coupler questions

Hi all,

Just had a pretty bad weekend. I have a 1980 Bahner mini day cruiser which has a "Mr" drive and a vortec 350 that I built. Its pushing approx 450 horse and about the same torque. The boat runs very well and I haven't had an issue until this weekend.

Got on the water Thursday and drove around a couple hours. I was heading back to the ramp and running pretty hard. WOT for about 15 miles and all of a sudden I heard/saw my tach bounce off the 7k peg. So I shut it down and notice its slipping above 2000 rpm.

Beach it and find out I spun a prop. Change the prop and all is good.

Friday comes around and I do the trip from needles ca to lake havasu city (havasu springs restaurant to be exact) and no issues. Grab lunch start heading back to needles (approx 50 miles each way). I get almost to the same spot that I spun a prop on Thursday and same thing happens. Tach bounces off the 7k mark. So I jump in check the prop and its fine. But this time its harder to move than Thursday was. I make it about 5 more miles up river and finally have to call for a tow.
The only thing I noticed was a loud screeching noise (similar to a drill press) and the smell of burnt rubber.

So far I have drained some drive oil and it is clean with no metal. The drive sounds good when spinning it over by hand. And after this I have finally narrowed it down to the coupler.

Now this coupler was brand new about 6 trips ago. And I just replaced both u joints and gimbal bearing. I also checked the alignment and it was dead on. I have also checked to make sure the motor doesn't move when running and it doesn't.

So I'm wondering if I am just pushing to much power through the stock style coupler? And maybe this is why it let loose. Or maybe it was a defective part? Another question is can I change over to the "triangle" style with my drive? Or is there a stronger alternative?

Thanks!
Steve

Re: coupler questions

I'm not going to help much other than wonder how you've been able to push that much horsepower and torque through and older MR drive and not have it grenade. I'm not thinking it's built for that much muscle.

Mark

Re: coupler questions

MarkSee said:

I'm not going to help much other than wonder how you've been able to push that much horsepower and torque through and older MR drive and not have it grenade. I'm not thinking it's built for that much muscle.

Mark

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Mark,
I know I'm way over what its rated for. I think I've been lucky because I never nail it out of the hole and my boat is pretty light about 2500 pounds. I only go to WOT when I'm completely on plane and I very rarely run it above 5k rpm. But I know I'm living on borrowed time

Re: coupler questions

That's supposed to be a jet boat. If it's truly 450 hp and you smelled burnt rubber, it's too much for that application. Not sure exactly what bounced off 7K means but if it slipped and went to 7K, replace your coupler and keep it 4K and under......:lol: Oh yeah, and plane gradually...

Re: coupler questions

bonzoscott said:

That's supposed to be a jet boat. If it's truly 450 hp and you smelled burnt rubber, it's too much for that application. Not sure exactly what bounced off 7K means but if it slipped and went to 7K, replace your coupler and keep it 4K and under......:lol: Oh yeah, and plane gradually...

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What do you mean supposed to be a jet boat? Just because of the boat style? I wouldn't trade my out drive for a jet any day.

By 7k I mean when the motor free revved I was wot already at around 6k rpm and when it let go it revved to the moon. I do plane gradually and that's why o think the drive has lasted so long. But I'm pretty sure the burnt rubber smell was the coupler slipping.

Re: coupler questions

Just like the guys that build a bigger motor,tranny,start blowing u-joint's/shaft's/rear end's. get a coupler that can handle the torque, then the drive will blow out. The weakest link. The hull is designed for a certain application,hull speed. Anything over that is nothing more than overworking what was already in place to begin with. Ya you can do it,just be prepared to pay up with stronger components.
By the way,,I like more power also....
Grub

Re: coupler questions

grub1grub2 said:

Just like the guys that build a bigger motor,tranny,start blowing u-joint's/shaft's/rear end's. get a coupler that can handle the torque, then the drive will blow out. The weakest link. The hull is designed for a certain application,hull speed. Anything over that is nothing more than overworking what was already in place to begin with. Ya you can do it,just be prepared to pay up with stronger components.
By the way,,I like more power also....
Grub

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Grub
I agree, and I do plan on going to a bravo eventually. Especially since I plan on building a 383 for it.

As far as the coupler. Any recommendations on finding a stronger one? Or where to get one? My stock one is the rubber one that bolts to the crank. Is the triangle shaped flywheel mount a stronger alternative? And will it work?

Re: coupler questions

They usually only fail because of bad alignment when the rubber goes. It could be because of power but would think alignment first if you are being easy on the handle. When was the last time the alignment was checked?

Re: coupler questions

thumpar said:

They usually only fail because of bad alignment when the rubber goes. It could be because of power but would think alignment first if you are being easy on the handle. When was the last time the alignment was checked?

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I did all of the bellows and gimbal bearing approx 2 months ago or so. I checked the alignment at that time and it was perfect.

Re: coupler questions

I agree with all the others. And it does sound very much like the coupler. Easy check is to have a look at the yoke (in the coupler going to the drive) while under way (might be a bit noisy)... But by the description... Yep....

Yes the new style couplers are stronger... BUT... You can't bolt them up in place of the old style. Ya need a different flywheel, then you need a different crank and block (one and 2 piece rear main).... Ya have what ya have....

Chris..........

Re: coupler questions

achris said:

I agree with all the others. And it does sound very much like the coupler. Easy check is to have a look at the yoke (in the coupler going to the drive) while under way (might be a bit noisy)... But by the description... Yep....

Yes the new style couplers are stronger... BUT... You can't bolt them up in place of the old style. Ya need a different flywheel, then you need a different crank and block (one and 2 piece rear main).... Ya have what ya have....

Chris..........

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Chris,
Yeah I have already replaced everything for the newer engine. I have a 1 piece rear main,new fly wheel, and all if the stuff related. The coupler that I went through was a brand new one for the 1 piece rear main. So I am thinking that I should be good with the triangle shaped one over the "original design" style I have now.

The coupler got so bad that it won't even go into drive on the trailer anymore no clunk or anything. But with the engine off it will go into gear and I can hear it spin the impeller when I turn it ccw by hand. Just seems like either something is severely broken or the coupler is that far gone. I'll get it home tomorrow and pull the drive

Re: coupler questions

It does sound like the coupler is that far gone. The new style couplers need 3 screw holes around the periphery of the flywheel, much like the screw holes for a clutch pressure plate... If you have those, you should be good to go. I don't know the spacing. It might be a 'suck it and see' exercise....

iBoats sells them, part number is Sierra 18-2175. Maybe you could give them a call or an email and ask if they'll measure it for you...



Chris......

Re: coupler questions

Steve, are you using the old mr transom set up and bell housing or is that switched to newer?

Re: coupler questions

I changed out a 1979 2pc rear seal merc 228 engine for a 1pc rear seal. I kept my old transom plate set up. I had used a 1995 merc 350 mag for some parts. this is what I found out. My 1979 bell housing had rear engine mounts spaced 12 3/4 in apart. the 1995 had rear mounts 9 1/2 inches apart, so I could not use new bell housing. I found the old bell housing would fit the newer 14"flywheel, and I tried using the triangle shaped coupler from the 1995 parts engine. it all looked good, but when I tried to turn the engine (by hand, on a stand), I found the coupler was rubbing against the bell housing on the outer edges. I ended up using a conversion coupler to match up.

if none of the above applies to you:

I just measured that triangle coupler by hand so don't use these as gospel, but there close enough to see if your flywheel is drilled for the new style coupler. 3 mount holes are 10 15/16 apart on center. holes are 6 7/16 from hub center. holes fit a 5/16 bolt. hope this helps

Re: coupler questions

84EdH said:

I changed out a 1979 2pc rear seal merc 228 engine for a 1pc rear seal. I kept my old transom plate set up. I had used a 1995 merc 350 mag for some parts. this is what I found out. My 1979 bell housing had rear engine mounts spaced 12 3/4 in apart. the 1995 had rear mounts 9 1/2 inches apart, so I could not use new bell housing. I found the old bell housing would fit the newer 14"flywheel, and I tried using the triangle shaped coupler from the 1995 parts engine. it all looked good, but when I tried to turn the engine (by hand, on a stand), I found the coupler was rubbing against the bell housing on the outer edges. I ended up using a conversion coupler to match up.

if none of the above applies to you:

I just measured that triangle coupler by hand so don't use these as gospel, but there close enough to see if your flywheel is drilled for the new style coupler. 3 mount holes are 10 15/16 apart on center. holes are 6 7/16 from hub center. holes fit a 5/16 bolt. hope this helps

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Ayuh,.... You discovered the fly in the ointment Ed,...

Ya can't swap flywheel covers, 'n the triangle coupler Won't fit inside the ole MC-1 flywheel cover,....

Until it's converted to an Alpha 1 transom assembly, ya Gotta use the conversion coupler with the 1 pc seal motors,....
That's WHY the retro-fit couplers are sold,....

'n, on a side note,... the triangle couplers bolt on, into the Chevy pressure plate mountin' holes,....
it's a standard production standard transmission flywheel,....

Re: coupler questions

Bondo said:

Ayuh,.... You discovered the fly in the ointment Ed,...

Ya can't swap flywheel covers, 'n the triangle coupler Won't fit inside the ole MC-1 flywheel cover,....

Until it's converted to an Alpha 1 transom assembly, ya Gotta use the conversion coupler with the 1 pc seal motors,....
That's WHY the retro-fit couplers are sold,....

'n, on a side note,... the triangle couplers bolt on, into the Chevy pressure plate mountin' holes,....
it's a standard production standard transmission flywheel,....

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Bondo,

Thanks for the info. I got hone today and verified that the coupler is indeed the problem and completely shot.

I guess I'll buy another one and double check the alignment then try again.

In the mean time I am going to start sourcing and buying parts for a bravo conversion.

Thanks everyone
Steve

Re: coupler questions

That's why I stated it should be a jet drive. If you power a 2-3k lbs boat with 450 hp and a Bravo, you'll be way over the top. That hull design figured 400 hp with a jet, then dropped to a 260-300 hp stern drive when they started getting law suits. 450 hp is safe with a 5k lbs boat.