Bedford MW failing to start.....

[Jelleyboy]

Hi Guys,

 

Ok so rebuilt lump, new fuel lines and new taps. New carburettor and new plugs + new coil.

 

Checked and have a spark, new battery installed, fuel lines are now providing fuel to the pump which is now feeding the carb, carb was checked and isn't seized up on the float inside the bowl.

 

Firing on TDC tappets have been correctly set any ideas? it's driving me mad at the moment

[fv1609]

Is the spark you have seen just the small gap across a sparking plug? Or is it getting on for 10mm from lead to an earth point? A spark across just the plug may not have sufficient voltage when in the engine under compression to produce a spark.

 

Is the new coil of the correct polarity?

 

Have you tested the rotor arm?

 

How new/trustworthy is the capacitor?

[Jelleyboy]

Is the spark you have seen just the small gap across a sparking plug? Or is it getting on for 10mm from lead to an earth point? A spark across just the plug may not have sufficient voltage when in the engine under compression to produce a spark.

 

Is the new coil of the correct polarity?

 

Have you tested the rotor arm?

 

How new/trustworthy is the capacitor?

 

The spark was from the plug to the nut it was pressed against for earth.

 

I checked the coil with Rippo so that should be fine, the capacitor - apologies for the silly question but what is that?

[fv1609]

So the spark was on the sparking plug itself? To get a measure of the magnitude of HT you really need to test over a greater distance. eg from the plug connector to an earth point with a gap 5-10mm. If it doesn't do that you HT is probably inadequate.

 

Capacitor = condenser

 

Who/what is Rippo?

 

Have you tested the rotor arm? I can explain how to if you are not familiar with the test.

[Jelleyboy]

Ah the condenser in the distributor? I think my friend who was helping me who owns 2 tillys and a k2 ambulance said that was ok,

 

Rippo is a member on here owns an MW and has a wealth of Knowledge on these, I run the new coil past him before purchasing.

 

Ok I will retest the spark - does this need to be done per plug?

 

Yes please Clive, this is our 3rd Rotor arm in this case brand new - it is the correct one.

[Jelleyboy]

Just to confirm, what is the correct gap for the sparks? In the manual I have 2 different clearances - prior to the restore I think they were set to 0.20 but there is also a note for 0.37? I might be off a little with the numbers I haven't got the manual in front of me at the moment.

[fv1609]

How was the condenser tested? With a multimeter? I'm afraid that gives very little idea of how it will behave when handling 300v. Needs to be tested on a Megger type device that can deliver that voltage rather than a multimeter that is only a few volts.

 

I would get the king lead from ignition coil, unplug it from distributor hold this lead 5-10mm from a earth point & flick the points closed & open. You should get a healthy spark as the points open. If you get this the condenser may probably be fairly ok.

 

Now hold the king lead end 3mm or so from the metal arm of the rotor with it still plugged into the shaft. See if you get a spark. If the rotor arm insulation is good there should be no spark.

 

The correct polarity of the coil is important so that you get a negative spark, if you have a positive spark you could need at least 25% more HT to get a spark in the plug under compression.

[fv1609]

The MW Drivers Handbook is none to helpful. It says the points gap should be a sliding fit for the feeler gauge that is incorporated at the end of the small screwdriver in the tool kit.

 

But it does say plug gaps .037" to .040"

[Jelleyboy]

The MW Drivers Handbook is none to helpful. It says the points gap should be a sliding fit for the feeler gauge that is incorporated at the end of the small screwdriver in the tool kit.

 

But it does say plug gaps .037" to .040"

 

 

I will check the plug gaps again, if I set them at 0.37 would it make sense to increase the gaps to 0.40?

 

I am also using NGK B6S plugs as this was what was in the the truck when we purchased it - they ran on these before I took the truck apart as we replaced the plugs and points back in 2012, are these adequate or should I be using something different?

Edited May 9, 2016 by Jelleyboy

[fv1609]

Yes set the plugs to the correct gap.

 

I think the thing to do is establish whether you can get a decent spark on the king lead & then test the rotor arm. Pity you aren't nearer, otherwise I could use my test gear on the whole electrical system.

[fv1609]

I will check the plug gaps again, if I set them at 0.37 would it make sense to increase the gaps to 0.40?

 

I am also using NGK B6S plugs as this was what was in the the truck when we purchased it - they ran on these before I took the truck apart as we replaced the plugs and points back in 2012, are these adequate or should I be using something different?

 

PS Is that a typo on the plug gaps by a factor of ten?

 

Sorry I can't advise on the plugs, but if the same type were in place then seems sensible to stick with that type.

[Nick Johns]

You describe the engine as "Rebuilt", to what extent? was the timing chain removed/replaced, if so non starting could be due to incorrect camshaft valve timing when the timing chain was fitted? Or incorrect ignition timing/firing order of the plug leads

Edited May 9, 2016 by Nick Johns

[Richard Farrant]

Which type of distributor is fitted, if it is the one where the whole body turns on vacuum advance, it needs an earth wire from distributor body to the engine block. Also to elaborate on what Nick has said, you may well have timed the engine on No.1 cyl, but have you got the other leads in correct order of rotation in the dist. cap?

[mike30841]

Are you absolutely certain you have timed the ignition to No1 TDC, and not No6 TDC? Both pistons are in same position, so you can't just go by the timing mark on the flywheel, you need to check that both valves on No1 are closed, indicating the top of the compression stroke. As Richard says, getting the plug leads 180 degrees out in the distributor cap would have the same effect.

 

Mike

[LarryH57]

It might be worth explaining what happens when you try to start. I presume that the engine turns over quite nicely on the starter motor and its not sluggish?

 

Incidentally my Lwt turns over nicely but fails to start but if I pull the choke out it fires up, so I bet its something very simple.

 

Returning to what Clive suggested in checking the condensor in the distributor, he will be the first to agree that there is no way of looking to see if they are OK and even ones out of the box might be duff, so try a few from your spares to reduce the chance it's the one you are using now.

[AndyB]

Had something similar, took over a week of frustration :nut: Engine would occasionally attempt a splutter, but not run. Went through the usual suspects, ensuring on a number of occasions that it was set to No1 cylinder. Finally with the rocker cover removed I noticed that the sequence of actions on one of the cylinders was wrong, exhaust opening when it should have been the inlet. On checking them all, it became apparent the cam was out of sequence, even though the manual states how the dots on the cam and crank should be aligned. I resolved this by turning the cam 180 degrees.

[radiomike7]

Had something similar, took over a week of frustration :nut: Engine would occasionally attempt a splutter, but not run. Went through the usual suspects, ensuring on a number of occasions that it was set to No1 cylinder. Finally with the rocker cover removed I noticed that the sequence of actions on one of the cylinders was wrong, exhaust opening when it should have been the inlet. On checking them all, it became apparent the cam was out of sequence, even though the manual states how the dots on the cam and crank should be aligned. I resolved this by turning the cam 180 degrees.

 

Would it not have been easier to rotate the distributor 180 degrees? Rotating the cam 180 degrees would have no effect on the valve timing as Mike30841 suggested.

Edited May 10, 2016 by radiomike7

[Grasshopper]

Rotating the cam 180 is the same as holding it and rotating the engine 360 degrees. Don't forget that the crank rotates twice for 1 rotation of the cam shaft.

 

After doing some head work on a CVRT, I made this mistake and set the cams to No 6 TDC and not No 1 TDC (which strangley enough look identical at the top of the engine!). Correcting this at the distributor was not an option so I had to reset the whole lot in situ as I'd already plumbed the engine in and didn't have time to pull it to correct it. We made the show that afternoon too