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Stuart Miller

Decoding drive belt specs

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Hi all,

 

I recently bought Progress - a 1936 wooden tug. She has a wonderful Fowler 2DYm engine, which deserves to be in the percussion section of an orchestra, never mind a boat! I'm trying to stock up on spares and am searching for a replacement drive belt. The current one has this inscription: 3002 592x91 12,5X1275LA 42-3388 DAYCO. Sadly, I am not familiar with how to decode this in order to buy another one. According to the very helpful chap in Midland Chandlers (Braunston), I'm after one that is 12.5mm wide and 1275mm in circumference. Trouble is, I can't fine one online anywhere. I can find something seemingly close - such as 13X1275 - but the letters are different (specifically, it reads '13AX1275C'). I am very new to engines and mechanics in general and have no idea whether the tiny extra width (13mm rather than 12.5mm) would make any difference (can't imagine it would) nor whether the letters mean something important. In other words, is 13AX1275C essentially a perfectly good replacement for a '12,5X1275LA'...?

 

Any help would be hugely appreciated.

 

Thanks in advance.

 

Stuart.

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Try going to a good motor factors, and take the belt with you. Once you find the right belt, check it really is (ie run the engine good and hard for a while) then go and buy two more. It will be critical what cross section it has, btw.

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You have/need an "A" section v belt which is 1275 mm pitch length.

 

"A "section is 0.5 inches wide in imperial dimensions, but 13mm wide in metric!!

In imperial dimensions the equivalent belt to a 1275 mm long belt  is 50.25 inches long.

 

A section belts are not common in cars, (they use Z section, or poly vee belts) so most motor factors will not be much help.

 

A 13AX1275 will be fine.  

 

Look on somewhere like the  Bearing Boys or Eriks (was Fenner) website, or go to your local bearing stockists.

N

Edited by BEngo
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Thanks so much for those prompt replies.

 

I will go ahead and buy the 13A1275C and give it a whirl - and will then buy another couple just in case.

 

BTW - any idea what the 'C' stands for at the end - and how it differs from the 'LA' suffix inscribed on the current belt?

 

Thanks again everyone.

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3 minutes ago, Stuart Miller said:

Thanks so much for those prompt replies.

 

I will go ahead and buy the 13A1275C and give it a whirl - and will then buy another couple just in case.

 

BTW - any idea what the 'C' stands for at the end - and how it differs from the 'LA' suffix inscribed on the current belt?

 

Thanks again everyone.

C might stand for cogged.

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Unlikely that C stands for cogged, as the cogged belts are wedge belts in the XYZ series.

Manufacturers tend to have their own prefixes and suffixes.  Sometimes they denote differing reinforcing material, sometimes it is the rubber blend sometimes it is something else.

The only way to get a handle is to study the makers catalogues carefully.  Unless you are a power transmission design nerd, this tends to be the sort of thing to when you are insomniac.

 

N

 

 

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15 hours ago, BEngo said:

You have/need an "A" section v belt which is 1275 mm pitch length.

 

"A "section is 0.5 inches wide in imperial dimensions, but 13mm wide in metric!!

In imperial dimensions the equivalent belt to a 1275 mm long belt  is 50.25 inches long.

 

A section belts are not common in cars, (they use Z section, or poly vee belts) so most motor factors will not be much help.

 

A 13AX1275 will be fine.  

 

Look on somewhere like the  Bearing Boys or Eriks (was Fenner) website, or go to your local bearing stockists.

N

Same as a belt marked A50?

 

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2 hours ago, Eeyore said:

Same as a belt marked A50?

 

Not sure, and I cannot find my copy of the BS to look.  Imperial sizes are mainly used by ancient machinery and American manufacturers.  Some belt lengths are quoted in either 8ths or quarter inches so a 50 inch A section belt could be labelled A50, A200 or A400.

 

If the belt is a bit over 4ft around, or nearly 2ft long when held in a tight loop I would expect it is 50 in pitch length.

 

If your belt tension is adjusted in the normal way by moving one pulley, or an idler wheel you can usually get away with either the next standard size up, or the next down.  Sometimes you can go either way.

N

  • Greenie 1

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4 minutes ago, Man 'o Kent said:

You could always look for "linked belt".

Very unlikely to cope with smaller diameter alternator pulleys; but specifications do vary.

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58 minutes ago, Eeyore said:

Very unlikely to cope with smaller diameter alternator pulleys; but specifications do vary.

Given its construction I would have expected it to be at least as flexible as a run of the mill "V" belt. With 50+ years in the engineering game on all sorts of special purpose machinery I cannot think of a single instance where there was such a problem.  In my experience every bit as durable as its "normal" equivalent too.

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Linked belts sacrifice two things for the convenience of fitting and easy sizing.  One is ultimate power transmission capacity, because of the gaps between the links.  The other is the ability to bend round a small pulley, because of the construction.

In industry no-one designs at the very limits of a belt, because belt life is then too short, and drives tend to be fast to slow. Linked belts will do well there.

 

  In boats it is usual to have a speed up drive,  push belts hard,  and accept short life and black dust everywhere.  A common example would be a 90A alternator with a modified pulley to reduce its diameter being driven by a single rubber Z section cogged wedge belt.  Squeals like a stuck pig at start up  (or is over tensioned) with a low domestic  battery but the alternator load soon drops and it quietens down and works all day.  Does that for not many days a year and the belt has to be renewed at annual service.    Poor design, but Owner is still happy, so no one changes anything.

N

 

 

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