[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!