Ransomes MG2 number 137

[expeatfarmer 591]

Tat's the ones, held in by 4 U bolts, I scaled up the parts book to get the sizes.

Still not running, have now taken off air tube,stripped carb again, tried running to watch fuel through carb, top of the float was quite dented so thought problem may be too high fuel level in float chamber, not that, tried swapping plugs, tried different gaps most I have had is four firings. Friend called in today so was able to get him to crank engine whilst I watched the start timing with a strobe,was firing at about 4degrees after TDC so reset mag to 0 degrees still wont go. I have now removed the mag from 225 which I will clean up and test.

[Wristpin 399]

Can you observe the mag while its being cranked in the dark to see if there are any stray sparks around the points etc ?

[expeatfarmer 591]

Having exhausted all other possibilities I have finally decided to remove the mag from 225 and fit it to 137 . 225 has not run for at least ten years so the mag needed to be stripped and cleaned. Having done so I noticed that in the process of just handling the mag it gave me a belt which the other never has. I hope that it has taught me a lesson in that because the 137 mag was refurbished by a specialist it would be right and the non starting issues arose from other causes. I have yet to fit it and try but the bench drill test was far more impressive than the 137 mag so fingers crossed for the morning.

[expeatfarmer 591]

The two mags cleaned up side by side. The one on the left is the mag from 225 which is the right model for 137, the right hand mag is the MA1 mag rebuild.

[Wristpin 399]

Any possibility that tha rogue mag was originally set up to run in the opposite direction ?

[expeatfarmer 591]

I did wonder about that but there is an arrow showing correct rotation . Fitted the new N1L mag today from 225, if anything it is worse plugs spark when decompressor is engaged as soon as there is compression sparking stops> Tried smaller gap no better. Beginning to despair now. 

[Stormin 4,458]

  Mag was tested with an electric drill. Slow and fast a decent spark. Several pugs have been tried, all with same result. Sparks when out but not when in. We used one of those gadgets you fit 'tween plug and lead that lights up. No sign of sparks in and around the points. It's getting fuel, so it's not that. I think we've exhausted everything we can think of.

[Rocboni 257]

That sounds like the condenser.

[Stormin 4,458]

That's been one of the thoughts.

[expeatfarmer 591]

Underneath the mag label there is a brass screw which contains a carbon brush, when I took it apart this brush appeared to be fixed and so I did not disturb it, turns out this  is a spring loaded earthing brush which is on the hT side of the mag if this is not in contact with the slip ring result is a poor spark under load. I will have to check this out in the morning but it means taking the mag out again !!!! ho hum !!!

[nigel 1,874]

Still sounds like condenser to me

[Wristpin 399]

Worth checking that in air the spark is going from the centre electrode to the plug body and not the other what around due to polarity problems. Seen that with a coil ignition set up but not sure if it can happen with a mag.

[expeatfarmer 591]

Hope it is not condensor as that is buried in amongst the windings on the armature which requires a full strip and re wind.

[Stormin 4,458]

Did we check the other mag like we did yesterday, to see if we had a spark under compression?

[expeatfarmer 591]

Yes we did, I have just stripped the original mag cleaned up all the brush contacts tested it on the bench and the spark is jumping 1/2" and cracking so going to refit . Also compression tested the engine 60 psi on the starting handle, thought that might be a bit low so tested two others that are good runners and they have just over 50 psi so more than 10% higher. Put some oil down the bore and tested again no change so no leaks.

[Anglo Traction 998]

Been following your dilemmas with this,  and after you've tried multiple setups with various parts, I too am thinking along the lines of iffy condenser/connection and/or an Earthing problem.

What is confusing me though is the sporadic run/firing you've had, maybe it is an inconsistent Earth/ground fault which prevents a Spark when the plug is fitted.

Maybe a copper wire from the Cylinder Head to a good earth point will rule that out?. Best I can offer, as I know nothing about the Engine/Mag version you have.

 

Really hope you find the 'Gremlin' soon to reward your high level of skills, patience and determination on an excellent project .   

[Rocboni 257]

I had a crawler that run well once and fired but couldn't get it to run agian, condenser looked new so didn't touch it. After testing for spark under compression and removed the mag I found that the condenser casing was fitted but it was empty! Fitted a condenser and off it went, proved engines do run without them intermittently although that was a wico magneto.

[Stormin 4,458]

I'll have a run up tomorrow Jonathan, for a bit more moral support.   That's if I can get up.  

[expeatfarmer 591]

I stripped the original rebuilt MA1 magneto cleaned the slip rings and brushes, reassembled it and tested it on the bench at low revs it produced a spark that jumped 1/2" to the vice and at high revs a brilliant white spark that crackled. refitted mag to tractor, fired once, adjusted throttle fired again, adjusted throttle and it ran for maybe 6 strokes. Would not fire again, changed the plug same again, changed plug again same again, strange thing is that once the plugs have stopped working, cleaning them does not make them work it is almost as if there is something being burned out in the plugs but I have no idea what. I will try an earth lead from mag to head but given alloy mag to alloy crankcase and cast barrel and head I can't see why continuity should be an issue but at this stage I will try anything. I had hoped not to resort to a later mag. but fearing personal injury from torn muscles and lack of time as I have other machines to get ready for Malvern I think I now have no choice but to use the later Wico mag which has an impulse starting mechanism.

[Wristpin 399]

May have missed this on an earlier post but have you tried either of the problem mags on another machine that has run ok with its own?

Also beware that by asking a mag to jump an oversize gap the spark may find an easier route inside the mag and permanently damage the windings. The received wisdom is that a mag should only be tested via an earthed spark plug set at the normal gap and not off the end of the HT lead.

[Rocboni 257]

Would be interesting to see if 137 will run reliably with a wico mag put enevrything else out of the picture if not already?

[expeatfarmer 591]

Not readily interchangeable to later machines. Have followed Lucas manual test procedures as far as I can.

[Rocboni 257]

The the series A won't fit on 137?

[expeatfarmer 591]

Yes it will that is todays plan I have a later MG2 Wipac Magneto to which I will fit new points and condensor and then fit it.

[expeatfarmer 591]

Refurbished mag ready to instal, turning it on the impulse fires plugs that were dead on the other two mags so fingers crossed third time lucky.