Changing Alternator Belt Yanmar 3YM20

[msfeldt]

I tried to change the alternator belt (V-belt) and water pump belt today on my Yanmar 3YM20. Looked pretty easy, loosen the set bolt and "slide" the alternator towards the engine to give enough space/slack to get the belt off. Problem is that I loosened up the set bolt but the alternator wouldn't budge. Tried using a wooden dowel to provide leverage but to no avail. I sprayed Corrosion Block on the groove/set bolt that allows you to adjust tension on the alternator belt because it was rusted and will try again in the morning. Any other suggestions. Is there something else that I need to loosen up. Thanks in advance.
Mike

 

[Don12364]

Two bolts on my alternator. One is the main pivot and the other slides along a slot in the arm which holds the belt tight. Also even the pivot on the arm itself where it attaches to the engine.
If both of the first two are tight movement will be difficult to impossible and even the third can still make life difficult.

I suggest identifying all three and slightly slackening the two which are not in sliding slots and then making the sliding bolt very slack.
After movement is achieved gently 'nip' up the pivot bolt and use a large screwdriver as a lever to get sufficient belt tension and then fully tighten all three bolts.

 

[Steve Dion]

1. it is amazing that a 3YM engine would have any corrison on this new of an engine.

2. The piviot bolt needs to be loosened as well as the tension bolt.

If it were me, I would remove both bolts and completely remove the alternator. Then you can clean and lube all of the parts to prevent this type of problem in the future.

 

[msfeldt]

Thanks for the response

I did loosen the front main pivot bolt but not the one in the back. I'll give that a try, sounds like it will do the trick.

Two bolts on my alternator. One is the main pivot and the other slides along a slot in the arm which holds the belt tight. Also even the pivot on the arm itself where it attaches to the engine.
If both of the first two are tight movement will be difficult to impossible and even the third can still make life difficult.

I suggest identifying all three and slightly slackening the two which are not in sliding slots and then making the sliding bolt very slack.
After movement is achieved gently 'nip' up the pivot bolt and use a large screwdriver as a lever to get sufficient belt tension and then fully tighten all three bolts.

 

[Alan]

Steve has the right idea. Removing the bolts and applying anti seize compound to the threads will make all the difference and will be easy in the future to make any adjustments.
I would suggest removing any bolts that you can on the engine, coating with anti seize and reinstalling them one at a time. You'll be bloody glad you did the next time things have to come apart. I spent the time shortly after buying my boat doing this job and have never had a problem with seized or rusted bolts and nuts including the exhaust riser which is notorious for rusting.

 

[Nelsonhow]

I think you need to loosen the lower bolt and the front AND back of the upper bolt. (Use antiseize compount too!!!) I purchased a pully spreader that makes adjusting the tension a cinch. A pic is attached. You turn the pipe between the two end and the threads force the ends apart spreading the pullies. I got it on line from one of the tool companies. Can't remember which but If anyone is interested I look for the reciept. With the belt tensioner it's a one person job and no busted knuckles.....

 

[msfeldt]

Today I loosened the back of the upper bolt, yesterday loosened the front of the upper bolt and the lower set bolt. After letting WD40 sit in there for a few hours I got the alternator to move but just barely. It took some serious prying. Now I've got the same problem with the setbolt to remove the water pump belt. Letting it soak in WD40 for a couple days. Man I miss my outboard, lol.

I think you need to loosen the lower bolt and the front AND back of the upper bolt. (Use antiseize compount too!!!) I purchased a pully spreader that makes adjusting the tension a cinch. A pic is attached. You turn the pipe between the two end and the threads force the ends apart spreading the pullies. I got it on line from one of the tool companies. Can't remember which but If anyone is interested I look for the reciept. With the belt tensioner it's a one person job and no busted knuckles.....