Application two 450 HP Crate 502 Big Blocks Gen VI . in 292 Formula SR1
Boat sees little air time and is not beaten often, unless I can get the bride and grandchildren off the boat for a blast or two.
I have been running the 861523A9 aluminum coupler for ten years and just blew the aluminum out of one coupling !
So I pulled the second engine and inspected that coupling, it showed signs of wear so I am going to replace them both.

They do offer a 861523A20 Steel coupling for a few more dollars!
I talked to Mercruiser and they commented I do not need the A20, that is primarily used on work boats ! It is also heavy and more difficult to install !
Then I called CP Performance and they told me that all I need is the A9 Aluminum coupler, if you use the steel you may break something else like a gear ?
So which way should I go ?
Thank You In advance for the replies !
Brian

I have 450 hours on aluminum couplers. 700 HP and 38 Fountain. I'd say run the aluminum. Just make sure alignment is perfect.

Engine alignment and lubrication is critical to the longevity of a coupler. I don't have a high hp/performance engine/boat but I do know that it is critical that every 100 hours or so (more often if you beat the snot out of the boat/engine) the drive has to come off and the alignment checked. The prior owner of my boat thought that the engine mounts were loose and he tightened them - only to ever so slightly knock the engine out of alignment-- ergo coupler went out- cost big bucks to have replaced.

Also, it is imperative that you use the correct lubricant specifically designed for a coupler. To the best of my knowledge there are not a lot of shear stresses on the drive shaft and coupler - but the trimming of the engine changes the amount of the shaft being inserted into the coupler and with each revolution heat is going to generated (movement of the shaft within the coupler splines) - without the correct grease things could heat up and fail.

I have an aluminum coupler and so far no issues at all

The engine is a pure stock 7.4 mpi 310hp with a Bravo 3

Hope this helps

Its all about alignment. The tool has to bottom out and then be able to pull it back out with two fingers.

you have to find the cause first before installing a new engine coupler. how about weak motor mounts area or a weak transom ? Is all of that 100 % strong and free of any rot ?

is your Motor and or motor mount flexing ?

Gimbal bearing 100 % in good shape ?

Engine coupler bolts tight to spec or any missing ?

Did you warp your last new engine coupler when installing it ? its a 3 pass and a proper torque pattern is required to follow plus proper torque specs.

Are you using the proper grease and or greasing it really well ?

You are only greasing the splines not the front of input shaft correct - Merc only wants the splines greased well not the tip of it before installing the outdrive .

Do you know how to actually check engine alignment properly - there is more to it than just stabbing the alignment tool thru the assembly into the coupler and I do not care if it pulls out easy ?

the proper way to check engine alignment is to grease up the alignment tool ( use thick grease ( Merc special 101is great for this if you can find it ) - install alignment tool fully and slowly then pull it out as straight as possible - next is to check the grease that the coupler splines made on the grease - the pattern of these markings on the grease should be completely full and completely even and all should have the depth all the way around the alignment tool. This is how you check engine alignment and basically the condition of the coupler if it is not brand new. .

Mercruiser has a service bulletin out to help with the installment of engine couplers. I can not remember the SB bulletin number at this time.. Also there is a special tool to help with making & checking engine alignment spot on that is more precise than the long bar alignment that everyone uses. This special tool not many really even know about it nor the SB for installing couplers.

Funny how you find out different things when you take things apart.
I found the coupler that failed was almost dry, not lubricated, and no grease fittings on the coupler.
The Yoke was seized in the engine coupler and I had to use Porter Power with tapered blocks to get it off, and let me tell you it would have been easy to damage the boat removing the drive.
It was easy to pull the second engine , I figured if one coupling went the other one cannot be far behind.
The second drive came of easily, this coupler had grease fittings in it and was lubed properly.
I have not remove the drives in probable six years, reason being I have not had time to use the boat and only used it five or six times a year and two years I never even got it out.
I have new couplers in route, U joints and yokes, along with two water pump rebuild kits, it is so simple to redo the pumps when the motors are out.
I very much appreciate you guys inputting.
This web site is really a great resource weather your a seasoned veteran boater or a new guy on the block, and there are many people on this site that enjoy helping people AND THAT IS WHAT ITS ABOUT !
Brian

I guess I can say glad you found the problem now -- you know what I mean.

Regarding lubrication to the coupler - I had made a long extension hose to be used with a grease gun dedicated to coupler grease so that I could routinely lubricate the coupler. Just as a heads up. The grease coupler that I had- at the time I bought at Harbor Freight -- as luck would have it I pushed it on the zerk fitting and couldn't get the sucker off-- Finally after numerous attempts and a long pry bar was I able to get the grease fitting off the zerk. Long and short I WILL NEVER BUY A CRITICAL TOOL FROM HARBOR FREIGHT AGAIN!!!!! I went to Napa and purchased a grease gun end and all is well. I typically squirt a little grease in there twice a year and check engine alignment every other year -- In my world that is around the 100 hour mark.

You are very smart in changing the water pumps. I also did the same thing a number of years ago with we replaced the coupler. The only odd thing - to me was the gimbal bearing that was replaced was sealed-- I now understand that you still can purchase a gimbal bearing that you can grease yourself -- I would have preferred that but haven't had one bit of problem.

Also while you have the engines out now is a great time to scrub the bilge -- I used very hot water and simple green -- did wonders!

take care and above all be safe out there!!

3pointstar

I already scrubbed the bilges, I use the simple green with some hot water and a little dishwashing liquid in a bug sprayer , let it sit for a few minutes and then pressure wash it.
The I shop vacuum all the sludge out and do it a second time.
I had to put a couple of battery ends on my cables at the starters so pulled both starters and alternators off and are having them reconditioned. Things are so easy to do with the motors out.
I'm tossing in a fresh set of spark plugs, distributor caps rotors, and replacing a couple of trim indicator cables that have rotted out. Once again thank you for the input.

Bring this subject up because I have my motor out looking for a leak. I have the coupler removed and my factory part number for my motor is 8M0098795, but I know CP has the Merc HP one listed 861523A9 which is cheaper. I'm assuming the one from CP will work fine . Only reason for thinking it needs to be replaced is about 100 hours ago I killed the drive and there were some small burs on the splines of the coupler, as result of the twisted the input shaft on my old drive at the time of failure.. My alignment knock the burs off and I have had no issues since. Thoughts?

This is what the current coupler looks like, should I just reuse it?