Ten Tips to Prolong the Life of Your Alternator

Posted by Darrell Nicholson at 06:30AM - Comments: (12)

The alternator belt on this Yanmar is easily inspected and adjusted, as needed.

So I was thinking about Bitcoin today, the digital crypto-currency that seems no less cryptic than what’s in my wallet these days, and this got me thinking about giant stone money on the island of Yap, and because I spent most of my time on Yap rebuilding an alternator, this got me thinking about alternator belts. Before you fire up ye ol’ iron genny for the season's first smoke-belching run out to the mooring, to the dock, or to the fuel station (I sure hope it’s not to the pumpout station), you, too, might want to think about your alternator belt.

Many of the following tips are culled from editor-at-large Nick Nicholson’s Offshore Log report on alternator care, written during his circumnavigation. For a more in-depth discussion of alternators, refer to Nigel Calder’s Boatowner’s Mechanical and Electrical Manual, which covers the topic in good detail.

  1. Check belt for excessive wear. Compare the belt width and depth with your spare belt (you have one of these, right?). When the engine area around the belt is coated with black dust, the belt is probably slipping or misaligned. Small-case, high-output alternators get very, very hot. There must be a constant, high-volume flow of clean cooling air through the alternator, if it is to last a long time. Black dust is like an insulator around your alternator. Paint can have the same effect: Don’t paint an unpainted alternator; it wasn’t meant to look pretty.
  2. Obviously, you must have the right size and type of V-belt. Look for A-series industrial belts, available from most autoparts stores. A quirk of these belts is that the belt number is not identical to the belt length: an A41 belt, for example, is 43 inches long.
  3. Check belt alignment. The belt must be properly aligned with the engine and alternator pulleys. Do not assume that the pulleys are aligned, even if you have a factory-installed alternator. A misaligned belt will often chirp—as opposed to a squeal or screech for a slipping belt. You can carry out a basic alignment check using a straight edge placed across the pulley faces. If the belt walks up one side of the pulley while the engine is running, misalignment is often the cause.
  4. Check pulleys for corrosion and proper operation. The pulley should not wobble on its axis. If the pulley-end bearings have failed (listen for distinct rumbling or roughness as you spin the unloaded alternator), check alignment carefully after replacing the bearings, as this may have contributed to the failure.
  5. Proper belt tension is an equally important issue. The correct belt tension depends on the pulley arrangement on the individual engine, as well as the type of accessories driven by the belt. A belt that is too tight can cause problems, but loose belts are more common. A loose belt will both reduce output and contribute to overheating. Again, check for black dust. If there is a significant amount of dust on your engine or alternator, the belt is too loose, the pulleys are misaligned, or you have the wrong belt size. Many engines send their RPM through the alternator, so if your RPM needle jumping around erratically, you could have a slipping belt.

    A properly tensioned belt should not deflect more than 5/16 of an inch when pressed with your finger. The Krikit V-belt tension gauge is handy for more accurate tension checks.

  6. A Gates Krikit V-Tension Gauge is a handy tool to have on board for checking belt tension. It is easy to use, and the instruction sheet gives belt tension guidelines for a variety of pulley and accessory combinations. You can find them at most auto parts stores (it's part # KR-1 at NAPA auto parts).
  7. The engine compartment must be kept clean. A lot of air gets sucked through an alternator. If your engine runs dirty, that dirt will find its way into the alternator, coating the windings and other components. Wipe the engine down regularly with a light solvent, and clean the alternator case and fan as well.
  8. Make sure the alternator gets plenty of airflow. This may mean increasing engine compartment venting. A beautifully insulated engine compartment that reduces noise is very efficient at keeping the heat inside.
  9. New belts tend to stretch during the first several times you run your engine. After replacing the belt, allow a run-in period of about 10 minutes and check tension again. Continue to monitor tension closely after belt replacement, and make it a part of your normal pre-ignition check to manually test belt deflection by applying pressure with your finger. If the belt deflects more than 5/16-inches, pull out the Krikit and re-adjust belt tension. If the belt is properly tensioned, sized, and aligned and black dust is still a problem, you may have to adjust the regulator to reduce the load on your engine—this applies primarily to high-output alternators.

10. After your final adjustments, make sure your alternator mounting bolts—at the bracket and at the alternator—are tightened down. Some manufacturers give torque for the bracket numbers, 70 to 80 foot-pounds or thereabouts.

Bottom line: By paying a bit of attention to your alternator belt before the season begins, you can save yourself some big Bitcoin down the road.

Comments (11)

If your alternator is not the main charging source, that is you have a generator or plenty of other main charging like solar, consider using a regulator that is set for battery float. At float voltage the alternator will never overcharge the batteries during long motoring.

If a battery is fully charged, when resting, at ~12.8V, why is there a need for bulk charging at say 14.4V? While motoring, the batteries will have a long soak at ~13.7V float. It would seem that under the circumstance, there is no need for higher voltage bulk charging.

Posted by: Locquatious | April 27, 2019 8:58 PM    Report this comment

This response may be a year late. Nonetheless... To align the pulleys you must first remove the belt. Then look for how each pulley is attached to its shaft. Usually there are one or more set screws in a shoulder on the pulley which either bear or the shaft or more commonly on a shaft key. Sometimes the set screw is at the bottom of the groove in the pulley. The shaft key prevents the pulley from rotating independently from the shaft. Use the crankshaft pulley as the reference, so don't loosen its set screw unless you absolutely need to to accomplish the alignments. Loosen the set screw of the pulley that is misalgned. Slide the pulley into alignment and tighten the set screw.

It is probably a good idea to take the pulley entirely off the shaft before you align it. Clean up the pulley and the shaft. Clean the shaft key. The key fits in a groove on the shaft and in a groove inside the bore of the pulley. Don't lose it. If you do drop it into the bilge, you can buy replacements at any auto parts store and some hardware stores. Clean off any penetrating oil you used to loosen the set screw. Put a light coat of oil on the shaft and shaft key. The oil will help keep the key on the shaft when you slide the pulley back on. When you're confident the pulleys are aligned use some blue Loctite on the set screw and torque it in place. It needs to be tight, but don't be Moose McGurk and tighten the bejeesus out of it. You don't want the pulley to slip. But you do want to be able to remove it at some later date.

Posted by: C Jenkins | April 11, 2019 2:31 PM    Report this comment

The smartest thing I ever did for my alternator was to install a serpentine belt modification.

~ ~ _/) ~ ~ MJH

Posted by: MJH | April 11, 2019 12:58 PM    Report this comment

"Would someone be kind enough to explain the best method to align the alternator pulley with the other engine pulleys. I have not been able to locate anything written about how this would be achieved. If it makes a difference, I have a Yanmar 4JH5E with a stock alternator. Thank You!"

Let me explain further that my question is how to make an alignment adjustment. This article was extremely helpful. Much appreciated! I understand the idea of using a straight-edge across the face of the pulleys to check alignment, but if I discover mis-alignment, how do I correct it. Perhaps this is dead simple, but in just looking at the owner's manual and searching the internet, I haven't come across an explanation of how to do this... My next move is to just grab some wrenches and see if I can figure it out, but thought I might ask first. Thanks for the help!

Posted by: Austin | April 19, 2018 12:25 PM    Report this comment

Thanks, great article.
As posted earlier by Austin:
Would someone be kind enough to explain the best method to align the alternator pulley with the other engine pulleys. I have not been able to locate anything written about how this would be achieved. If it makes a difference, I have a Yanmar 4JH5E with a stock alternator. Thank You!

Posted by: hrsail | April 19, 2018 11:26 AM    Report this comment

Thanks - a great review to help prep for a new season! K. Grace

Posted by: akagrace1@aol.com | April 19, 2018 10:44 AM    Report this comment

Would someone be kind enough to explain the best method to align the alternator pulley with the other engine pulleys. I have not been able to locate anything written about how this would be achieved. If it makes a difference, I have a Yanmar 4JH5E with a stock alternator. Thank You!

Posted by: Austin | April 19, 2018 9:27 AM    Report this comment

Here's a couple of more:

1- Practice good battery management. Charging in bulk takes a toll on alternators and the larger a bank gets in relation to the alternator the longer the alternator is in full-field/bulk mode and running hot. It is very easy for a non temp compensated alternator to exceed 230F, in an engine space, when driving a large load. Don't regularly discharge below 50% SOC and try to size your alternator, when hot, to a minimum of 20% of bank capacity. With AGM or GEL you'll want more alternator capacity.

2- Clean pulley grooves of all rust at the beginning of each season. Rusty pulleys eat belts.

3- When changing/upgrading alternators beware of the pivot bolt holes. I see lots and lots of upgraded alternators running sloppy fitting pivot bolts. The pivot bolt should be properly sized for the holes.If the bolt is not sized properly it leads to misalignment issues and damage to the alternator foot/feet.

4- On the adjustment arm tension bolt buy a longer bolt and back it up with a nut and lock washer. These tend to come loose over time in the soft aluminum alternator ears. Loose tension bolts are perhaps the number one cause I see of belt dust/slipping..

5- When upgrading the alternator consider going up a size or two beyond where you have decided you need. If using a Balmar external regulator you can limit the alternator in "belt manager" to the current handling capability of your belt. De-rating the alternator via belt manager allows your alternator to run cooler and last longer. It also allows for a future serpentine pulley upgrade.

6- When upgrading the alternator be aware that many large alternators ship with 1/2" pulleys and many small aux engines use 3/8" belts. I see 1/2" pulleys in use with 3/8" belts quite frequently and the owner is always complaining of short belt life. I am amazed at how many professionals miss this.

7- Know what your belt can safely handle. I find 70-80A is about max for a 3/8" belt and 90-100A max for a 1/2" belt. If you want to drive more than that you will need a multi-groove/serpentine type belt or a dual pulley set up.

8- When driving large banks it is often best to choose external regulation and take advantage of an alternator temperature sensor to prevent the alternator from cooking itself..

9- Pay attention to belt wrap around the crank and alternator pulley. The more wrap the more HP you can drive. If you have minimal wrap and a large bank consider a pulley upgrade.

10- Machined pulleys seem to do better with heat and driving large loads than do the cheap stamped steel pulleys on many factory alternators..

11- Treat your alternator and battery bank as a system and think of them as a team. Neither one can carry all the weight.... When upgrading the battery bank to add more capacity you will very often need to consider the alternator.

12- I know it has already been eloquently said but alignment, alignment, alignment...

RC Collins
Compass Marine Inc.

Posted by: RC Collins | September 30, 2013 6:08 PM    Report this comment

The Krikit V-Tension Gauge sound like a great little tool. The the tools claims to measures true belt tension, but unfortunately, most engine makers (such as Yanmar) don't provide true belt tension specifications. They provide a force per deflection specification ( ie. like 6mm(0.236in) deflection when pushed with a force of 10kg(22lb). This is clearly not the same.

Simple physics shows that T = F * L/(4d) where the belt tension is T, F the applied force, L pulley span length, and d the midpoint deflection length.

I have also read that there is a universal standard for measuring belt tensions which is that a belt should deflect 1/64in per inch of span. For the Yanmar water pump v-belt specifications given above: 0.236in * 64 gives a span length of 15in which by my approximation makes sense. Given these as facts, then T = F * 16. So for F = 22lbs, the tension T= 22lbs *16 = 352lbs. The Krikit shown above covers this range but the Krikit with the part number given only covers 30 -160lbs. Maybe the Krikit is measuring the applied force after all.

Posted by: dreuge | June 28, 2013 2:01 PM    Report this comment

It is also important to check sheaves (aka pulleys) wear. The belt is suppose to drive by contact on the two "V" sides (profile) of the sheave, not the bottom of the "V", as some mistakenly think. As the belt and or sheave wear, the belt moves deeper into the V groove and eventually bottoms out, causing the belt / sheave contact to be compromised and slippage occurs. At this point, over-tensioning maybe a bandaid to allow you to limp in, if it doesn't throw the belt. Hoverer, this excessive tension will cause bearing damage, depending on the amount of tension and how long it is operated.

There are many ways to check sheave wear, including a template type gauge, placing a new belt in the sheave or using a straight edge to simply observe the worn contact area. Shinny metal in the bottom of the V groove may be a wear indication (shinny sides are normal).

A sting can be used (across the faces of the sheaves) to check for proper alignment.

Posted by: Unknown | May 22, 2013 12:43 PM    Report this comment

If the distances between the pulley faces and the centers of the vee grooves of the two pulleys are not the same, a straight edge on the pulley faces will not work. In that case a straight dowel rod or arrow shaft laid in one pulley vee groove and floated over the other will point out any problem.

Posted by: wsmurdoch | May 22, 2013 9:33 AM    Report this comment

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