Air problem, help please

[Simon Daymond]

my mk1 militant has an air problem, can you help?...

 

a weeks ago now, the militant moved from the farm, a resting place for the last few years, down to my place of work.

She started fine, and built air straight up. Then on the 5 mile journey to work, she built air up to over 160psi, basically of the clock, I pumped the brakes a few times, and the gauge settled at 120psi. However, after a few minutes, the air pressure started to drop, finally reaching 40psi.

As work wasn't far away by this time, I continued, as I was easily able to stop her on the ratchet handbrake when required.

 

Last week I stripped the compressor, the oil in it was like mud! I removed the sump and cleaned it out in the parts washer. Then removed the compressor head. I found that the inlet valves were roughly 50% blocked, and the exhaust valves were badly seated.

I cured the inlet valves with the aid of a soak in the parts washer and an airline. I removed the exhaust valves, and found they were badly pitted, so here I cheated a little, and turned them around, which worked perfectly!

 

I rebuilt the compressor, filled it with fresh oil, then refitted it to the militant. It worked loads better, building up air really quickly. But it would only build to 80psi.

Also, I found that when I stopped the engine the air is escaping from the system, not back through the compressor as I had originally thought, but from a pipe connected to the unloader valve.

 

I am assuming that the unloader valve is u/s, and is constantly unloading, which is why the militant cannot build pressure fully, and why it loses air when idling or stopped?

 

I have briefly examined the unloader, by taking the front cover off, it seems full of foreign matter, bits of seeds, rust etc, I think this is because the air system had the air filtration removed for the cab rebuild, and has been sat on the farm for several years without it, allowing water and assorted muck into the air system, clever I know.

 

Am I right to assume the unloader is the problem, if so do they come apart easily, or do I run the risk of bits flying everywhere if I undo the wrong bolt?

 

The unloader is made by Clayton Dewandre, I do have a book, but it doesn't go into much detail, and the diagram isn't very clear.

 

Any help/advice gratefully received.

[N.O.S.]

I'm sure your unloader valve is the problem - this is the most likely way the original trouble of building up too much pressure would have occurred.

 

Had an identical situation with a Matador, but the unloader valve was very easy to strip out and clean.

 

Cannot help with detail as no experience on Militants. Good luck!!

[Richard Farrant]

Simon,

 

The problem will undoubtably be the unloader valve, with this debris and contamination in it. I have worked on these but so long ago now, cannot visualise it. Did have a troublesome one on a Matador recently as well. As a general rule, an unloader would cut out around 120 psi, then cut back in around 90 psi. I think when these ones unloaded the air was exhausted at this valve, where as some other vehicles compressors have a pressure line to them to relieve a valve in the cyl head.

 

If you strip it, try not to disturb any of the adjusting screws, or if you need to move them, measure the length before disturbing. This will give you a datum point to start off from when you refit it.

 

There is an advert in a recent CMV mag for someone dealing with Mk1 spares, number is 01200 429448

[Simon Daymond]

many, many thanks guys, I'm very good at taking stuff apart! - but I get worried if I don't have any spares, to replace the bits I sometimes lose/break! :-)

 

I will give that chap a ring tomorrow.

 

Whilst I have your attention :-).....

 

the workshop at work is a golden opportunity for me to do some maintenance, in paricular getting the militant lubricated.

 

However, I notice that some of the nipples, according to my book, are for oil not grease, will it do any harm to grease or does it have to be oil?

 

 

[Richard Farrant]

 

 

 

However, I notice that some of the nipples, according to my book, are for oil not grease, will it do any harm to grease or does it have to be oil?

 

 

 

 

Simon,

 

It may depend on the actual greasing point, but in general, spring shackles, steering ball joints, etc, the modern chassis grease is more fluid than the sticky grease that was used in the 1950's when these old wagons were made.

[Simon Daymond]

that's something we thought, that grease was avoided because it was sticky and dirt, sand etc would have loved it, so hence oil was used?

 

I'll give it the once over tomorrow, we've one of those airpowered grease guns and I'm all for an easy life :-)

 

 

[Richard Grosvenor]

 

 

However, I notice that some of the nipples, according to my book, are for oil not grease, will it do any harm to grease or does it have to be oil?

 

 

 

 

I think it's the nipples on the rear hubs that are lubricators for oil rather than grease. But oddly the front hubs must have grease rather than oil :?. Luckily I've not had to put any oil in the rear hubs as they've always been fine. Probably best to stick with what the book says even though any lubricant has got to be better than no lubricant .

With the regards the un-loader valve, I had a look in my illustrated parts book to see if it showed the valve in any detail.....but it didn't!

 

Regards

Richard

[Paul101Clark]

Be careful when dissmantling the unloader valve, a favourate is the spring siezes in the compressed position and only releases it's self when you have all the retaining bolts out. To overcome this problem wind the retaining bolts out but leave them on the body, give the valve a tap with a copper hammer, this should help. Hope you have it fixed soon.

 

 

[Simon Daymond]

if it goes well, I'll post some pictures, if no pictures, assume the worst :-)

[MilitantGraham]

There's a diagram of a Clayton Dewandre unloader valve here.

It may not be exactly the same as yours, it looks different to the one on my Mk3 and I can't think what the one on a Mk1 looks like at the moment, but the principle will be the same.

 

As for the grease nipples, the correct oil would be OC600, a very thick and sticky oil.

My Matador had "Use Oil" on the UJs and the manual specified it, but I used grease everywhere except the brake cylinders. You should be fine using grease on a Mk1.

[Simon Daymond]

thanks for that :-)

[Simon Daymond]

ok, first of all I rang the number, it's for a chap called Charlie, who turns out to be quite a sound bloke :-) Unfortunately he didn't have an unloader valve, but he is the owner of yet another mk1 militant gun tractor!

 

Thought I'd let you know the progress so far,

 

http://i203.photobucket.com/albums/aa246/sdaymond/Inthebeginning.jpg[/img]

 

this was before I started, the union the spanners were on came undone, however the remainder required heating and plenty of it.

 

 

http://i203.photobucket.com/albums/aa246/sdaymond/strippeddown.jpg[/img]

 

 

after removing the unions, I decided that the unloader valve bolts were too dodgy to attempt to remove it from the bracket, so I opted to remove the bracket from the chassis. It was a bit awkward, but there was one bolt I couldn't quite manage, but there's always one isn't there?

After 5mins struggling it was off.

 

The unloader assembly stripped easily, but the unloader valve was solid, so I tapped it out, this sticking valve along with all the cack is the problem I hope?

 

http://i203.photobucket.com/albums/aa246/sdaymond/fullofcack.jpg[/img]

 

I removed the felt filter carefully :whistle:

 

 

http://i203.photobucket.com/albums/aa246/sdaymond/feltfilter.jpg[/img]

 

then set about trying to dislodge some of the cack inside the body

 

 

http://i203.photobucket.com/albums/aa246/sdaymond/fullofthis.jpg[/img]

 

all went well, and the body is soaking overnight in a paraffin bath, which I hope will dislodge the rest of the muck, and will blow through with the airline tomorrow.

 

The only thing I'm a little worried about are these.

 

http://i203.photobucket.com/albums/aa246/sdaymond/bellowsslightlycracked.jpg[/img]

 

they are the bellows but they are badly cracked, they will refit, but I could do with a replacement sometime if anyone knows of any?

 

More to follow later.

 

 

[Simon Daymond]

just to update, it's rebuilt, and refitted, and still leaking. But I think I know what's wrong, the unloader valve is either not seating, or isn't lined up properly or perhaps both, as now I can only get 30psi, so it's worse than before :-(

 

But I'll try again tomorrow :-)

 

Can anyone recommend a supplier for air fittings? The unions have two different types of threads, on one half of the union the threads are 1/2" BSP but on the other there is a really fine thread. I thought I'd try a local supplier, but to no avail, 1/2" BSP wasn't an issue but the fine thread, (whatever it is) was.

[Tony B]

Get a thread file and gauge. if you can identify the thread a thread file may well work wonders. Classic parts do an excellent reline job on cylinders and pistons for brakes etc. Stainless steel liners are inserted and modern seals. not expensive and a superb job.

[Richard Farrant]

 

Can anyone recommend a supplier for air fittings? The unions have two different types of threads, on one half of the union the threads are 1/2" BSP but on the other there is a really fine thread. I thought I'd try a local supplier, but to no avail, 1/2" BSP wasn't an issue but the fine thread, (whatever it is) was.

 

 

Simon,

 

I think this is probably ANPTF thread on the pipe nuts. It is American National Pipe Thread Fine, a b*gger of thread to get started and easily damaged. It was common on British vehicles of 50's and 60's, like AEC, Leyland Martian, etc. Regarding your unloader valve, I would forget trying to repair that one as it is obviously in poor condition, why not substitute for something similar, with suitably threaded ports, cut out and in pressures are all similar, ie 120 and 90 psi. There is a chap called Bernie who deals in army surplus parts of this era, especially AEC and the like, comes from Northampton or Leicestershire area, but cannot find his number at present, think he gets on Ebay.

[N.O.S.]

Simon -

 

I've pm'd you Bernie Smith's number.

 

Does just what Kewelde says, and more!

 

A very good guy to deal with, I'm sure he could find something suitable with his contacts.

 

Tony

[Simon Daymond]

thanks very much for your comments. I particularly relate to the bit about the fine thread being easily damaged! Which is exactly what I did with one of the unions, as I wasn't paying attention.

 

If I get stuck, I'm going to fit a modern valve for now, to get me out of the mire, and fit the correct one later, as I'm sure it'll turn up in time.

[MilitantGraham]

NPT is very close to BSP, in fact it is common practice to fit BSPT male threaded fittings in to NPT threaded ports.

The very fine thread is more likely Enots as this was used widely on Matadors and still to a lesser extent on the Mk3.

If the bellows is cracked I don't think there's any hope of the valve working properly. It may be possible to repair by soldering, but as the whole idea of a bellows is that it flexes, I don't know how long that would last.

I'd go for the new, modern valve option and adapt the pipes to suit.

[Simon Daymond]

I reckon, if the bellows being cracked was the only problem, it just wouldn't unload, as it is the bellows extending that unseats the unloader valve, allowing the air to escape.

 

the air is escaping at the moment because I think I have failed to seat the valve properly, before I stripped the valve down, the unloader valve was most definitely stuck in the bore, it would not move at all. Now I've lightly cleaned the bore, the valve moves freely, as it should.

 

I couldn't get to work on the militant this weekend, as work got in the way :-( but for bedtime reading, I did notice that the manual does say that if the valve is not correctly seated air will escape, which is what I hope is the problem.

 

Even if at the end of the day it still didn't work, at least I've learnt a little more. The lads in the garage are completely baffled by the whole concept of repairing something, as nowadays it's all about throwing away and fitting new.

 

The diagram HTML you sent me is almost the same, the only difference being that the Mk1 militant unloader valve also comprises a safety valve as well.

 

 

 

 

[Simon Daymond]

ok, just to bring this thread up to date, got a new valve in the post yesterday (from that scrapped militant on ebay) stripped it down last night, and after a bit of sweat, missing my tea etc, I left here at midnight but all is now working fine, builds up pressure and holds, so sorted, finally.

[Tony B]

Great news. Have you enough left over to build a spare?

[Simon Daymond]

yep, nearly.

[Tony B]

Might be worth contacting Pastparts see if they can recondition it for you. They do seem to be able to rebuild/find or recondition the most obscure parts. http://www.pastparts.co.uk/