cotswold Posted July 10, 2015 Report Share Posted July 10, 2015 I swapped my old fan belt with a new one sold as suitable for my car. The one I took off is circa 900mm x 15mm which did not look that worn but the tensioner on the slotted arm dynamo bracket was at the max setting. The new one is 900mm x 20mm and will only fit with the dynamo hard up against the engine and with my turning the engine by the fan whilst pressing the new belt onto the water pulley with the result that there is really no slack on the belt (only about half an inch in the centre. Any one have this problem? Is 20mm the right size for the wide belt fitting? Thanks Charles Quote Link to post Share on other sites
RAHTR4 Posted July 11, 2015 Report Share Posted July 11, 2015 Hi Charles, The Ferodo Fan Belt Pocket Guide (1969) provides the following : TR4A with fan and generator Original Triumph part number 58924 Ferodo belt number V391 Dimensions Top width 3/4" Thickness 15/32" Side wall angle 32 degrees Internal circumference 35.1/8" Outer circumference 38.1/16" Hope this helps. Regards, Richard Quote Link to post Share on other sites
BlueTR3A-5EKT Posted July 12, 2015 Report Share Posted July 12, 2015 Charles, Who supplied your replacement belt, was it one of the known specialists? The belt width of 20 mm is sort of correct as it is a metricated re-creation of an imperial design. The 900 is the length inside, the length outside will probably be 975mm. This links nicely with Richard's very helpful info from the Ferodo catalogue. Your old 15mm wide belt I would guess was running low in the 'V' of the pulleys, drive should be on the sides of the belt not the bottom. - if the bottom of the pulley is shiny it confirms this. Run the new one you have, they usually stretch quite quickly so will need re-tensioning. I personally carry a pre stretched fan belt in the boot as a spare as new ones are tight to fit - as you have no doubt noted. Peter W Quote Link to post Share on other sites
lynchpin Posted July 12, 2015 Report Share Posted July 12, 2015 (edited) Hi Charles Fitted a new belt only yesterday bought it from the tr shop, the size is 900 x 20 which is the same as the one it replaced which had been on there for 8 years and had started to crack on the inside, wonder if its still under guarantee. The dynamo is quite away from the engine block with about 3/4" of slot left in the adjusting bracket and the belt fills up the space in the pulleys to the top,perhaps someone has changed a pulley at sometime, Also I believe that the large belts should be quite slack so as not to knacker the water pump or dynamo bearings.. Phil... Edited July 12, 2015 by lynchpin Quote Link to post Share on other sites
RobH Posted July 12, 2015 Report Share Posted July 12, 2015 Charles As an alternative to the advice above, you can also use a modern 17mm wide 'cogged' raw-edge belt which is much more flexible than the old solid type. The raw edge grips better on the sides of the pulleys so does not need as much tension and 17mm fits the standard pulley without bottoming as Peter mentions. Being thinner top to bottom makes it easier to get through the narrow gap when fitting on a '3A but I guess that is not so relevant for your 4A. I use a 17 x 965 but that is with an alternator which has a smaller diameter home-made pulley and a different adjustment arm, so that length might not be right for your application. Rob Quote Link to post Share on other sites
cotswold Posted July 12, 2015 Author Report Share Posted July 12, 2015 Thanks all for your helpful comments, as usual this site comes up trumps. I will stay with the current 20mm belt (bought on Ebay but a good one) although the 17mm may be the one I go with if it doesn't stretch as Peter W suggests it might as I dont want to ruin any bearings. I am fitting a Dynamater this week so will have to take off the old dynamo pulley. Thanks again Charles Quote Link to post Share on other sites
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