Yanmar 3YM30 Sea Water Pump Pulley Diameter?

[Gypsy23]

My Hanse 370 2008 model has a Yanmar 3YM30 motor. The belt on the sea water pump is slack and slips, yet it is at the end of the adjustment range. With finger pressure it flexes 20-25mm. The service manual for this motor shows a belt type M19 (M profile, 19” length). The spare which came with the boat when I bought it 2 yrs ago is an M19. I am aware that earlier motors used an M20 with a different bracket.


However as I prepared to replace the belt with the M19 spare I saw the belt installed was an M18.5 and yet the adjustment is at max.


Two months after I purchased the boat I had an engine service and part of that service was a sea water pump overhaul recommended by the mechanic. Replaced bearings, seals and the face plate. He also replaced the pulley with a bright shiny new one because the other was rusty. He did not mention the use of a shorter belt.


I am thinking the pump pulley may be smaller than the original size. The pulley installed is 90mm dia.


I have sourced an M18 belt which I will install and see the range of adjustment, hopefully sufficient to stop the slippage, but I am keen to know the size of an original pulley. Does anyone know the outside diameter of the pulley on the pump? Can somebody with the same motor measure theirs and report please?


I would appreciate any info even if I find the M18 suits, I just want to know.


Thanks, the forum is a fount of knowledge, this should be easy.

[tkeithlu]

Can't tell you, but..

Roughly speaking, to reduce the total path of the belt from 19 to 18 inches would require dropping the diameter of one pulley from 90 to 70mm diameter. I think that would be pretty obvious. On the other hand, belt wear and stretch could account for the slack you've found. Just tension it too much, or have the two pulleys out of alignment, and you've got it.

If your mechanic did slip you a smaller pulley, you've got a pump that is throwing more water per engine RPM, not a bad outcome as long as the load on the belt is not too high and it starts slipping. I understand your curiousity; I like knowing that sort of thing, too, but I do doubt that you've got a problem.

[Gypsy23]

Yes, I take your point about the pulley size change to explain the situation. When I get the M18 belt I will try to make the change. I have an M19 available too, but I will also look closely at the bracket to see if there are any possible changes or mounting variations which can explain it.


In the end it could be as simple as a VERY stretched belt, but because the alternator belt has to come off before the water pump belt can be removed I am looking for explanations before I get my hands on the hardware.


A comment from another source is surprised that an M18.5 could be fitted as he struggled to install an M19.



Tks for your input.

[ggray]

I have a 3GM30, and I know that one of the improvements of the YM was changing the orientation of the sea water pump, so there may be other differences in this department.

But with this small a water pump, I'm told that most yanmar mechanics don't rebuild the pump, they install a new one. Yeah, they aren't the one paying for it.

But years ago I installed a new impeller on the pump, and not too long after, the seal started leaking. So since then, I've just run pumps (two engines here) until there is a problem ( usually leaking seal) and then replace the pump w/ a new one. Which comes with a new pulley. By the time you replace impeller, seals (and what about the shaft wear?), the price of a brand new one isn't so bad. And you get the new pulley

They aren't hard to change.

I could measure mine, but it might be different.

[Gypsy23]

Tks ggrey, valid points. It's so hard to know/predict the useful life of these things. My previous boat had a Volvo D2-55 and almost 3000 hrs on the clock when I sold it 16yrs old. I replaced the impeller about 5 times and the face-plate once in that time and no leaks or bearing problems. It was driven from the same belt as the alt.


This motor has half the hrs and is 5yrs younger but had a pump rebuild and new faceplate. My Volvo cruise revs were 1800-1900 but the Yanmars in my experience, even for similar size, cruised at 2500 so maybe their pump wear is greater.


I'll find out more next week when I pull the belts off and try new ones but I can fully understand the economics and safety of your method.

[Gypsy23]

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.

[Wotname]

^^ thanks for the update.

[tkeithlu]

Good work, Gypsy23. Yeah, when it comes to sizing belts, use the length that works.

[Gypsy23]

A 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, forum member ‘tkeithlu’ put it very succinctly, “when it comes to sizing belts, use the length that works”.


That is the end of the lesson.

[Compass790]

Originally Posted by Gypsy23

A 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, forum member ‘tkeithlu’ put it very succinctly, “when it comes to sizing belts, use the length that works”.


That is the end of the lesson.

Thanks for the lesson cobber,
I'm far from a pedant & am in the tkeithlu school but assumed belt sizing was standard. Would never buy a Yanmar belt as dont see the point of paying 3-10x the price but now know to take old belt to auto chain store.
Wish more people were like you & posted their learnt lessons.

[dfelsent]

I too am in the school of “if it fits” especially since one of my alternators has an entirely non standard mount. I ended up buying more than one belt to find the perfect size. I was able to return the unused belts that did not fit. I spoke with the store before I did that.

But you pushed me into looking for a bit more info on belt sizing. Gates has always been my go to for technical belt info.

https://ww2.gates.com/IF/facts/documents/Gf000204.pdf

The link is to a rather interesting note on size measurement.

The note says that some size designations are nominal, some should not be used, and some are unreliable.

I just use photos of my belt markings and rely on the local auto parts store to look up the cross reference. I ask for the heavy duty truck/bus service belts. Not all the big retail chains carry these, I go to the places that cater to mechanics. And I carry more than one spare.

[Gypsy23]

Well, defelsent that really proves the point!


The experts 'Gates" use a properly specified measurement method but it is almost impossible for the lay person to measure. However I do understand it is important to have a measurement which relies on repeatable methods agreed by industry.


So back to the 'use what fits' method and good for you that you have a shop that will allow you to take a selection and return the unused ones.