Text stamped in has all but gone, ive scrapped off the paint put all i can make out is Lucas, made in England and below that what looks like a directional arrow and then a number 4. I think it is a E3HM as they are 165mm long, have parallel sided shaft and a threaded portion on the drive end of the shaft. The 4 could be 200304 ?? or am i jumping to conclusions ?I presume these were never fitted to M20's in the 40's and it is a later add on. I am not that familiar with the history of dynamos.
The 'short' dynamo, the 42Watt E3HM was standard fitment for an M20 during the war and up to the introduction of the of the later higher output dynamo. That was the 'long' dynamo, the 60Watt E3LM....
As you have deduced the short dynamo has only one countersunk screw in the body that holds the field coil in place, whereas the long dynamo has two...E3LM types were retro fitted post war when a dynamo replacement was needed, along with the later MCR2 regulator (as opposed to the smaller MCR1 used with the E3HM)...
It sounds as if you may have been sent an armature for the later dynamo...Ian
Checking it out as far as I can deduce the E3MD armature is the one used with the pre war '3 brush' dynamos that have the regulator made integrally with the dynamo...So unfortunately, it appears the problem is that you have ordered the wrong type of armature...Ian
I hope I've got that right...I'm not very familiar with the 3 brush dynamos myself...However, if your enquiring with your supplier with a view to swapping to the correct one they may be able to confirm any differences between the E3MD and the E3HM...Ian
I think that's right Ian, i note that the E3HM has a threaded portion on the drive side of the armature that has a collet to retain it in the Dynamo end plate. The MD is a straight shaft and doesnt have that. The HM is also 20mm longer overall. It stacks up, ive ordered the wrong one. Cheers Ant
All is well, replacement armature arrived today and its spot on!
Can i just confirm that if i want to test that the dynamo motors, i bridge the two connections and put a positive lead to the bridge with a negative to the dynamo shell ?
Last daft question i promise !! I have replaced the field coil and i fashioned a couple of G clamps and a hardwood timber pack inside the dynamo body to compress the coil into the body. I then tightened up the coil screw but no matter what i do i still get a 1/2mm gap between the coil metal core and the body. On assembly the armature spins freely but im sure it cant be right ? Any advise ? Do i need a special tool ?
There is a special tool for compressing the pole shoe (the core) against the body....I'll speak to the chap that used to rebuild my dynamos and get some information on it...I'll post tomorrow.....Ian
The pole shoe compressor tool is like a small scissor jack which is wound up to push the pole shoe against the body...The chap who did my dynamos for years said he'd seen an illustration of one but had never actually seen one...I've also seen the illustration...He made up a small jacking tool to exert the pressure...He also said that even with a tool the screws should be tightened with an impact driver to do them up really tight...
Care should be taken with the short dynamo, that only has a single retaining screw, to ensure the assembly remains square to the axis of dynamo body and doesn't contact the armature....Ian
I woke up at 3.00am this morning wondering if the field coil screw was too long (its a new one) and sure enough its almost a mm longer than the female thread. No wonder i couldnt tighten it up :smiley:
I've had a few like that lately...I've got a problem with my B33 not running correctly after fitting a new engine and after a few days at it I haven't been able to identify the problem yet...So, the brain's working overtime in the early hours...:laughing: ...Ian