2000 mercruiser 7.4 coupler issues....

[thegoat86]

So....... my nephew was racing my boat across the intercoastal last weekend. :nono: The obligatory burning rubber smell came up through the boat. Followed by shuddering and shaking. We Idled the boat back to shore, Called tow boat and headed back to the launch. I thought he smoked the motor. When I got it home I started it on muffs and the idle was perfect. Figured out the problem then. I ordered the replacement part from sierra. I am going to tackle this project myself. Looking for any advice and pointers on other things to look for while I have the motor out. I am shopping for an alignment tool this weekend. I read about gimbal bearings and rubber sets and such. I plan on changing the motor mounts. They are showing signs of heavy corrosion. Maybe a link or video as to its replacement would be cool. Thanks Ya'll

 

[alldodge]

Guess we should say that it was a problem racing the uncle's boat, it wasn't the nephew's fault the coupler went out.

The coupler will be as easy as it takes to remove and reinstall the motor. Having corrosion on the mounts may be an issue (don't know, no pics) but corrosion would not be a litmus test. If the mounts are solid, stringers also, you should be good. The alignment bar would be the determining factor.

Replacing them prior to reinstall would take away the need to remove again to replace them.

Check the wiring, bilge and hoses. See if they are still pliable

 

[thegoat86]

Sup AD, missed ya buddy. I will send some pics once I start the removal. Going to invest in a freshwater cooling system as well. Was hoping the motor was toast. I have in mind a stroker kit with a nice cam........

 

[alldodge]

Was hoping the motor was toast. I have in mind a stroker kit with a nice cam........

Say WHAT, if that's the case, it was smoking and there is no fixing it

Closed cooling with an old motor is not that great either

 

[Scott Danforth]

Need to rebuild motor to out a heat exchanger on it

 

[HT32BSX115]

Sup AD, missed ya buddy. I will send some pics once I start the removal. Going to invest in a freshwater cooling system as well. Was hoping the motor was toast. I have in mind a stroker kit with a nice cam........

Howdy,

Sounds like you operate in salt water. If you want to install closed cooling, you'll need a new block, heads, manifolds and probably risers......although if your risers are ok, you can continue to use them (since they'll still have salt going through them)

Putting closed cooling on a previously salt engine and manifolds usually results in a clogged heat exchanger.

 

[Goldie627]

Look up Frisco Boater, I believe he has a video of himself glassing in motor mounts. If your motor mounts are soft or even suspect I would replace them before dropping in any motor. Soft / weak motor mounts could cause a multitude of alignment issues.

If the motor mounts didn't look too bad but I was on the fence about replacing the motor mounts I'd at least take a core sample. Sometimes the glass can be solid but the wood is soft underneath.

Also, if your motor mounts are bad, they could have lowered your motor a lil bit which in turn could throw off your alignment

 

[tpenfield]

So....... my nephew was racing my boat across the intercoastal last weekend. :nono: The obligatory burning rubber smell came up through the boat. Followed by shuddering and shaking. We Idled the boat back to shore, Called tow boat and headed back to the launch. I thought he smoked the motor. When I got it home I started it on muffs and the idle was perfect. Figured out the problem then. I ordered the replacement part from sierra. I am going to tackle this project myself. Looking for any advice and pointers on other things to look for while I have the motor out. I am shopping for an alignment tool this weekend. I read about gimbal bearings and rubber sets and such. I plan on changing the motor mounts. They are showing signs of heavy corrosion. Maybe a link or video as to its replacement would be cool. Thanks Ya'll

I think you implied that the coupler went bad (and smoked) but I don't think you actually said that. :noidea:

Anyway, if you are going to pull the engine, it would be a good time to clean up the engine bay and look for any issues around the engine (rust/corrosion, etc)

No messing with high performance cam kits - stay with the marine cams with less valve overlap. No closed cooling for you if you have been running in the salt, because the inerds of the engine block are already toast with rust scale and will quickly clog up a heat exchanger.

 

[Scott Danforth]

Ted, nothing wrong with a cam change. just have to do the homework. for a stock block/head Gen VI bbc in a marine application I would run a comp cam XM-284HR. its a mild boost in power (and it is a marine cam) it is also the largest cam you can put in a stock L-29 BBC.

http://www.superchevy.com/how-to/en...power-on-a-junkyard-454-with-simple-cam-swap/

However the OP also mentions desire to build a stroker. that indicates a full blown re-build. for that I would start with the desire as to what you want to run for power. then look at the drive, then build the motor to suit. it may be new drive and motor

just to cover the coupler issue. they dont simply go. hot-rodding around doesnt cause them to go. failure to maintain alignment kills couplers. a properly maintained stock boat with stock coupler could be held to WOT on the water for hours or until you run out of fuel and repeat

things that cause alignment to move out of spec - age (rubber takes a set), poor alignment from factory, rot in motor mounts, corrosion of aluminum casting, etc.

 

[Lou C]

While you have the motor out, check the oil pan, front and rear main seals, starter, seal of the exhaust Y pipe for leaks, what about the Merc steering arm bolt leaks, all that should be looked at when you have the engine out. I'd check those front engine mounts very carefully. As noted, couplers don't just fail, they get run out of alignment and then fail. Although, I seem to recall hearing about Merc couplers made of aluminum, that had a higher than typical failure rate, maybe one of the Merc guys (I've only had OMC) will remember this. Might be an upgraded better one available.

About closed cooling, as noted once you have run a cast iron block/heads in salt water, there will be so much flaking rust in the cooling passages, that they will clog up the antifreeze side of the heat exchanger. The time to do it is when you re-power.

 

[HT32BSX115]

just to cover the coupler issue. they dont simply go. hot-rodding around doesnt cause them to go. failure to maintain alignment kills couplers. a properly maintained stock boat with stock coupler could be held to WOT on the water for hours or until you run out of fuel and repeat

I'll add a +1 on that one.......My last boat (66 Marktwain) went almost 35 years on the original coupler!

 

[thegoat86]

Thanks for the great advice. I am on the fence about the rebuild. I am most likely going to replace the coupler this weekend and just run it til' she's done. Then I will be shopping for a new drive to go with my build. Scott has the right idea about what I am going for.

I lost a prop hub a while back from hitting something. I don't know if this was just collateral damage from that event that finally let go. Who knows. I will be checking the mounts carefully. And the stringers. I am borrowing an alignment tool from a buddy of mine. He told me not to buy one as this is not a common event and to use his. It looks like a bar with splines on the end.

On another note, There was mention of salt water use with closed cooling. This boat gets about 50% use on salt water. It is out every night and trailered home. Then hooked on muffs and run even if I'm tired. Would this still be the case with the rust and scale? All of my runs home involve a 20 minute trip up a fresh water river to the launch. (unless I get towed back)

 

[Bondo]

I am borrowing an alignment tool from a buddy of mine. He told me not to buy one as this is not a common event and to use his. It looks like a bar with splines on the end.

Ayuh,...... Alignment bars don't have any splines on 'em,...... None,.....

'n alignment oughta be "Checked", anytime the drive comes off,.....

 

[thegoat86]

Maybe this is home made bar?....

 

[HT32BSX115]

Maybe this is home made bar?....

It probably is. Someone probably made it using an old yoke. You DO NOT want to use anything with splines on it. It will not align as accurately as a correctly machined alignment tool and may be off enough to prematurely wear out the soft aluminum inner splines in the coupler.

Absolutely nothing wrong with a "home-made" bar as long as the dimensions are correct.
I made my own on a neighbors lathe. Took me about 30 min once it was all set up.

 

[Bondo]

Absolutely nothing wrong with a "home-made" bar as long as the dimensions are correct.
I made my own on a neighbors lathe. Took me about 30 min once it was all set up.

Ayuh,...... 'n the dimensions are in the Adults Only Section,....

 

[thegoat86]

Here is the mess. Obvious rust/corrosion to cause the failure. Motor mounts toasted. Will be replacing all tonight. I broke lots of bolt heads getting the motor out. Maybe stainless steel replacements? I will have to see how close the strength is to grade 5 like what I took out.

 

[alldodge]

That do look like toasted to me

 

[tpenfield]

That do look like toasted to me

Yup, not even Gorilla Glue will save that thing

 

[thegoat86]

Stainless steel only has grade 5 strength, mercruiser had grade 8 in my block to connect to drive housing. So i will go back with same. Paint the heads and maybe a little anti-ox on the threads.

Side note, My stock MPI 7.4, since motor is out.... even worth it to do dual exhaust? Other than to make it annoyingly loud?