Small Alternator

[jonclancy]

Most kind, Sir!

[erictharg]

A word of caution following my experience at Spa recently. After 30 mins of practice I found my fan belt to be looser that ideal and set about adjusting it only to find the water pump casting had cracked just inboard of the alternator mounting bolt hole. So after an hour's racing total it had failed. I note that the pump castings today are sand cast vs die cast of the originals which won't help casting quality. I would advise that if using one of the little single hole mounting alternators (Denso or copy) that you think about making a mounting bracket that still uses the old rear mounting point the Lucas item used to take some of the bending load away from the front mounting bolt and water pump bracket. I run my belt pretty loose to give the pump and alternator bearings an easy time so it wasn't excessive tension that did it. Certainly if I carry on racing with the A Series I'll devise a steel "subframe" to carry the alternator that uses both mounting holes. For a road car it might be fine but for racing with extended high speed use it is clear the load and vibration is too much for the water pump bracket.

[jonclancy]

Thanks for the feedback and warning, Charles. I'll have a look at this when I am reinstalling my rebuilt engine (collected yesterday - in major parts - to be reassembled during installation).

[adamwilkinson]

We found this with the first small bruise alternator we ran as it only had 2 mounting points.

We tried beefing up the mounting points but still suffered fracturing of the mount. We've since swapped to the 3 mount version and, touchwood, we've had no issues with cracking.

[Westfield 129]

More than 20K miles on mine, race and road. Lots of high RPM. No failures. The water pump tab is just fine.

However, the lower mount must be rigid. I don't use a pressed steel or a cut steel strap mount. I use a tubular mounting with rod ends.

I also check to see that the belt is running true, as the problem that caused the cracking could be elsewhere. It is possible that the standard crank damper pulley could develop a wobble at over 6000 RPM (the reasonable limit for this standard part) should it slip or otherwise fail. I have a box of these... I have been replacing them with Med engineering dampers, or an Aussie make that works pretty well. I can't remember the name off hand.

And if you have an old water pump that has been stressed... Well, anything can break.

For us, So far, so good. Our local vintage and SCCA racers use just two mounting points without any problems.

However, if you want to run a bolt through the whole upper assembly using the old alternator block mounting with a spacer to keep the thing from moving fore and aft, that would not be a bad idea.

Meanwhile, all of the cars that I have built, including the ones that are racing, don't have any problems with cracking of the water pump mount tab. All have an uprated crank damper/pulley.

[erictharg]

I run the Ozzie Romac damper, not a stock one. And that adjuster stay with rod ends adds no stiffness to the mounting in bending which is "pure", but not helpful in this instance. An adjuster in 6 or 8mm plate that adds some bending stiffness would however help, if bolted up nice and tight. Could just have been a particularly bad pump casting but significant porosity not evident. Two point mount clearly fine for 95% of applications. But if you want to be sure...

[Westfield 129]

I use the Romac as well.

Interestingly enough, the little alternator has only one mounting tab as well. Not much mass to deal with, provided that it is balanced, and is not vibrating hard enough to break the tab. We use these little alternators on all sorts of cars, using a single mounting tab, and they don't seem to fail.

However...

The easiest thing to do is to run a long bolt and spacers through the water pump tab to the old alternator backside bracket that was bolted to the side of the block. This will stabilize the assembly and end any fore/aft bending moment on the tab, replicating the standard mounting used for generators and alternators. No need to do any special fabrication. This is an easy fix, and is an effective method used to fit all sorts of alternators having a front and rear mounting tab to the A series engine using the alternator mount tab that bolts to the side of the engine. 'No need to fabricate anything, save for a piece of tubing to fit over the bolt between the brackets to stabilize them. You probably have the old block bracket floating around in a coffee tin...

I imagine that the tab could break off, but I have removed heavier, less securely mounted stock alternators and generators from the water pump's tab. I have not found any information in my research that shows this to be a weak spot. Not a single race spridget running an alternator here has even the long bolt, and I have not seen any alternators littering the track after a race.

The little ND alternator is less than half the weight of the old Lucas, and about 25% that of the old generator. I am pretty sure that a bolt through mounting using the old alternator tab on the block with a spacer in between should eliminate any possibility of a problem.

All of the small alternators that I have used, including the cheap Chinese copies, have run true, and didn't vibrate at high RPM.

If the alternator is not properly balanced, it can cause a problem that would not otherwise exist, especially if it were to loosen in service. There is no reason that the small alternator should break off the tab. In fact, everyone recommending the use of that type of alternator here, recommends that it be bolted directly to the pump tab. That's what I have been doing for some time now, without problems, in 100% of the cases, road or track use. Engine redlines are between 6700 and 7200 RPM. Full race spridgets here turn closer to 9000 RPM...

Of course, proper fit of the mounting bolt into the water pump tab is important. I know that some builders have used a slightly loose fitting ("close enough" is what I was told) metric bolt instead of drilling the alternator for a proper fitting fractional bolt that fits the water pump tab. Any play or looseness that can occur at the water pump tab can cause a failure. Using the correctly sized bolts is one way to make sure that everything works properly.

I drill the alternator and the water pump tab (if necessary) for a tight fitting fractional bolt. I also drill and tap the lower mounting tab of the alternator to a fractional thread size to eliminate a nut, and to simplify the installation. This also eliminates a metric wrench that I have to carry in addition to the 3/8, 1/2 and 9/16 sizes that I have around for engine maintenance. All of my W11s have fractional bolts at every service point. Only one set of tools is necessary to service or repair the engine and drive train.

[adamwilkinson]

Charles, we must be imagining this issue because obviously if it hasn't happened to Jan then it cant possibly happen...

[Westfield 129]

It isn't much of an issue if you use a long bolt mounting incorporating the rear mounting tab that is used with much heavier alternators and generators. You can also use a Subaru Samurai alternator that has two upper mount tabs like the Lucas alternator if you are looking for a lighter unit.

Your chances of loosing the top ring land on the stock pistons if revved to 6000 RPM on a constant basis are actually far greater than having your ND single tab alternator fall off.

You can break anything. That doesn't mean that it is a recurring problem that requires re engineering. Sometimes, just using the original design (long bolt through two mounting points) eliminates a perceived problem. Sometimes, its just a better quality water pump, or a thorough inspection of the parts you already have.

It was a good heads up to a potential problem. I offered a very simple fix that eliminates the problem, and a couple of other things to look for when doing the initial installation. As I have done several of these conversions, have nearly 100,000 miles and a dozen years of experience with them, and the subject here had only a single event prior to failure... I thought that the information might be helpful.

[erictharg]

Well now, we all know Jan has a certain "style" of writing. His input is always welcome. But there is a world beyond his, no doubt vast, experience. And hopefully we'll all just continue to "get along"!
BTW, I use a 10mm bolt through the tab and alternator with holes drilled to size (not clearance).