1989 2.5L (not 3.0) mercruiser crankshaft pulley

F

FrMDL

Cadet
Joined
Feb 24, 2023
Messages
12
Hello, all.
I had the boat out yesterday and she did great. However, I went to do some general maintenance today and discovered the drivebelt in the bilge. It must have snapped when I trailered the boat. There was also a thin, stretchy thing that looked like a belt of some sort but there is no other belt on the engine (I don't have power steering). So first, any idea what this second, thin, rubbery, stretchy, belt-like thing is? Could it come off the crankshaft pulley?
Second, on the crankshaft pulley, I have searched for info on it and it's hard to come by. I don't know if I need to replace it, depending on the aforementioned rubbery thing. The last run yesterday, and why I went poking around today, was the smell of burning rubber - a belt issue. However the alternator and water pump spin freely and the boat was running, so the crankshaft obviously spins. I guess they could be misaligned but they don't appear to be.
I think this post is too general, so my apologies, but any thoughts on the topic would be much appreciated.
 
C

cwella

Seaman Apprentice
Joined
Jul 10, 2026
Messages
36
FrMDL said:
Hello, all.
I had the boat out yesterday and she did great. However, I went to do some general maintenance today and discovered the drivebelt in the bilge. It must have snapped when I trailered the boat. There was also a thin, stretchy thing that looked like a belt of some sort but there is no other belt on the engine (I don't have power steering). So first, any idea what this second, thin, rubbery, stretchy, belt-like thing is? Could it come off the crankshaft pulley?
Second, on the crankshaft pulley, I have searched for info on it and it's hard to come by. I don't know if I need to replace it, depending on the aforementioned rubbery thing. The last run yesterday, and why I went poking around today, was the smell of burning rubber - a belt issue. However the alternator and water pump spin freely and the boat was running, so the crankshaft obviously spins. I guess they could be misaligned but they don't appear to be.
I think this post is too general, so my apologies, but any thoughts on the topic would be much appreciated.
Click to expand...
The thin stretchy piece is probably not a separate belt; it may be a strip from the belt that failed. A belt can delaminate and leave long rubber strands that look like another part. I would inspect the crank pulley/harmonic balancer closely for wobble or a separated rubber ring, since a failing balancer can throw belts and create a burning rubber smell. Check pulley alignment with a straightedge and replace the belt before running it again. A picture of the crank pulley and the mystery rubber piece would help identify it.
 
Bondo

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,463
FrMDL said:
Hello, all.
I had the boat out yesterday and she did great. However, I went to do some general maintenance today and discovered the drivebelt in the bilge. It must have snapped when I trailered the boat. There was also a thin, stretchy thing that looked like a belt of some sort but there is no other belt on the engine (I don't have power steering). So first, any idea what this second, thin, rubbery, stretchy, belt-like thing is? Could it come off the crankshaft pulley?
Second, on the crankshaft pulley, I have searched for info on it and it's hard to come by. I don't know if I need to replace it, depending on the aforementioned rubbery thing. The last run yesterday, and why I went poking around today, was the smell of burning rubber - a belt issue. However the alternator and water pump spin freely and the boat was running, so the crankshaft obviously spins. I guess they could be misaligned but they don't appear to be.
I think this post is too general, so my apologies, but any thoughts on the topic would be much appreciated.
Click to expand...
Ayuh,..... Welcome Aboard,.... The 2.5l doesn't have a harmonic balancer,(the 3.0l does, the 2.5l has just a pulley) so my guess is the rubber you found came from the v-belt itself,.....
Are the pulleys clean, 'n smooth, or rusty,..??

ditto what cwella just posted, while I was typing,....
 
F

FrMDL

Cadet
Joined
Feb 24, 2023
Messages
12
Okay....update a mere hours later. Both of you are right. I was sure the 2.5 doesn't have a harmonic balancer, but thanks for confirming.
The "2nd belt" was indeed the separated belt. There was a lot of what I assumed was carbon burn off from a bad alternator. Not so! It was actually the old belt that had been shaving off. The new belt (same part number) was a whole 1/16" thicker than the old.
The problem: An out of alignment alternator. Somehow the adjusting arm was bent, ever so slightly, that caused the misalignment.
There was no rust on the pullies and the crankshaft pully had zero wobble or movement, so I'm gonna go with it's fine. I was happy to discover that the 2.5 also has the access point to replace the belt so I didn't have to remove the entire engine support.
Hope this helps someone else down the river.
 
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