Tightening Alternator Belt

Post here if you want to discuss a topic specific to the MV/32, MV/34, and MV/41.
Post Reply
User avatar
AMCarter3
admiral
admiral
Posts: 433
Joined: Thu Apr 21, 2016 8:32 am
Location: Bellingham, WA
Contact:

Tightening Alternator Belt

Post by AMCarter3 »

I replaced both of my alternators recently with refurbs. Both were acting wierd and when bench tested were rated as "close to failure". Two questions... First, what do you use as a LEVER to hold the alternator in place while you tighten the bolts. It seems like it takes 3 hands and some kind of 20" long lever. Has anyone found a lever that really works well?

Second, all alternator manufacturers recommend using a tool to accurately set the belt tension. Yet, literally all of the boat mechanics I know do not use a tension tool. They all rely on their own experience and some vague rule-of-thumb (literally pushing the belt with their "thumb"). And, as far as I have observed, some younger, less experienced mechanics simply do not know how to do it properly. Do any of you use a belt tension measuring TOOL like the Gates 91107 Krikit V-Belt Tension Gauge? <t.ly/Xa9f>.
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98; twin 100 HP Yanmars
Home Port: Bellingham WA 98229
Member of San Juan Sailing & Yachting Charter Fleet: http://sanjuansailing.com/charter-detai ... .php?id=35

AlanH
admiral
admiral
Posts: 183
Joined: Mon Apr 25, 2016 3:55 pm

Re: Tightening Alternator Belt

Post by AlanH »

Mac,

I am like the mechanics you have talked to. I have done most of my maintenance on cars and boats since I was a teenager. I have never used a belt tensioning tool. On my boat, I loosen both bolts on the alternator, push the alternator with one hand very tight and tighten the top bolt with the other hand. Then I check the belt for play. If there is more than a half in of play I tighten it a little more. You do want some play or it is hard on bearings.

Alan
Alan Hendry
Catbo
2006 34' Hull #81
75hp engines

duetto
admiral
admiral
Posts: 897
Joined: Wed Jun 15, 2005 11:18 am
Location: ICW (32043)

Re: Tightening Alternator Belt

Post by duetto »

i have never used a belt tightening tool either. i just loosen the tensioner bolt on the arm and then i use one of these techniques: 1) put an open end wrench in the slot and then a big screw driver in the remaining slot as a lever or 2) a huge channel lock pliers and squeeze the end of the adjuster bar and the adjuster bolt. i'm not on boat but i think #2 only works on one side but i'm not positive. as you probably can tell, i don't adjust them often.
john & diane cummings
duetto mv34 #23

scgck
deckhand
deckhand
Posts: 13
Joined: Sat Dec 18, 2021 12:18 pm

Re: Tightening Alternator Belt

Post by scgck »

All true in my experience.
Generally just use my hand to tension properly. ( 1/2 to 1 inch play )
You may have to loosen/retorque the 14mm lower pivot support bolt as well.
Chris
Expatriate 068

User avatar
AMCarter3
admiral
admiral
Posts: 433
Joined: Thu Apr 21, 2016 8:32 am
Location: Bellingham, WA
Contact:

Re: Tightening Alternator Belt

Post by AMCarter3 »

Thanks for the replies. I do understand the “thumb” technique. That’s what l’ve been doing. I don’t understand why so many people ignore the Manufacturers recommendation on this when it is so important for optimizing the efficiency of the alternator and avoiding damaging the bearings in the water pump or alternator.

I saw data recently from a manufacturer’s test that shows that only 2 out 100 people even came close to matching the belt tension spec using that method. Whereas every person using a tension tool like the Gates Krikit easily get it right. This baffles me.
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98; twin 100 HP Yanmars
Home Port: Bellingham WA 98229
Member of San Juan Sailing & Yachting Charter Fleet: http://sanjuansailing.com/charter-detai ... .php?id=35

duetto
admiral
admiral
Posts: 897
Joined: Wed Jun 15, 2005 11:18 am
Location: ICW (32043)

Re: Tightening Alternator Belt

Post by duetto »

so mac are you going to get and use the tool?
john & diane cummings
duetto mv34 #23

User avatar
AMCarter3
admiral
admiral
Posts: 433
Joined: Thu Apr 21, 2016 8:32 am
Location: Bellingham, WA
Contact:

Re: Tightening Alternator Belt

Post by AMCarter3 »

Yes... I'm actually going to get and try two tools: 1) Supco adjustable Belt Tension Jack <t.ly/o_gd> and 2) Gates 91107 Krikit Tension Gauge <t.ly/p5V3>....
Attachments
Jack.png
Krikit.png
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98; twin 100 HP Yanmars
Home Port: Bellingham WA 98229
Member of San Juan Sailing & Yachting Charter Fleet: http://sanjuansailing.com/charter-detai ... .php?id=35

duetto
admiral
admiral
Posts: 897
Joined: Wed Jun 15, 2005 11:18 am
Location: ICW (32043)

Re: Tightening Alternator Belt

Post by duetto »

mac,

plz let us know how they work. i may try the gates myself.
john & diane cummings
duetto mv34 #23

deising
admiral
admiral
Posts: 345
Joined: Mon Sep 15, 2014 3:48 pm
Location: Punta Gorda, FL
Contact:

Re: Tightening Alternator Belt

Post by deising »

I have never owned or used a special tension tool. Speaking of manufacturer's recommendations, the Yanmar Operator manual has the following:
Untitled.jpg
Duane Ising
m/v Diva Di
Punta Gorda, FL
2006 PDQ MV 34 - hull 91, 75HP, 3-blade

User avatar
AMCarter3
admiral
admiral
Posts: 433
Joined: Thu Apr 21, 2016 8:32 am
Location: Bellingham, WA
Contact:

Re: Tightening Alternator Belt

Post by AMCarter3 »

The issue I've routinely bumped into is the difference in tension required for a serpentine belt vs. a V-belt. I believe Yanmar assumes the boat owner has the original 80 amp Hitachi type V-belt alternator. Well, I have that kind on my STBD engine only. I have a Balmar AT-165 amp alternator on my PORT engine and it has a serpentine belt and 3 Balmar 10-ribbed pulleys. The tension requirement is much tighter on the latter.

Again, I was struck by two things in my research on this topic: 1) how physically difficult it is to tighten the alt pulley with some kind of a lever and at the same time use two wrenches to tighten the two bolts that hold the alternator in place; and 2) the amount of evidence I found online that indicates that most (like 98 out of 100) people are not able to consistently or accurately set belt tension using the common "Thumb" pressure technique...

I acknowledge that EVERY engine mechanic I have asked in our area uses the "Thumb" technique. The issue is... no one I've talked to can tell me how to duplicate the amount of thumb pressure they apply when setting tension. They all sort of mumble when asked... "oh, just push on the belt a bit" or some vague statement like that. There simply is no "scale" to measure the amount of pressure someone uses to produce the right amount of deflection. It is entirely subjective... that is what the surveys show -- there is a wide variance between people and their judgment / feeling of what the right thumb pressure should be.

In any case, I have the two tools I mentioned now and used them to set the V-belt tension on our STBD engine last week. The Tension Jack worked perfectly. It took all the effort and struggle associated with using a lever to put pressure on the alt pulley. The Krikit tool was super easy to use. But since the alt manufacturers mostly use "deflection" distance more then lbs of pressure to set tension, I'm not sure the Krikit tool is needed.

And, regarding the tension jack... I decided it should NOT be used as is on a serpentine belt pulley. The curved metal ends of the jack are made to fit only the curve of a V-Belt pulley. When you place it against a serpentine ribbed pulley, the curve sits on top of only 2 of the 10 ribs. I could imagine how, under pressure, the jack might damage the ribs. I called the manufacturer of the tension jack about this... They confirmed their jack is only made to fit V-Belt pulleys and "might damage" a ribbed serpentine belt pulley.

I searched but, as odd as this sounds, did not find a single tension jack for a serpentine belt pulley. So, I cut two pieces of hard plastic hose that I can use to cover the ends of the tension jack to spread the load and protect the pulley ribs from being damaged. I have yet to fully try it, but I think this will work.
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98; twin 100 HP Yanmars
Home Port: Bellingham WA 98229
Member of San Juan Sailing & Yachting Charter Fleet: http://sanjuansailing.com/charter-detai ... .php?id=35

deising
admiral
admiral
Posts: 345
Joined: Mon Sep 15, 2014 3:48 pm
Location: Punta Gorda, FL
Contact:

Re: Tightening Alternator Belt

Post by deising »

Your research and quest for "perfection" is admirable, Mac. With the billions of belts tensioned by thumb alone, and the (I guess) tiny number of failures due to improper tensioning, the non-scientific conclusion is that there is a LOT of leeway in the tension values before it becomes a problem. Having said that, I always use a torque wrench for what I deem to be critical items like cylinder head bolts (or nuts).

Cheers!
Duane Ising
m/v Diva Di
Punta Gorda, FL
2006 PDQ MV 34 - hull 91, 75HP, 3-blade

User avatar
AMCarter3
admiral
admiral
Posts: 433
Joined: Thu Apr 21, 2016 8:32 am
Location: Bellingham, WA
Contact:

Re: Tightening Alternator Belt

Post by AMCarter3 »

Agreed, Duane. You may be right that there is a lot of leeway on how to tension a alterantor belt. However, I don't feel like I'm seeking perfection by a long shot. I'm just baffled when a traditional rule-of-thumb (literally and figuratively) appears so out of sync with the guidance from virtually every alternator manufacturer and professional mechanics' guidance. And given the battery charging load placed on a high capacity alternator like mine, the importance of regulator settings and belt tension goes way up in my mind. Here's what Balmar's alternator installation manual says:

"Belt tension is a critical aspect of alternator performance. Monitor belt tension after every charge cycle for the first several weeks of engine operation. We recommend a belt tensioning gauge for accurate deflection measurement. Make belt tension monitoring and adjustment a part of regular maintenance."

In any case, the tension jack I found is a "win" for me. It's a simple, inexpensive and effective way to eliminate the need for 3 hands and a pry bar when setting tension on a V-Belt. For my serpentine belt, if my modified jack doesn't work, I'll get Balmar's solution. They make a "Belt Buddy Kit" -- Includes a Universal Adjustment Arm (UAA) with a Belt Buddy Adjustment Mechanism ($70). <https://balmar.net/?product=belt-buddy-ubb>. Either way, eliminating the need for 3 hands is my basic quest on this task.
Attachments
Belt Buddy.png
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98; twin 100 HP Yanmars
Home Port: Bellingham WA 98229
Member of San Juan Sailing & Yachting Charter Fleet: http://sanjuansailing.com/charter-detai ... .php?id=35

James Power
admiral
admiral
Posts: 263
Joined: Tue Apr 01, 2008 3:30 pm
Location: Georgian Bay

Re: Tightening Alternator Belt

Post by James Power »

If removing Yanmar's v belts and installing a serpentine belt might want to look into installing a belt tensioning pulley.
James

User avatar
AMCarter3
admiral
admiral
Posts: 433
Joined: Thu Apr 21, 2016 8:32 am
Location: Bellingham, WA
Contact:

Re: Tightening Alternator Belt

Post by AMCarter3 »

Here's a pic using the belt tension jack on serpentine belt pulleys. Note the small pieces of hose I used to protect the ribs on the pulleys. It worked quite well... no longer need that "3rd hand" to set tension.
Attachments
IMG_0308.jpeg
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98; twin 100 HP Yanmars
Home Port: Bellingham WA 98229
Member of San Juan Sailing & Yachting Charter Fleet: http://sanjuansailing.com/charter-detai ... .php?id=35

Post Reply