Help please! Alternator Bracket Slipping!

[Cap Bill Des]

I've just finished installing the "improved" alternator bracket kit for my Universal M25 engine- and the bracket keeps slipping, losing belt tension! Any advice?

In the picture, the bolt which clamps the adjusting arm ( partially hidden by the belt at top) is a Grade 5 bolt, 5/16-18 (provided with the kit) which I have torqued to 13 ft-lbs (dry). Underneath the bolt head is a split locking washer and a USS thick flat washer.

To check the position of the adjusting arm I use a low-angle wedge as a gauge between the end of the arm attached to the lower alternator ear and the bulkhead. That's only with the engine shut down of course. Each time I tension the belt and run one hour the end of the arm moves about 1/4", enough to make the belt as loose as shown in the photo. (At this loose condition the belt squeels briefly on engine start when the alternator turns on...)

Any advice? Is more torque allowed? Grade 8 bolt? The bracket is threaded- I don't know what it is made out of and surely don't want to damage those threads. I have read other links on this M25 bracket, have taken most of those actions (M10x100 pivot bolt, locking nut on extended ear bolt). I have seen no comments on the bracket slipping.

Any advice? Thank you!

When I re-tension this next time I will mark the bolt head and make sure it is not loosening itself. ( I would like. Longer bolt so I could add a locking nu on the back of the bracket, but it needs to be fully threaded, and the nearest Fastenal is difficult to get to from my current anchorage in the Chesapeake...)

[jimbunyard]

You can probably tighten the 5/16 grade 5 bolt to 15-20 lbs, or get a grade 8 replacement, but more importantly, after adjusting the belt to the proper tension, you should also tighten the main mounting bolt (looks like 3/4 or 19 mm head) sufficiently to hold the tension of the belt with the adjustment bolt loosened (temporarily!). If not, sooner or later, the proper tension will be lost.

If the fit between the mounting bracket and the alternator foot is too loose to allow this, it should be shimmed (flat washer[s]) to allow secure clamping pressure without distorting the bracket.

[Lepke]

Use a type of lock-tight that is not permanent. If you have nuts on bolts, replace the nuts with elastic stop nuts. You can over torque with care.

Also you can redrill the holes and go to a large size bolt. If you do, use NF not NC threads and rethread as necessary. Finer threads put more individual threads in a given space. Go to grade 8. You can find them all over the web. A NF 3/8 tap is about $8 on Amazon.

[mickt243]

That’s a very large lever acting against a very small contact area.... I can’t imagine any amount of torque applied to the locking bolt ever keeping the belt tension long term.

What is the gold coloured bit bolted to the other end?

[Chotu]

This bracket looks to be designed all wrong. It looks like there is a torque around that bolt. Like the bracket will spin around the bolt that is partially hidden by the belt in the pic.

The entire bracket should be attached somewhere down where the oil filter is, or be a c-shape single piece. That’s how it is on most engines. It would be a curved piece of metal with a slot in the middle. Like this ..



Or this, attached down by the oil filter area...

[coopec43]

I agree with mick243t. You'd have to torque the bolt up to near breaking point to get it to hold. Would a much larger washer tend to spread the load over a bigger area and increase the friction on the arm?

I can't understand the principle of the tensioning device either.

[Chotu]

Here is a Universal M25 engine with a normal alternator bracket. Get one of these.

[dgmultimedia]

Originally Posted by Chotu

Here is a Universal M25 engine with a normal alternator bracket. Get one of these.

On this engine the adjusting bracket is the wrong way round - the “slot” should be at the alternator end so it is clamped by a nut and bolt with washers and the single round hole is used where the bolt screws into the engine casing which is a threaded hole in a casting and would strip if you tighten too much.
Previous post mentioned tightening the alternator pivot bolt to hold the correct position - check that you have the correct sliding bush rear bearing sleeve so that the clamping force is all on the front mounting lug.

[GordMay]

Originally Posted by dgmultimedia

On this engine the adjusting bracket is the wrong way round - the “slot” should be at the alternator end so it is clamped by a nut and bolt with washers and the single round hole is used where the bolt screws into the engine casing which is a threaded hole in a casting and would strip if you tighten too much ...

Good eye for detail, dgm'.

[Chotu]

Originally Posted by dgmultimedia

On this engine the adjusting bracket is the wrong way round - the “slot” should be at the alternator end so it is clamped by a nut and bolt with washers and the single round hole is used where the bolt screws into the engine casing which is a threaded hole in a casting and would strip if you tighten too much.
Previous post mentioned tightening the alternator pivot bolt to hold the correct position - check that you have the correct sliding bush rear bearing sleeve so that the clamping force is all on the front mounting lug.

I agree, but didn't have the free time to find an even better picture on Google.

[coopec43]

Very poorly designed adjustor?



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[capt jgw]

Originally Posted by Chotu

Here is a Universal M25 engine with a normal alternator bracket. Get one of these.

The stock bracket WILL break the engine casting it's bolted to. That setup was designed for the tiny little alternator on the tractor version of the engine and can't handle the load of our larger alternators. You can't get that part anymore so when it breaks the engine is totaled. That's why they came up with the new bracket. Doesn't work great but it won't destroy the engine.

[Chotu]

Originally Posted by capt jgw

The stock bracket WILL break the engine casting it's bolted to. That setup was designed for the tiny little alternator on the tractor version of the engine and can't handle the load of our larger alternators. You can't get that part anymore so when it breaks the engine is totaled. That's why they came up with the new bracket. Doesn't work great but it won't destroy the engine.

I see. In that case, he should definitely just go to a machine shop. And get something like this. In a c-shape. Should be very cheap. Probably cheaper than that one he bought and is struggling with. Just a piece of plate with some cuts and holes drilled

[Cap Bill Des]

Hi, this is Bill, the OP. Thank you for all the responses! To answer a few questions:
- what I installed, as shown in my picture, is Universal Kit 256891, the improvement over the original bracket shown in Chotu's photo.
- the original bracket did start a hairline crack on the "ear" of my gear case cover and a little oil started leaking.
- I'm not very happy with the new bracket, but at least it is totally supported off the exhaust manifold and head, so I don't need to worry about the cast aluminum gear case cover, which I patched with JBWeld.
- I like the photos of the simple C-shaped bracket, but that's not where I am right now
- I have taken the advice to tighten the large pivot bolt to help clamp the alternator, and I've gone to 15 ft-lbs on the arm bolt. We'll see what happens when we pull up the anchor tomorrow (I'm taking today off!!)
-I do plan to look for a large, thick fender washer to put under the adjusting arm bolt ...
- Oh, I forgot- the gold bit of bracket is something I had to make up myself- without it the J-shaped arm hit the alternator "fan blades"(?) before there was any tension on the belt .

Thanks again! I'll give another update after a few more engine hours.

[roland stockham]

See if it is possible to replace the adjusting arm and bolt with a rigging screw. Not only does it stop adjustnent slipping but it also makes it much easier to get the right tension. Can't be done on all engines as it depends on the alignment but if you can it is a really whorthwhile upgrade