V-Belt Replacement

lehighsail

lehighsail

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Feb 21, 2008
413
Hunter 33 Metedeconk River
At the end of last season I noticed that the belt that powers my seawater pump on my Yanmar 3YM30 was slipping. When I removed the belt it appeared to be in good condition with no real wear or cracks. It was a Mitsuboshi M20 belt which is 20" OD. I tried to tension the belt further but could not because of the limit of the sliding clamp. I figured that the belt had stretched. I got a new one and when I tried to install it, I still could not fully tension the belt.
My question is then is, do I get a 19" belt or do I grind out the end of the slot where the bolt tightens the retention arm to allow further stretching?
Screen Shot 2022-02-27 at 6.44.17 PM.png
Grinding would make the end very thin. A 19" belt is available.
Thanks
 

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Tom J

Tom J

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Sep 30, 2008
2,320
Catalina 310 Quincy, MA
Definitely go with the smaller belt. It's better to have a little extra room to adjust the tension later. You should retension the belt after it has run awhile. It's not unusual to have to experiment a little to find the belt that fits your engine best. If it is a v-belt, make sure the v matches the pulleys.
 
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lehighsail

lehighsail

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Feb 21, 2008
413
Hunter 33 Metedeconk River
Thanks for the input. I have located a Gates 19" belt with the same profile as the M-20.
I was wondering if using a shorter belt would affect the function of the pump....the Yanmar replacement was 20". I just did a little research and think that the length of the belt does not seem to be a factor in function, only the size of the pulleys would make a change.

I will retension the the belt after a couple of hours as suggested. After this initial retensioning, is it common for the belt to continue to stretch? I don't recall ever having to adjust seawater belts before.
 
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Ken13559

Ken13559

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Oct 29, 2005
2,362
Hunter Marine 326 303 Singapore
Check both pulleys, pump and crankshaft. Any rust on pulleys works like sandpaper on belt, thinning it's side walls and changing belt diameter.

Ken Y
 
Crusty Ol Salt

Crusty Ol Salt

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Aug 19, 2021
505
Hunter 280 White House Cove Marina
Ken13559 said:
Check both pulleys, pump and crankshaft. Any rust on pulleys works like sandpaper on belt, thinning it's side walls and changing belt diameter.

Ken Y
Click to expand
I would not touch anything. I imagine your belt is worn on both sides due to slipping. If you measure the width at the top it will be narrower than the design width if 1/2". If you look at the sides the will be grazed or shiny.

You may find the old belt is worn out and a new 20" belt will fit perfectly.

Changing the the belt size only changes the center to center of the pulleys or the sheaves. if you change to a different diameter pulley or sheave that will change the rpm or speed of the driven pulley.

Good luck
 
Ward H

Ward H

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Nov 7, 2011
3,774
Catalina 30 Mk II Cedar Creek, Bayville NJ
Try the 19". Also check to see if there is a 19.5". Pretty sure the Dayco Top Cog belts I use come in 1/2" increment lengths. I do remember buying buying a few different lengths to try and took back the ones that didn't work. (I had changed out the alternator to a new one and wasn't sure of the size belt needed)
I wouldn't be grinding out anything to make a new belt fit.
 
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Crusty Ol Salt

Crusty Ol Salt

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Aug 19, 2021
505
Hunter 280 White House Cove Marina
Tom J said:
OP tried a new 20" belt.
Click to expand
I did use the word may the other side being may not. Then you must proceed to the next sentence.

"Changing the the belt size only changes the center to center of the pulleys or the sheaves. if you change to a different diameter pulley or sheave that will change the rpm or speed of the driven pulley."

Return the 20" belt and get a 19" belt. Very rarely does the sheave or pulley wear out. That said checking the width of the groove(s) may not be a bad idea. The width at the top of the groove should be just a little over 1/2". This allows the over cord and the tensile cord to ride just inside the groove. If the over cord and tensile cord are outside the groove it will allow the softer under cord to wear more rapidly.
 
RoyS

RoyS

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Jun 3, 2012
1,742
Hunter 33 Steamboat Wharf, Hull, MA
Also consider using a belt with notches on the underside. Often the pump pulley has a very small diameter and the notched belts will conform better and slip less. Belts that also turn the alternator are more likely to wear from slip as alternators are harder to turn as current demand increases. Go with the smaller length.
 
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Ward H

Ward H

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Nov 7, 2011
3,774
Catalina 30 Mk II Cedar Creek, Bayville NJ
Maine Sail has also recommended the Dayco TopCog belt, which has the notches on the top of the belt. I believe for the same reasons Roys mentioned a notched belt, more flexible for better contact.
 
lehighsail

lehighsail

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Feb 21, 2008
413
Hunter 33 Metedeconk River
The only belt I was able to readily get was a Gates 19mm OD circumference belt. It had the same profile as the Mitsuboshi M-20. It was a little tricky to get on in the cold and dark but after I removed the pump from the engine it went on fairly easily. There was very little play in the "slot" now in the other direction. Just as a spare I am going to try and locate a 19.5 cm belt but after a couple of hours after launch, if it stretches a bit, it should be perfect. Thanks to all and I will give an update once the season starts.
 
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Stu Jackson

Stu Jackson

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Feb 26, 2004
22,986
Catalina 34 224 Maple Bay, BC, Canada
lehighsail said:
Just as a spare I am going to try and locate a 19.5 cm belt but after a couple of hours after launch, if it stretches a bit, it should be perfect.
Click to expand
These days they simply do not stretch in any appreciable manner.
Ward's right, get the right size belt. Once you're sure of it, go buy two more, and label them, and throw any other ones away.
When I installed my new alternator in 2005 or so, I went through finding the right belt. 7400 was too big, 7390 was too small, but 7395 worked perfectly.
Only way to do it I know about.
Good luck.
 
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Ward H

Ward H

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Nov 7, 2011
3,774
Catalina 30 Mk II Cedar Creek, Bayville NJ
Belts don't shrink so you should be good.
 
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