Alternator bracket replacement M25

[Amontyg]

I’m gearing up to do some spring maintenance on Misty and one of the things I was planning on getting around to is installing the more robust alternator bracket on my M25 engine. After taking a look at my specific engine and comparing to the photos of others retrofits it seems mine is a bit different. Rather than having the alternator bolted to a single point on the case it has a supporting bracket on the front which ties it to four other points. This configuration does seem more robust than the other failure prone configurations I’ve seen photos of. Does anyone know if this configuration shares the failure rate of the single mount point design? I’d rather not tear into this thing if I don’t have to.

 

[bigd14]

That’s an interesting solution. It almost looks like an easier and better solution than the “standard” fix. Less work to install maybe.

 

[Christian Williams]

Mainesail probably has written most about this. The scenario is the timing case breaks, so check that attachment.

https://pbase.com/mainecruising/universal_alternator_bracket

As you know, the recommended replacement bracket goes under, not over. But you may have an upgraded bracket, it appears to have the wide pulley and belt. What rating is the alternator?

A bit of belt dust at the moment, you might consider checking the alignment of belt and pulleys. Or slippage, if it's a monster alternator.

 

[goldenstate]

Are the grooved teeth on the belt supposed to face inward?

 

[Amontyg]

Mainesail probably has written most about this. The scenario is the timing case breaks, so check that attachment.

https://pbase.com/mainecruising/universal_alternator_bracket

As you know, the recommended replacement bracket goes under, not over. But you may have an upgraded bracket, it appears to have the wide pulley and belt. What rating is the alternator?

A bit of belt dust at the moment, you might consider checking the alignment of belt and pulleys. Or slippage, if it's a monster alternator.

Not sure on the details of the alternator - I’ll have to take a closer look at it later, and I’ll definitely check the alignment.

Mainsail’s site is actually what I’m referencing for the difference in configuration. I’ve attached his photo of the original problematic bracket, my setups seems significantly different. It doesn’t appear the bracket in use on my engine could be implemented on his as the necessary bolts on the front of the case aren’t present. Makes me think I perhaps have a later year model with a solution for the problem already implemented from the manufacturer?

 

[Second Star]

I like the arrangement you have. It seems to be better for applying tension to the alternator. The lower attachment looks very good. The pic doesn't show the details of how the adjustment bracket is attached to the engine, but as seen it appears that it relies on rotating on the bolt and jamming against the thermostat. That may eventually wear the body of the themo but that would take a long time and could be mitigated. You do seem to be at the near max adjustment so could probably go down a size in belt.

 

[Kenneth K]

Universal's only solution (that I know of) was the "new" bracket shown in Mainesail's blog, which became OE on later M-25s.

My guess is that a PO came up with a pretty creative idea of his/her own in you case. It looks to me like they built a metal flange that attaches to 3 points (the green and red dots below) versus the original installation which bolted solely to the crankcase "ear" (the red dot).



While I think that was a great idea, what might still bother me is the upper pivot arm, which bolts to the lower thermostat housing. Again, now you have a lot of alternator torque applied to a single, small bolt (and this is one of the smallest bolts in the assembly) housed in a cast aluminum part (circled in red).



The good part about this, though, is that if your lower thermostat housing cracks, it doesn't ruin your engine (like the cracked crankcase ear would)--provided you can find a replacement part. At a minimum, I'd probably try to source a spare lower thermostat housing and gasket to keep around, just in case.

Or, you could try to devise a multi-point mount flange (like your PO did) to spread the load on that single stud out to one or two more anchor points.

 

[Afrakes]

That lower bracket is identical to the one I have on the 87' M-12.

 

[nquigley]

Are the grooved teeth on the belt supposed to face inward?

My v-belt (came with the boat 8 years ago) has teeth on top. The name on the belt (barely visible) is 'Top-Cog'
I can't read the part number and can't find a possible replacement (~40" outer circumference), so I got a 40" (teeth on the bottom) belt last weekend from NAPA, but it's a shade too long: when the alternator adjustment arm is at max position, the belt is a bit loose. I ordered a 39" belt from Amazon - gonna try it tomorrow, but I think it'll be too short for the alternator adjustment range.

 

[nquigley]

Follow-up...
I found the same belt as my old one (TopCog) at Advanced Auto this morning - 39". Fits perfectly, as did another 39" belt I got off Amazon. So that answers the question of correct v-belt length for an M25, with the upgraded alternator bracket.
Now I have a spare ... if I ever need one.