Bedford head gasket

[mark4974]

Hi folks,

I've got the wonderful task of having to change the head gasket on my Bedford QL!

Has anybody got any tips or horror stories to guide me in the right direction (I've got the gasket set and workshop manual).

Also, is there anything else I should be checking for or replacing whilst the engine is stripped?

Cheers, Mark

[paulbrook]

I am sure you will get lots of really good advice but here's my two pen'noth;

 

1. In my experience head gaskets go for a reason. Look for the reason. Even before you strip it down have a really good look around for any issues and only when you are sure you have looked everywhere start to undo stuff.

 

2. Before you undo the head bolts try tightening them. You might find a slack one or two studs - which while they may not be the cause might point you in the right direction.

 

3. Give everything, head and block, a really good clean and inspect for cracks. Use a dye penetrant if necessary. Have a close look at the old gasket and where it has given way, as it may point to a specific location to inspect carefully.

 

4. if you really really cannot find a cause then it may just be the gasket itself. But have the head skimmed anyway.

 

5. Only put the new gasket in when you are 100% sure that all is well with the block and the head - flat and crack free. Both should be scrupulously clean.

 

6. A good gasket on clean flat metal surfaces will not need any sort of goo, but if you feel the need then the only choice for an engine of this age is Wellseal. Even then only use it sparingly.

 

7. Torque it down gently and in the right order. It might sound daft but when I am done I like then to slacken it all off, then do it all again.

 

8. Re-torque after the engine has been run and warmed up a few times.

 

As I say - others will have other stuff to add I am sure!

[mark4974]

Thanks for your help, plenty for me to think about!

[mike30841]

Hi Mark,

 

If you need any work done on the head, I can thoroughly recommend Chris Watson who is fairly local to you (Just off Gaisby Lane). He is vastly experienced with everything from veterans to moderns. He has done a couple of engines for me, and his prices are reasonable too. Let me know if you want his contact details. Hope you don't find any nasty surprises once you get the head off.

 

Kind regards,

Mike

[mark4974]

Thanks Mike,

Working on the truck tomorrow so we'll see what I find!

If you could PM me the details that would be very helpful. Hope all is well with yours?

Mark

[mark4974]

With the help of a 81 year old REME veteran (aka Dad!) I've got the head off. This is what I found whilst stripping the engine.

 

- About a gallon of coolant in the sump!

- The head gasket has gone. Between the nos 5 and 6 cylinders.

- Rusty coloured "sludge" lining the coolant pipes, hoses and appears to be in the head.

 

So the next question is:

 

- Can't see any other reason why the gasket has failed, but at least it's gone at a weak point. Should I be worried about anything else.

- what's the best way of cleaning / flushing all the rusty "crap" out of the cooling system.

- Going to replace all the gaskets. Anything else I should look at / replace whilst I'm at it.

 

Cheers, Mark

[mike30841]

Hi Mark,

 

PM sent with Chris Watson's details.

 

Only way you will get all the crud out of the waterways in the block is to remove all the core plugs (including the one behind the flywheel, unfortunately) and flush repeatedly, alternating with fishing around inside with a small magnet. It is extremely awkward and tedious - I took about 3/4 of a kilo of scale from the engine on my OX, and that doesn't include what Chris got out of the head. Chances are the radiator will be full of crud as well.

No easy way, I'm afraid.

 

Kind regards,

Mike.

[paulbrook]

And you need to really clean up between those cylinders and have a good look both at the block and on the head. with it all clean (steal one of those scotchbrite pan scrubs from the domestic department). You are looking for any depression (feel with your little finger) or other anomaly. Stare at it and look for cracks. When cold they can be tiny, human hair thickness.

 

In that coolant has got into the sump one must assume that there has been quite a major leak either via the head or a crack between cooling jacket and oilway. If it is via the head then I would suspect some warping. In any event get the head skimmed.

 

There is a bit of cause and effect here- a crack or casting anomaly can cause the gasket to be over stressed and eventually fail, but slow gasket failure can also stress the metal of the block/head. Hence the need for very careful examination and rectification - otherwise you will be doing this all again soon!

 

As for getting the crud out then only time and effort is required - when you have it all together run it with half a cup of washing soda in the coolant for the first few weeks then drain it all again before putting coolant proper in it. Oh and if you have a lot of muck in the block you will have even more in the rad, so back flush that too.

Edited April 5, 2016 by paulbrook

[Sean N]

Paul, I'm going to argue with you about the head skim.

 

I know a lot of people have heads skimmed automatically when they're doing a head gasket (particularly on modern aluminium heads), but I've never understood the reasoning behind it. If the head is straight / flat and serviceable it seems to me you achieve little, waste money and risk introducing faults by having it skimmed.

 

Obviously if the head is warped or the face damaged or corroded then yes, by all means skim, but make sure the procedure will rectify the fault.

 

While you're checking the head, make sure the manifold mating faces are straight and not burnt.

 

Are the bores etc. on this thing all clean, and how high was the water level in the sump? Has the gasket just gone, or has it been sitting with water in it? Just wondering if it's worth stripping the whole engine just to make sure all is OK...

[paulbrook]

To skim or not to skim? Personal choice obviously, but I would have to be seriously sure things were dandy before replacing a head on an engine that has blown a gasket without a light skim. In the circumstances of this particular 28HP I would even contemplate decking the block too.

 

Anyway this is what I would be looking for. In this case the pair of cracks not only caused the gasket to blow on a Standard engine but it just would not run right - the gasses from cylinder 3 were blowing into cylinder 4.

 

[Richard Farrant]

It could be something plain and simple like the head was not tightened down correctly when last fitted. There are no torque figures listed in the wartime military manuals for Bedfords, so it is quite possible the head was not tightened enough, causing water to creep past a transfer port and down past the pushrod chamber.

 

For reference, the head torque for a 28hp is 78 - 83 lb/ft (from 1947 Bedford civilian wksp manual)

[matchlesswdg3]

I am no expert on these things (Richard fixed my MW motor!), but it occurs to me that it is possible that the water in the sump got there when you cracked open the head, as this is surely a heck of an accumulation for a running engine? Usually you get that sort of mousse/mayonnaise stuff forming in the rocker box, etc when water gets into the oil? Not much to do with the failed gasket, though.

[mark4974]

Thanks again for the advice folks.

wont get chance to do anything now until next week. First job will be to check the block for cracks (worst case scenario). Decided I might as well do a proper job whilst the engine is part stripped. Will be removing the core plugs and flushing all the crap out. New clutch and anything else I find whilst I'm at it. At least that way I shouldn't have to do it again!!

 

Unfortunately, due to work commitments and holidays it won't be a quick job and will mean missing a few shows but should be worth it in the long run. No doubt I will be back on the forum asking for more advice in the weeks to come.

 

Cheers, Mark

[MWMike]

Hi Mark,

 

I didn't go quite that far with my MW, she was misfiring on no 5 and 6 cylinders, so I removed the drain tap from the back of the engine, (through the panel in the footwell) and similarly the front drain tap, then I used a pressure washer at full bore to jet out the block, took quite a while to get the loose stuff out, then i treated the engine with Holts two part heavy duty engine coolant cleaner, from Halfords i think. This is a first stage acid treatment, which dissolves all of the rust and scale, and there are precise instructions on how long you leave it in the system with the engine hot and running, then a long flush to get all the dissolved sludge from the engine and radiator, and you add the second stage passsivating system which neutralises the acid (so it doesn't eat the block!) and creates a layer of magnetite on the iron components to help heat transfer and prevent corrosion. This fixed the misfiring (as 5 and 6 were getting hot) and made me feel a lot better, she hasn't missed a beat since then and handled the 2014 Arnhem tour without a problem....hopefully the same for Normandy this year! Obviously with the head off, you are further into the engine so its probably worth knocking the core plugs out and getting better access! A pressure washer will come in handy! ("core plugs international" on the internet can resupply you with any sort of replacement plug so you need not pay through the nose.)

 

As far as the head is concerned, to see if its flat I normally "blue" them with engineers blue and then use a surface table to check for flatness, but I don't have one big enough for this beast though a good engineering shop may have one....!

 

bonne chance!

[Richard Farrant]

As far as the head is concerned, to see if its flat I normally "blue" them with engineers blue and then use a surface table to check for flatness, but I don't have one big enough for this beast though a good engineering shop may have one....!

 

 

Hi Mike,

When checking a head for bow or low spots a precision straight edge and feeler gauges are the normal way of checking.

 

regards,

Richard

[paulbrook]

I seem to recall that civvy bedfords came with a cranked spanner for head tightening. It was cranked to access the centre dolts with the rockers in place. The torque was the maximum a man could pull on the spanner (which was about 8 inches long) - about 80 foot pounds!

[Richard Farrant]

I seem to recall that civvy bedfords came with a cranked spanner for head tightening. It was cranked to access the centre dolts with the rockers in place. The torque was the maximum a man could pull on the spanner (which was about 8 inches long) - about 80 foot pounds!

 

That spanner was supplied in the army Bedford tool kits as well, along with another special spanner for the manifold bolts.

[paulbrook]

That spanner was supplied in the army Bedford tool kits as well, along with another special spanner for the manifold bolts.

 

Aha! So I have not gone completely senile yet then!

[Brooky]

I think I may even have one somewhere in the mess I call stores