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Old 01-04-2014, 18:40   #1
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Adjusting V Belt tension and removing alternator Yanmar 1GM

Hi all,

I have a Yanmar 1GM 10 on my boat which I bought a few months ago. I'm slowly learning more about the engine. I know this is pretty basic but I would greatly appreciate any advice on how to adjust the V belt on the engine because it's way too loose and my efforts at adjusting it this afternoon were a dead end . To show you what I did, I've attached a photo (left most photo). The yellow arrow points to a bolt on the top of the alternator. My first step was to loosen the nut that was on the back of the bolt behind the alternator (I made sure I had a wrench holding the bolt as I loosened the nut with a 2nd wrench). I thought this was the "pivot" bolt but the alternator did not move after I completely loosened this nut. i then loosened the nut that the blue arrow is pointing too, which I thought was the "adjusting" bolt (also had a wrench holding the bolt behind it in place as I loosened the nut). However the alternator was still fixed in place and I couldn't move it even after I loosened the 2nd nut. I saw a mechanic tighten the belt a couple of months ago and I thought this was what he did but he did it so fast that I can't be sure. Any suggestions or ideas would be greatly appreciated! I've also attached a second overhead photo if that helps illustrate what I'm doing. The reason I'm also interested in possibly removing the alternator is because the zinc plate is behind it and I spent an hour and a half today trying to get at it but the alternator (and to a lesser extent the starter) is blocking access.
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Old 01-04-2014, 19:09   #2
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Re: Adjusting V Belt tension and removing alternator Yanmar 1GM

The top bolt is the pivot. Loosen it a turn or two. Then the bottom bolt locks the alternator in place. Loosen it a couple of turns. Then with a large screw driver or something similar pry the alternator outwards to tighten the belt. Holding tension on the screw driver, tighten the bottom bolt to lock it and then tighten the top.

David
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Old 01-04-2014, 19:42   #3
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Re: Adjusting V Belt tension and removing alternator Yanmar 1GM

The Yellow arrow points to the, pivot bolt, which only needs a couple of turns to loosen.

The blue arrow is the adjuster/tensioner. Because they used a straight tension arm instead of a curved arm.

You will also have to loosen the lower bolt on the arm, to get the alt to move. Just loosen enough to get the arm to swing with a little force, then use a prys to tension the belt.

Lock down the blue arrow bolt, then the lower bolt on the arm, and finally, the pivot bolt(yellow).

Properly adjusted...you should have about 1/4 inch deflection in the belt using a good stiff finger.

Lloyd

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Originally Posted by Overlord34 View Post
Hi all,

I have a Yanmar 1GM 10 on my boat which I bought a few months ago. I'm slowly learning more about the engine. I know this is pretty basic but I would greatly appreciate any advice on how to adjust the V belt on the engine because it's way too loose and my efforts at adjusting it this afternoon were a dead end . To show you what I did, I've attached a photo (left most photo). The yellow arrow points to a bolt on the top of the alternator. My first step was to loosen the nut that was on the back of the bolt behind the alternator (I made sure I had a wrench holding the bolt as I loosened the nut with a 2nd wrench). I thought this was the "pivot" bolt but the alternator did not move after I completely loosened this nut. i then loosened the nut that the blue arrow is pointing too, which I thought was the "adjusting" bolt (also had a wrench holding the bolt behind it in place as I loosened the nut). However the alternator was still fixed in place and I couldn't move it even after I loosened the 2nd nut. I saw a mechanic tighten the belt a couple of months ago and I thought this was what he did but he did it so fast that I can't be sure. Any suggestions or ideas would be greatly appreciated! I've also attached a second overhead photo if that helps illustrate what I'm doing. The reason I'm also interested in possibly removing the alternator is because the zinc plate is behind it and I spent an hour and a half today trying to get at it but the alternator (and to a lesser extent the starter) is blocking access.
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Old 01-04-2014, 19:52   #4
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Re: Adjusting V Belt tension and removing alternator Yanmar 1GM

I have two of the 1GM10s on my boat. Sweet engines and very easy to maintain and rebuild. Speaking of rebuilding....Check your oil lines while you're down there.

The Zinc is number 17 on this diagram. Right under the head, I thought it was high enough on the engine to pop out without moving the alternator.


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Old 01-04-2014, 19:53   #5
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Re: Adjusting V Belt tension and removing alternator Yanmar 1GM

Thanks guys. I didn't even think to move the bolts after I had loosened the nuts. This makes a lot of sense, I'll try again.

Is it difficult to remove the alternator altogether in order to access the zinc plate? Do I need to completely remove both yellow and blue bolts? If it's too much trouble I'll keep trying to get at the zinc with the alternator in place.

Thanks again for pointing me in the right direction here.
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Old 01-04-2014, 20:01   #6
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Re: Adjusting V Belt tension and removing alternator Yanmar 1GM

loosen the yellow, now loosen the Red bolt lower tension arm, then loosen the blue bolt, drop the alt enough to remove the belt, then swing the alt, high as far as the tension arm allows, re tighten the blue bolt.

Then replace the zincs, then loosen the blue bolt lower the alt , put the belt back on, and tension, as per my previous post.

Lloyd

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Originally Posted by Overlord34 View Post
Thanks guys. I didn't even think to move the bolts after I had loosened the nuts. This makes a lot of sense, I'll try again.

Is it difficult to remove the alternator altogether in order to access the zinc plate? Do I need to completely remove both yellow and blue bolts? If it's too much trouble I'll keep trying to get at the zinc with the alternator in place.

Thanks again for pointing me in the right direction here.
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Old 01-04-2014, 20:07   #7
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Re: Adjusting V Belt tension and removing alternator Yanmar 1GM

Thanks Tropic Cat for the diagram. Today I tried to loosen bolt #16 with a wrench and I was successful. The problem was trying to loosen the bolt on the opposite side of the zinc plate (not labeled with a number on your diagram). I tried to stick a wrench in there but just couldn't get it on the bolt that was further in because I'm sticking it in between the alternator (above the wrench) and the starter (below the wrench). I even tried using a 10mm socket and although I finally managed (once) to get the socket on that further bolt, I didn't have any room to turn it at all because the wrench was basically pinned between the alternator and starter.

If you look back at my original post in the left hand photo, you can see the zinc plate located below the alternator and above the starter; it's very tight in there unfortunately.

I agree with you on the engine being really sweet. When i first bought the boat in July it was a byzantine complex mess of what is this. Now I know a lot more about engine work and can see how simply and easy it is to work with as far as engines ago. And the engine gave us almost no trouble in taking myself and my wife down the ICW from Maryland to Miami between November and February.
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Old 01-04-2014, 20:09   #8
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Re: Adjusting V Belt tension and removing alternator Yanmar 1GM

Lloyd, great idea, thank you again. I'll give that a shot.
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Old 01-04-2014, 20:09   #9
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Re: Adjusting V Belt tension and removing alternator Yanmar 1GM

Google alternator belt tensioner.

Like this:

Alternator Belt Tensioner FLIX
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Old 01-04-2014, 20:15   #10
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Re: Adjusting V Belt tension and removing alternator Yanmar 1GM

Good call Stu, thanks for the tip.
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Old 03-04-2014, 19:36   #11
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Re: Adjusting V Belt tension and removing alternator Yanmar 1GM

Just wanted to thank everyone again for all the helpful advice here. It took me a couple of hours to figure everything out but I was successful today in changing the zinc and tightening the v belt. Thanks again!!
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