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FAQ: Alternator Belt Tension / Pulley Size

 

 

How do I Adjust the Alternator Belt Tension?
Do I use one pulley or two?
Do I need different belts for different size alternators?
Do belts put too much side load on the engine pulleys?

Subj: Re: [C34] M25 & M25-XP Belt Tension & Alternator Sizes
Keeping belt tension is a constant problem for some of us using a 100amp alternator with single pully systems. I found that after tightening it didn't take long before the belt started squealing and smoking, then the tightening procedure starts all over again. This is not a nice or easy job while shorthanded in the middle of the ocean while the boat is rocking and the engine is hot. So the best thing is to add a second pulley and a second belt.
I really feel that one belt is not enough for a Balmar 100. I never had any problems with the original setup.
Leo Missler, Dutch Lion, #1183, DutchLion1@aol.com

Subj: Re: [C34] M25 & M25-XP Belt Tension & Alternator Sizes
Ron, As always confusion reigns supreme. There are different size pulleys for the Balmar alternators - I had 3 different ones while trying to solve last summers "belt eating" problem. The trick turned out to be to get one that was sized for the same size belt as the pulley on the engine. While too large a pulley on the alternator allowing the belt to bottom out in the belt groove was not conclusively the problem, finally getting the "right" pulley installed ended the chewing up of belts.
Fore and aft pulley alignment was not the problem for us. It was checked by each of the mechanics we stopped to consult and none found it to be off. My biggest concern after this conversation is that tension on the belt is putting too much side load on the engine pulley. Don't know what I can do about it except make sure that the belt is not over tensioned.
Mike Ingham, Air goddess, #584, mikeingham@mediaone.net

Subj: Re: [C34] M25 & M25-XP Belt Tension & Alternator Sizes
The engine is seated on rubber mounts to take up the lateral vibration. A ridged attachment like a turnbuckle (alternator to the bed) will negate the mounts and like Leo said may even tamper with shaft alignment.
If you are eating up belts there is one primary cause - the pulleys are out of alignment! Take a 18" to 24" straight edge and place it on the bottom drive pulley (touching both sides of that pulley) and angle it up to the alternator pulley. The straight edge should also just touch both sides of the alternator pulley. If not - the belt is running at a side angle and wearing. If that's so you'll need to adjust the top alternator spacers until it's straight. If you look at both the engine and alternator ends of the adjustment arm you'll see that the female holes (in the engine & alternator) are the drilled and taped all the way through. I replaced both 1/2" length bolts with 1" length. Each should also have a "live" lock washer against a solid washer. Then you can really tighten without worry of stripping the threads. Also make sure that the belts have "cooling" ridges and aren't solid. Don't buy bargain belts, get the Gates brand.
Go to a NAPA auto parts store and buy a $8 belt adjusting tool - it's money well spent. No more screwing around with long screwdrivers and pries while the other person tightens the bolts . It's a one person task with that tool. Word of caution - if you over tension the belt you'll be replacing the internal water pump because of too much side tension on pump bearings!!
I kept the same 7/16" Gates belt on for 5 or 6 years in which we went to Key West and back to the Chesapeake Bay with the fridge running 24hrs a day. A few thoughts.
Ron APACHE #788, ronphylhill@erols.com

Subj: Re: [C34] M25 & M25-XP Belt Tension & Alternator Sizes
Just a thought on the issue of chewing up alternator belts.
Just prior to a trip to Maine last year we added the Balmar 100 alternator. After a long and frustrating series of torn up belts and conferences with various mechanics along our route, we discovered 2 things. First, and the biggest problem was that the belt sheave on the alternator was the wrong size for the belts required by the sheave on the engine. Because the sheave was too big the belt bottomed out on the sheave. It would tear up a top quality Gates Green Stripe belt in a couple of hours.
The second problem was that the mounting bracket configuration ( I am not sure whether it was the original Catalina or not) would loosen and ease the belt tension.
The fix was to get the right size sheave and to have a mechanic build an alternator mounting bracket that did not slip.
In the process of going thru this I talked to the Balmar factory. Their feeling was that a single belt was marginal for a 100 amp alternator. Based on that input, I would have gone the 2 belt route but that would have meant replacing the water pump (not the original) so I am going to try the single belt. It got us back from Maine OK last year so we are hoping.
Mike Ingham, Air Goddess, #584, mikeingham@mediaone.net

Subj: Re: [C34] M25 & M25-XP Belt Tension & Alternator Sizes
How do you determine how much tension should be applied to the alternator belt when tightening. I have the Balmar 100 on a M35B engine with one belt, I used it this way from August thru October last year with good results, however I am keeping a close eye on it. I talked to the Balmar distributor at last years Catalina get together in the Solomon's and he stated I should have no problem with this arrangement and a 7/16 belt.
Ron mentioned a belt adjusting tool from NAPA, does anyone have a part number and what does it consist of.
Richard Beecham, rbeecham@home.com, "Refuge", C34 MK II Hull # 1430, Rock Hall, MD

Subj: Re: [C34] M25 & M25-XP Belt Tension & Alternator Sizes
Mike, Dick and Stu : Ron Hill did in fact state in many recommendations that the maximum size of the alternator should be a 90 amp. What should have been viewed with this recommendation is that I take into consideration a boat's year and hull number so I know which engine is involved. I always recommend a maximum of 90 amp, especially for the M25 (21 hp). I have a 75 amp dual output Balmar (on an M25XP--23hp) which has a smaller case and "almost" has the same output of 100 amp at the lower rpm a Universal engine turns at. For those who have the 30 or 35 hp M35 engine, the problem isn't side load drag down of hp, it's simply the geometry of fitting a larger alternator in the space available. My "75" generally starts out with an output of 65 amps at 1500 rpm. As the batteries recharge, the amperage of course, goes down as the voltage builds.
As with all companies, you need to know who to talk to so you get the
Right story. I like to work with Gary or Bill at Balmar. Over the years I have gathered that Balmar has the same "deep V" pulley on all their single pulley alternators. The "deep V" will accommodate numerous thickness of belts. That's why they do it. Mike, it isn't the depth of a pulley that will eat up a belt, it's the misalignment fore and aft of the belt going into the pulley that eats up a belt. The "deep V" will give you better traction the deeper the belt goes into the V on the alternator pulley, but if it isn't aligned laterally it will chew up the belt faster because it is in a "deep V." That's why the alignment procedures that I mentioned yesterday are so important.
Dick, I can't give you the NAPA part number for a belt adjustment tool because I don't know the number and I didn't buy it at NAPA. You ought to be able to get this at any automotive supply parts store. Here's what it looks like.
There is a concave curved bracket that fits in one pulley on one end, and a curved concave bracket that fits in an opposite pulley. There is an adjustment screw in the center and one end has a left handed thread and the other end has a right handed thread. So as you screw the adjustment in one direction, it tightens both ways. When you screw in the opposite direction, it loosens.
Ron , APACHE, #788, ronphylhill@erols.com

Subj: Re: [C34] 25 & 25-XP Belt Tension & Alternator Sizes
Ralph, Sorry about the delay, but I had to get the M-25XP parts list out to get the number for you. It is 302159 (Universal #) for the main pulley. It's in the Westerbeke/Universal edition 1 parts manual. Marysville Marine can be contacted by 800 367-0987 for their outlet in Michigan. This is a big company, so you want somebody that is familiar with the M-25. For instance the water pump pulleys for the M25 and the XP-25 are different. One has to be careful.
The dual pulley conversion is very easy to mount. Simply lay the pulley over the front pulley on the engine and screw in the three allen-head machine screws that come with the kit and that's it. You will also need the two groove water pump pulley. There is no part number for it, but Marysville Marine knows about it. It comes off with three small retaining bolts. BTW, the water pump is also a weak link in the system regarding side-load on belt tension.
A couple of years ago Balmar changed the output ratings of it's models so there is some confusion about what is what regarding alternator output. It seems the 75, 90 &100 amp models are the most recommended models as they are the best compromise between output and stress on the existing mount and pulley setup. These models vary a lot with how much they put out at what rpms. Some are designed for high output at low rpms at the cost of maximum output. These are probably best suited to what we are doing. Who wants to run the engine at 2800 rpm to charge the batteries?
I remember Herb Schneider mentioning in a Mainsheet about running a Balmar 90 and saying that he thought that that was about the max amount that could be pulled over a long period of time from a single belt. Manufactures don't want a lot of liability in regards to over stressing their products either. A lot depends on how big your battery bank is and the settings on your regulator. Everything else being equal, a larger battery bank will pull more current from the alternator over a longer time period.
Balmar (blamarvst.com) is very knowledgeable about this engine also as they use a variant of a similar Kubota block in some of their water-maker / generator equipment. They will be glad to tell you about problems they had while trying to use the front pulley for power takeoff. Balmar stresses that all PTO belts are not the same and they make strong recommendations about using only top quality belts. If there is black residue around the alternator, then there is probably an alignment problem. My installation only required that the alternator adjustment arm had to be modified by adding exactly one inch to the alternator end. $10.00 and an extra trip to the boat/shop.
It seems that from the best information I could assemble from these sources the two belt route was the most logical and trouble free way to go.
After the install I did notice that the two belts have slightly different tension. (ok, so I'm a bit anal) It seems that the added belt is somewhat tighter than the inner belt. I'm not sure that this is a problem yet. I need to get some more hours on the setup to see if this is going to be a concern. If it is, I'll get the shop to take a little off of the new pulley.
I'm running a small case Balmar 150 dual output into four golf cart batteries and a small starting battery, so the acceptance charge is not going to seriously tax the alternator for long. If you are running larger batteries then you will have the alternator working harder longer because the increased capacity of the batteries and their greater acceptance will put more demands on the system.
When you start adding up all of the pieces, this turns into a pretty significant upgrade. It would be well to make it as reliable as possible.
Please confirm this information from primary sources for yourself. The list is fine for ideas, but for peace of mind and responsible care of guests and crew, you need the best quality information possible. "When the thing blows up in your face, it really is going to be your fault". (That's what Ken's dad used to say). He also had some ideas about women, but that's off topic!
Ken Dickson, Family Affair C-34 876, kdickson@mo.net

Subj: Re: [C34] M25 & M25-XP Belt Tension & Alternator Sizes
In twin belt installations ALWAYS buy belts in a matching pair! They are sold that way. Change both at the same time and you'll save heartache. You will also maximize your benefits and reason for going to twin belts in the first place.
Gary Wiseman, Up Spirits #894 gwiseman@ftn.net

Subj: Re: [C34] M25 & M25-XP Belt Tension & Alternator Sizes
Gary is correct. If you can't purchase the size you need as a matched pair, just make sure that all those other numbers on the belts ( beside the size) are identical. That means they were cut out of the same extrusion.
Ron, APACHE #788, ronphylhill@erols.com

Subj: Re: [C34] M25 & M25-XP Belt Tension & Alternator Sizes
Mike : Gary at Balmar led me to believe that Listic had one standard "deep V" pulley. Sorry to add to the confusion. As I said I've had my 75 amp duel output sense 1991 and it's been problem free. I did upgrade from a BRS to an ARS III regulator. I changed the belt after 5or6 yrs. on general principles. Don't over tension. I like to be able to press on the belt and have it move about 1/2 inch between the water pump pulley and the alternator pulley
Ron, APACHE #788, ronphylhill@erols.com

Subj: Re: [C34] 100 Amp alternator w/ m25xp
I installed a Balmar 91-75 alternator on Sjora last spring and have had no problems whatsoever with the belt. The only problem was finding an appropriate adjusting bracket. While the 75 does not have the same maximum output as a 100 amp model at typical charging rpm's it's output is the same or greater so I would expect belt loading to be about the same also. I think it's important to use a regulator that allows a time delay at engine startup and a gradual ramp up to max output which takes high starting stresses off the belt. When I removed the belt this fall for lay-up it was as good as new except for one chipped cog.
Bob L. Sjora #1420, SvSjora@aol.com

Subj: Re: [C34] 100 Amp alternator w/ m25xp
<<I'm determined to go with 100 amp, could I hear from those of you that went the 100a route. I would really like to know what make, model and what the cost was.>>

At the risk of adding more confusion to the alternate alternator discussion, here's what I did: We have a local (northern Wisconsin) alternator-starter rebuilder who does a lot of business nationally and has supplied rebuilt units for many boats in our marina over the years. While at his shop a couple of years ago, he told me he could supply a 100 amp alternator for an external regulator at a reasonable price. I purchased one for around $120 if my memory serves me correctly and he put a fan on it which would clear the stock Universal bracket. The pulley was matched up to the old alternator so that the belt would ride properly as well, so it fit the engine without any modifications.
I've used this now for two years with a Heart Interface smart regulator and several others at the marina have purchased them as well. Never had a bit of trouble with either belts or alternators. Though the units are rebuilt, not new, the stators, bearings and all wearing parts are new and they provide a warranty - and the price is definitely right. The company which supplied the alternators is called Blue Circle Electric. If anyone is interested, I will get the details and post them to the list.
Both Balmar and Heart Interface smart regulators are $190 in the West catalog and a bit less in the Defender catalog. Either will plug directly into the alternator Blue Circle alternator.
Jim Moe, Windseeker #976, jmoe@worldnet.att.net

Subj: Re: Duel Alt. Pully
Ralph : Approach the duel alternator pulleys with caution. As I mentioned the duel pulley will even put more of a moment on the water pump bearing - being that much further out.
Ken corresponded with me a couple of years ago. He was planing to put on a 200 amp alternator so he could have AC while motoring! I think that Westerbeke (on my insistence) discouraged him from that venture. He later said he had decided for AC on dock power. Never figured out if that original AC was for the cabin only or whether he had some kind of enclosure for the cockpit - or the helms person just had to take whatever ambient was?
When you measure let me know if you'll have to remove any of the insulation on the inside of the steps - to accommodate the double pulley on the water pump or if your engine is mounted too far forward.
Ron, ronphylhill@erols.com

Important: The opinions expressed here are those of the individual contributors to this page, and not those of the Catalina 34 National Association or Catalina Yachts, Inc. Additionally, this material has not been reviewed by Catalina Yachts, Inc. for technical accuracy. This page's maintainer cannot guarantee the accuracy of this information or the desirability of suggested modifications or upgrades. Please obtain assistance from a competent marine mechanic or boatyard prior to making any significant modifications to your vessel.   

 

Last modified by Phil Imhof, Wednesday, August 11, 2004 . Copyright 2001 by Catalina 34 International Association.  All rights reserved.