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Thornycroft 90 belts


NikaVinyl

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I changed my alternator and noticed my belts seem bit loose, I think my engine is Thornycroft 90, bmc 1500? I uploaded a video can I get bit of advise on two points, are they to loose and how to slacken the water pump (first belt) to allow me to replace them both.

It would help if  I had part numbers for both belts to use as reference.

YouTube video I made

https://www.youtube.com/watch?v=GyMmLsN_0uU

 

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Bit difficult to see but the water pump seems to be fixed by bolts to some sort of flange, maybe washers / spacers under the bolts to push it out a bit? As for the alternator as you know it is fixed at 3 points, two on top and one below, loosen all three and swing it out till the belt is a bit tighter, then tighten everything. If you are doing this then you might as well change the belts, take them to any bearing or power transmission supplier (nearly every town will have one on an industrial estate) They can match the belts. If you have no more adjustment left on the alternator then they will have a slightly shorter belt, same for the pump.

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54 minutes ago, Bee said:

Bit difficult to see but the water pump seems to be fixed by bolts to some sort of flange, maybe washers / spacers under the bolts to push it out a bit? As for the alternator as you know it is fixed at 3 points, two on top and one below, loosen all three and swing it out till the belt is a bit tighter, then tighten everything. If you are doing this then you might as well change the belts, take them to any bearing or power transmission supplier (nearly every town will have one on an industrial estate) They can match the belts. If you have no more adjustment left on the alternator then they will have a slightly shorter belt, same for the pump.

Or you can buy them by post. I buy from  BearingBoys  and use their cogged belts -

https://www.bearingboys.co.uk/Cogged-Belts-3831-c

They last much longer than plain V-belts, especially if one of the pulleys is small.

 

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I replaced alternator yesterday slight upgrade on the standard one, it was then I noticed the belts were bit bouncy even though does not look like they are slipping I thought best to replace them, I will wait until I move so I will have two weeks to sort it, I think your right looks like two bolts holding water pump in place shall check Sunday.

Can someone confirm if it is a bmc?

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Looks like one to me but I'm not an expert in them.

Water pump belt (the front one)  looks slack, and also looks like it is bottoming out on the water pump pulley, so might be the wrong section belt. I can't see from the video if there is any adjustment on the raw water pump. If there isn't, it might be worth replacing with a linked belt, such as a Fenner belt.

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There are many different versions of BMC 1.5 raw water pumps and on the one shown it is VITAL that the belt is kept on the slack side. The pump shaft runs in the plain drilling in the pump body so if you tighten the belt as typical then you tend to pull the pulley to one side and wear the pump body. Then it needs the gland replacing frequently, leaks lots of grease and will not self prime.  They seem to drive adequately with the belt very slack. Some BMCs had slots in the brackets where they mount onto the engine foot so you can loosen the bolts and slide the pump and bracket up and down the slots plus twist the bracket to move the pulley towards or away from the engine. I have no idea what yours is like. I suspect that you may well be able to pull the belt over one part of the pump pulley lip and turn the engien by the big hexagon on the crank shaft without damaging that belt because it runs rather slack.

The alternator belt needs to push in about 10mm in the centre of the longest run by finger pressure. This is usually between the alternator and the crankshaft pulley. As you can not carry out the test on a running engine I have no idea if the belt is tight enough or not but it looks OK to me but could be too tight. The water pump belt looks pretty typical for that sort of 1.5 with that raw water pump.

Just had another look at the vid - I think its a 1.8. It looks like a cast timing cover by the alternator (the i.5 has a tin thing like BMC B series petrol engines) and I cant see the injector pump as I would expect on a 1.5. Lets have a photo of the injection equipment side of the engine.

Only an idiot on here would give you belt part numbers because there are so many variations and modifications done to these engines- especially as it may well not be a 1.5. As others have said, take your old belts to a bearing supplier for measurement or you may find numbers on the outer face when you get them off or turn the engine so the markings become visible. make sure you get a notched/cogged belts for the alternator so it grips the small alternator pulley better.

 

PS- if the raw water pump mounting bracket does have the holes I describe when you slacken the belts in ether the pump or the bracket the whole thing can usually twist forwards and down so the belt slackens.

Edited by Tony Brooks
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18 hours ago, marji said:

I replaced alternator yesterday slight upgrade on the standard one, it was then I noticed the belts were bit bouncy even though does not look like they are slipping I thought best to replace them, I will wait until I move so I will have two weeks to sort it, I think your right looks like two bolts holding water pump in place shall check Sunday.

Can someone confirm if it is a bmc?

It looks like a BMC 1.8 to me.

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Wonderful response thank you all so much. Lucky I asked because I would have tightened the water pump belt like a car belt tension.

I shall get more photos this week.

Just to add I did get a 110 amp alternator but it was different socket lucky for me, as I then found out it would have been to much for my engine, after speaking to the company and sending photos they sent me a slight upgrade I think just 55 amps the old one was 35 amp, the company were great ecusdirect I have no connection to them, might be of interest to members here.

Edited by marji
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Bit late now but I would have gone for one of the 70 amp A127s that seem now to be about as the most cost effective upgrade.

I don't like this talk of a socket.

It sounds like you had an old ACR or early automotive A127 with the rectangular  socket containing 2 x 9mm blades and one by 6mm blade. Although not absolute by far the majority of those have the 9mm blades paralleled and in automotive use one charged the battery and one fed the car's electrical system. This split the alternator's output reduced the load on the connections to something  sensible for most of the car's life.  In marine use far too often the whole alternator output is passed through just one 9mm blade leading to overheating, loss of tightness and voltdrop. In an ideal world I would always seek to get hold of an alternator with a stud connection for the main output and change the terminal on the lead. Failing that I would strip back rather more insulation than normal and split the conductors, twist them up, fit two 9mm blades and insulate the now exposed conductors.  Then connect to both blades. The 6mm blade is for the warning lamp and even if the bulb shorted the current is limited to 3 to 4 amps so its not an issue.

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2 minutes ago, Tony Brooks said:

Bit late now but I would have gone for one of the 70 amp A127s that seem now to be about as the most cost effective upgrade.

I don't like this talk of a socket.

It sounds like you had an old ACR or early automotive A127 with the rectangular  socket containing 2 x 9mm blades and one by 6mm blade. Although not absolute by far the majority of those have the 9mm blades paralleled and in automotive use one charged the battery and one fed the car's electrical system. This split the alternator's output reduced the load on the connections to something  sensible for most of the car's life.  In marine use far too often the whole alternator output is passed through just one 9mm blade leading to overheating, loss of tightness and voltdrop. In an ideal world I would always seek to get hold of an alternator with a stud connection for the main output and change the terminal on the lead. Failing that I would strip back rather more insulation than normal and split the conductors, twist them up, fit two 9mm blades and insulate the now exposed conductors.  Then connect to both blades. The 6mm blade is for the warning lamp and even if the bulb shorted the current is limited to 3 to 4 amps so its not an issue.

I got a Chinese equivalent of the A127 for a little over £50, where the output was via a stud. I thought as well as the paralled blade connections?

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