JaayTeee

Just for sh!ts and giggles, swap the props from side to side ( you’ll have to run the shifters backwards )and see how it comes on plane….I know mine broke loose easier when turning out, also, if your props are the issue with the RPM
difference, it should change to the opposite side, if it stays the same, it’s an engine issue.

Brad Christy

Baja33Outlaw,

In the event swapping props works.... Just don't run them like this for long. You don't want to be putting "forward" pressure on the "reverse" gear. Or more to the point, on the top cap of the drive, that is designed to withstand pressure from the thrust of the bevel gear in reverse. I've heard of guys testing a LH prop on a RH drive and cracking the thrust bearing through the top cap. It's not pretty.

Thanks. Brad.

baja 33outlaw

okay, I'll give that a try. I've got 2 sets of props, the current ones on there have been labbed, and run the same rpm, but they plane worse. The set that has a 400-500rpm gap are new and haven't been matched plane slightly better. I'll have to try both sets to turn in, and see how they do.

Brad Christy

Baja33Outlaw,

I don't see the drive showers in any pic you've posted. To be clear, the drive shower pickup should be on the side that would catch water as it is slinging off the prop tips. If the drives have been swapped, or whatever, and the drive shower has not been relocated, they can suck air in instead, and could very well, at the very least, contribute to your issue. It would actually make a lot of sense.... The props are fine as long as the outlet of the drive shower, over the top cap, is below water. As soon as you start to take off, the water evacuates behind the transom, elevating the drive shower cap above the waterline, allowing air to be sucked down the drive shower hose to the prop, causing cavitation, and the props blow out. And, the higher the RPM, the worse it gets. Hmmmmm....

We need a pic....

Thanks. Brad.

baja 33outlaw

okay, thanks for the warning. I'll just try to plane, and if it's able to I'll get up to 50mph just to see if my cruise rpm speeds are any better. Let me know if I shouldn't try going up to that speed.

Brad Christy

Baja33Outlaw,

I'm not the expert. I'm just helping solve a puzzle and forwarding advice based on what I've read or been told.

I've been told be people, trying to sell me a prop, that running a LH prop in reverse won't hurt anything. Upon asking others who work on drives, I'm told it's frowned upon. After doing some research on cone clutches (I will probably be addressing mine this winter), and seeing how the whole mechanism actually works, I will never run a LH prop on my RH drive.

Look at the pic

Specifically, the gear set assembly. The top gear is "reverse", and bevel gears apply "thrust", pushing the gears away from each other. This puts all that pressure against the top cap of your drive, which is only designed to withstand (mostly) idle speed gear thrust pressure.

In your case, it's fine for a quick proof of cause test. Just keep it short. For me, prop testing is seeking WOT top end speed, so I would be putting maximum pressure against the stock, cast aluminum, top cap of my drive for a semi-extended run. Just nope....

Thanks. Brad.

JaayTeee

Bravo drives aren’t rotation specific, I’ve switched them over, and back multiple times without issue, you’re going to need to run it at WOT to find out if the RPM issue is still occurring

baja 33outlaw

Okay, sounds good. I'll try it and see how it does.

Brad Christy

JaayTeee,

I get that. But, with twins, the engines are typically counter rotating, correct? (Genuine question) Or do they just put all that gear thrust against the top cap of the LH drive?

I suppose with just 496HOs, it's probably not enough HP to really hurt anything. But, from a mechanical engineering standpoint (Which is where most of my reasoning comes from), it just seems like a bad idea to place the higher force against the weaker structure, even if failure thresholds are not exceeded.

Thanks. Brad.

PQ290Enticer

Is anyone on this thread using 2" shorter lower units? I'd like to see a pic if you are. I was looking at the video again and it appears that the props are simply loosing bite and it's not a case of BOTH drives popping out of forward or the hubs spinning because IMHO the rpm would INSTANTLY go to the limiters and his does not. I had an old school press in rubber hub let go and that's what happened to me. Anyway, I thought in the interest of eliminating variables I would take a pic of my stone stock B-1 lower units with a tape measure in the pic showing the drop from both "plates" to the centerline of the prop shaft and in doing so, I now am wondering where the 2" loss in height comes from. I see the 2" between the plates, is that it?? Is there still the lower cavitation plate on a 2" shorter unit or does that just go away? FYI, the one dimension is 10-1/2" and the other is 8-1/4".