Technical Generator belt Size

[fiat500]

I have had two brand new belts from different suppliers and both of them have been right at the limit of fitment even from new. There was a small amount of improvement when I replaced the worn pulley wheels.

I'm wondering if anyone has a code number or actual belt size that I could use in order to buy one independently of the regular online suppliers? or has anyone bought a belt that actually needed lots of spacers when new?

Although you can read webpages that imply that the pulley is usually smaller on an alternator, on the Fiat 500/126 this seems not to be the case; can anyone confirm?

 

[fiat500]

The size that seems to be quoted and requoted is AVX 10 x 800.
There is arange of sizes and I am going to try for an AVX 10 x 787 and will report back if this fits better.

 

[Vitesse]

Crumbs the the things I do for you!!!! Got up walked across a cold garden to the garage, woke the dog up from its deep slumber. The dog wasn't locked in the garage btw but was asleep and wondered where I was going, so followed me.

My 650 engine has a belt that is nice and tight, is marked up 10 x 800, obviously width and length. My 500 equally has a nice belt on it. It isn't marked 10 x 800 but it does have 800 on it, so from that I would say you need a V belt 10 x 800.

 

[fiat500]

It makes a change for my belt to be too loose.
Thank-you for that but no way am I going out in the cold and dark to re-check my belt against your data.
Maybe I'm doing something wrong? but if so what????

 

[Vitesse]

Maybe not running across the garden fast enough to dodge the cold!

Mind you even in soft southern land it's a bit chilly tonight. But the wood burning stove kicking out its warmth so its nearly too hot.

I must admit when sticking the fan belt on the and the two parts of the pulley, at first with no shims its way too tight but I reckon I have 3 or 4 shims on both engines and it is just about right and maybe two or so on the outside.

It's probably down to the fact the you do so many more miles than your average 500 nowadays. It's not going to take too many miles to stretch the fan belt, its only held together with a bit of string impregnated in the rubber after all. Or if it slack from day one maybe the pulleys are worn?

 

[fiat500]

Update on belt.
I got a new one actually intended for the bigger engine but decided to use it as I have a longish journey next week. For the first time I have one that fits. I have used up all the shims and probably should find a couple more.
I definitely tells me that all belts are not the same even if the sizing is the same.

 

[F123C]

Update on belt.
I got a new one actually intended for the bigger engine but decided to use it as I have a longish journey next week. For the first time I have one that fits. I have used up all the shims and probably should find a couple more.
I definitely tells me that all belts are not the same even if the sizing is the same.

Motor (Auto) Factors used to have a gauge to measure old 'v' belts, (it looked like two 1/2 circles that you fitted the belt over, then moved them apart tensioning the belt, attached was a scale that gave you the belt length/size) so if you had an old belt without markings you could measure it up to find a suitable one to fit. We used to just hold the old and potential new belt side by side and stretch them using our hands/fingers to keep the same curvature each end to check we had the correct belt. Some say that belts stretch with wear/age, I think the reinforcing fibres don't really stretch, certainly after initial 'bedding-in', but that the sides wear. So an old and new belt can be the same size lengthwise but different in width due to wear. This means that a shim rearrangement will likely be needed even though the old and new belts are the same length.

If you have to fit too many shims between the pulley halves, especially if you use more than is supplied inside and outside the pulley, be careful the belt doesn't 'bottom out' in the pulley groove. It needs to run in the 'v', otherwise it will slip and wear.

Iirc the next size smaller than 10 x 800 was 10 x 785mm. but I can't remember the brand name.

If you're measuring a belt by hand (say by using a piece of string working you way around the belt length or tracing the belt onto paper and measuring it or using one of those little distance measuring wheels, I seem to recall that you don't measure the inside nor the outside circumference but half way up the face of the 'v' side. Maybe someone could try measuring a brand new/unused belt and see where it needs to be measured in order to match the stated size of the belt.

Al.

 

[fiat500]

If you have to fit too many shims between the pulley halves, especially if you use more than is supplied inside and outside the pulley, be careful the belt doesn't 'bottom out'. It will slip and wear.

Iirc the next size smaller than 10 x 800 was 10 x 785mm. but I can't remember the brand name.

Thanks Al. This is the third belt in the two years I have had the car on the road.
The previous one was fitted at the same time as a new dynamo pulley and never allowed me to fit more than one spacer. I had wondered if the new pulley was at fault (it wouldn't have surprised me), but I have eliminated that.
I had worked out that a 785 might be a good thing to try but have now revised that opinion.......800 is spot-on this time.
I must check on the manufacturer of this one; I know the annoying previous one is a Gates belt.

 

[F123C]

A few more thoughts.

I'm surprised you had trouble with a Gates belt. They're a long established American Co. with a great reputation for their 'v' belts, hoses and timing belts.

Their 'raw-edge' 'v' belts were supposed to be better than traditional 'wrapped' belts. Gripped better, stretched less (after initial 'bedding-in') and ran cooler. I'm not sure but I think the reinforcing fibres were a bit more than pieces of string, possibly aramid fibres or maybe even kevlar? A lot of people in the trucking world swore by their products.

Might be worth contacting them to see what they'd recommend to fit your car. They had a reputation for listening to their customers and solving problems.

When cars started to switch from dynamos to alternators, it was normal to fit a smaller drive pulley so that the alternator was turned faster in relation to engine rpm than a dynamo would have been. Dynamos don't like being spun too fast, alternators don't really mind.

But, of course, if you change the drive pulley size, then the belt size will likely also have to be changed. I suspect that this may be causing people problems is selecting the correct belt. I mentioned that when I worked on Fiats, back in the day, we often compared the old belt to the replacement. The parts book/microfiche wasn't always correct. Plus nowadays, so many years later, people may have swapped parts around so the correct belt is no longer the correct belt!

If you fit a belt that requires all shims to be removed between the pulley halves in order to get the adjustment correct, then you've no further adjustment remaining, so this size is no good. On the other hand, don't be tempted to fit a belt that's too tight assuming it will slacken as it 'beds-in'. This is not good for dynamo bearings. (Alternators are hardier).

One final thought. Iirc the belts used originally on Fiats in the 60's/70's were 9.5 x , not 10x .Maybe try measuring the width of any belts you have to see if this is the case. A 9.5mm belt will sit lower in the v of the pulley so a shorter? belt will be needed, possibly 9.5 x 785?.Tried to recall the OEM belt suppliers :- Pirelli, possibly Magnetti Marelli (the electrical equipment supplier) and one other make that eludes me :bang: There were also several aftermarket belt suppliers - Goodyear, Quinton-Hazell, Continental, Ferodo? Uniroyal etc. So if one make of belt doesn't fit, don't give up, try another.

Al.

 

[IanEmery]

Just been to the garage to photo the Fiat dashboard for another posting and took the opportunity to check the drive belt on my '62, this one is fitted with an 800 x 9.5mm belt. So far with no problems

Sorry, didn't think to look how many shims were used

 

[F123C]

Ian, thanks for taking the trouble to check out the belt size

My old memory gets a bit hazy at times ( it was c.40 years ago afterall.)so I wasn't sure of the 9.5mm size. Just thought I'd mention it in the hope that it might help someone.

Thanks again,

Al.

 

[fiat500]

A few more thoughts.

When cars started to switch from dynamos to alternators, it was normal to fit a smaller drive pulley so that the alternator was turned faster in relation to engine rpm than a dynamo would have been. Dynamos don't like being spun too fast, alternators don't really mind.

The pulley size being unchanged for the alternator may be because the engine is designed to rev so freely in any case.
I have been back to the car after a bit of a run and the belt has has settled in already and will probably need a shim taken out by the end of the week.

 

[fiat500]

Update:
Having replaced the belt and comparing with the old one, the slack fitting one looks much thinner in section. The most likely thing is that it has been worn down by the "V" of the crankshaft pulley which, on checking, seems a little rough so will be replaced at the next logical opportunity.
Now I have fitted an alternator, the same, fairly new, 800 belt is a much better fit, with lots of spacers being needed on the initial setup.
It seems like the pulley halves have a slightly different geometry and the effective diameter of the pulley looks smaller, which would make mechanical sense but defies logic; anyway, it's nice and taut and that's what matters.