Pulley alignment

sailboatshaka

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I have an 1976 built sailboat with an old Perkins 4108 inboard diesel. I was told by the chap who sold it to me that he rebuilt it shortly before I bought it, and the engine has always started easily and run well. The problem is, that not long after I bought it I noticed that there was a fine coating of black dust on the inside of the engine box, fortunately painted white so easy to notice the dust, on the side where the alternator sits. Closer inspection revealed wear on the alternator drive belt, resulting in very premature drive belt/water pump failure, on two separate occasions, once at sea in an oily calm, and the other just motoring out of the marina, so both times reasonably easily fixable. I've tried several times to realign the alternator with the engine pulleys by eye using washers as spacers, with moderate success, and subsequent wear being slowed down, but still not functioning normally to my non mechanical mind. Does anybody know of a way, that I could align the alternator pulley up with the engine pulleys, so that it would function as it should normally, say from one servicing to the next, and perhaps more crucially, why would the alternator pulley be out of alignment in the first place, when it appears to be mounted on the original engine alternator mounting lugs ?
 

rogerthebodger

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Use a straight edge or ruler across the faces of the pulleys to check both the axial and longitudinal alignment.

Alignment%20Drawing.jpg


v-belt-installation-and-tensioning-108-1-11-638.jpg
 

lw395

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I would suspect either something's been put together wrong, or the alternator is not the original.
I had this problem when I fitted a more powerful alternator.
I got around it by a combination of filing a little from a bracket, adding a washer under the alternator pulley and a washer or two here and there.
On some engines, you can just drill new holes in the bracket and re-bolt it to the block.
The most difficult thing is measuring how much it needs to move.
First thing to do is to check the alternator pulley is in a plane parallel to that of the crank (and waterpump?) pulley. And that both those pulleys are square on their shafts, not wobbling as they go around.
A steel rule across the crank pulley should enable you to measure the offsets to the centre of the v at the crank and alternator?
If you use the 'cogged' type of belt, they tolerate a little misalignment better than the plain v sort.
 

Major_Clanger

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Use a straight edge or ruler across the faces of the pulleys to check both the axial and longitudinal alignment.

Alignment%20Drawing.jpg


v-belt-installation-and-tensioning-108-1-11-638.jpg

Except that all those illustrations presume the two pulleys have the same depth and width characteristics. Alignment cannot be assumed from using the outside face; it should be taken from the centre of the pulley.
 

Fr J Hackett

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If you are not sure the pulleys are misaligned, checking by eye is not the best method, it is a possibility that you are using the wrong belt and it is bottoming in one or all the pulleys. Do they look polished?
 

RichardS

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Check that the outer surface of the belt is flush with the outer rim of the pulleys as mentioned above.

I've fitted alternative alternators in the past and it's usually easy to space the alternator mountings if the new alternator pulley runs too close to the block. The problem is when the pulley is too far away from the block. In that case I have removed the pulley and ground down the inner face so that it sits a bit further on the shaft. You can usually correct up to a cm of misalignment but any more than that and a new pulley/alternator mounting bracket would be required.

If you run the engine and look carefully from the side, it's not usually difficult to see any misalignment. A cogged belt will be more tolerant of slight misalignment.

Richard
 

Balbas

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If you've got a laser pointer you can usually point along the groove in one pulley and see if it's lined up with the groove on the other pulley.
 

Plum

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I have an 1976 built sailboat with an old Perkins 4108 inboard diesel. I was told by the chap who sold it to me that he rebuilt it shortly before I bought it, and the engine has always started easily and run well. The problem is, that not long after I bought it I noticed that there was a fine coating of black dust on the inside of the engine box, fortunately painted white so easy to notice the dust, on the side where the alternator sits. Closer inspection revealed wear on the alternator drive belt, resulting in very premature drive belt/water pump failure, on two separate occasions, once at sea in an oily calm, and the other just motoring out of the marina, so both times reasonably easily fixable. I've tried several times to realign the alternator with the engine pulleys by eye using washers as spacers, with moderate success, and subsequent wear being slowed down, but still not functioning normally to my non mechanical mind. Does anybody know of a way, that I could align the alternator pulley up with the engine pulleys, so that it would function as it should normally, say from one servicing to the next, and perhaps more crucially, why would the alternator pulley be out of alignment in the first place, when it appears to be mounted on the original engine alternator mounting lugs ?

Hi, from what you have said, If you do not have a method of accurately checking alignment, how do you know you have a miss-alignment problem? Yes, you have a premature belt wear problem, assuming your belt is failing after, say, 200 hours (my belt has lasted over 10 years although not the same engine), but that could be incorrect tension or someone has fitted a higher spec alternator without upgrading the drive leading to slippage.

Www.solocoastalsailing.co.uk
 
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TQA

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If you have the pulleys anywhere near being aligned [ the odd 1/16th does not matter ] and you are using a toothed belt then you probably have not got enough tension.

If you are running a biggish alternator and a smart regulator the belt needs to be tight/ As soon as it slips and 'dustes' you need a new belt.
 

rogerthebodger

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Except that all those illustrations presume the two pulleys have the same depth and width characteristics. Alignment cannot be assumed from using the outside face; it should be taken from the centre of the pulley.

If the pulleys are of different widths then all you need to do is measure the centre line to edge distance on each pulley and use a packer of the thickness to allow the edge alignment.

This is only an issue with parallel alignment as angular misalignment would be noticeable anyway to the required tolerances.
 

sailboatshaka

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great diagrams, steel rule straight edge, bottoming belt polishing pulley, 'cogged' belt, laser pointer, upgraded alternator, all great advice, thank you all very much. I assumed that the pulleys were miss aligned because of all the black dust on the inside of the engine box, which logic dictates came from the alternator belt, it could have been an inferior belt, but the same thing has happened on two more belts, albeit to a lesser degree because of my attempts to align the pulleys by eye by adding washers ........ but you know what they say about assuming ! Thanks again all and I'll let you know how I get on
 
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