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

[Big D]

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[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!

[Big D]

More photos.

[Big D]

This week has been another busy one with getting the hull and engine ready for the installation, and then setting everything up once inside.

After another successful test run, I stripped everything off the engine that could potentially get in the way or get damaged while it was being fitted. I also gave the engine bay a freshen up with some new paint. There were lots of marks and scuffs from the many times I’ve got in and out of the thing!

Ed gave me a hand again. We used a strop on the front part of the engine and a strop and chain block on the gearbox end. One of the guys from Action Engineering next door came in with the Hiab truck and we were set to go. I’d have to say the installation of the engine and gearbox assembly was straightforward. The hiab crane made it easy and gave us the height and manoeverability we needed. I was guiding the motor in from the rear of the hull so I didn’t get a picture from the side but you do need quite a pitch on the assembly to get the gearbox under the cross member in the hull. Then it was just a matter of lowering the front of the engine and raising the gearbox end. A short time later I had the engine mounting pins in and the large bolts through the bellhousing mounts into the engine mounts on the cross member in the hull.

While the engine and gearbox assembly was straightforward, the radiator installation was a pain in the butt. The radiator was one of the few things I did not test fit. I didn’t see the point as there were only the two mounts and its positioning would be determined a little by the fan positioning once the engine was in, right?

You might recall that I have reproduction engine mounts, back plate that sits under the engine mounts, and radiator shrouds. The order in which to fit the radiator is to put the fan shrouds over the pulleys, fit the fans, then lower the radiator and fit the shrouds to the radiator. Easy eh? It wasn’t so straightforward for me. The first problem we struck was with the reproduction back plate that sits under the steel engine mounts and over the pintle hook. The cavity in the plate for the pintle hook was too long (toward the front of the vehicle) and extended under the radiator by about 1/2". The result was that the radiator would not come low enough and kept sitting on this raised piece at the back of the plate. I was was left with little option but to get the grinder and cut off disc out and cut a small section of this raised piece out. This allowed the radiator to come down low enough so that it was starting to line up with the fans.

The second problem was in aligning the radiator and shrouds with the fans. I had already had to slot some of the mounting holes on the reproduction shrouds so that the holes lined up with the captive nuts on the radiator, and I don’t think these shrouds were a great reproduction either. The radiator still seemed too low in relation to the motor though and I found I had to use three of the small rubber packers (instead of the one specified in the manual) under each radiator mount to get it to the height required to line up with the fans, once the shrouds were fitted.

I started to suspect the rear engine mounts then. Thanks to Stewart, he confirmed the height of the engine mount at 3 3/8" at the engine end and 1 5/16" at the other end. I measured mine and they measure 3 9/16" at the engine end and 1 5/16" at the other end. So, the engine mounts are holding the front of the engine 3/16” too high. That would account for one of the extra spacers but that would still leave the radiator too high. As it is, the radiator is only sitting about 3 mm above the engine mounts so there is not a lot of room and I'm not sure I would want to go too much lower for the preservation of the radiator.

Were there differences in the radiators and potentially the radiator mounts in the hull? Where the radiator sits now (with three spacers) it looks about right for height but as I say, the mounts in the hull appear too low.

I fitted the plates under the fuel filter. They are not easy to access and fit. Interestingly, the one at the front that sits under the gas tank, will only go in if you remove the gearbox filler plug. Otherwise, this obstructs the fitment of the plate.

I received the new brush springs for the starter motor. These were shown as being replacements for the original brush springs which are part number AL- MZ19. I don’t think they are correct as the end of the spring does not fit centrally on the brush. However, I have ‘adpated’ them to fit and I’m hoping they will do the job.

That’s it for this week….

[Big D]

More photos.

[Big D]

Hi all,

With Covid19 here, I haven’t been able to do much to the M8, but prior to the lockdown I got a few things done.

I fitted all the bits and pieces back onto the engine after I had stripped it back for the installation. Ed and I fired up the engine again and it went well. It looks like my tweak with the starter motor brush springs has done the job. I note though that I have got coolant seeping from the water pump elbow and the thermostat housing where it bolts to the head so It looks like I will have to drain the radiator and fix those up. Bugger.

Thanks to Michael for his tips on my generator problems. You will recall I didn’t think the generator was charging. I had previously read about polarising the generator but just assumed that the auto electrician would have done this when he tested it. Anyway, Michael suggested I check on this and sure enough it was the problem. I did a whole lot more reading again about generator polarising and confirmed I needed to establish what type of grounding my generator had before trying to polarise it. I had read that if you have a non-insulated Field terminal on the generator case, then it was likely you had a Type B grounded generator which is one which is internally grounded. The generator on the M8 was certainly one with a non-insulated field terminal but just to be sure I checked the resistance between the field terminal on the generator and the generator case, while I lifted the brushes. The continuity remained the same which confirmed a Type B internally grounded generator. Once I confirmed that, I removed the Field wire from the Regulator and flashed that field wire to the positive terminal on the battery. Once connected back up to the regulator, that did the trick and I then had a generator that was charging the battery.

I fitted the lower engine covers around the battery side of the engine. I have to say, it does make the engine area look really smart. I need to modify the brake line going into the hydrovac though as the way I have folded it, it won’t allow me to fit the lower engine cover on that side.

I made up a rod for activating the carburettor arm from the throttle slave cylinder. I made it straight although I have seen a number of variations; straight and with several bends in it. The straight one works well in my setup though and the hydraulic throttle works well.

You might recall I had a Voltmeter and Ammeter that weren’t working. I figured I would have a crack at seeing what the problem was with the voltmeter. This is a Stewart Warner voltmeter and not sure if you have ever tried fixing one of these but for starters you have to get the bezel off. I used a small screwdriver with a bent tip on it, to pry the edges of the bezel up. It takes some time so you have to be patient.

Once you have the bezel off, you need to remove the assembly from the outer housing. There are two insulators holding the positive and negative terminals and you have to remove these first. Once they are off, you can push the assembly out of the housing. There are two small rivets holding the faceplate on. I couldn’t see a way to easily remove them without damaging the gauge so I filed the ends of the rivets off and just pushed them out.

Once inside you can see the bi-metal strip that is connected to the pointer. When this is connected to a power supply, the bi-metal strip bends and the pointer moves. In testing, I found the circuit on the voltmeter was open. I couldn’t quite work out why as everything appeared to be connected, albeit through glue holding the wires onto the terminal posts. I eventually found that the wire from one end of the bi-metal strip was not connected to the positive post, despite it being glued down to the terminal along with the other wire. I’m not sure how this would have ever worked but it looked like it had been glued in place, but had never ever made contact with the terminal post.

I’m not used to dealing with wires that are the thickness of cotton but I removed that wire from the glue, wrapped it around the other wire and then tried to connect it to the positive terminal. I couldn’t get solder to take to the terminal so in the end, I left a blob of solder on the wire and using a drop of super glue, connected it to the terminal post. I fitted it to the instrument panel and tested it and it worked. I couldn’t reuse the rivets so I put a small droplet of glue on each side of the wee panel. I then cleaned up the bezel, fitted it and folded over the edges of the bezel. Job done. Haha.

Back to the engine, and all you clutch gurus…..

I’m having some clutch issues and would be keen to get some ideas from you all. I was a bit suspicious about the clutch before we put the engine in, but we did appear to get some pressure so I ran with it. After bleeding the clutch though, there is a problem.

The issue seems to be that the fingers on the clutch pressure plate are compressed too much during assembly of the pressure plate and clutch disc. When you activate the clutch using the arm on the side of the housing, there is about 10mm free play in the arm, and then about 25 mm of ‘soft’ throw in the arm. I say soft, as it appears that it is just the release bearing movement on the shaft I can feel, and only finger strength is required to move it. The arm ends up in roughly just past the vertical position at the end of its travel. As a result, the disc is not released. I’ve had the clutch and gearbox in and out now a couple of times and it is still not right.

Here’s what I’ve done/checked:

• The clutch release bearing assembly looks correct. The yoke and arm are as I received them and were already wired. They match the configuration in the manual.

• The clutch release bearing is a recommended replacement model. It is about 90mm in diameter while the inside diameter of the fingers is 70mm. The clutch release bearing has about 25mm of travel on the retainer on the main shaft.

• I’ve put the clutch disc in the right way, with the long end of the hub toward the flywheel. This puts the raised portion of the hub inside the circular opening in the pressure plate. Note that the 1943 TM 9-743 manual suggests fitting the clutch with the short end of the hub to the flywheel. This error was corrected in the 1944 TM 9-743 manual and described in an issue of Army Motors. The disc will go in the other way around but I imagine the springs on the hub would clash with the crankshaft bolts.

• The clutch disc fits neatly and flat on the flywheel face. The end of the hub on the clutch disc is clear of the pilot bearing so it is not bottoming out on that.

• I have examined the pressure plate and the clutch disc alongside a spare pressure plate and clutch disc. They are the same diameters and thicknesses, to within a couple of millimetres. The height of the pressure plate face and fingers within its housing is the same as the spare pressure plate, again to within a couple of millimetres. The pressure plates are as I received them and they have not been professionally set up.

• I wrote a while ago about the differences between the White Scout car and M8 clutches. The Scout car pressure plate is bigger so won’t fit, so the clutch pressure plate on this is correct.

• From what I’ve seen, the M8 hub setup on the clutch disc is different to the White Scout Car, with the short end of the splined shaft on the raised portion of the hub on the M8. The White Scout car hub has the long end of the splined shaft on the raised portion of the hub. I think I have this right, but thinking about it, I don’t think it would matter. Interestingly, I saw a picture of someone restoring a Scout Car clutch and the clutch disc in that was the same as these M8 (?) ones.

• Each time I have fitted the disc and pressure plate I have ensured the disc is central on the flywheel and under the pressure plate. The raised portion of the hub sits neatly in the middle of the pressure plate with about 10mm of clearance around the circumference of the circular opening.

• I’ve been using an old output shaft to align the clutch disc during the tightening of the pressure plate. The output shaft doesn’t go fully into the pilot bearing because of the threaded section on the end, but it is enough to align the disc. The gearbox fits into the bellhousing and engages with the pilot bearing without any problems. It bolts up neatly, so I believe I have everything aligned, otherwise the gearbox wouldn’t slot into place.

• The flywheel is an original one with new ring gear fitted. It appears to be seated on the crankshaft and in the bell housing correctly, but I have nothing else here that I can compare the depth to.

• When the pressure plate and clutch disc assembly is tightened down on the flywheel, the fingers on the pressure plate drop around 20-22mm from their neutral position. This seems excessive to me and I think this is the problem. The fingers end up so low that the release bearing is not making contact with them.

What have I missed? Any ideas would be appreciated.

Thanks.

[Big D]

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