarily fitted and fitted the clutch assembly and gearbox. The shorter side of the hub on the clutch disc goes inside the pressure plate. I used an output shaft to align the clutch plate. You can’t get this shaft all the way into the new pilot bearing but it allowed me to align it well enough to get the gearbox spline in there.

All looks good at this stage for putting the complete engine assembly into the hull next week. In preparation for that, I’ll remove the fans, carb, starter motor, exhaust and generator. I figure the fewer things to get in the way, the better!

More to come next week!