Urgent - Fan Belt

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MikesDexta
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Urgent - Fan Belt

Post by MikesDexta »

yet another problem with my Fordson 'Bitza' (like others before me my Dexta seems to be made up of lots of non-Dexta parts - when I get chance I will write it all up in a post).

My dynamo wasn't putting out any volts using the link and measuring DC volts revving slowly to 1000rpm - only millivolts. I then began to remove the dynamo but the belt wouldn't come off until I removed the 2 of the mounting bolts! I sorted the dynamo problem (stuck bush) and reassembled it only to find that no matter how I tried I couldn't get the belt back on with the dynamo pushed all the way in. I checked the size and its a BEPCO 12.5 x 1145La (not sure what the La means - it could be something has been smudged off).

Anyhow I am fortunate to have a local Agriline distributor and they had a 12.5 x 1150 which Agriline says is for the Dexta but that wouldn't go on either! This leaves me to wonder if one of the 3 pulleys is non-standard, the dynamo seems genuine (Lucas 22756E C40t although I can't find the Lucas stamp on it only 'Made in England'. The dynamo pulley has seen better days and needs replacing. To cap it all I noticed the said belt had rubbed a groove in my bottom hose so that will need replacing and adjusting now. I realise this is a common problem. So, I have three urgent questions:

Where can I get a tapered or narrower bottom hose?
What is the normal size fan belt I should be using?
Any possible ideas as to why the 'standard' Agriline belt won't fit?

thanks in advance

Mike
1959 Dexta
I'm not retired just re-deployed

Bensdexta
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Re: Urgent - Fan Belt

Post by Bensdexta »

I would just get a fan belt that fits, and not worry too much about whether it's 'correct' or not.

Ref lack of clearance of the belt on the bottom rad hose, yes that is a common problem. The repro hoses are a bit variable, so it's pot luck what you get.

I solved the problem but cutting a small piece of curved tin out of the side of an old tin can and clamping it around the hose with a couple of small plastic zip ties. Looks a neat job.

The fan belt has eroded a very small groove in the tin and the tin has trimmed off the very edge of the belt, so now there is a minimal clearance. Been like that for 5 years now, with no problems, so I've never given it further worry.
Last edited by Bensdexta on Fri Jun 08, 2018 12:47 am, edited 1 time in total.
Bensdexta - 1961 working for a living!

basewindow
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Re: Urgent - Fan Belt

Post by basewindow »

Had a similar problem with mine, fan belt and lower radiator hose rubbing. Cut the hose and fitted small length of pipe that fittted inside the hose for that section, couple of clamps, and now no issues. Im just about to fit a new fan belt, so I'll see how mine goes size wise.
62 Super Dexta.

MikesDexta
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Re: Urgent - Fan Belt

Post by MikesDexta »

Thanks both, I decided to set the dynamo at mid point and use a length of thick, round electric cable to measure the length I need. It turned out to be 1175mm as opposed to 1150mm sold by Agriline et al. I bought one from our local auto parts shop and it fits fine.

However I still have the problem of the belt rubbing against the hose and I wondered if it could be corrected by adjusting the bracket that fits the dynamo to the engine block? i.e moving the dynamo and the belt to the right by altering the adjusting bolt setup? If I used a longer bolt to the right of the bracket shown below and adjusted the left hand nut and bolt setup?

Image20180608_093936[1] by Michael Jones, on Flickr
1959 Dexta
I'm not retired just re-deployed

Bensdexta
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Re: Urgent - Fan Belt

Post by Bensdexta »

That might work, but would it upset the belt's alignment with the crank pulley?

Alternatively try and source slightly better formed lower hose. EG ask Bertie Dunlop to see if he can find you a better one.
Bensdexta - 1961 working for a living!

MikesDexta
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Re: Urgent - Fan Belt

Post by MikesDexta »

Just for completeness the problem with the belt cutting into the bottom hose was solved by removing the rad and twisting the bottom hose away from the belt, this resulted in a 10mm clearance.
1959 Dexta
I'm not retired just re-deployed

MikesDexta
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Re: Urgent - Fan Belt

Post by MikesDexta »

Since I changed the dynamo and regulator it charged the battery but only at over 1600 rpm. I have only used her for long spells topping last summer/autumn and not much over the winter, so it hasn't been a problem. However, now I'm having to start and stop quite often, only using her at lower revs, and the battery isn't charging.

In summary, I've changed the dynamo and regulator but used the old pulley and, as you can see from earlier posts, I had trouble with a standard Dexta fan belt being too short, so sourced a longer one. It never occured to me until now that the pulley might be the wrong diameter so reducing dynamo rpm and output! See here for a post on the same problem search.php?keywords=dynamo+pulley+diame ... 0180728b8c

Suppliers are mostly pretty vague on dimensions except Anglo https://www.ebay.co.uk/itm/Dynamo-Pulle ... SwCGVX3ABX which gives an OD of 80mm and ID of 45mm and pulley groove width of 18mm; however, the manual states effective generator pulley diameter should be 88.4mm to get 1:1.5 ratio to engine speed yet a standard Dexta belt width at LoNR is 12.5mm width which means it would sit well down in this pulley so reducing the effective diameter well below 80mm!

The existing suspect pulley has an OD of 110mm and ID of 74MM and max groove width of 14mm so a 12.5mm belt would be ok if the effective diameter was correct which it clearly isn't; I estimate the effective diameter would be over 100mm with a standard belt (if I could get it on which I couldn't).

Although not important at this stage I have a Lucas Premier 91Ah Calcium battery that charges perfectly on a charger and lasts for a few starts (never counted but it always runs flat when I need the tractor most!).

My questions are:
In order to see charging start at 620 rpm tickover what is the correct OD of the pulley and max groove width? Also which belt do I need?

I've done all the dynamo tests from previous posts plus read the manual so if anybody can help solve this sticky problem you deserve a virtual pint :beer:

Anybody? :scratchhead:

Mike
1959 Dexta
I'm not retired just re-deployed

Jerry Coles
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Re: Urgent - Fan Belt

Post by Jerry Coles »

The other option is to replace the Dynamo with an alternator especially if your only using it for short sessions.
That of course means a different puley size! I had the same problem with the bottom hose.
Re moving the dynamo back on its bracket even a few mm might make a difference. The belt would be displacing a little but I would think well within tolerances. IMHO.
Jerry
Jerry Coles
Camerton, Bath, UK
West Highland White Terriers, Dexta's, E27N's and DUKW's

MikesDexta
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Re: Urgent - Fan Belt

Post by MikesDexta »

I swapped my 110mm dynamo pulley for a 85mm one from Anglo and installed a correct size fan belt (12.5mm x 1150mm). It now charges at 1200 rpm instead of more than 1600 rpm so is much better. The generator light starts to flicker at around 1000 rpm and goes off at 1200 rpm. After a few minutes at 1200 rpm the light stays off when reduced to tickover, so I'm assuming that means the battery has recharged? Here's the new pulley in situ

Image

Although this seems to have fixed the problem, I'm a little concerned that this pulley looks small compared to pictures I have of other Dextas. Also the belt is sitting quite low in the pulley, possibly running on the bottom.

Could someone whose Dexta is charging at or below 1000 rpm do me a big favour and measure the diameter and width of the 3 pulleys please?

many thanks

Mike
1959 Dexta
I'm not retired just re-deployed

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