Is the battery too small

[larryowner]

I have a 3.5 V8 carb engined comp safari Land Rover,only electrics are fuel pumps, ignition and 2 X 12'' cooling fans. But the alternator V belt wear's out very quickly, (one event). When both fans are switched on with the engine running at tick over, the engine speed will drop by app 400rpm. This must put quite a load on the V belt. The fans are in good condition and turn freely. My thought is that the battery out put is to small, leaving the alternator to work hard when a few amps are needed, although the battery does start the engine ok. Numbers on battery are type069, 68HA, 535 amp SAE. Is this battery a bit on the small side?

[ian.stewart]

The first thing I would do is put a straight edge across all the pulleys to make sure they ar aligned up, the belt will not last if its at an angle, and check, with the engine at tickover that they are not bent,

[ChrisJC]

But does the belt squeal? Or does it run in a mixture of mud, grit, slurry, water etc?, which just eats it away.

I believe the RV8 develops very little torque at idle, and there was a fix on the SD1 auto's as the engine tended to stall when you put it in drive because of the extra load. But dropping by 400rpm does sound a lot.

You could raise the idle speed.

Any idea what current the cooling fans draw?

Chris.

[DaveEFI]

Apart from at idle, the alternator should supply all the requirements of the electrics plus some spare to charge the battery.

I'd be looking at the mechanical side of the drive, like tension and alignment etc. Dunno about mud and grit.

The anti-stall mod to the SD1 EFI auto is more to do with the flapper injection not maintaining the correct AFR at idle under all conditions. It's not needed with a MegaSquirt.

[marcjagman]

Maybe convert to a multi rib belt?

[stevieturbo]

Is the alternator in good working order, and is it of enough output to supply your electrical demands ?

As Dave says, with the engine running the alternator is the main source of power for all devices. The battery is charged with any excess, and there as a damper/reserve for the most part.

Your problem could simply be a poor alternator, or some dodgy wiring.

[larryowner]

Thanks for replies. Iv'e checked all the normal things i.e. belt alignment, belt tension, alternator condition etc. But two things mentioned may be on the right track. Firstly the large drop in RPM may not be because there is a heavy load on the alternator, but rather the lack of torque at low RPM, compounded by the engine running with a Kent 234 camshaft.
Secondly I will need to improve the under engine mud/water protection, as this may be a contributing factor to the excessive belt wear.

[jan_rrc39v8]

are you using an adjustable cam-gear? If yes try advancing the timing of the cam in relation to the crank, this will restore some of the low rev torque that was lost due to installing a sports cam.

also: what is the condition of the battery? do a load test (with a shunt and amp meter) on the fully loaded battery to check how many amps the battery can still deliver. Over time the capacity of a lead acid battery decreases. If the battery can only hold a small charge it will mean that the alternator will have to work harder causing more drag on the engine.

if you need to get a new battery, consider buying a gel battery, these are a lot more robust and can handle offroad/rally use better.
Expensive but worth it if you do lots of offroading.

[larryowner]

Up date on the above. Now that Iv'e had the vehicle a bit longer i find that the engine is throwing the alt/water pump belt off on a regular basis. I've tried several different make's of belt with the same resault. I have added a guide pully on the unloaded side (crank to alt) as this is where the belt seemed to be jumping around and rechecked pulley alignment but belts still coming off. Had another look at it today and found the crankshaft end float is .018'' (.45mm) this is far more than it should be and will be looked at asap. But would this amount of movement be enough to cause the belt problem?

[stevieturbo]

What sort of belt is it ?

The end float is a lot, but doubt it would be enough to cause belt issues. Ive seen pulleys misaligned by more and they've run pretty reliably.

[ChrisJC]

Are you sure that the pulleys are all aligned and square?

Chris.

[Ian Anderson]

Is the belt the correct width for the pulleys?

It should not run on the base of the V but be "trapped" between the sloping sides.

Also a test on the belts you are using. Hols it and press the 2 ends of the circle together. If it tries to make an 8 shape by twisting then there is a good chance it will climb off the pulley. (This used to be a problem on Formula V aircooled engines and back then only the uber expensive genuing belt would not turn itself upside down / inside out before jumping off!)

IAn

[ChrisJC]

Yes, good point Ian. Are all the pulleys the right width?. On a Range Rover for example, there are 10mm belts and 13mm belts, so if you have a mixture of pulleys, you could well have problems.

Chris.

[larryowner]

Thanks for all the advice, over the last few weeks i've checked or look at just about every thing mentioned. I was pleased that no one thought the .018'' crank end float was the cause, (big job to put right). To day i had the crank and water pump pulley's checked on a lathe. The crank pulley runs true, but the dial gauge shows a raised area in the V of the w/pump pulley. It seems that one side of the V has a raised area of .030'' over app 1'' of the circumference of the pulley. Effectively making the V narrower at this point. I have been advised that this ''bump'' causes one side of the belt to clime up the pulley and at high revs the belt will flip off. Can my problem be this simple, as it is not a std item I will have a new one made and find out.

[larryowner]

Update on above. The new water pump pulley seems to have solved the belt problem. Recently completed two comps and the belt showed no sign of stress, doesn't even need adjusting for next event.