propshaft failures

[james69z28]

I am having problems too. my son broke 2 or 3 on his hpdi stock lower unit on a hydro tec modified motor on a stroker. losing 3 high dollar props! so we had one made out of a Dana 60 axle shaft ( they handle 7 or 800 hp to solid ground, they will twist but not usually break) but with around 40 hours it has worn about 16 thousandths under the rear needle bearing area. I had a fat shaft merc checked and they said it was a Rockwell c 37-39 hardness, the Yamaha "fat shaft" my son had made, read as a 47-49 Rockwell c, we are now thinking of using a harder material ( which may shatter easier) and we are going to use the mercury fat shaft needle bearings which is approximately .3 wider this will spread out the load by 30% thus reducing the wear, we hope? I got on here to ask if anyone had checked the stock Yamaha shaft on the Rockwell scale also to see if they had checked a mercury fat shaft also
because I do not believe the new one we had made is harder than the factory mercury? or if anyone has a better material I need to know what to use.

not wanting to hijack just adding more info.

[Mr. Demeanor]

I am having problems too. my son broke 2 or 3 on his hpdi stock lower unit on a hydro tec modified motor on a stroker. losing 3 high dollar props! so we had one made out of a Dana 60 axle shaft ( they handle 7 or 800 hp to solid ground, they will twist but not usually break) but with around 40 hours it has worn about 16 thousandths under the rear needle bearing area. I had a fat shaft merc checked and they said it was a Rockwell c 37-39 hardness, the Yamaha "fat shaft" my son had made, read as a 47-49 Rockwell c, we are now thinking of using a harder material ( which may shatter easier) and we are going to use the mercury fat shaft needle bearings which is approximately .3 wider this will spread out the load by 30% thus reducing the wear, we hope? I got on here to ask if anyone had checked the stock Yamaha shaft on the Rockwell scale also to see if they had checked a mercury fat shaft also
because I do not believe the new one we had made is harder than the factory mercury? or if anyone has a better material I need to know what to use.

not wanting to hijack just adding more info.

Cant help on the hardness but I switched from the stock rear carrier bearing to the type that has a "blank" between each needle. Didnt make sense to me as there is less needle bearing surface area but a couple people recommended it and so far so good.
Read this thread for more: http://www.screamandfly.com/showthre...opshaft-repair

[powerabout]

I guess Mercs next step is to support the shaft with tapered rollers at each end, which is going to make it way more complicated but that allows the shaft to bend, so its pay for that model or break the modified fish motor gearbox that gets surfaced.
They have taken great steps forward with pinion bearing/gear support but the propshaft is much more problematic to modify

Perhaps multiple narrow bearings in the carrier might help?

[mrcrsr]

I guess Mercs next step is to support the shaft with tapered rollers at each end, which is going to make it way more complicated but that allows the shaft to bend, so its pay for that model or break the modified fish motor gearbox that gets surfaced.
They have taken great steps forward with pinion bearing/gear support but the propshaft is much more problematic to modify

Perhaps multiple narrow bearings in the carrier might help?

that is already being done, the verados use it, i actually have one apart rite now. they use a tapered roller bearing inside fwd gear, and another in the carrier, with shims behind the bearing in the carrier to set endplay, similar to the way wheel bearings work.

[CharlieN]

James, you are definitely not hijacking, you are spot on what this thread is intending. Good information leading us to the best chance to not have breakage.
Chris, the needle cages just keep the rollers in line. You could see your stock ones were getting out of line which caused the chatter on the shaft. It is good you take the time to inspect and learn, that saved you from a failure.

James, the original Dana axles are not anything special, the ones you would buy from Moser, Stange of one of the race axle companies will be either 4340 or 300M. We changed to 300m in the endurance Porches a few decades ago and have not had a shaft failure since. That material is very springy if that term is fair.

My mind is leaning toward the needle bearings being the true issue with the fatigue failures. They need a very hard surface to roll on, much harder than the material should be to remain "springy" to withstand the flexural loads involved.

With 17-4PH being mentioned as Yamaha's material my metallurgist can not comprehend it being hard enough for a roller bearing to run on it.

Hearing that Mercury is looking into tapered rollers on the shaft is cool, My thoughts for us might be to used ball bearings with a good material shaft hardened to the RC35 range or whatever would be the springiest temper for the material.
But we do need to know what the shafts are now to determine how to fix this.

[Mr. Demeanor]

I wonder if a roller bearing stacked behind the needle bearing would work. You would need a carrier with an extended bearing section but you would get the support of the needle with the roller being more forgiving at the flex.

[CharlieN]

Nice thing with billet carriers is total freedom to try different bearings and location on the shaft. The ball bearings I intend to try just need consideration to exhaust flow due to larger OD.

[Mr. Demeanor]

Just drill more holes

[CharlieN]

Or the way I will be going at it is with a turbocharged 4 stroke that will not be exhausting down the mid.

[Mr. Demeanor]

Getting the bearings and thrust washer as close together as possible would seem to be the best if exhaust flow is not a concern.

[patchesII]

If I remember right Scott Jordan's were some type of axle steel that was plated. I believe he just recreated the Mercury propshaft. As was said earlier, they're not SS and they're not friction welded multi piece

[CharlieN]

Eric, are Scott's shafts holding up to surfacing? The good axle steels are generally 4340 and sometimes 300M

[powerabout]

needs to be very hard for rollers to roll on

[patchesII]

I'm sorry, I was wrong. Scott's were 17-4

http://www.screamandfly.com/showthre...2-5&highlight=

[outasite]

My take on broken shafts is that the primary cause is "prop hammer" almost all of the props that we run,if you slide them up to the washer you can move the front of the prop up and down on the shaft.Most will have .075 to .100 clearance.Even with a new washer and a tight nut,when surfacing the prop will hammer the shaft,every time a blade hits the water the hub will hit the shaft.If you look at the inside of the prop quite often you will see a shiny ring.this will work harden the shaft and failure is likely.I turn a thin bushing for all my props that gives a snug fit at the front.No problems yet