Installing a J10 Serpentine Belt on an Universal M25

[vanilladuck]

Welcome to Puzzle Time. I'm your host, Bryan.

I'm upgrading the alternator on Rumour's Universal M25 engine to a serpentine belt -- the J10 variety to be specific. I picked up one of the last Balmar 48-USP-M25 pulley kits I could find on the internet last year. It arrived with pretty blue anodized aluminum 10-groove pulleys which should match the alternator, cooling system water pump, and crankshaft pulleys. When I received the kit, I opened the box, smiled, made a sigh of relief, and promptly put the box in a safe corner of the garage.

The crankshaft pulley is supposed to mount over the top of the existing crankshaft pulley. Here's an excerpt from the data sheet/install guide which came with the kit:



To my surprise, there is no three-bolt pattern in the existing crankshaft pulley for the new fancy blue pulley to attach. Insert record scratch here.



I did some research and reading online and found that the crankshaft pulleys on our M25 engines is counterbalanced. Combined with a balance internal to the engine it reduces vibration when things are spinning. I felt around the backside of the crankshaft pulley and sure enough there was more material on one side of the circle than the other. Is this important? ¯\_(ツ)_/¯ Maybe someone here knows..

So, then I found a parts list document for the M-25/M-25XP: https://www.westerbeke.com/parts manual/200142_m25_m25xp_parts_list.pdf (I'll paste some screenshots below for easier reference). On page 40 of this document is an exploded view of the Water Pump Group, which includes the cooling system fresh water pump and crankshaft accoutrement. Behold:



Here are the part numbers from the parts list document:


I think #12 is the crankshaft pulley that's on Rumour's engine (Universal Part #300190). The shape is the same and I can see the two little holes peeking out from behind the crush/lock washer on my engine. But, look at #20, which is a power take off wheel (Universal Part #302159). It makes sense why it's not on my engine, because there's no external device to run from the engine. But, it has a three hole pattern which seems to match the pretty blue crankshaft add-on pulley from Balmar. I search around and #302159 is not made anymore by Westerbeke and I can't really find one elsewhere.

Here's where it gets weird[er]... #16 in the diagram points to the fresh water pump pulley, BUT, in the parts list it calls for #301515 which is labeled "Pulley Fan M-25 - Use 302189"

When I search online for 302189, I find this at several retailers with the same grainy picture: Universal, Pulley, Crankshaft M-25Xp, 302189. And this looks like it might fit the new shiny blue add-on pulley. I'm wondering if this is a typo in the Universal parts list document. I reached out to Discount Marine Source to ask for better photos and/or some measurements so I can see if it might fit; waiting to hear back.

Does anyone have any experience upgrading an M25 to a serpentine belt? Did you use the Balmar kit? What did your engine look like before?

Experience, hints, guesses, and jokes welcome

 

[vanilladuck]

And wouldn't you know.. as soon as I post this thread, I found: https://forums.sailboatowners.com/threads/universal-m25-front-v-belt-pulley.1249939249/ It has a response from Maine Sail (bless him) with this image:



Seems like the three-hole #302189 pulley might be the right one?

 

[vanilladuck]

I ordered a #302189 from Discount Marine Source, along with a new crankshaft pulley nut and washer. I figure the washer will be too beat up to reinstall and the current nut has quite a bit of rust on it. Will report back what I receive... **fingers crossed**

 

[Kenneth K]

Yeah, I'd say the universal part numbers in post #1 are screwed up.

It looks to me like part #12 / 300190 was the original crankshaft pulley. Then later, they added parts # 20 & #21 (302159 and 302046) which appear to be the 3-hole crankshaft pulley and the 3 screws. Note that these parts are sloppily hand-sketched onto the diagram vs the original factory drawing (including the sloppy circles around part #s 20 & 21). Part #16 / 302189 should have nothing to do with the crankshaft (it fits the water pump) and yet, the 302189 part you ordered from DMS seems to be the right one.

If the original pulley is counterbalanced, make sure you mark the exact position on the crankshaft where the pulley was mounted (although, the key may allow it to only be installed in the correct orientation). I don't know how you'll be able to tell if the new pulley has the same counterbalance properties (which could be important for balancing the crankshaft so it doesn't wear too heavily on the internal bearings). Maybe you could consult with a diesel engine shop. If need be, maybe the new pulley could be drilled out or weighted to give it the same counterbalance properties as the old. Once that's done, make sure you locate the weighted side of the new pulley in the same orientation on the crankshaft that the original pulley had, which could require cutting a new key slot for proper orientation.

 

[vanilladuck]

Yeah, I'd say the universal part numbers in post #1 are screwed up.

Thanks Ken -- I think/hope you're right

If the original pulley is counterbalanced, make sure you mark the exact position on the crankshaft where the pulley was mounted (although, the key may allow it to only be installed in the correct orientation). I don't know how you'll be able to tell if the new pulley has the same counterbalance properties (which could be important for balancing the crankshaft so it doesn't wear too heavily on the internal bearings). Maybe you could consult with a diesel engine shop. If need be, maybe the new pulley could be drilled out or weighted to give it the same counterbalance properties as the old. Once that's done, make sure you locate the weighted side of the new pulley in the same orientation on the crankshaft that the original pulley had, which could require cutting a new key slot for proper orientation.

This is a really great point and one that I started thinking about, but was going to ask later if the part # was the correct one. The exploded parts diagram seems to suggest there is a "feather key" on the crankshaft for getting the orientation right. I'm going to take your suggestion and be sure to mark, measure, and replicate the positioning of the pulley on the crankshaft.

Happy Thanksgiving to all!

 

[vanilladuck]

I have received part number 302189 and it appears to be the right one.



But wait there's more...



Pictured above is the new crankshaft pulley (#302189) on the left and the Balmar serpentine add-on pulley on the right. We can see the matching three holes for attaching a PTO (power take off), which in this case is the Balmar pulley from the 48-USP-M25 kit.

However, the next hurdle is the Balmar pulley does not fit over #302189. The diameter is larger than the original v-belt pulley on Rumour's M-25. Measuring with a caliper, #302189 about 2-3mm too large. This is a similar problem seen on other message boards/forums (including the thread linked above).



I needed a machine, auto, or engine shop anyway to help check the balance of the new pulley and ensure it's the same as the original pulley. Maybe they can put the pulley on a lathe and remove a few millimeters from the diameter. The v-belt groove won't be needed once the serpentine pulley is mounted.

 

[Christian Williams]

Serpentine belt is definitely high class. But for the record, I ran my M25 with 100 amp alternator on the factory belt, and do so also on the 5432 with 100 amp alternator. No dust or slippage.

 

[vanilladuck]

Aye, Christian. I have an Arco 220A alternator going in. There's probably no chance of running it that hot, but I'm hoping for somewhere in the ballpark of 150A output.

I've never had a "zero belt dust" engine bay, no matter how much I tuned and aligned the v-belt pulleys ¯\_(ツ)_/¯

 

[Kenneth K]

If the Balmar pulley mounts in front of the factory pulley, the drive belt will be pushed out forward (further away from the engine than the previous pulley). How do you extend the water pump and alternator pulleys forward to keep them all aligned?

Also, extending a drive pulley out further away from the driven device gives it more side-ward leverage against the device's bearings. If the tension is kept the same, the side loads on the bearings increase. Have you evaluated whether the serpentine belt allows you to lower the tension vs what a v-belt required? If the tension isn't lower, forward-extended pulleys will likely cause more stress on the water-pump and alternator bearings than you had before.

 

[Loren Beach]

I am informed that the serpentine belt on our 2018 Betamarine needs less tension due to the large increase in contact area on the sheave. Perhaps there is not much change in side load compared to a properly adjusted V-Belt. (?) And better yet, it should last for years (decades?) in our sort of light duty use.

Regarding belt dust... years ago I had a dust problem with the belt installation on our OEM Universal M25XP with the stock Motorola 50 amp alternator . After some helpful advice from other owners here and some research on belt models and types, I did find a "heavy duty" Gates belt that did not shed dust. There seemed to be a -lot- of choices in belt design and stated benefits!

 

[vanilladuck]

If the Balmar pulley mounts in front of the factory pulley

The Balmar crankshaft pulley mounts over the existing v-belt pulley, which appears to center the serpentine load over the v-belt pulley. The other two pulleys for water pump and alternator are wholesale replacements.

Have you evaluated whether the serpentine belt allows you to lower the tension vs what a v-belt required?

Yes - less belt tension is required for serpentine belts. V-belts acquire grip through tension wedging the belt into the V of the pulley system. Serpentine belts have multiple small ridges in which fit into multiple grooves on the pulleys, acquiring more grip through increased surface area.

Also, there are two types of serpentine belts: K6 (6 ribs) and J10 (10 ribs). This setup will be J10.

 

[Kenneth K]

The Balmar crankshaft pulley mounts over the existing v-belt pulley, which appears to center the serpentine load over the v-belt pulley. The other two pulleys for water pump and alternator are wholesale replacements.

Yeah, that's better!

Yes - less belt tension is required for serpentine belts.

Okay, you should be in good shape then!

 

[vanilladuck]

I really appreciate how everyone watches out for everyone else on this forum

 

[vanilladuck]

Update

After some shenanigans getting a harmonic balancer puller, I've removed the stock M25 crankshaft pulley. The tricky part was finding M6x1.0 hex head bolts -- which were also 100mm long. The M25 crank pulley pulled right off. Mechanical advantage is great.



Good chance to cleanup and maybe paint the engine behind the pulley



I'm looking around SF Bay for engine shops to see who can take a few millimeters off the diameter of the new v-belt pulley, to which the Balmar serpentine pulley will be mounted.

I'm also looking ahead at how to install the new pulley, which is a very snug fit on the crankshaft spindle. The crankshaft has no internal threads at the end for a harmonic balancer installer. The only advice I've found so far is to heat the new pulley in the oven and then use a block of wood and hammer to knock it into place. I'm not a fan of this method... any other suggestions from the group here?
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