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MG MGB Technical - Fan belt change.

Right me again, yes the annoying guy who is new to all this. My fan belt needed changing and when I bought the car the previous owner had bought a new one so I thought today I would change it.

Took the old one off no problems, went to put the new one on and it would not go on? The alternator was as far up as it could go with the old one on. Even with it as far down as possible it still wouldn't go on. Is it the wrong size fan belt? Or am I doing something wrong?

The one I was supplied says: gates auto master 6216MC.
MD Rice

Is the new belt the same size as the old one?

IIRC the "top" 2 bolts need to be slackened and there is a curved bracket with a long slot below the alternator and attached to it. Both lower bolts will need to be slackened to allow this bracket to move sideways whilst rotating to allow it to move. The Moss parts manual (free) shows it quite well.
Michael Beswick

I matched up the two I got with the car and they are both shorter than the one that was already on the car. One of the replacements is a 900mm one which I know is standard.

Not quite sure what to do.
MD Rice

As Michael says, all four bolts need to be slackened otherwise the range of adjustment is restricted.
Brian Shaw

4? I did the two on top of the alternator and the one that controls the movement and slack but where is the 4th? Also just checked my Haynes guide and it only shows 3 bolts to undo?
MD Rice

Ricey,
forget the Haynes get that Driver's Handbook (relevant to model) and it will clearly show you how to do this and other service work - http://www.mgocshop.co.uk/catalog/Online_Catalogue_Handbooks_5.html

(like how to correctly fit CB points (if they can't be cleaned) so that you don't get problems from the installation like some do)

there are 4 bolts as said

two that swing on the bracket, another on the adjusting slide fixing it to the alternator and the fourth is a different size and fixes the length of the slide bracket
(so three on alternator and one to adjust slide bracket)

don't fix the belt too tight or you could damage the water pump bearings, check after a while to see if the belt has 'stretched out' with use and needs slack take out

as you've not got your vehicle profile for public view (if you want to) and you've not said which year you'll need to look at Paul Hunt's web site to see if your fan belt should be 900mm or 950mm - http://www.mgb-stuff.org.uk/hometext.htm
Nigel Atkins

Nigel, you are really helpful. Thank you. I will update my profile with all my vehicle details. As its a 1973 with a non electric fan it requires the 900mm I'm lead to believe.

Whilst digging through my docs that came with the car I found that handbook and will go and check it out now. I will have a look and if I still have problems will post again.
MD Rice

Perfect! I did consider undoing that bolt but decided not to risk. A job for tomorrow. Lets hope it all goes to plan.
MD Rice

A tip on changing the V-belt is to get the belt over the pulleys of the crankshaft and the alternator first as they wrap furthest round these, and then the water pump lastly, having got it over the mechanical fan blades first, of course!
Stephen Strange

I'm going to sound stupid here but which one is the water pump? I know the alternator. Is it the biggest one that's lowest down or the smaller one to the right of the alternator?
MD Rice

the later
(to right of alternator as you look at the car from the front looking toward the windscreen)

depending on your car the water pump has the radiator fan, hence the name fan belt (it's a drive belt)

the biggest pulley lowest down is the crankshaft pulley

to give you a rough idea of the layout of your car (they also vary depending on year) click on the photos at the bottom of this page from Paul's site - http://www.mgb-stuff.org.uk/cutaway/cutaway.htm

if you know the next bits sorry but if you don't it could save you confusion later -

references to LHS (left hand side) and RHS (right hand side) are normally referring to viewing the car from the rear (another thing it tells you in the Driver's Handbook, get my hint)

hence we drive Right Hand Drive cars (normally)

the passenger side of a UK car is the nearside (N/S) (nearest the kerb when parked facing the correct way), so the driver's side is the offside (O/S) - so LHS is nearside and RHS offside
http://www.gendan.co.uk/article_21.html
Nigel Atkins

A rough guide to tension is, the belt from alternator pulley to crank pulley can be pushed in with your fingers by about 1/2". Best done when the engine is not running :)
Michael Beswick

Fan belt change complete. Thank you everyone.
MD Rice

Run it for a week and then check the tension. The belt should have about 1/2" deflecton midway between the alternator and water pump. Fan belts, contrary to common logic, shrink when they reach operating temperature, so don't be tempted to over tighten the belt. It will only shorten the life of your alternator and water pump bearings. RAY
rjm RAY

Cheers ray, will do that. I didn't over tighten it made sure it had the 1/2" deflection. And as I'm a newbie to this got a friend who works with cars to check over and he said its fine.
MD Rice

the way the fan belts are packaged and stored/displayed in a double twist loop can make them 'tight' to fit especially when the belt is cold so they may possibly 'straighten' with use and loosen fractionally plus you may have missed breakfast that day or let the tension slip when tightening the nuts and bolts, no problem if fitted correctly but always worth checking anyway

tension test for fitting . . . as per Driver's Handbook

fan belt is fitted so all well and good, best to change it at some time or mileage interval in the future (before 'distress' need to do so) and keep present fan belt as emergency spare if you feel the need to carry a spare, as it has been proven on the car for size, fit and function already
Nigel Atkins

Another option is to completely remove the bolt going through the slot in the adjuster, as on some cars that can give a bit more movement to the alternator. I've not had to do this on an MG but after the belt failed on the M6 just after I had got a Scimitar, and after trying half a dozen belts from four service vans and two spares vans and none fitted, I suggested doing that with the first belt they had tried and it went on ...

The belt size will vary with pulley sizes, and even originally the Parts catalogue specifies 900mm for all engines except 18V797/798, 18V846/847, and all engines from 1977 on. If you have different pulleys to originally for any reason it could well be different from the original 900mm, in fact if a 900mm won't go on then that must be the case, or a non-standard slider with a shorter slot perhaps.
Paul Hunt

This thread was discussed between 09/06/2013 and 11/06/2013

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