How to test engine coupler?

silverga01

Cadet
Joined
Jun 30, 2005
Messages
27
After the great help I got in my last thread, I thought I'd throw this question out.<br /><br />I bought my boat from family. 1973 Century with a 3.0 Mercruiser I/O of that era. My family member had taken the old motor out. I bought a used motor to put in, and he dropped it in. Went out and found out first thing out that it needed a new lower pump. Replaced that myself, refilled the gear lube to proper levels, and ran it in the driveway with ears. Temp was good. <br /><br />Took it to the lake again. Temp was great. Going down the lake for about 10 minutes and then things came unglued. The prop felt like it slipped out of gear and the engine started heating up. Got a tow with my family.<br /><br />After looking at it at home, I started to wonder if I hadn't busted a driveshaft, so I took it all apart. First I checked my pump kit and it was in great shape. So then I spun the drive shaft in the lower unit and the prop spun. Next I checked the gear housing, taking it off. The drive shaft and u-joint was in good shape. Put the gear housing and the lower unit together and rotated the driveshaft and it was fine.<br /><br />That leads me to think it's the coupler. When my family ripped the motor out and then helped me put the new one in, I was brand new to boating (and mostly still am), so I didn't know about aligning the motor, and my brother in law apparently didn't either and never mentioned it. So I'm wondering if it wasn't aligned and ruined the coupler. So I disconnected the distributor, and rotated the engine without spark to see if the coupler turned. It does, but that's without a load on it also.<br /><br />So after this horrible narrative, my question.<br /><br />I have the stern drive off, with just the bell housing left. How do I test the coupler to be sure that's the part I need? I'd hate to scavange one up, rip the motor out, only to find it's still in good shape. Anyone know a way to test it for certain?<br /><br />Again, sorry for the length of this, but I felt you had to have the whole story here to this point for the best possible reply.<br /><br />Thanks.
 

KaGee

Admiral
Joined
Aug 14, 2004
Messages
7,069
Re: How to test engine coupler?

I would think it would be self evident. You should see rubber or metal particles.<br /><br />How did the splines on the drive shaft look? If rounded, you got one more additional problem. :(
 

vipzach

Lieutenant
Joined
Feb 15, 2005
Messages
1,283
Re: How to test engine coupler?

First off I am no expert! Your motor does have to be aligned when put back in or your will destroy the u-joints( is that what you mean by coupler?) from what I have been told and read you can usually hear a u-joint begining to fail. <br /><br />My other thought since you thought that the prop was slipping.........maybe it was. Most props have a rubber bushing in them to help absorb an impact. They do fail sometimes.
 

Trent

Captain
Joined
Nov 17, 2001
Messages
3,333
Re: How to test engine coupler?

Since it was overheating... Its the coupler<br /><br />You should see black rubber dust back their also, But not always. Pull the engine and replace the coupler. Then align the engine. Take a look at the rear mounts for sagging. Its one of the main reasons couplers fail.<br /><br />Pic of the coupler...<br />
im850.jpg
 

silverga01

Cadet
Joined
Jun 30, 2005
Messages
27
Re: How to test engine coupler?

KaGee, the driveshaft on the gear housing looked decent enough, for a 25+ year old piece. It's hard to see into the bell housing, but there was a big piece of rubber in there. Didn't see much particulates though. I may try to snap a picture and post it. I do know that the engine was not aligned when we put it in. I was brand new to boating, and really still am, and my brother in law is famous for cutting corners at things, so I bet that's what he did here. Such as, when he removed the old motor and tore it down, he cut the crank shaft out with a sawzall. Doh!<br /><br />vipzach, I did mean coupler. The U-joints were greased and appear in good shape. Both the lower and gear units seem to be in working order. If the prop had hit something or the bushing failed, wouldn't I still have the impeller to cool the motor? Instead we lost everything at once.<br /><br />No engine power is making it to the rear. The pump kit I put in is fine, the lower unit alone works if you turn the shaft. The gear housing works if you turn the shaft. And if they are mated, everything turns as it should. I would think it has to be the coupler. Lack of alignment when engine was installed, worked for about 10 minutes or so when the failure happened. Just the fact that I can't get any movement to the stern drive seems like the culprit.<br /><br />*Edit - Trent, your reply wasn't up yet when I started typing. So you think with a fair degree of confidence that it is the coupler? That's the direction I've been pursuing, but like I said, wish I could be certain. I'm not a mechanic though, and just doing backyard work because I can't afford anything else.<br /><br />But my next question. You mention sagging, and to check for it. I'm sorry, I'm not familiar yet with sagging. Would it be the 2 rear mounts collapsing? That's the impression I get. If I'm wrong, please correct me. :) <br /><br />And thank you for the replies so far.
 

Trent

Captain
Joined
Nov 17, 2001
Messages
3,333
Re: How to test engine coupler?

Seen your problem many times. Believe me its the coupler!! If she is slipping and loosing power to the prop and the temp goes up...Its the coupler!! <br /><br />Your right on the sagging... Mounts collapsing
 

vipzach

Lieutenant
Joined
Feb 15, 2005
Messages
1,283
Re: How to test engine coupler?

Originally posted by silverga01:<br /> vipzach, I did mean coupler. The U-joints were greased and appear in good shape. Both the lower and gear units seem to be in working order. If the prop had hit something or the bushing failed, wouldn't I still have the impeller to cool the motor? Instead we lost everything at once.<br /><br /><br />But my next question. You mention sagging, and to check for it. I'm sorry, I'm not familiar yet with sagging. Would it be the 2 rear mounts collapsing? That's the impression I get. If I'm wrong, please correct me. :) <br /><br />And thank you for the replies so far.
OK, I just wanted to make sure we were on the same page, there seem to be alot of questions on iboats about u-joints, not as many coupler questions. So I was just clarifing. I also missed the part about it over heating. Yes, if the prop was slipping, your boat would still cool. I think what he was wanting you to check would be soft spots around the rear engine mounts. You need an alignment tool to properly set the engine when you reinstall it. I think you do have a coupler failure.
 

KaGee

Admiral
Joined
Aug 14, 2004
Messages
7,069
Re: How to test engine coupler?

Yea, he meant the rear motor mounts pushing or digging into the stringer they sit on. That would mean the stringer is rotten, or worn/torn bushings and that would affect the alignment as well. <br /><br />If you saw a piece of loose rubber, there's your evidence. Start pulling the motor again and take off the bellhousing. It's the only sure way to investigate and replace the coupler. <br /><br />Get an alignment tool and a service manual off of Ebay before hanging the drive back on.
 

Trent

Captain
Joined
Nov 17, 2001
Messages
3,333
Re: How to test engine coupler?

No check the rubber on the rear mounts. The 3.0 rear mounts dont mount to the stringers.
 

silverga01

Cadet
Joined
Jun 30, 2005
Messages
27
Re: How to test engine coupler?

KaGee. Question about the bell housing. Do I need to remove that? Does it buy me any more easy of removing the coupler?<br /><br /><br />Also, to anyone. I've been looking for a coupler on ebay (new ones are $$$, and my boat is a '73 anyway). Problem is, I see ones that look the same, like Trent's picture, except for the number of bolt holes. I've seen a few that look the same, except have 3 holes and some have 6. I found a page last fall (when I started thinking I lost the coupler) that sells couplers, but I've used it to try to identify mine. I figure the 18-2171 is the candidate. I know mine is 17 spline, which all these appear to be. So am I right? and what should tip me off on ebay that it's the right one?<br /><br />Example of used on ebay: coupler <br /><br />Except I'd like to find a used one for as cheap as possible as money is a major concern for me. :( I know it's not the best to use old parts, but I just gotta keep a budget.
 

Trent

Captain
Joined
Nov 17, 2001
Messages
3,333
Re: How to test engine coupler?

Never buy a used coupler! Your just asking for trouble. Look here.
 

KaGee

Admiral
Joined
Aug 14, 2004
Messages
7,069
Re: How to test engine coupler?

Silver, I am not sure if the bellhousing has to come off, but I believe it would be a lot easier to change it if it was.<br /><br />As far as the coupler itself, stick with the OEM or a direct replacement... experimenting around will only end up giving you more grief and wasted $$ in the long run.
 

silverga01

Cadet
Joined
Jun 30, 2005
Messages
27
Re: How to test engine coupler?

So does anyone know if the 18-2171 part number is correct? My Mercruiser book is quite old, and it seems none of my part numbers in it match anything made today. <br /><br />I'll probably end up trying to get a new one I suppose. But the $140 area is about as far as I'm willing to go. I've never even gotten a decent ride out of this boat. Damn coupler went bad so early on, I've thought of either parting it out or just scrapping it as a whole. :( <br /><br />And once I have a coupler, I still have to rent a hoist (found a tow-home 1200lb capacity with more then 94 inches of height clearance since my boat sits quite high on the trailer), get an alignment tool, and then actually fight the motor out of position. A big order to fill for me.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,137
Re: How to test engine coupler?

So does anyone know if the 18-2171 part number is correct? My Mercruiser book is quite old, and it seems none of my part numbers in it match anything made today.
Ayuh,.......<br />That's the current NAPA or Seirra # for the replacement Coupler for your drive,+ motor...... <br />It's the early Chevy Crankshaft Bolt Pattern,....<br />The Newer couplers bolt to the Flywheel,+ Won't fit your boat.......<br />It Lists for $216.14,........$138.22 Jobber Price...... How Well do you Know your Parts Guy...??..... :rolleyes: <br /><br />If you're going to Roll the Dice,+ Ebay it,..... <br />It's the Early Chevy Crankshaft Bolt Pattern coupler that Looks like the 1 Trent posted......<br /><br />It doesn't look Good for your $140.00 Ceiling.....<br />As stated above,.... Used Couplers Aren't Really the Best Bet in the World............<br />Many of the Sellers,.. Just Don't Know that their Junk.........They just Don't Know what to Look for.....<br />
I still have to rent a hoist (found a tow-home 1200lb capacity with more then 94 inches of height clearance since my boat sits quite high on the trailer), get an alignment tool, and then actually fight the motor out of position. A big order to fill for me.
Well,...... Cranking the trailer jack, All the way Up, Lowers the Transom abit,.......<br />And,... For that matter,.......<br />We're talking about a little 3.0l here,......<br />A Couple of Stout Friends can heave that motor out far enough to pull the Bellhousing/Rear Motor Mount Plate,+ Slip in a New Coupler.......<br />A Tree,+ Come-a-long,.. or a Garage Door Frame will work too.... <br />The Alignment Bar is a Must Have.......<br /><br />If your Lucky,.........<br />You Won't be finding a Rotten Transom that allowed things to Sag,+ Destroy the Coupler.......<br />That's a Pretty Common Cause for Coupler Failure on a 33 Year Old Boat..........<br /><br />Good Luck with it...... ;)
 
Top