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Old 20-05-2019, 08:58   #1
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Perkins 4.236 v-belt/alternator issues

I recently purchased a 42' 1959 Stonington motorsailer, powered with a Perkins 4.236 engine. The engine itself is fantastic, however I can't seem to keep the belt properly tensioned. I'm having to tighten it every couple of days, especially if the batteries get drawn down and the alternator comes under a load. I don't want to over-tighten it and potentially damage the crank shaft, so I'm trying to figure out another way to give the belt system more 'grab'.

I have looked into a serpentine belt system upgrade, but Trans Atlantic Diesel wants $675 for the kit! I'm sure it's the perfect kit, but that seems awfully steep for a few pulleys and a belt... Is there any middle ground that doesn't cost an arm and a leg? I'm not pulling a ton of amps from the alternator, maybe 50-75 tops. I was considering 2 v-belts in parallel, but I can't find any 'kits' for that.

Any and all comments welcome.

Thanks, Arthur
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Old 20-05-2019, 09:17   #2
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Re: Perkins 4.236 v-belt/alternator issues

Hmm, There may be another problem at hand. Do try Gates Green Stripe Vee belts to see if this helps a bit. With 70 amps The load on a Vee is closet to the limit and a great belt may help.

If you do decide to convert to a Serpentine Belt take a look at this conversion.

Who makes the TAD and SW Diesel Serpintine pulleys?

And this one where I change over to a truck alternator (delco 28Si)

Converting Delco 28Si to external regulation
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Old 20-05-2019, 10:19   #3
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Re: Perkins 4.236 v-belt/alternator issues

I have a 4,236M lowline with a 70 amp alternator and the belts last much longer than you are experiencing.

Suggestions of things to check

a) Ensure all the pullys are rust free to save the belts being chewed up
B) Have lock washers on all the nuts
c) check everything is aligned properly, if you are seeing a lot of belt dust things are not right

Good Luck
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Old 20-05-2019, 10:46   #4
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Re: Perkins 4.236 v-belt/alternator issues

Thanks guys! Yeah, there is probably an underlying issue here... The previous owner said the pulleys on the alternator and crank shaft are for different belt types. He also has a bracket connected to a bracket and an unusually long belt, and there's belt shavings everywhere...

I guess I'll start with a new, quality belt, and maybe a new bracket, as the current one is starting to bough, due to the second aftermarket bracket stressing it. Thanks for the links!
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Old 21-05-2019, 04:35   #5
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Re: Perkins 4.236 v-belt/alternator issues

Greetings and welcome aboard the CF, Arthur.
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Old 21-05-2019, 05:24   #6
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Re: Perkins 4.236 v-belt/alternator issues

If you can press on the belt and it moves the alternator, start over. This sounds like tightening the belt destroys the alignment. You're going to eat belts, even very good ones, until it stays aligned under load.
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Old 21-05-2019, 05:30   #7
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Re: Perkins 4.236 v-belt/alternator issues

my motor has 3 different alternators, a purpose-built bracket fabricated for one of them.

As mentioned see if you have the correct belt/pulley sizes.

Adjust tension accordingly.

Look for rubber dust accumulating as this is a sure sign of a belt wearing away.
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Old 21-05-2019, 05:34   #8
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Re: Perkins 4.236 v-belt/alternator issues

Have been using a Dayco Gold Label Top Cog v-belt on our 4.236 for years spinning our 90 amp alt. Top quality belt and last for years.
Will say the 4.236 original belt arrangement is too small of a throw, which make it difficult to replace the belt (almost need to remove alternator). That said, I've kept the original set up since the alt. bracket was beefy and the pulley alignment was spot on.
If your brackets are bending then the pulley alignment will be off, shortening belt life significantly.
Another thing to look for is the proper belt size. Fairly obvious is the length, but less so is getting the V to sit properly in the pulley. The belt should not be bottomed out in the V of the pulley and should be riding in the middle upper part of the pulley using the sides of the V as the main contact source. If the belt is bottomed out it will be difficult to keep a good tension and you may see a lot of belt dust on the pulleys.





Hope this helped.
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Old 21-05-2019, 08:58   #9
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Re: Perkins 4.236 v-belt/alternator issues

There was no kit when I doubled the pulleys on my 4.108 for a 200 amp alternator, but I found fittings to make it work. In my case, the alternator was the tensioning device.
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Old 21-05-2019, 13:13   #10
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Re: Perkins 4.236 v-belt/alternator issues

Thanks for the tips, Bill. I was not aware that V-belts could 'bottom out' so to speak and lose traction, but thinking about it, it makes perfect sense. Now that you mention it, I notice that the base of the alternator pulley is sparkling clean, making me think that the belt is bottoming out on the alternator pulley as you suggested. Not the case on the crank pulley. I can't get a good look at the water pump pulley, but one thing at a time.

I'm not a master mechanic, but I can usually figure things out with enough time and research. I'm hesitant to start fabricating things without a 'kit' to follow, as I don't have enough faith in my engineering/fabrication skills. Also, it doesn't sound like 75 amps is too much to ask of the OEM setup, so I'm just going to try to get back to OEM specs and see if that solves the problem.

Just to give you an idea of what I'm up against, here's a picture of the 'dual alternator bracket' BS that I'm dealing with right now, with a wayyy too long belt and the alternator pushed way out in left field (note: I have complete overhead access to my engine, but access to the front of the engine is a little tight):

https://photos.app.goo.gl/BkJ7hywKCbsQBpzE6


I know, I know, it's all wrong on so many levels. Tomorrow I'm going to try a new, smaller belt with just the one alternator bracket, and see if I can get some decent traction.

Thanks again for everyone's help.

-Arthur
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Old 21-05-2019, 13:39   #11
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Re: Perkins 4.236 v-belt/alternator issues

are the pully`s rough inside the V as this will grind the sides of the belts like sand paper ,,, we had this problem on a volvo penta that was left for a few years , there wasnt much on the inside of the pully but when they spin for hours it chops the sides out of the belt ,, I took the pully`s off and stuck them in a lathe and polished then , Problem solved , hope this helps
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Old 21-05-2019, 13:57   #12
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Re: Perkins 4.236 v-belt/alternator issues

30 years of troubleshooting aircraft belt driven alternators. Sounds like your belt us bottoming out in one or both of the pulleys. The load is supposed to be on the sidewalls of the belt and the pulleys. If the belt is riding on the base ( bottom of V ) of the pulley it's going to fail shortly. If sized correctly and aligned properly belts can last a really long time.
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Old 21-05-2019, 16:51   #13
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Re: Perkins 4.236 v-belt/alternator issues

I had this problem for years on my Yanmar 3YM30. Tried all the forum suggestions with limited success. Noted in US forum members recommended a Green stripe belt which wasn't avaialble in Australia. Then I discovered the equivalent up market belt and haven't had a problem since.
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Old 22-05-2019, 05:29   #14
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Re: Perkins 4.236 v-belt/alternator issues

Arthur,
Thanks for the pic that was helpful. As you've already noted, the belt width is not wide enough for the alternator pulley and will have to take your word that the crankshaft is fitting properly. Measure the width of each pulley to figure out the correct width needed. You may find the alt. pulley is way too wide for the crank pulley to handle the difference for the "proper" belt with for each.
It looks like the bracket coming off the motor is the original alt bracket w/another extension added on. Again hard to tell from the photo if that is a small case alt, but if it is, it should be able to fit on the original bracket and help w/pulley alignment.
Originally the 4.236 came w/a Delco Remy 10SI alternator (based on wiring diagrams) and were very good alternators w/spare parts available worldwide. The 12SI would also fit and has a better cooling fan design rated up to 90 amps for the stock versions.
Personally I'd stick w/ the Delco Remy and go no higher than a 90 amp output especially if you have alternate power sources on the boat. We have solar, wind and hydro on our boat and do not need to depend on our drive motor to recharge the batteries. If you have room and could only have 1 alternate source, solar would be the way to go.


Also would love to see some pics of your boat.


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Old 22-05-2019, 05:45   #15
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Re: Perkins 4.236 v-belt/alternator issues

I think the previous owner hit the nail on the head when he said the crankshaft pulley and the alternator pulleys are different sizes.Replace the alternator pulley so that it matches the crankshaft pulley as they both should be 13A or 11A or A section or B section and then run the appropriate sized belt.I have seen this on Mercruiser v8's and the pulleys are different widths and the belts wear out prematurely.Cheers Kevman.
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