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MG MGA - Twin Cam - Dynamo pulley out of line

Have just rebuilt the engine and having fastened the dynamo in place, the pulley is about 10mm out of line (forward)compared to the crankshaft and water pump pulleys?? The top mounting points of the dynamo pick up correctly (on the water pump casting at the front and the inlet manifold at the rear). Everything is in the right place, yet something is wrong. I tried the alternator from my 1600 pushrod car, same problem. Both Dynamo's are C40 and appear to have standard size fan blades etc, so the pulley should be in the right place. The engine was dissasembled when i got it, so i have no reference. I will post this on the Twin Cam board later. Any pointers would be appreciated.

regards
Colin
C Manley

Ooooppss. I meant to say "I tried the DYNAMO from my 1600 pushrod car" not 'alternator'.
C Manley

Is the dynamo to far forward or too far back?
Is the dynamo fitted to the front of the water pump hole and the front of the manifold hole?

Mick
Mick Anderson

Mick,
The dynamo is too far forward. Yes, it's fitted to the front of the water pump hole and the front of the manifold hole. Photo should show the misalignement (you may have to drop the image into a graphics package to view close up) but there is quite a bit of glare from the flash so it needs careful study.

regards
Colin


C Manley

Colin,

I have not had that problem, but I have photo of another Twin Cam which also seems to be misaligned.
Would you compare the attached photo to your engine, particularly the area between the dynamo front plate and the pulley. Also the thickness of the dynamo front plate.

Mick


Mick Anderson

Hi Colin I should think you need to talk to Bob West re this problem as he builds these engines all the time


gordon
g c pugh

Mick,
Visually comparing, i think it appears to be about the same amount of misalignment dimensionally, it's hard to judge as your image with the belt fitted appears to show it to the extreme. Both also appear to have dynamo front plates of equal thickness and fan blades of the same depth. I could take 2-3mm off the water pump boss and the inlet manifold, plus perhaps 1mm off the mounting face of the dynamo front plate to take the dynamo back a bit (& shim the rear mounting fixing to suit), but i'm reluctant to start butchering. Another alternative is to remove the water pump and crankshaft pulley and shim them out some. This is preferable as appears to fix the cause, rather than the symptom, doesn't involve butchering & is reversible. I have put a call out to Peter Wooods to tap his brains and will update this thread if i get any advice from him. Of course, i could do nothing and live with the short life expectancy of the fan belt - not a good idea.
(p.s. correcting your earlier question and my reply; the dynamo mounts on the front of the water pump boss and the REAR of the inlet manifold boss)
regards
Colin
C Manley

Colin

It may be worth giving Bob West a ring. He is probably the most experienced in Twin Cam issues in the UK. 01977 703828.

Steve
Steve Gyles

Colin,

I hope to be able to take some measurements tomorrow on a Twin Cam that has the pulleys lined up.
One point, the 1600 and the Twin Cam have the same part number fan behind the dynamo pulley.
Can you see if reversing the dynamo pulley is possible and if it has any effect. Does your pulley have a part number cast on it anywhere?

Mick
Mick Anderson

This may seem like a very dim question, so no change there then, but are the L shaped brackets that bolt to the block reversable which would move the dynamo backwards,


gordon
g c pugh

Colin

Clausager says that the Twin Cam dynamo was a C39PV-2, modified for the application and had Lucas part number 22295 (whatever that was). Could be your answer. Speak with Bob.

Steve
Steve Gyles

Gordon,

To answer your question, there are no brackets. The front plate of the dynamo bolts directly to the water pump casting. This shows clearly in the photographs.
The rear dynamo plate bolts directly to a hole in the inlet manifold casting.
This is what makes it such a puzzle.

Mick
Mick Anderson

told you it was a dim question, knew I should never get involved with technical questions I'll stick to my tools in future


gordon
g c pugh

Have spoken with Geoff Barron and he advises that the TC and the pushrod dynamo's had different pulleys and fans - the TC fan being slimmer.
Twin cam; pulley part no = AEH605, fan =1G1783. Pushrod; pulley = 12H1178, Fan = 17D11
I'll check my part no's over the weekend, if they are all pushrod, i'll call Bob West etc. Don't know why MG didn't simply design the TC mounting points in a position such that the standard depth pulley and fan could be used i don't know. Thiner fan blades implies less airflow through the dynamo.

Mick,
There seems to be an issue over whether a C39 or C40 dynamo is correct. Moss list C39 as original for the pushrod engine with C40 as a replacement, while they are completely silent on the dynamo P/No for the TC. Could you check in the body casing for any ident? My experience of buying & exchanging dynamo's years ago was that you retained your own pulley & fan so i think C39 or C40 will make no dimensional difference.

regards
Colin
C Manley

Colin

I recall from previous threads that the pulley fan throws the air out, not draws it in. In other words, the fan pulls air through the body of the dynamo. A slimmer fan could have the the drawing power if it rotates faster for any given engine RPM. i.e. maybe the TC dynamo pulley is a smaller diameter and therefore rotates faster. Or, maybe there is no overheating problems anyway with these generators and the size of the fan does not make a lot of difference. There are some electrics wizzes on this forum who I am sure will tell you the right story!

Steve
Steve Gyles

Not sure if this helps. I ran into this some years back. I carried a spare in my trunk on a long trip. Sure enough, the gen went out. no problem just swap them out. Well, you guessed it, the pulley didn't fit properly. it fouled on the casting. As I recall, the front casting on the replcement gen was different. I now wonder if that has something to do with this problem.

I have read somwhere that there are other versions of this gen with a real rear bearing that was used on Ford tractors. How many variations of the basic generator (not including fan and pulley) are there?

Chuck
C Schaefer

Colin,

There seems to be some confusion about items that are common and those that are different with the Twin Cam and Pushrod dynamos.
I have looked at all the Service Parts Lists and looked at a dynamo on a Twin Cam, that fits correctly.
Firstly, and most important, all fans are the same on the 1500, 1600, and Twin Cam. Part Number 1G1783.

The pulleys are all different. The 1500 is 2A412. The 1600 is 1H998. The Twin Cam is AEH605.

The Twin Cam dynamo is a C39 with nuts holding on the terminals. Most C40's seem to have push on terminals (at least on my Triumphs). Any differences between a C39 and a C40 should not matter, as only the front plate, fan, and pulley have significance to your problem.

The measurement on the Twin Cam from the centre of the pulley groove to the front plate is 0.875" and the plate is 0.350" thick.

Your problem is almost certainly that you have the wrong pulley. The Twin Cam pulley groove and the pulley centre must have more offset. The Twin Cam pulley is part number AEH605, but I cannot see it marked on the actual pulley. If you cannot find one, you might find a superseded Twin Cam pulley part number AEH504 (marked on the pulley) which has an overall diameter of 4 and 3/4 inches compared with the later type which is 4 inches. The older pulley will align properly, just turn a bit slower.

Mick
Mick Anderson

Colin,

I have spent the weeekend gathering information that may help you.
The first step is you must get a correct Twin Cam pulley. Peter Woods or Bob West should be able to help you. Jim Alcorn in California has also offered to sell you one.

There are two types of Twin Cam pulley. Both will fit correctly. The later type is better, it is smaller and therefore turns faster.

For information on the two types there is a PDF file on website:

http://www.angelfire.com/amiga/mga/index.html

I have attached a photo to this message to identify a Twin Cam Dynamo. Also the next two messages with two more photos. You are unlikely to find a genuine Twin Cam dynamo, but if you fit a Twin Cam pulley and also reduce the dynamo fan blade width so that there is 13/16" from the front face of the dynamo front plate to the centre of the "V" of the pulley everything should be OK.

I don't know why your dynamo fan blades are so wide, the 1500, 1600, and Twin Cam should all have the same fan, but your photo and my photos seem to indicate a problem with blade width.

Mick




Mick Anderson

Colin,

A second photo attached.

Mick


Mick Anderson

Colin,

A third photo attached.

Mick


Mick Anderson

Mick,
Thank you for all your effort. I have just finished sorting out, cleaning up and painting the pulleys i had. I found a slimmer fan blade in my remnants box - it has no P/No but is visibly much slimmer. Each of my dynamos had deep fan blades. I removed one fan, plus the deep spacer from behind, replaced it with a slimmer spacer, put on the slimmer fan and, having reduced the depth of the aluminium boss on the back of the pulley (which was the 4" smaller diameter one - but not AEH 605 or 504)now have alignment. Incidently, neither of my pulleys are as large as those in your images. The repainted offending items are now drying on top of the heating boiler, so i will try and post an image tommorrow, once paint has dried.

I think the whole issue of slimmer fans on Twin Cams all stems from a cock up by MG when they dimensioned the castings for the mountings (manifold and water pump) and when they found it brought the dynamo too far forward, they got round it by using shallower fan blades and spacers, rather than retool the investment castings and simply move the mounting points back.

Thanks all for your help.

Colin
C Manley

I believe we have come to the conclusion that Colin has an incorrect thicker than normal fan on his dynamo. This would apparently also require a thicker spacer washer behind it to prevent fouling the blades on the front plate. While changing to the correct thinner fan he will also need the correct thinner spacer washer.

Notice also in Colin's picture that the (too thick) fan has notches in the back corners of the impeller blades. These notches are needed in a large diameter fan to clear the adjuster bolt in an early application dynamo. The tip of this bolt can be seen in Colin's picture. Early dynamos, possibly all 1500 type with the threaded connector studs, have the adjuster bolt located slightly closer to the armature rotational axis. I believe the difference in part numbers for the fans is due to the larger diameter fan on the later model (1600 type) dynamo, not any difference between pushrod and Twin Cam engines, and that they all use the thinner fans.

The problem here is that the larger diameter (thinner) fan cannot be mounted on the early type dynamo, as the blades will foul on the adjuster bolt. I ran into that problem some years ago when installing an aftermarket plastic pulley and fan (all one piece) on my original 1500 type dynamo. When installed the fan blades straddled the adjuster bolt and prevented rotation. The expedient solution at the time was to nip the corners off the fan blades to clear the adjuster bolt.

Colin's pulley is also (by the picture) a pushrod engine type pulley composed of two sheet metal stampings riveted to the alloy hub, where the Twin Cam standard issue pulley is one piece iron material. Both pushrod and Twin Cam applications called for two different diameter pulleys (and different length belts to match) at various times in production. There will therefore be four part numbers for pulleys. I do not know if the pulley groove offset will be the same or different between sheet metal and iron pulleys. I suspect the offset is similar, as the pulley sits quite close to the fan. If the offset is the same then sheet metal and iron pulleys would be physically interchangeable (with the correct belt length).
Barney Gaylord

This thread was discussed between 15/11/2007 and 18/11/2007

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