Replacement Alternator Bracket FYI - M25 vs M18

[mherrcat]

Can’t believe this has never been mentioned in any documentation of the replacement of the bracket for the M25 and M18 Universal engines.

If you install this bracket on the M18 engine it is NOT ADJUSTABLE without modification. The bracket was apparently designed for the M25 engine with the M18 engine as an afterthought.

The M18 engine only has two cylinders, and the manifold studs on the aft cylinder are in the opposite orientation from the studs on the middle cylinder of the M25 engine. The holes in the bracket that match the aft cylinder studs for the M18 engine are not elongated, therefore the bracket is not adjustable without having those holes elongated.

Also, using the belt that came with the bracket kit, the adjusting arm does not have enough adjustment range to tighten the belt without the adjusting arm contacting the fan on the alternator. And since the M18 engine is shorter (one less cylinder) than the M25, the starter is closer to the front of the engine, so a shorter belt may cause the alternator to contact the starter - right where the positive starter post is located.

I ordered this bracket kit 12 years ago, but never installed it. When I discovered that the alternator on the engine was not functional, (just one more “Easter egg” left by the previous owner), I also discovered that the bolt that attaches the original alternator bracket to the engine case was permanently frozen in the engine case mounting tab. The head of the bolt on the front of the bracket sheared off even after using penetrating oil, alternating heat and cold, and vibration to try to loosen the corrosion. The bracket had to be cut off.

So now a new adjusting arm is being fabricated and if any pulley alignment needs to be done the alternator bracket will also need to be modified.





These pictures are not of my engine, they are from the "https://pbase.com/mainecruising/universal_alternator_bracket" website.

 

[Prairie Schooner]

@mherrcat - Mark, I'd be interested in seeing a photo of the new arm installation and hearing any details about how it was fabricated. I'm thinking of making a new one for our M25.

 

[mherrcat]

The original adjusting arm that came with the kit was used as a template. The fabricator cut it with a plasma cutter. We extended the angled slot end that attaches to the bracket about 1/2". The other end, that attaches to the alternator, was supposed to be extended about 3/4", but the fabricator made it even longer with a slot. That additional length brought it too close to the fan if the slot was used, so we drilled a new hole where we originally thought it should be and that worked perfect. Also, I was leery of having two slots in the arm; seemed like just more opportunity for slippage, not saying it would happen, but never say never. The additional length with the slot didn't interfere with anything so we just left it intact.

Here are the pics. The new arm is 3/16" steel, like the original. I don't have a pic of the finished install but will get one next time I am down at the boat.

 

[Prairie Schooner]

Thanks Mark. Be really careful of unintended consequences.
post #21 - https://ericsonyachts.org/ie/threads/catastrophic-oil-loss.22120/post-181042

I want to make a new arm this off season. Seeing your project is helpful.

 

[mherrcat]

FYI, it was a little bit of trial and error. We traced the original arm and made a cardboard template to hold in place to try to judge how to adjust the new arm for a better fit. That's how we came up with the additional length for each end. You might also have to adjust the radius of the curve. We didn't but it might have helped even more. And you're right, keep an eye on where the lower end of the arm is going to be positioned when you tighten it in place.