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wallism
United Kingdom
65 Posts |
 Posted - 09/04/2008 : 16:36:09
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Hello everyone. I would appreciate any help with the following problem. While building up a small dynamo engine I find that the dynamo will not bolt down to the front housing because the crank bevel gear appears too far forward. The gap between the dynamo and front housing is perhaps 100thou. (A lot more than I would expect to shim!) If I remove the gear, replace the dynamo and put the gear on the crank the wrong way round, then everything turns nicely suggesting to me that the dynamo, gears and housing are correct. What does this leave? Front bearing inner race too thin? Bevel gear too thick (it's 750thou)? I could just turn a bit off the back of the crank bevel gear but that’s a bit irreversible. If my description is poor then please say and I'll post a drawing. Thanks in advance for any ideas.
Mark Wallis |
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kimber
United Kingdom
1529 Posts |
Posted - 09/04/2008 : 20:11:17
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This does sound to be a rather odd state of affairs. Without having everything in front of me, it is a little difficult to know where to advise you to start looking for a solution.
My first guess would be that the dynamo bottom bevel gear is incorrect. The P-type one sits a little deeper and might give rise to the problem you describe.
I suppose it is possible that someone has 'messed about' with any of the components, but unless you have some known good ones with which to make a comparison it will be difficult to check.
I think you may be able to shim under the dynamo bottom bearing (outer) to raise the armature in the body which might reduce your 100 thou shim requirement to achieve the correct gear meshing with minimal backlash. I believe that the dynamo top cover plate will allow the top bearing to sit a little higher, but you will need to carefully check this before tightening anything.
It does sound curious though. I had the opposite problem on a P-type engine recently i.e. the dynamo gear wasn't meshing deeply enough into the crank gear, which is of course more easily overcome. (In my case the reason was that somebody had machined about 0.040" off the back of the dynamo bevel gear).
I suppose it is not critical how you resolve it and there may be several ways of doing so but it is always preferable to know why there should be a problem in the first place.
In fairness, I should say that I have no direct experience of the small dynamo engine, but I imagine that the same principles apply. |
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ags
United Kingdom
275 Posts |
Posted - 09/04/2008 : 22:57:35
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Hi both,
Another possibility, based on my own P experiences is that the crankshaft is actually in the wrong position. On the P type the fore and aft float of the crank is controlled by a grooved white metal washer which fits around a protrusion on the front main bearing and butts up to the flat face of the crankshaft gear. If this washer is the wrong thickness then the position of the crank can easily vary by your 100 thou. On the P type quite a lot of shims may typically be needed, between 15 and 25 thou is quite common, but I do think that your figure means that something is wrong somewhere.
I am not sure how the M engine crankshaft end float is controlled, except that there has to be some arrangement to do this and this might need to be adjusted, shimming of ball races fore and aft for example or a similar arrangement to the P's at the rear main bearing.
This is another possibility to be examined before you take any drastic steps like grinding thickness off gears. As has been mentioned I would certainly advise that you make sure that you are trying to assemble a correct set of parts, and do some swaps to obtain a proper set if you have been unfortunate.
Good luck with the detective work and please report your eventual findings.
Andrew Smith MMM571 |
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talbot
United Kingdom
718 Posts |
Posted - 10/04/2008 : 09:02:18
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I had the same problem a couple of weeks ago. I have fitted a new, split inner race front crank bearing and I think the one I am using is a little thicker in the centre than the original. I have ground the crank bevel gear and now only need a thin shim under the dynamo to give me the required "click". Unfortunately you can not face the gear in a lathe it's far too hard. It is probably worth checking the dynamo but the positioning of it's bevel gear is set by the poosition of the bottom bearing. One possibility is someone has shimmed the gear lower.
Cheers
Jan T |
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davies
United Kingdom
699 Posts |
Posted - 10/04/2008 : 09:43:41
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| I can lend you an M type bevel gear if you would like to check.Regard Rich |
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wallism
United Kingdom
65 Posts |
Posted - 10/04/2008 : 10:01:16
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Thanks everyone for some great ideas.
Jan T: I just fitted the same bearing! Perhaps I should have mentioned that.
Rich: If you can just tell me the thickness that should help (mine is 0.750") Thanks for the offer.
All: Yes, I'll check everything else before I start removing any metal as none of these parts have ever met each other before. Thanks folks and expect more from me when I fix this snag. Mark
Mark Wallis |
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talbot
United Kingdom
718 Posts |
Posted - 10/04/2008 : 12:41:38
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Mark,
You say you are using new parts. It's important that you set the alignment of the bevel gear box/dynamo to the pinion in the cylinder head. This could involve rotating the bevel gear box casting (and re dowelling)or more pertinently shimming the box away from the block.The latter will change the gear meshing. The job isn't difficult and it has been covered in these pages before.
Cheers
Jan T |
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kimber
United Kingdom
1529 Posts |
Posted - 10/04/2008 : 15:47:23
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quote:
Originally posted by talbot
Mark,
You say you are using new parts. It's important that you set the alignment of the bevel gear box/dynamo to the pinion in the cylinder head. This could involve rotating the bevel gear box casting (and re dowelling)or more pertinently shimming the box away from the block.The latter will change the gear meshing. The job isn't difficult and it has been covered in these pages before.
Cheers
Jan T
I agree that it is important to align the dynamo armature centrally with the camshaft drive pinion and the method described but this will not have any bearing on the meshing of the crank/dynamo bevel gears as the whole assembly (including the crank) will move forward if the housing is shimmed off the crankcase. The dynamo bevel gear meshing can be dealt with with the crank on the bench with just the front housing fitted. |
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wallism
United Kingdom
65 Posts |
Posted - 11/04/2008 : 11:57:39
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Thanks. I understand that from the books and have read some very good descriptions of it all here. In the couple of hours a week I get to do this I'll chip away at it and update this thread with progress.
Mark Wallis 1930 M-Type DV5170 |
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davies
United Kingdom
699 Posts |
Posted - 12/04/2008 : 11:34:46
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| Mark, I have just measured the thickness of a crankshaft bevel gear and it measured 11/16 inches. Regards Rich |
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