srah1953
Member
Looking at a website trying to source alternator belt for a Yanmar engine. On one site some are described as V belts and some as serpentine belts. I'm curious as to the difference. Many thanks
V Belt and Serpentine Belt
- Thread starter srah1953
- Start date
VicS
Well-known member
V belts are a simple V shape with the bottom of the V cut off Usually about 3/8 " wide across the top. They may or may not be cogged ( toothed if you like). Cogged are better IMHO but they are the ones you here squeal in peoples cars when they get a bit slack. Not used so much these days
Serpentine belts are broader flat belts with several small V shaped ridges running all round the the inside. I call them poly-V belts for obvious reasons . I prefer to reserve the name serpentine belts for the hugely long ones that run around countless things like a serpent!
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RichardS
N/A
The terms seem to be getting mixed up.
A V-belt has a V-section and is tightened by moving the pulleys further apart. It may be toothed (cogged).
A sepentine belt is a flat section, usually longitudinally ribbed on the inside. It can be tightened by alteration of pulley distance or by an idler pulley.
However, I bought a flat belt for a car a couple of weeks ago which was called a v-belt on the packaging!
For some of the Yanmar engines you can buy V-belts or cogged V-belts to fit. I would recommend the cogged version as I find they are less prone to wear and squealing.
Richard
VicS and I crossed in post. His point about Poly V-belts is clearly the source of the confusion I referred to. I had not thought of the ridges as many Vs. Interesting!
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srah1953
Member
Thank you both very much. Much appreciated.
Mistroma
Well-known member
Minor point about cogged belts mentioned above. You don't need to change the pulley to use cogged belts, they fit the same pulleys as equivalently sized normal V-belts. The cogs don't engage in anything, the cut-outs help the belt to turn around a small pulley more easily and also provide a bit of cooling (more surface area). I think that they run a bit cooler, last longer, and are slightly more efficient than the standard "un-cogged" V-belts.
So just use v-belts (standard or cogged) unless you have problems with wear and dust from your present setup. I think that it can be a bit pricey switching to poly-V belts as you'll need to change all the pulleys. Changing to a 140A alternator would be one reason for changing as v-belts give problems powering alternators much over 100A.
Some belts do have cogs to mate with toothed drive sprockets, but you can ignore these as they are for specialised use (e.g. engine camshaft belts which keep rotating parts synchronised).
So just use v-belts (standard or cogged) unless you have problems with wear and dust from your present setup. I think that it can be a bit pricey switching to poly-V belts as you'll need to change all the pulleys. Changing to a 140A alternator would be one reason for changing as v-belts give problems powering alternators much over 100A.
Some belts do have cogs to mate with toothed drive sprockets, but you can ignore these as they are for specialised use (e.g. engine camshaft belts which keep rotating parts synchronised).
VicS
Well-known member
just to round things off
A manky old V belt
A cogged V belt
A poly-V belt
and what I would call a serpentine belt
A manky old V belt
A cogged V belt
A poly-V belt
and what I would call a serpentine belt
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macd
Active member
"Serpentine" is preferred in the USA, "polyvee", in Europe. Much superior to V-belts (which is why cars haven't used Vs for decades).
As mistroma writes, 'cogs' on V-belts don't engage on anything. They're mainly to help them run cooler, partly through the reduction of internal friction.
As mistroma writes, 'cogs' on V-belts don't engage on anything. They're mainly to help them run cooler, partly through the reduction of internal friction.
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sailorman
Well-known member
i would suggest this is a serpent belt
VicS
Well-known member
i would suggest this is a serpent belt
There must be a witty reply to that
charles_reed
Active member
I've used the standard V belt satifactorily on alternators of up to 110 amps. The "cogged" belt seems to be referred to, in the trade as "heavy-duty" and certainly will work effectively with far higher loads than toothless belts. Whilst I'm sure the cut-outs probably aid cooling their most significant effect is to effectively double the area in contact with the pulley.
I would also make the point that the pressed 2-peice pulleys frequently supplied with V-belt-driven ancillaries are utterly useless - I make a point of fitting machined from solid pulleys.
I'd definitely change to polyV (serpentine) belts if one was driving more than 2 ancillaries. To be really effective they need their own tensioner (as shown in VicS's photo) and idlers to ensure wrap-round all the pulleys.
As to the variable length belt - excellent as a get you home and probably as good as the traditional nylon stockings (now tights). I ran a 1946 Fordson Major, with a aftermarket dynamo and starter for 8 years with one of those - fortunately the dynamo was only being asked for about 10amps.
I would also make the point that the pressed 2-peice pulleys frequently supplied with V-belt-driven ancillaries are utterly useless - I make a point of fitting machined from solid pulleys.
I'd definitely change to polyV (serpentine) belts if one was driving more than 2 ancillaries. To be really effective they need their own tensioner (as shown in VicS's photo) and idlers to ensure wrap-round all the pulleys.
As to the variable length belt - excellent as a get you home and probably as good as the traditional nylon stockings (now tights). I ran a 1946 Fordson Major, with a aftermarket dynamo and starter for 8 years with one of those - fortunately the dynamo was only being asked for about 10amps.
VicS
Well-known member
Sorry. Perhaps i am being dense this morning but you will have to explain how cogged V belts have double the area in contact with the pulley.
rogerthebodger
Well-known member
i would suggest this is a serpent belt
I would call that a link belt
https://www.google.co.za/search?q=l...&ei=BVAFVYufEubd7gaNmoCADw&sqi=2&ved=0CBsQsAQ
http://www.ebay.co.uk/sch/i.html?_f...elt.TRS0&_nkw=link+v+belt&ghostText=&_sacat=0
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macd
Active member
+1
They reduce the area. As said, their main benefit is in reducing internal friction and thus running temperature. Excessive heat is the primary cause of premature failure.
pampas
New member
One definite advantage of the poly "V" belt on a boat is that belt dust is practically eliminated. As mentioned rather expensive and difficult to obtain the pulley ratio required.
Present engine a BMC 2.5. it`s the water pump pulley that stops me from converting to this type of belt.
Present engine a BMC 2.5. it`s the water pump pulley that stops me from converting to this type of belt.
charles_reed
Active member
I stand corrected.
Perhaps this .pdf will amplify.
https://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/replace_vbelts_motor_systemts5.pdf
macd
Active member
Pulleys are actually dirt cheap from specialist suppliers. The difficulty is in finding one to fit your shafts etc without machining.
The lack of dust isn't their only asset: they last. The polyvee on my last boat did 2000hrs without adjustment.
macd
Active member
Thanks, Charles. That piece refers to extra area with synchronous belts - notched belts running on toothed pulleys, not the plain pulleys most boat engines use
VicS
Well-known member
but it looks like a scaly serpent.
RichardS
N/A
I'm not sure why that pdf refers to synchronous belts, which keep all the pulleys in a constant relationship to each other, as cogged belts.
No wonder these terms seem to be getting mixed up.
Richard
