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Kenomac · 27-05-2016, 06:05

I'm in the middle of replacing my alternator belts on our Yanmar 4JH3-HTE turbo diesel. Work came to a stoppage half way through when I noticed that the six spare belts were a different kind, but same size. The one pictured on the right is the type that came off the alternator (there are two), and the one on the left is what the spares look like. I have no idea which kind was originally on the engine. Is there a difference between the two types and their intended use, or are they basically the same? I'd of course replace both parallel belts with the same kind. But the question is which kind geared or solid?

Second question: When replacing two parallel belts on the same alternator, does it matter if one seems to be just a little longer that the other? A few millimeters, just enough so they don't tension the same. Both have the same part number from the same manufacturer.

Thanks in advance for your thoughtful replies.

Ken

David Hughes · 27-05-2016, 06:43

I had mine replaced recently and the new ones were also the geared variety. I read somewhere else that the geared kind wore better....

rolandcavanagh · 27-05-2016, 06:51

The toothed belt is designed to accommodate sharper turns, and usually will transmit more power. I'd recommend looking at the specs on a manufacturer's website to see which one you need. I've subscribed to the position that you can't go wrong with the toothed ones as they take more bend and typically grip better.

Belts are available in matched sets for running in parallel.

I'd make a visit to a commercial power transmission component supplier for these, not an auto supply.

Safe travels

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Kenomac · 27-05-2016, 06:54

Thanks for the first two replies; I'll check to see if any of the six seem to be closer in length.

Maine Sail · 27-05-2016, 06:59

If you have dual pulleys then yes it definitely matters that they are the same length. These days it is very, very tough to find matched pairs. Years ago manufacturers used to physically zip tie them together as a set, not so much today.. I usually hit my NAPA regional master warehouse and sort through 20-40 of the same size belt looking for same factory code and consecutive Lot then manufacturing numbers or as close as I can get.

For these Gates belts the yellow number ending in SS is the factory code. The white bar code numbers are lot # then manufacturing order.

These two belts are from the same factory and manufacturing lot and the belts were only manufactured 3 apart as belts #56 & #59 of lot #83167XWZ.

They match as close to identically as can be expected and it makes a huge difference in both belt dust, slippage and heat. The owners previous belts, same part numbers, had been made in different factories and one had nearly 1.25" of deflection when the other had about 3/8"..

I have some on-line suppliers of belts but have had horrendous luck getting well matched pairs out of them. This is why I prefer to physically match them by factory, lot# and manufacturing order.

**a64pilot** · 27-05-2016, 07:23

Matched set used to be common, easy to get, even lawnmowers used matched sets.
I'd guess though since serpentine belts maybe not so much anymore?
The teeth on the inside of the belt makes it able to go around sharpers turns without having to make it thinner and lose surface area, there are also belts that have the "teeth" on the outside supposedly for cooling.

It ain't cheap, but bite the bullet and buy a serpentine conversion. No more belt issues, nearly as I can tell from the 200 or so hours I've had it, nearly zero wear, maybe it will last like they do on automobiles, I've seen serpentine and toothed belts on automobiles last nearly forever.
I changed the cam drive belt on my 97 Miata not long ago, but that was because the water pump was leaking and to change that, the cam belt comes off, and I wan't putting a 1997 belt back on, but it did make me wonder just how long that thing could last?
Buy the serpentine conversion, then forget about it.

Dymaxion · 27-05-2016, 07:27

One solution to mismatched belts is to replace both v-belt pulleys with toothed style. The flat drive belts can handle much more power than v-belts.

fuentes · 27-05-2016, 08:05

If you have a two or more belt pulley system, the belts must be matched. Otherwise one belt will be pulling and the others slipping. This will cause heating, wear and loss of power transfer. Think of a 100 HP electric motor with several belts that are not matched.

Kenomac · 27-05-2016, 08:17

Thanks much everyone. I found two identical belts that tensioned up equal, same manufacturer and the kind with teeth. I also modified the tensioner bolt to have two nuts and a spring washer to be able to tighten down the tensioner effectively. My hunch is that a previous mechanic may have dropped the tensioner nut and then just secured everything with the single nut. But I can't figure out a way that could have happened.

Anyway, now everything can be locked down and shouldn't work itself loose like before. Now I need to head back the store to purchase a second 19mm spanner (wrench) to tighten the one nut against the other. You wouldn't believe the vast selection of tools I have onboard, but neither the adjustable spanner or nor the channel locks could fit into the tight spot.

It's always something.

Pyxis156 · 27-05-2016, 08:29

Ken,

I have been going through a similar issue with our setup, a 4JH4-HTE driving two large frame alternators (approx. 4kW each), with two belts per alternator in addition to the main engine belt. I was having a terrible time chewing through automotive belts because one was always slightly longer than the other and it was impossible to get even tensions and the tighter of the two always blew first. I was lucky to get a year out of them, often less. I spoke to a local Gates representative and he said "Use our industrial belts, they are intended for multi-belt drives and length matched by design." With his help we decided on trying Gates Tri-Power belts because of the smallish 3" pulleys on the alternators. The belts have a scalloped back that lets them run cooler and more efficiently around smaller pulleys. So far they work as advertised, sit in the grooves better and run about 50 degrees F cooler than the automotive belts. The Tri-Power belts are also rated to a higher temp which the rep said will greatly extend belt life since it is hot in the engine compartment. He also encouraged me to get a belt tension gauge (for only $14 had to try it) and really glad I did, my "finger press gauge" was way off! It also showed all my belts are now tensioned just about exactly the same (something I never achieved with automotive belts) so the length matching appears to be working.

Industrial belts are identified a bit differently than automotive belts, an "A" belt is size equivalent to a typical 4L (1/2") automotive belt. Automotive belt lengths use the outside length, industrial belt lengths use the inside length so to order the same size belt in industrial, subtract 2" from the automotive belt length. So for example if you have a 1/2" x 47" (4L-4700) automotive belt, you would need an A-size 45" industrial belt. To denote the Tri-Power belt with scalloping, they add an X to the designation so in this example AX-45 is the equivalent industrial belt.

On a related note, our Yanmar OEM main engine belt also has the scalloped back. The Gates rep said that made sense given the small stock alternator pulley diameter. So if you do seek a non-OEM replacement belt, the scalloping is recommended.

You can order these belts online through Amazon or any local Gates dealer.

Hope this helps...