My M8 Greyhound breaks down out of town.    (Ver 1)


On a Sunday afternoon I decided to take the Greyhound for a road test as I had been having problems with a miss at idle. This problem has been on going and numerous mechanics have failed to find the cause. We went out of town (I live close to the edge) and had driven probably 10 or so km and were on the way back; the engine had been running like a swiss watch, except for the idle miss and all was well....... I had been keeping an eye on the temperature guage and noticed in the last few minutes that it was now well up but still at an acceptable temperature.

Soon after, I looked down again and it was sitting on 100C, oh, oh. So I then started watching it every couple of seconds and it suddenly started going up; pulled straight over to get off the road and switched the motor off. Then there was this heavy rumble both audible and also being able to be felt coming through the body of the vehicle.
First off I thought the motor was "running on" and that was the last thing I wanted if it was in danger of seizing - so I put the accelerator flat to the floor. (I have a tacho retrofitted into the vehicle but it is electric and I had lost it when I switched off the ignition). I then got a report over the intercom that there was "all this smoke coming out of the engine bay". 'Smoke!', then I put 2 and 2 together and realised that the rumble and smoke was the engine boiling and steam from having switched it off and stopped.
One small mercy at least, I could do without a fire.

Just great, out in the sticks with a broken tank and a very large puddle of water on the ground and its 4pm on a Sunday!
Luckily I had brought along my wife's mobile phone after a mate (Steve - who was absent for this little drama) had pestered me about not having any communications when I went out of town in my vehicles. So I rang her and asked for her to come and get me. She arrived with some cold drinks (10/10 for smart thinking!) and then we went and collected some tools (I suspected the new head gasket had leaked and the situation could be recovered by retorquing the head) and 40 litres of water.

After letting the motor cool off I trickled water into the radiator while having Richard in the driving seat turning the motor over (the Greyhound has a seperate ignition and starter switches, so you can turn the motor without having it try and start) as I was worried about cracking it. Well, the water started running out as quick as I was pouring it in - great!

I have never seen a motor leak coolant so quick and I have blown my share of hoses and welch plugs (for the Americans = freeze/frost plugs and for the English = core plugs). It appeared to be coming from the back of the motor well below head gasket height, in that impossible to get to location where there is a heavy cross member and the petrol tank in the way. So no field expedient was possible. Time for another trip back into town to get the APC and the "A" bar. Due to all the chatter in the last few days on the MV lists, I had been reading the do's and dont's of towing heavy vehicles and as luck would have it I had bought the very same model of tow bar at a scrap yard a few years back that has been the subject of discussion. I had therefore downloaded the tow bar manual from Chuck Chris' "Olive Drab" site and read it only 2 nights previous. My bar came with the knuckles, but not those gadgets that allow you to connect it to a bumper bar. My thanks to all concerned in those discussions and Chuck.

So after connecting up the tow bar there remained the uncertainty of whether the Greyhound would be a passive tow or one of those vehicles that would try and do its own thing. Also, towing a 6 wheeled vehicle behind a full tracked vehicle is mixing 2 very different steering geometries, so I was worried they would fight each other.
So I stationed Richard in the Greyhound's driver's seat with an observer (a kid from down the road who had come for the ride). As it turned out, Richard said the Greyhound behaved very well. So we set off at a sedate pace that I gradually increased to 18 mph and which saw us with the whole contraption back in my shed by about 6pm. By the time everything was packed away etc I finally ended up at home and eating at 7.30pm, which was before dark, so that was one good thing as I had no desire to be in command of that lot after dark.

During the following week I got into the engine bay with a mirror and a light and confirmed that there is a welch plug at the back of the motor and that it had blown. Further examination showed that, actually, it was missing! So it looks like some army mechanic didn't do his job properly. I have never heard of a plug blowing out of a motor before, doubtless I am not the first this has happened to. When I made that comment on the 2 Military Vehicle email lists I very soon got a couple of replies recounting similar experiences but with different types of vehicles.

Now the problem with replacing this plug is that it is at the rear of the motor (the Greyhound engine is actually mounted about face so the motor rear is facing front), there is the petrol tank in the way and below that a heavy channel cross-member with an electric distribution box mounted in its valley.
I then had the bright idea of removing the petrol tank and unbolting the cross member which blocks the lower 1/3 of the plug diameter and gaining sufficient access to replace the plug. Not so easy, as I discovered that someone had welded the crossmember in instead of just trusting the bolts (nice of them) so now the engine has to come out as I did not have the option of removing the cross member any more. A check via the MV email lists soon got responses from M20 owners (a kindred vehicle to the Greyhound) saying that all their vehicles also had welded cross-members with bolts, so looks like it was done at the factory - rather odd.

The manuals proved to be no help.
In which case it was still looking like the motor would have to come out as I was unaware of any way of getting access to this area unless I could do so by removing the fuel tank and the cross-member.

It was then that I received an email from Brandon Kunicki in the USA as below:

> I have seen replacement freeze plugs for automotive
> engines in the US that install (expand) with a spanner
> wrench and are intended to be installed with an engine
> in place. Perhaps one of these would be worth a try?

This is one of those things I have never even heard suggested should be made. Which just goes to show the worth of the MV email list and the people on it.

> I can check my local auto parts store in the US if you
> can't find any locally. I'd just need to know the
> diameter of the hole.

First off I went and annoyed my local parts store to see if these things existed in Australia and got blank looks...... I expected as with all these "work around" designs that they are not as durable in the long term as a correctly (I couldn't resist putting that word in) installed welch plug? If it saves me from having to pull the engine out then I don't care if I have to change it everytime I change the oil. I was soon informed by a couple of emails of just how successfull and surprisingly long lived these plugs are.

Brandon promptly purchased 3 plugs covering my estimation of the diameter of the missing one (unreachable location without a mirror and parralax error) for me and airmailed them. Unfortunately it turns out that the plugs only proved suitable for "cup" type plugs (that have a 5mm or so lip) where a hole is bored all the way into the water jacket.
The ones in the Greyhound are "saucer" type (like a discus or gladiator shield) where the hole is counter bored only part way into the water jacket and the rest of the depth of the hole is just the rough casting with a very irregular hole.
Thus the soft plugs won't fit. No matter, they have gone into my spares draw and will doubtless serve some purpose in the future.
Many thanks to Brandon for his time and help in this matter.

So, back to the thought of having to do a motor pull, something I was not at all keen on as I really didn't want to disturb that 60 year old, - unique to Greyhound and M20's - exhaust manifold and have it fall apart when being retightened.

It was then I had the bright idea of jacking the rear of the motor after having released the gearbox mount so that the plug hole comes high enough to allow access to hammer in the new one, but hang on, the cross-member goes over the top of the bell housing - something is odd here! A crawl under the vehicle soon revealed one of the oddest mounting designs I have yet seen - but it worked in my favour as there is no gearbox mount, instead there are 2 heavy section pieces of angle which attach to flat parallel pads on the side of the bell housing and to the underside of the cross-member!

As I have no desire to have to pull the petrol tank in 10 years time when the replacement plug rusts out I wanted to replace the steel ones with brass. This then presented the problem of what size plug, as it is not uncommon to find more than one size used on a motor, measuring the size of one on the side of the motor may not work. An email off to the MV lists soon got a couple of responses including one from an owner of the appropriate parts manual specifying exactly what was required. So I ordered some brass ones.


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  Here you see Richard contemplating how much work is involved in just replacing one errant welch plug. We have already removed the armoured covers over the motor and the "spine" they are hinged from along with the armoured cover from over the petrol tank. A check of the Greyhound workshop manual lists 5 steps to remove the petrol tank. Obviously written by a comedian as experience would teach us that it is more like 25, with some damn awkward parts to it. It doesn't mention needing 3 people either.


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Here are Richard and Joe with the petrol tank out "just hold on a sec while I get a photo", 'yeah, thanks Doug this thing is heavy'. It took 3 of us to do it due to the awkwardness of nearby conduit and electrical boxes that didn't want to be removed. The tank itself is a self-sealing rubber bladder of the same design as used in fighter planes. What you can see in the picture is actually the metal shell that encloses it, this thing is assembled around the bladder from one heck of a lot of bolts. It is worth noting that bladder tanks do not like alcohol/petrol mixes as sold in certain areas of the USA and now Queensland, Australia. You end up with a goopy mess but only after your entire fuel system has been blocked with goop. Vehicles known to be affected are US halftracks, M20 and M8 Greyhound. There may be others as I think I recall that the British CVRT (Scorpion etc) family also has a rubber bladder.


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  Joe having a rest after we have got the tank out of the way.


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  A rather awkward photo, but it shows the area where the petrol tank lives. The white area with the cross braces is the fire wall leading to the crew compartment. All the black muck is the dust from when I had the interior of the crew compartment sand blasted and it leaked through.


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  If you look carefully you can see there is actually 2 plugs at the back of the motor, the missing one is obvious, whereas the other one is well disguised by paint. Note the electrical distribution box and the tricky slotted screws which swing little retainer wings so you can remove individual segments. Also note how the cross-member partially covers the plugs (not as noticable here due to the amount of parrallax error in the photo).


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  Here you can see how I have jacked up the motor to the limit allowed by the cross-member and have gained sufficient access to be able to insert the new brass plugs. It is worth commenting that the remaining steel plug showed no corrosion and appeared to have been hit with a round object of about 3/8" to set it rather than properly installed.


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  The plugs are in and the motor has been let back down to the correct height and the mounts done up.

So it was now a matter of putting the whole thing back together and doing a road test. There is still the problem of the idle miss which has become a real mystery, as I have pulled everything apart that would even seem remotely likely to cause the problem. This included installing a new head gasket and was the reason for the road test where the welch plug blew out. It seems I have come full circle to where I started a few weeks ago...............

Some days it is better to stay in bed.

I would like to say thanks to my helpers, Richard and Joe and also to Brandon in the USA and numerous other Americans who offered suggestions, took measurements and consulted manuals for me..

In 2004 I was at a car parts place in Adelaide, South Australia and was looking at some auto diagnosis instruments when an elderly Italian served me. When he asked why I wanted them and I explained my never ending quest to solve the idle miss, he told me that he was a mechanic. He then said "by any chance does this thing have a brake booster?" - bingo! When I told him it was a very early hydrovac he immediately said, "check your control diaphragm, I bet you have a leak there". Sure enough, when I got back to Broken Hill and pulled the hydrovac out and dismantled the control head, there was this crinkled up perforated diaphragm. I then got in touch with the place that had rebuilt it and told them how I had been having problems from son after they rebuilt it and asked if they could source a new one this time instead of an NOS one, they said they would try. They succeeded and supplied it at no cost, which was good of them. So, finally, the problem is solved and the darn thing idles like it should.


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