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MG MGB Technical - Change to a Serpentine Belt?

Hello,

I was just wondering if anyone knows anything or has any information on how hard and/or if it is possible to change the standard fan belt on my 73 MGB to a serpentine.

I currently have the standard belt running between the alternator and the water pump and the crankshaft, so I would have three pulleys to change out.

I know at car shows I have seen cars in which the belts have been changed, but they also always seem to have lots of other modifications. I was just thinking it might be nice, if it is not too difficult (i.e. major modifications) to change to a serpentine belt.

Comments? Has anyone done this?

Thanks,

Robert
Robert Browning

Whassa point? You'd also need an idler to serpentine it around, which is a profoundly ridiculous way to replace the simple adjustment link at the alternator.
FRM
FR Millmore

Now, Fletcher - there you go again throwing the cold water of logic and common sense on an otherwise warm-blooded proposal. People who haven't read your posts for years might assume you're a C.O.B. (Crusty Old Bastard), and get all offended. Thank God, you didn't type your response in caps! <snicker>

But, I think you're right. For the average enthusiast who only puts a few thousand miles each year on his MG, it just doesn't make sense. For cars with the mythical "100 thousand miles between tuneups", and assuming those miles accumulate in two or three years, the spring loaded idler may be more feasible.

So, barring custom automobilia, it's just too easy to reach over and push on the V-belt with an experienced thumb, to see if the wrenches need to come out of the drawer. And, if I really wanted to make the change, I understand the new Moss Supercharger kits already include a 4-rib serpentine, that's about eight feet long, with an automatic adjuster.

But, who's got the loose $3000+ that it takes? - - Best wishes - - Alec
Alec Darnall

FR
Wouldn't there be enough contact patch on each of the three pulleys with the generator acting as the adjustable pulley?

The major reasons for adopting the flat belt was 1/ more load capacity for air conditioning, power steering, etc. 2/ less friction than the V belt.

Given the modest parasitic load on the belt, I doubt the efficiency difference would be noticed. The added load capacity would be unused as the load is not that great.

I'm running an "underdrive" on my car and see no disadvantages at all. -- The small early crank pulley with the late model large water pump pulley and an aftermarket 35 amp alternator. It is a lot cheaper than custom flat belt pulleys.

Barry

Barry Parkinson

Just tryin' to sound like a couple guys with a couple beers, eh? It's a valid question from Robert, and a reasonable question from me, I thinks. But I am always logical when discussing real things, even if beer powered.
Given the load conditions, any modern V belt will last until the rubber dies of old age; it won't die of use if tensioned correctly. I recently changed the original, factory, much more heavily loaded 3/8 V belts on my Dodge pikin-up truck at 16 years and 100,000 miles. The "serpentine" belt will also last the life of the (same) materials, unless the invariably cheaply made idler falls apart and eats it at 50k or so.
Barry - Yes, but then it's not a "serpentine" belt, which by definition has a curve inversion in its run; rather, it's a multi-rib belt. This would be fine, but as your analysis shows, infinitesimally useful. The one thing you didn't mention is that the serpentine (and especially a two faced serpentine), by virtue of its convoluted run, can drive a bunch of pulleys in a single plane, which a v-belt can't do, because of lack of contact arc. All of this saving a bunch of precious inches, especially on tranverse engined cars with power everydamnthing.
In all, the only thing it has going for Robert's car is a tiny bit of "coolth", but for the same basket of shekels, you could probably get a crossflow head, or some really nice wheels with stickies, or a 5 speed setup, which all have both more coolth and more usefulness.
So, what ya got agin COBs, eh? Don't think I'm quite there, but I think I'm agittin close to my OF badge; damn sure not qualified anymore for "the kid with the funny lookin' cars!
FRM
FR Millmore

Boy, I ask a simple question and see what trouble I start. :) !!!!

Honest, I was not planning on changing to a serpentine belt, however, I was just wondering if it is something that MG owners do and I was not aware of it.

What made me think of all this up is that when I ride my bicycle, I see broken V-belts laying in the street all the time, but very rarely see one of the serpentine belts. So I was just wondering if there would be an advantage to the serpentine belts on our type cars.

Now I know. Thanks
Robert
Robert Browning

Robert, there are some advantages of serpentine belts over V belts, but on a MGB they wouldn't be worth the cost and effort IMHO. They are excellent at transmitting relatively high torque for a very small surface area, so if you had power steering and air conditioning with the necessary high torque required to run these pumps and compressors it might be a good update. I also believe that the precise tension offered by the spring tensioners helps improve bearing life in water pumps and alternators over what I've experenced with V belts. The problem with them lies in the fact that they take a high degree of contact with the pully, at least 180 degrees in most cases to work well and with a simple three element system (crank, waterpump, and alternator) getting that much contact becomes a problem. Usually the water pump gets driven by the back side of the belt in most cases which requires a reverse impeller pump. I'm working with an engine in my current project which had a serpentine belt originally, and with only a three element drive system I have had to back date the crank pully and water pump to conventional V belt design. Fortunately these parts were available from an earlier version of this engine. I'd hate to think of the cost of conversion without the earlier style parts.
Bill Young

Wow, sounded a little like James Hesser there. Speakin' of which...??

Wayne
Wayne Pearson

Indeed, the Moss blower system uses a serpentine belt but does not utilize an idler pulley. The adjustment system, under the alternator, is a bear to get at and requires several special tools to access properly. The V belt system on stock cars is just fine, thank you. Ray
RAY

Robert-
Ya want trouble - yer in the right place! Seriously, your questions are always valid and with good intent, I just wondered if you saw some point I didn't, and so you have - fan belt snakes. I suspect that the broken V belts you see are a direct result of over or undertensioning on clunkers or other victims of the incompetent. That's an advantage of the spring tensioners. Also, where there is one V belt, there are usually several, and one broken frequently derails all of them, increasing their numbers but not the real failure rate. There are also some seriously garbage v belts around, probably less serpentine/multirib in that class.
Now about that bike - mebbe we could replace that crank-n-sprocket doofus with a shaft drive and a correct oil bath gearbox, know a guy with a BMW swears that's the way to go.
Bill- These belts don't really require that much contact, multirib drives work fine with 2 or 3 pulleys; but since more contact is available, it lets you use less tension to drive the load, and we all could use less tension. Still, the space saving single plane factor is the big reason for these drives.
FRM
FR Millmore

Since the flat multi ribbed belt came out i have found that water pumps last much longer than they used to, I believe this is due to the larger friction contact patch requiring less belt tension. While it used to be a water pump lasted 60K miles they now last well over 100k. A spring tensioner is not necessary as my 88 Mercury had two flat multi ribbed belts and each was tensioned by moving the alternator or power steering unit just like in the old days. The original belts also laste 100k miles.
John H

the V belt is an interesting device. The belt travels at a particular speed which is a compromise or average between the speed of the outside diameter of the belt/pulley contact patch, and inside of the V shaped contact patch. The inside is a smaller radius and is by definition traveling at a slower speed. Result is that some slpppage/friction occures on each pulley - no matter what. That slippage 1/ takes power, 2/ produces wear/ and 3/ reduces the power transmitting capability of the belt. Because of the V factor, as the belts wear they tend to slide further into the V pulley and become loose. That is not typical of flat belts/pulleys. A flat belt on a flat pulley only has it's internal friction to deal with. It is a wide thin belt and has much less internal friction. Result 1/ it lasts longer 2/ it is more efficient at transmitting power, and 3 requires less adjustment.

With an MGB on high beam headlights, heater fan on and water pump pumping, I doubt if the total load equals 1 hp.
V belts seem to last a long time in those conditions.

Barry
Barry Parkinson

Barry-
Yes but, the V bends around the pulley such that the radius of the belt equals the radius of the pulley at every point, so there is no slippage. If there were actual belt slippage, failure would be very quick, as anyone knows who runs a belt loose, or a multiple V drive on unmatched pulleys. My big truck had been run with only one of two alt belts in place, so one line of pulleys was worn; trying to run the two belt set resulted in destruction of the looser belt in a couple of hours, but a single belt lasted for 50K or better. There is however "slippage" in the form of deformation of the rubber in the belt (as it enters and leaves the pulley), leading to heating and parasitic losses. The multi-rib, serpentine or not, is not a flat belt, but is rather several small V belts in cahoots. Both transmit power by wedging against the sides of the pulley grooves. The advantage of the multi-rib is that there is much less deformation of the rubber due to the reduced section depth, so less loss; and, there is room for proportionately more reinforcing in the belt width, which means they are stronger and less stretchy, and more stable laterally. Typically a multi-rib has about the same total "side" area as a V in the same application. Either belt cannot transmit much power when it or the pulley is worn to where the belt contacts the bottom of the groove, eliminating the wedge effect, which causes it to act as a flat belt. If there is belt contact on the bottom of the groove, or the top of the ribs on a multi pulley, something is worn out and failure approacheth quickly.
FRM
FR Millmore

FRM
Your points are mostly right.

Your dual v belts of different lengths because of one being fractionally longer than the other would obviously cause the looser belt to slip and wear quickly.

The ribs on the flat belt locate the belt but aren't that critical to transfer the load. On point, many loads are driven by the flat backside of the belt. Because of the lack of the wedge effect the total surface are and tension are both typically greater than the v belt. The portion of the radius of the pulley driving or being driven by the belt is a greater radius resulting in more surface contact.

The flat belt does not have the wedge effect where it compress into the v groove and the unwedges. More Kevlar or other hi tech fabric keeps the flat belt in shape. The reduced wear because of the lack of the wedge affect makes the belts more reliable.

I'm sure if we work on this we can keep this going longer than iron smog plugs.

Barry
Barry Parkinson

Yah! My info comes from belt manufacturer's design catalogs, and from other reading about the development of multi-rib belts when they were being introduced before they were prevalent. Loads driven by the flat side are specified to be smaller "minor loads", "major loads" are driven by the ribbed side. If there are equal loads to be driven, as in some machine tool and similar apps, a two sided ribbed serpentine is used. More contact arc is beneficial on both flat and ribbed sides. I will stand on my statement that in correctly engineered same-power drives, the total side area of the single V and multirib design is equal. If there were no wedging effect, there would be no point at all in having the ribs, as it would simply act as a flat belt of equal or more likely, significantly lesser width, only touching the pulley at the peaks. The pulley peaks would then attempt to saw through the belt in a "rip cut", separating the reinforcing strands.
You'd possibly be surprised at how many people insist that the tight belt in an unmatched double V drive will wear out first, as it is working harder.
And, I ain't done wif da plugs, or rather, the other issues raised in that ballywho.
FRM
FR Millmore

Robert-
If the one of the reasons that you are considering such a radical proposition is that a flat belt absorbs less power than a V belt, switch to a toothed V belt. They flex more easily in order to absorb less power than the usual solid-sided V belt and cost a lot less than the conversion that you're considering. Easier to install, too.
Steve S.

FR
Steve makes a point. The Gilmer type belts have a V shape to their teeth. I'd like to see a reference to a "v" Chamfer with a flat belt with linear extrusions running the length of the belt rather than extrusions cross wise to the face of the belt.

Is there a web source on these issues??

Barry
Barry Parkinson

Steve - Robert expressly said he wasn't considering such.
Barry,
As I read it, Steve is referring to the fairly common V belt on which there are notches on the V bottom, as he says for flex (and cooling); and also to lessen the rubber compression/decompression, which causes changes in the running V angle of the belt, which in turn can only be roughly compensated for by subtle alteration of pulley groove angles on different sized pulleys. I use Dayco notched belts by preference, as they seem to last better.
"Gilmer", or more correctly, synchronous, belts actually have an involute form to the tooth sides, or some other approximation of a true gear tooth. This gives a smooth transition on and off the pulley, without "shaving" the teeth off the belt.
I don't understand your third sentence: "...flat belt with linear extrusions running the length of the belt" seems to me to be the description of the multi-rib design.
I spent a couple of hours last night trying to find you a good web reference on multi-rib design, not much luck. The way I learn about such is to go to a bearing and power transmission supply house, where there are usually large piles of free design/spec catalogs for the taking, from the manufacturers. Gates website is useless, as are many big company sites, although if you really dig and think about it, you get some info. (BTW, Gates wants you to replace the belt AND ALL the contacting pulleys, idlers, etc every four years" Tell me they aren't in league with big $$! - gotta be about $5k on a Benz)
You may find the MFR's catalogs in Thomas Register Catalog file at your library (I finally threw mine out since I am sorely short on space). Trade journals like Machine Design are great, but difficult to access unless you are employed as an engineer - been trying for years to get a subscription, which they give out free, but not if you don't have a degree and title and company address (and they check out your story!).
FRM
FR Millmore

Robert,

To answer your question. Yes you can change to a serpentine belt, and no it is not hard.

When you order the Moss Supercharger it comes with all the pulleys for this change over. This was not hard at all. Simple pulley changes. 1 hour tops.

When I ordered my GM Delco alternator I needed a 4 rip pulley and asked the guy I bought it from for a pulley and he put one on. Pulleys are all over the place.

I myself like the serpentine belt setup. As to advantages and disadvantages Barry and FRM laid that to rest.

Regards, Ray


Ray 1977mgb

This thread was discussed between 30/08/2006 and 05/09/2006

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