Yanmar 3YM30 Sea Water Pump Pulley Diameter

[Gypsy]

The belt of the sea water pump on my 3YM30 is slipping. For my motor the Yanmar belt is an M19 (19" long) but I find there is an M18.5 belt installed and the adjustment is at max but the belt flexes 20-25mm when pressed, lightly.

The pump was overhauled 2yrs ago and a new pulley replaced a rusty one. The mechanic made no mention of a new belt size. I wonder if the new pulley is smaller than the original?

Does anyone know the outside dia of the standard pulley or could run a ruler over their own motor's pulley to help me understand the situation. Mine is 90mm dia.
I can source an M18 belt which I expect would give correct tension & adjustment, but I am curious to know why a shorter belt is required.
Tks

 

[Scillypete]

https://j109.org/docs/yanmar_3ym30_parts_catalog.pdf

diagram 13 and parts listed shows two options, a 20 inch or 19 inch belt. I’m pretty sure mine is the 19, if I get to the boat today or tomorrow I’ll measure the pulley

 

[Gypsy]

https://j109.org/docs/yanmar_3ym30_parts_catalog.pdf

diagram 13 and parts listed shows two options, a 20 inch or 19 inch belt. I’m pretty sure mine is the 19, if I get to the boat today or tomorrow I’ll measure the pulley

Thanks. The 20" is for older engines. Mine should have a 19" belt but even with the smaller 18.5" I have run out of adjustment. I'll be interested to know the dia of your pulley.

 

[Scillypete]

Thanks. The 20" is for older engines. Mine should have a 19" belt but even with the smaller 18.5" I have run out of adjustment. I'll be interested to know the dia of your pulley.

mine is 90mm diameter same as yours and have really good tension on the belt. To be honest (having the experience of changing belts) I’m surprised that there was enough slack to get the 18.5 on there as the 19 was a struggle to get on before tensioning it.

 

[Gypsy]

mine is 90mm diameter same as yours and have really good tension on the belt. To be honest (having the experience of changing belts) I’m surprised that there was enough slack to get the 18.5 on there as the 19 was a struggle to get on before tensioning it.

Tks for the confirmation of 90mm. Interesting point you make about the difficulty of getting an M19 on. Oh well, I'll have the M18 in a few days and will pull things apart. I haven't taken the belt off yet because, as you know, the alt belt has to come off first and I want to have the parts ready when I get my hands dirty.

Since it seems my pulley is correct it may come down to a VERY stretched M18.5 belt or the mounting bracket.

I appreciate your input.

 

[Gypsy]

The belt of the sea water pump on my 3YM30 is slipping. For my motor the Yanmar belt is an M19 (19" long) but I find there is an M18.5 belt installed and the adjustment is at max but the belt flexes 20-25mm when pressed, lightly.

The pump was overhauled 2yrs ago and a new pulley replaced a rusty one. The mechanic made no mention of a new belt size. I wonder if the new pulley is smaller than the original?

Does anyone know the outside dia of the standard pulley or could run a ruler over their own motor's pulley to help me understand the situation. Mine is 90mm dia.
I can source an M18 belt which I expect would give correct tension & adjustment, but I am curious to know why a shorter belt is required.
Tks

Here is a follow up to the belt/pulley size question.


I received the M18 belt I ordered and removed the installed M18.5 belt. I then taped them together, along with the spare M19 belt, as close as possible to the same shape with one end aligned as a reference and looked at the difference in length between the 3 of them. See photo below.

At the bottom, the M18.5 is about 20-25mm longer than the M18 so it has probably stretched. The curious thing is the M19 belt (top) is shorter than the M18! I know it is a rough comparison as the belts are not laying in perfect alignment but clearly this belt length business is far from precision. Note also the M18 is visibly wider, probably by abt 1mm..

I decided to install the M18 to see how it sat in the pulleys and how much adjustment was available. I expected the M19 to be OK but it would sit lower in the pump pulley.

The end result is I have plenty of adjustment available and did not ‘lever’ it tight, just a firm locating push by hand. Great grip, and no slip.

I will watch it over the next few trips to see if it settles in to give slack.

I was clearly over-thinking the problem. I guess if I had put the M19 spare on immediately I could have achieved adequate tension. I was surprised at the ‘stretch’ of the M18.5. It did not look worn or stressed but I expect the more experienced of you may not be as surprised as me, I am more at home with electronics than mechanics.


Thanks to everyone who offered info/input.

 

[RichardS]

Here is a follow up to the belt/pulley size question.


I received the M18 belt I ordered and removed the installed M18.5 belt. I then taped them together, along with the spare M19 belt, as close as possible to the same shape with one end aligned as a reference and looked at the difference in length between the 3 of them. See photo below.

At the bottom, the M18.5 is about 20-25mm longer than the M18 so it has probably stretched. The curious thing is the M19 belt (top) is shorter than the M18! I know it is a rough comparison as the belts are not laying in perfect alignment but clearly this belt length business is far from precision. Note also the M18 is visibly wider, probably by abt 1mm..

I decided to install the M18 to see how it sat in the pulleys and how much adjustment was available. I expected the M19 to be OK but it would sit lower in the pump pulley.

The end result is I have plenty of adjustment available and did not ‘lever’ it tight, just a firm locating push by hand. Great grip, and no slip.

I will watch it over the next few trips to see if it settles in to give slack.

I was clearly over-thinking the problem. I guess if I had put the M19 spare on immediately I could have achieved adequate tension. I was surprised at the ‘stretch’ of the M18.5. It did not look worn or stressed but I expect the more experienced of you may not be as surprised as me, I am more at home with electronics than mechanics.


Thanks to everyone who offered info/input.

The width of the belt is also a very important consideration when it comes to choosing belts, unless the pulleys are not correctly matched when the situation will arise that you can match the belt to one pulley but not the other.

When I bought my boat the belts were too narrow and I was always adjusting them. I bought two new belts of the same nominal length but the correct width and have not adjusted them since fitting five years ago.

Richard

 

[Gypsy]

The belt of the sea water pump on my 3YM30 is slipping. For my motor the Yanmar belt is an M19 (19" long) but I find there is an M18.5 belt installed and the adjustment is at max but the belt flexes 20-25mm when pressed, lightly.

The pump was overhauled 2yrs ago and a new pulley replaced a rusty one. The mechanic made no mention of a new belt size. I wonder if the new pulley is smaller than the original?

Does anyone know the outside dia of the standard pulley or could run a ruler over their own motor's pulley to help me understand the situation. Mine is 90mm dia.
I can source an M18 belt which I expect would give correct tension & adjustment, but I am curious to know why a shorter belt is required.
Tks

Here is a follow up to the belt/pulley size question.


I received the M18 belt I ordered and removed the installed M18.5 belt. I then taped them together, along with the spare M19 belt, as close as possible to the same shape with one end aligned as a reference and looked at the difference in length between the 3 of them. See photo below.

At the bottom, the M18.5 is about 20-25mm longer than the M18 so it has probably stretched. The curious thing is the M19 belt (top) is shorter than the M18! I know it is a rough comparison as the belts are not laying in perfect alignment but clearly this belt length business is far from precision. Note also the M18 is visibly wider, probably by abt 1mm..

I decided to install the M18 to see how it sat in the pulleys and how much adjustment was available. I expected the M19 to be OK but it would sit lower in the pump pulley.


The end result is I have plenty of adjustment available and did not ‘lever’ it tight, just a firm locating push by hand. Great grip, and no slip.


I will watch it over the next few trips to see if it settles in to give slack.


I was clearly over-thinking the problem. I guess if I had put the M19 spare on immediately I could have achieved adequate tension. I was surprised at the ‘stretch’ of the M18.5. It did not look worn or stressed but I expect the more experienced of you may not be as surprised as me, I am more at home with electronics than mechanics.


Thanks to everyone who offered info/input.

 

[Gypsy]

Postscript:

After further research with the help of Mr G, I now understand the variables of the belts I have had in my hands.

It all comes down to inconsistency about the way they are measured/specified. Some are specified with OUTSIDE circumference (length) and others with INSIDE circumference, even from the same manufacturer.

It seems ‘Classic’ belts used for cars and machinery are specified by INSIDE measurement, whilst smaller belts known as a group as Fractional HorsePower (FHP) belts and usually used on electric motors under 1HP are specified by OUTSIDE measurement.

My guess is that those from the one manufacturer using different measurement methods were aimed at different market/user groups.

Specifically the Mitsuboshi M-18.5 measured 18.5” INSIDE and 20.25” OUTSIDE. This follows the metric M profile method. The Mitsuboshi M19 measured 17.5” INSIDE and 19” OUTSIDE. It also had a marking 3L/190 which my research shows is an FHP spec for a 3/8” (10mm) wide belt 19” long by outside measurement.

As a declared pedant I am pleased to have an explanation of the differences and I log them here for other pedants and generally interested players.

However, as a member of another forum put it very succinctly, “when it comes to sizing belts, use the length that works”.

That is the end of the lesson.