Adjusting the Alternator belt

[srah1953]

Greetings
I have 2 books on diesel engine maintenance. One suggests that there are generally 2 bolts to be loosened to adjust the alternator belt; another one suggests 3 bolts. I have attached a picture of the engine (taken when new, hence cleanliness). I'm clear about two of the bolts that need to be loosened- the bolt on which the alternator pivots and the adjustment bolt. I can't see a third bolt that needs to be loosened, except possibly the one further along the adjustment arm, just visible under the top line of the belt. If this, I can't see why it might need to be loosened.
I'd much appreciate any help.
Thanks

 

[Heckler]

Greetings
I have 2 books on diesel engine maintenance. One suggests that there are generally 2 bolts to be loosened to adjust the alternator belt; another one suggests 3 bolts. I have attached a picture of the engine (taken when new, hence cleanliness). I'm clear about two of the bolts that need to be loosened- the bolt on which the alternator pivots and the adjustment bolt. I can't see a third bolt that needs to be loosened, except possibly the one further along the adjustment arm, just visible under the top line of the belt. If this, I can't see why it might need to be loosened.
I'd much appreciate any help.
Thanks

Youve got it, the one under the top line of the belt, just slacken it a touch, it allows the brqcket to swivel a touch
Stu

 

[srah1953]

Excellent. Thank you.

 

[pvb]

Generally alternators have two pivot bolts; one at the pully end and one at the other end. The third is for adjustment. It is unlikes that the alternator is just cantilevered from the pully end. Very unlikely that the alternator back end is "floating".

Never seen a Volvo Penta engine?

 

[theoldsalt]

pvb,

I withdrew my comment as a whisper in my ear told me I was living in the past. I'm not familiar with recent and upmarket engines !!

 

[Mistroma]

That looks very much like the Yanmar 4HJ4AE on my boat and that has 4 bolts (3 on the alternator).

2 at bottom of alternator where it pivots, one at the front and another at the rear. Both screw into a long spacer with flats for a spanner. I normally but a spanner on the spacer and loosen the front bolt slightly to make adjustment easier.

2 bolts on the top arm. I normally try to get away with only loosening the one at the end of the arm, where it connects with the alternator. The inner bolt is where the arm pivots and only needs adjustment if replacing a very stretched belt with a new (& much tighter) one.

I found one weird thing with the inner pivot bolt on the top arm when tracing a small coolant leak. Removing the arm entirely revealed that the pivot bolt screws into a waterway in front of the engine. So coolant dribbled out when I removed the bolt. I had to make up a gasket to fix the problem and always need to use a small amount of sealant in that if the arm has been moved. No gasket shown on the service manual. It's pretty weird to mount a moving arm on top of a hole into something filled with coolant.

 

[cliff]

Originally Posted by theoldsalt
Generally alternators have two pivot bolts; one at the pully end and one at the other end. The third is for adjustment. It is unlikes that the alternator is just cantilevered from the pully end. Very unlikely that the alternator back end is "floating".

Originally Posted by pvb
Never seen a Volvo Penta engine?

pvb,
I withdrew my comment as a whisper in my ear told me I was living in the past. I'm not familiar with recent and upmarket engines !!

Bukh, 30 years young - front pivot only - rear end "floating" - nice to know they are "recent and upmarket engines" in your book.

 

[srah1953]

That looks very much like the Yanmar 4HJ4AE on my boat and that has 4 bolts (3 on the alternator).

2 at bottom of alternator where it pivots, one at the front and another at the rear. Both screw into a long spacer with flats for a spanner. I normally but a spanner on the spacer and loosen the front bolt slightly to make adjustment easier.

2 bolts on the top arm. I normally try to get away with only loosening the one at the end of the arm, where it connects with the alternator. The inner bolt is where the arm pivots and only needs adjustment if replacing a very stretched belt with a new (& much tighter) one.

I found one weird thing with the inner pivot bolt on the top arm when tracing a small coolant leak. Removing the arm entirely revealed that the pivot bolt screws into a waterway in front of the engine. So coolant dribbled out when I removed the bolt. I had to make up a gasket to fix the problem and always need to use a small amount of sealant in that if the arm has been moved. No gasket shown on the service manual. It's pretty weird to mount a moving arm on top of a hole into something filled with coolant.

Thanks for this. Engine is a Yanmar 3JH5E. Where you talk about "2 bolts at bottom of alternator where it pivots, one at the front and another at the rear", I'm counting that as one adjustment bolt. Re “The inner bolt is where the arm pivots and only needs adjustment if replacing a very stretched belt with a new (& much tighter) one”, I have an engine maintenance video in French (where I don't always understand the words but try to follow the images), which shows the mechanic only loosening 2 bolts but tightening three.

 

[VicS]

Thanks for this. Engine is a Yanmar 3JH5E. Where you talk about "2 bolts at bottom of alternator where it pivots, one at the front and another at the rear", I'm counting that as one adjustment bolt. Re “The inner bolt is where the arm pivots and only needs adjustment if replacing a very stretched belt with a new (& much tighter) one”, I have an engine maintenance video in French (where I don't always understand the words but try to follow the images), which shows the mechanic only loosening 2 bolts but tightening three.

You must have deduced from the previous posts that the mountings vary.

Sometimes they pivot on one bolt, sometimes on two. Slacken both if there are two.

As Stu says just slacken the inner bolt on the adjustment strap so that it can move if necessary........( Even they vary. Some engines have curved straps that don't need to move.)

Obviously slacken the adjustment bolt. Retighten that one first then all the others.

 

[Mistroma]

I only loosen the bottom rear when removing the alternator completely. It can normally be left alone as the font and rear bolts screw into a long spacer. The alternator only requires the front to be loosened in order to move freely. I mentioned the front above but didn't explicitly say not to bother with the rear.

I try to avoid loosening the adjustment arm pivot bolt for reasons mentioned above. You will need to adjust it when fitting a new belt and probably later as it beds in. After that, I often manage to leave it tight and slide the other bolt along the slot a bit. Perhaps it won't leak on your Yanmar. I've always suspected that there's a seal missing from behind the arm, just where the pivot bolt enters the block. I've never found a Yanmar dealer who knows anything about such a part and just made up my own seal.

Probably worth putting a tissue underneath this bolt if you do loosen it and check for leaks after a few days.

I'm pretty certain that your alternator mount will be similar to mine but will try to dig out the service and operation manuals to check (Let me know if you want a copy).

Just looked at the manual and it only covers 3JH4E, not the 3JH5E. Mount and adjustment for 3JH4E is identical to the 4JH4AE I own (but alternator is LR160-741 60A vs. 80A version on mine).

 

[cryan]

My tip would be loosen as few as you can get away with. The more you loosen the harder you make the job.
Looking at the photo I would loosen the bottom bolt and the one at the end of the slot. Loosen them just a touch so that your not needing more than half a turn to nip it up again. That way you are not in an awkward position trying to hold the alternator against the belt tension and having to make twenty spanner moves. Your looking for about 10mm of deflection when you press on the middle of the belt.

 

[nigelmercier]

While on the subject, is there a way of getting the tension correct that is better than pressing with your thumb or twisting?

 

[VicS]

While on the subject, is there a way of getting the tension correct that is better than pressing with your thumb or twisting?

Belt tension gauge. Vital bit of kit. Dont know how i have managed without one all these years ��

 

[nigelmercier]

Belt tension gauge. Vital bit of kit. Dont know how i have managed without one all these years

Like this? http://www.amazon.co.uk/exec/obidos/ASIN/B0012MEN6C/dolcetto-21
I actually bought one of these for checking my cam belt, didn't think to use it on the alternator!

The next question is, what tension?

 

[Hydrozoan]

I seem to remember an item (in PBO?) where a reader had used a turnbuckle in place of the standard adjustment arm on his alternator to facilitate fine adjustment. Looked like a neat idea if one can find a turnbuckle of suitable size, but I haven't tried it.

 

[nigelmercier]

I seem to remember an item (in PBO?) where a reader had used a turnbuckle in place of the standard adjustment arm on his alternator to facilitate fine adjustment. Looked like a neat idea if one can find a turnbuckle of suitable size....

Perhaps something like this:
http://www.ebay.co.uk/itm/281212601286

Sadly, I don't think I have room:

But something like this may work:

 

[Hydrozoan]

Perhaps something like this: http://www.ebay.co.uk/itm/281212601286

Nothing like as posh and colourful - nor £25! Just a standard galvanized turnbuckle I think - perhaps he ground flats on the eyes, I can't remember. Just as an example, a 6mm one adjusting from 122 to 182 mm (overall) costs just 89p http://wireropeshop.co.uk/wire-store/index.php?main_page=index&cPath=26_168.

PS That would obviously too long for yours, but I think his standard adjusting arm was configured differently and a good bit longer (as is ours).

 

[RAI]

I've seen both the turnbuckle and simpler bolts with L-brackets and nuts used. A rather neat design uses a spiral cam. It just needs to hold the tension long enough for the adjustment bolts to be tightened.

 

[nigelmercier]

... It just needs to hold the tension long enough for the adjustment bolts to be tightened.

Not on mine, the bolts are not enough to hold on their own.

 

[nigelmercier]

That would obviously too long for yours, but I think his standard adjusting arm was configured differently and a good bit longer (as is ours).

I've been investigating, and I've decided that I need a slightly longer belt, both ends from a turnbuckle, and one of these with a L/H thread one end:

Any suggestions?