View Full Version : Old VP MD7A Alternator Options

12-11-2008, 12:54 PM
"Resurrecting an old VP MD7A engine which had been submerged. Alternator is odd... a French SEV Marchel unit. Its likely history. What alternatives are possible? Seems to me any self regulating 35 to 60 amp that could be made to physically fit and use an appropriate diameter pulley could be used. Direction of rotation on an alternator is immaterial from what I know. No, I am NOT buying a VP part at 10x price!"

12-11-2008, 03:15 PM
"I had the Marchal 25 amp unit and it went bad in the Bahamas, Nassau.
They said there were no parts available.
I tried a couple of inexpensive alternatives. The issues were the space on the underside of the unit where it bumped down against the engine block. The next issue was having the pulley the same distance from the front of the alternator to line up with the fan belt and have the lower bolt holes properly spaced so the pulley lined up with the fan belt. The next issue was having the new alternator match with the tensioning bar, meaning allowing for the tensioning bar to have the appropriate amount of wiggle room to get the proper tension. Too long or too short did not work. The next issue was that the tension bar needed a curve to wrap around the alternator to get to the tightening post. A straight bar did not work. The next issue was to get the new size of fan belt to fit.
I ended uip with a Volvo Penta alternator for $300 or so.
This alternator shop was very helpful but none the less I made about 10 trips back and forth returning and buying different parts.
Ultimately the most important part was lining up the pulley with the fan belt. Only the VP would do that.
Once you have tried some other brands of alternators you will understand what I mean.
I was fortunate that it was only a 15 min dingy ride and then a 10 minute walk to the alternator shop. We became best friends by the time I was through. They had this preehistoric giant machine to test alternators that looked like it was out of a Frankenstein movie...dials and gauges all over with motors and levers you wouldn't believe. The work room was piled everywher you could see with old trashed alternators, torn apart , guts hanging out, piled in piles, in boxes, in drums, on chairs, workbenches everywhere.
I ended up making a tensioning bar out of a piece of angle aluminum and an old bracket. The original was too short. Believe me I tried everything. Good luck."

12-11-2008, 04:25 PM
"Thanks Joe, I appreciate your long reply. Sounds like you really had a lot of problems. Truth be known, I have a lot more time and shop capability than I do money. Re-bracketing for a common $50 alternator will just require a bit of time and thought. I have a antique Van Norman H/V mill as well as a metal lathe which will help too.

Some thoughts:
- the v-belt is not an issue as I need a new one anyway... I use generic industrial duty Gates "green" on everything, from the pickup, cars, tractors, farm equipment and the mower deck. Yes, cost about double but last four times longer than typical by the way.

- already have a curved-over-the-top long slotted tensioner thats basically stamped 3/16in plate... will bolt up to any flat surface.

- can mill a new base bracket if needed... and align the pulleys in the typical way... gives me an excuse to play with the mill anyway.

Biggest trick will be figuring out which alt lends itself to the re-application... thought that maybe some others (like yourself) had already did this and has a shaft that will accept a generic 6" pulley or the original tapered key way type on this Marchel unit. This old engine drives the alt from the outside of a 13 in (or so) diameter flywheel turning 2500 at full throttle, so the modern little 3 inch or so pulley will be trying to turn the alt at 10k plus on rpm and really suck up a large portion of its torque. Needs to be about 5k.

Its a brand new inboard installation (conversion from outboard) and will be totally rewired... I can design the wiring harness as to whatever will be needed.

Any specific 12 vt alternator suggestions?

Thanks, Dave"

12-12-2008, 12:47 AM
"I ended up returning everything except the Volvo Penta Marine. It was the only one that kept the pulley in line with the fan and fit in the spacew when bolted up.
Find a local place with an acceptable reeturn policy, then try a few.
As I said redoing the bracket was the final step to make it work.
I have an MD11C."