FYI Bravo1 HP Coupler
 

You to can lose a motor if you don’t follow this. The HP coupler it will put pressure on the crank thrush bearing when under a load.

Talked to merc racing this morning the HP coupler that was sold to me was not right for my application. The shaft on my unit has a longer taper with 2 o-rings on it which makes it stronger. The shaft for the HP coupler taper is shorter with 3 o-rings. Merc says to either change shaft or have mine turn down. I told them that if I did that it would weaken the shaft either way but this was their fix. So I am going to turn down the coupler end down 1/2” instead.

Been there. Done that. I used the coupler with my long shaft and didn't realize that when I tightened the drive the shaft pushed the coupler forward which in turn had the crank thrust surface bound tight against the rear main cap & journal. One new crank later and a rebuild I machined 1/2 inch out of the rear of the coupler.

Ya learn something new everyday. Are you guys referring to the coupler with the extended snout?
Eddie

I've been using the HP coupler with the 2-ring shaft for 3 seasons going on 4 without any problems. Was totally unaware of clearance issues. How do you determine if the shaft is too long?

I found out when I was removing the drive. It would not come out with any amount of prying. Had to cut the input shaft on the inside of the transom with a sawzall, then pull the drive. Engine had to come out, took off the coupler and had to beat the remaining splined piece of input shaft out of the coupler. Once done, thought no big deal, replace the input shaft. I had my motor hanging on the hoist. Went to reposition the motor so I pulled on the crank pulleys. The pulleys and crank moved about 3/16th of an inch forward first then everything else followed. It should be .070 thous max. Upon teardown, found the crank thrust surface completely destroyed. At that point I just replaced everything in the motor with new. Bear in mind that my transom thickness is 2 1/2 inches thick instead of the recommended 2 - 2 1/4 inch which pushed my drive back even further from the coupler. I guess if I had standard transom thickness I would have noticed this problem when installing the drive as it would of bound up tight before the drive pulled all the way in. Oh well, expensive lesson learned.

Good thing ya caught it. I guess I just lucked out by not having this problem. Do you have HP gimbal's?

What is the part number of the hp coupler? I just lost the coupler I installed about 100 hrs ago I believe I had the a11 coupler.

I got a call from a customer in a panic last night regarding this issue so I figured we would take some measurements. We measured from the part of the U joint yoke that sits against the gimbal bearing to the rear of the coupler (which would be the flywheel).

There is a difference of up to .278. The point of interference is the spline on the long couplers/old shaft , the new style shaft is the same length but more spline. On the short couplers the shaft runs into the plug that closes off the spline cavity.

The new 3 o ring shaft is used after serial 0M10000, roughly 2000 model year.

What we don’t know is the dimension from the bearing to the flywheel on an installed engine. Anyone want to measure?

What I am finding in my case is the spline is bottoming out before the nose of yoke shaft hits the back plug on the coupler. Even if the plug was not there it would not go any further...Then next interference would be the taper on the shaft if I could get it to go deeper. I have the 9 1/2" two o-ring shaft. My question is on the three o-ring shaft is the spline them self longer than 3" or 3.250 from the nose of the shaft to the end of the spline. If the spline is more than 3.5” long from the nose with the plug knock out and turn around this would give it 0.250" more clearance and correct the problem then.

So, if I understand correctly, the coupler with the long snout would probably not work with an old-style bravo1 input shaft, (2 o-rings), because of bottoming out on the shorter splines?

Thanks for the info, guys!