1985 30 HP welding driveshaft

[G DANE]

I got a bargain on a 1985 30hp that was on a boat that sunk. I cleaned it ud and took powerhead apart, but crankshaft, bearings and rods are shot, cylinders needs bore to oversize. Going thru my partspile i found I have a 1978 powerhead with fine compression. I can make a bracket to hold the new style "no start in gear mechanism" no problem. But I will have to make a costum driveshaft welded from an old 4 spline 25 HP shaft and a short 1985 driveshaft i found too. Is this doable ?? Anyone ever tried to weld and corretc warp on a driveshaft ?? will it hold up, I have a TIG welder, and some experience in stainless welding.

 

[5150abf]

Re: 1985 30 HP welding driveshaft

It is certainly doable, often times welds are stronger than the metal around them.

Make sure it is super clean and put a good bevel on both parts, do a base and cover pass with the correct filler rod, grind it down and you should have it.

I would think getting the length right would be the hard part.

 

[G DANE]

Re: 1985 30 HP welding driveshaft

I do have the original driveshaft from the 1985, I would just hate to cut it. I will compare the length it enters the rusty cranck to the length the old 25 Hp 4 spline goes into the 78 cranckshaft. Then I can calculate the length I have to end up with from that. My concern is too if the 4 splines is strong enough, as I will use bypass cover, intake and a carb from a 35 HP, and hope to get 30 HP out of it on the propeller. But the center portion of the original driveshaft is actually turned down to the same diameter the old 25 ran with, probably to make it flex if the prop hits something, and save the gears. Do you think I will be fine ??

 

[crb478]

Re: 1985 30 HP welding driveshaft

I once had two shafts turned down to a pencil point on one end each and then welded together. Then the single shaft was turned to the shaft size on a lathe. It was perfectly straight and round when done. It worked fine, and was definately strong, but it was beyond my skills. A friend with a mechine shop did it for for less than $50, but that was several years ago.

 

[G DANE]

Re: 1985 30 HP welding driveshaft

Did the weld today. The were a couple of smalle groves, where I didnt fill quite enough material in, but they were minor when it was turned afterwards. I figure if the 4 splines could stand the turque of the motor, the solid shaft must be much stronger. Time will show if the 4 splines are strong enough, as it will get 5 - 7 more horsepower, but I never heard there should be problems with the old driveshafts on the old 30 HP and its same size. Guess they calculated in some safetymargin when calculating shaft thickness and splines. It was surprisingly easy to correct in the lathe, did it while it was still warm, up against the center pinol.