Alternator Alignment

I have a small Yanmar with a dual foot alternator. I get some belt dust and the belt is difficult to get tight because of play in the pivot bolt. Also the 8mm bolt has sleeves to bring the size to 10mm or 3/8" for the holes in the alternator feet. This also causes some slop. This quote from another forum describes the situation.

"One of the biggest issues on Yanmars is that the M8 pivot bolt fits VERY sloppily in the engine mount hole and the alternator mount holes. If you are brave you can drill the engine mount to accept a larger bolt that fits more snugly and is not a "sloppy" fit...."

So if I wanted to drill out that 8mm pivot bolt hole to 3/8" what would be the best method? The casting is aluminum I think. My fear is that rather than drilling a perfect hole the bit would wander slightly and result in worse alignment. Perhaps a gradual increase in bit size?

The first thing I'd do is put a straight edge across the alt pulley and the engine pulley and see if it's aligned and square. The hole being a little sloppy is less of a problem.
Dust usually comes from misalignment (alt too far forward/back) or alt shaft is not parallel to the crank. Dust also comes from too much hp passing thru the belt. Alt at full charge beyond the belt rating.

In redrilling the hole, if you could use a drill press, you'd have better luck getting a square hole.

If the belt was properly tensioned, wouldn’t the slop be gone? Or is this front to back slop?

A brand new drill bit will usually create the best hole.

I'd look at industrial supplier such as McMaster-Carr to find a bushing the right size before I would drill out an existing one.
And there is always machine shops to get it perfect.

Last thing i would do is drill an engine block mount. Why isn't the pivot bolt tight? Check alignment as above. can you shim the bolt or the mount boss for better alignment?

Lepke said:

The first thing I'd do is put a straight edge across the alt pulley and the engine pulley and see if it's aligned and square. The hole being a little sloppy is less of a problem.
Dust usually comes from misalignment (alt too far forward/back) or alt shaft is not parallel to the crank. Dust also comes from too much hp passing thru the belt. Alt at full charge beyond the belt rating.

In redrilling the hole, if you could use a drill press, you'd have better luck getting a square hole.

Click to expand...

+1 on what Lepke says. I had a 4LH Yanmar with the same issue. Used a straight edge and sure enough the alternator was not properly aligned. From memory I think it was set back from the plane of the crank pulley. I loosened and cleaned everything up and re aligned using a washer here and there as a spacer. Didn’t need to drill any holes. Make sure you have the correct belt.

Also check that the belt is NOT riding on the pulley bottom. That will guarantee a poor fit and high belt wear. The belt sides should contact the pulley sides only. Also that the belt is in fact the correct shape for a proper fit. There are a number of similar belts that although they will fit they will not fit properly.

I will be watching this because I am going to replace my alternator with a larger output one this winter. All good advice so far as I can see.

I use alternator adjuster like this:

I also use a Gates Krikit to set belt tension. The problem is the alternator pivot bolt is such a sloppy fit that when I release the adjuster I loose a lot of belt tension. So it is trial and error over tightening then loosening the adjuster and hope for correct tension.

Regarding the loose fitting bolt. Rather than drilling the hole out or trying for a bushing can you have a slightly larger diameter bolt made. It would mean a machinist or a lathe equipped friend.

C lectric said:

Regarding the loose fitting bolt. Rather than drilling the hole out or trying for a bushing can you have a slightly larger diameter bolt made. It would mean a machinist or a lathe equipped friend.

Click to expand...

That may be the best and safest way to go.

Assuming a 3/8" then M10. or 7/16" then maybe M11?

C lectric said:

Regarding the loose fitting bolt. Rather than drilling the hole out or trying for a bushing can you have a slightly larger diameter bolt made. It would mean a machinist or a lathe equipped friend.

Click to expand...

+1