Slipping drive belt! Help!

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steelfloats

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I have a marinised ford 1.6 diesel, the drive belt is exactly as per the original set-up drivingbthe alternator and cooling water pump via the main pulley on the crankshaft. I have the seawater pump piggyback off the cooling pump. A fanbelt lasts about 10 starts, then it has stretched enough to cause it to slip! Any advice on why this should be? The engine ran fine as a vehicle with no problem, can the extra load turning over the seawater pump be enough to cause this problem? Any advice welcome, having to jump into the "engine room" unexpectedly is becoming the norm when entering port.
 
Is the stretching accompanied by black dust from the belt? If so I'd check the pulleys for rusty grooves. Perhaps not obvious without a fairly close look but a killer on vee belts.
 
I have the same engine but in my case the alternator has been moved to the left hand side due to the engine bearers being in the way.

The 'fan' belt drives the alternator and engine coolant pump only. The alternator is 'downstream' of the coolant pump in terms of the pull from the belt which is not ideal as it should be the first item the belt sees due to the load on it. However it works fine (55 amp alt). My raw water pump is driven off the crankshaft so no extra load on the belt.

Initially the belts used to go slack due to wear from a rusty alternator pulley. Changing the pulley to a new one and cleaning the other pulleys means the belt is now on its fourth season.

Do you have any black dust indicating excessive wear. You may need to check pulley alignment as well.
 
The light dawns! I have black dust, assumed it was the result of the belt slippage, but from your posts it may be the indicator of rusty pulleys. I did change the alternator, but as it was a bare unit I used the same pulley. I will investigate my pulleys for corrosion tomorrow. Many thanks
 
If it is the standard Lucas A127 Alternator then a new pulley can be had cheaply off Ebay. The crankshaft and water pump pulleys can be cleaned up with emery paper.
 
If you have a lot of black dust it could well be rust but that does tend to be be self-cleaning after a while. Does the belt sit it the grooves with the flat top of the belt level with the outer circumference of the pulleys? If not, the belt could be too low in the V which will have a similar effect to rust but is not self-curing.

Richard
 
I have the same engine and set up. When purchased the boat had been laid up for two years so probably had a lot of rust in the pulley grooves - belts did not keep their tension or last very long. I also had problems keeping the belt tight and suspect the alternator was pulling back in against the securing bolts.
Improved the securing bolt problem with spring washers. As mentioned in an earlier post the amount of black dust has also reduced with use. I now get one season, around 100 hours running from a new belt.
You also need to watch the bearings on the fresh water pump, the salt pump load can cause them to wear rapidly (about 5 seasons / 500 hours between replacements) and the play is amplified at the salt water pump causing excessive vibration and possible chafe damage to pipework.
 
A quality belt such as Gates may be a little better than some others?
Don't let the engine idle too slowly, the alternator is trying to regulate to a constant power, and the lower its speed, the more torque it needs.
If you have multiple batteries, can you let one charge for a few minutes before switching in the others?
Check the pulleys are all in the same plane.
Check the belt is not bottoming out in any of the pulleys.
Check everything is turning as freely as it should. Impeller pumps can be a lot of drag if the impeller is too fat and the gasket too thin.
Is there lots of back-pressure for the impeller pump? e.g. heat exchanger full of dead seahorses etc.
 
RichardS said:
+1

Or indeed any belt which is cogged (toothed) rather than solid. However, getting the flat of the belt across the circumference of the pulleys is more important with any type of belt.

Richard
Click to expand...

+1 On a different engine, I found switching to a cogged belt - coupled with cleaning of the pulleys - did a great deal to reduce belt wear and dust. I presume that the cogging reduces 'bulging' of the belt's side walls as it travels round the smaller diameter pulley in particular.
 
I have the 1.8 version from Lancing, and mine has only alternator driven off the crank pulley - although the sea water pump is crankshaft mounted. I noticed when I installed a brand new belt that the adjustment was well towards the limit, so ordered a couple of slightly shorter belts of the same polyvee config to great effect. Generally my engineer doesn't tighten the alt belt enough at the start of the season, by a gnat's wossname...
 
All marine and car engines I've seen have a slide where you undo a nut and pull the alternator forward, I used a long screwdriver, to tighten the belt then tighten the nut. Make sure it is really tight you shouldn't be able to twist it if it does twist it won't stay tight long. I assume you have a slide? A long screwdriver gives serious force on the alternator and you can hold it place when you tighten the nut.
 
Last edited:
steelfloats said:
I have a marinised ford 1.6 diesel, the drive belt is exactly as per the original set-up drivingbthe alternator and cooling water pump via the main pulley on the crankshaft. I have the seawater pump piggyback off the cooling pump. A fanbelt lasts about 10 starts, then it has stretched enough to cause it to slip! Any advice on why this should be? The engine ran fine as a vehicle with no problem, can the extra load turning over the seawater pump be enough to cause this problem? Any advice welcome, having to jump into the "engine room" unexpectedly is becoming the norm when entering port.
Click to expand...

When you have belt slip be careful of putting too mush tension on the belt as this will increase the radial load on the bearings of the water pump and alternator.

Also look at the wrap or the belts as too little belt wrap can also cause belt slip.

One other thing to consider when extra load is applied to a drive belt is the belt section. Most engine drive Vee belts are of Z section but a slightly bigger section could reduce the problem if the pulleys will allow the bigger section.

354509.jpg


Changing from Z to SPZ may help in your case
 
Gladys said:
I have the 1.8 version from Lancing, and mine has only alternator driven off the crank pulley - although the sea water pump is crankshaft mounted. I noticed when I installed a brand new belt that the adjustment was well towards the limit, so ordered a couple of slightly shorter belts of the same polyvee config to great effect. Generally my engineer doesn't tighten the alt belt enough at the start of the season, by a gnat's wossname...
Click to expand...

I don't think that the OP's engine uses polyvee belts. If it does most of the advice I have given is meaningless. :(

Richard
 
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