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peejay4A

Alternator options

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Decision time on the new project:

 

I want to go for an alternator conversion but there are options it seems.

 

I like the look of the Moss Dynalite dynamo/alternator product - keeping the wide fanbelt and tractor fan.

or

Standard alternator conversion, narrow fanbelt without crankshaft damper and original fan

or

Standard alternator conversion, narrow fanbelt with crankshaft damper plus electric fan

 

Any other options? I'm attracted to the Moss fake dynamo but at a price though.

 

 

...and why isn't the forum picking up my new photo?

Edited by HPA 510K

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Guest ntc

;)

Decision time on the new project:

 

I want to go for an alternator conversion but there are options it seems.

 

I like the look of the Moss Dynalite dynamo/alternator product - keeping the wide fanbelt and tractor fan.

or

Standard alternator conversion, narrow fanbelt without crankshaft damper and original fan

or

Standard alternator conversion, narrow fanbelt with crankshaft damper plus electric fan

 

Any other options? I'm attracted to the Moss fake dynamo but at a price though.

 

 

...and why isn't the forum picking up my new photo?

 

 

You will be in for a long wait for the alternator mounting bracket ;) make your own

Edited by ntc

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Any other options?

 

Why not try a lightweight 40 Amp (Denso based) alternator from http://www.bastuck.de and you won't need a heat shield at all as the diodes are buried where the heat will not affect them. Fit this with the mounting kit, and a thin belt conversion with alloy pulleys including a harmonic dampened bottom pulley.

 

Paul

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Hiya, I had a similar decision point a couple of years ago on my 4a. I went for the Revington wide belt alternator together with their own fitting kit and heat shield. The only problem I was trying to fix was that of charging, so I retained the manual fan as I didn't want to invite any other (e.g. damper) issues. All previous (dynamo) charging issues disappeared with this approach. It wasn't the cheapest option, but it was an easy fit and it works well.

Hope this helps.

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Replacing the cheap and easily repairable dynamo with an expensive alternator seems unnecessary if you are simply trying to fix a charging problem. With a reconditioned (or at least, cleaned and with new brushes) dynamo the most likely problem is the voltage regulator. There is plenty of discussion on the Forum about this, as well as links to one or two companies that can properly overhaul and set them up. I would only fit an alternaor if I planned on doing an inordinate amount of night driving and using supplementary driving lights. Otherwise (in my experience), a heavy-duty battery and well-maintained dynamo+regulator will cope just fine.

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Together with Jim Christie (remember him?), an article will appear soon in TR Action (probably at the end of this month) on fitting an alternator from a Moss "kit". Why, you ask (since Cornish wrote an article years ago and it is available in Section J4 of the Technicalities CD)? Simple, says the Meercat, it's because Jim, Dave Larnder and others were having difficulty fitting the Moss "kit"! And since Jim lives in France and Dave in Spain, sorting things out via e-mails and photos was not that easy!

 

I have read Revington's alternator fitting instructions, which include a parts list and which recommend the use of Revington's mounting bracket (described in my original article), and I have to say that one should NOT have a problem fitting an alternator from Neil's emporium! Other suppliers offer kits, too, of course.

 

I started with the TR7-style alternator (a modest 34 amp rating) with wide belt, but finding a wide belt of the right length (the dynamo belt is really too short - I had to remove the locking bolt and ram the alternator against the block to get it over the pulley) was very difficult and finding a suitable spare belt proved expensive. Eventually, when a water pump failure forced me to address the problem, I switched to a narrow, internally-notched, belt and have never regretted it - just wish I had done it sooner. So much easier to fit the belt and, all of a sudden, there seems to be so much more space available in that area.

 

Ian Cornish

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After rummaging through the box of bits I've found that the original fan is quite bent so I'll not be using that. Also I've no idea if the dynamo, from another box of bits, is serviceable. So it looks like a damped narrow belt conversion plus electric fan is the way to go.

 

Thanks for the contributions.

Edited by HPA 510K

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I have read Revington's alternator fitting instructions, which include a parts list and which recommend the use of Revington's mounting bracket (described in my original article), and I have to say that one should NOT have a problem fitting an alternator from Neil's emporium! Other suppliers offer kits, too, of course.

 

 

I used the Revington mounting bracket and heat shield which worked very well, but I wasn't so impressed with the adjuster bracket which utilises one of the water pump fixings - bolt snagged the underside of the water pump (thin) pulley and alignment wasn't quite right. Ended up using the Moss adjuster bracket.

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I used a high output but very small Edge alternator which I think is similar to that of the Kubato mini tractors and the like. Due to it's small size it is further away from the adverse heat of the exhaust manifold. I fitted narrow belt pulleys but kept the original fan. (Just another option to consider).

I would tend to agree with Brian however, that a 1960s era classic car with average type on road classic car use with minimal night time use will cope quite well enough with its original dynamo provided it is in good condition.

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Neil is right. The damper is a non-dispensable part of the crank, under death penalty.

IMO, the harmonic damper should be only installed when rebuilding with balancing of the whole clutch/crank/rods/damper together.

You can remove the fan, no worries, but you definitely need an electric fan.

 

The large belt means a loss of 5 bhp plus awful time if breaking on the road.

So thin belt conversion it should better be with a NipponDenso alternator (any supplier, it's the Kubota unit Trevor is mentionning). Bracket is easy to find, easier to make with a length of threaded axis and three nuts (totally adjustable).

 

Badfrog

Edited by Badfrog

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With reference to the Damper. I do not think that anybody has done a survey of broken cranks with/without the damper.

The cranks do break - that's a fact.

 

The 'normal' failure site is at the #4 big-end/crank web attachment.

The failure mode is tensile fatigue cracking due to flexing of the crank reacting against the flywheel.

 

The damper at the front end may absorb some sort of radial effects and may even out some harmonic vibrations but little else.

 

Can anybody explain why/how the damper works.

 

If it does work why didn't Triumph install/recommend it on the later four pots, they had plenty of experience with broken cranks through the 50's.

 

My views are purely from obsevation and noting that #4 is the suspect.

 

Roger

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Can't explain why they usually break at the rear end but I do recall developing software to calculate bending/flexing of rotating shafts in the Ship Division at the National Physical Laboratory as a summer job as a student in the 60s.

 

Even perfectly balanced shafts and assemblies flex and take up the appearence of a sine wave to a miniscule amount and may have varying numbers of waves depending on rotational speed. All well beyond me then and now, although at least back then I did just about understand the maths theory.

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Guest ntc

A harmonic balancer (also called crank pulley damper, crankshaft damper, torsional damper, or vibration damper) is a device connected to the crankshaft of an engine to reduce torsional vibration and serves as a pulley for drive belts.[1][2]

 

Every time the cylinders fire, torque is imparted to the crankshaft. The crankshaft deflects under this torque, which sets up vibrations when the torque is released. At certain engine speeds the torques imparted by the cylinders are in synch with the vibrations in the crankshaft, which results in a phenomenon called resonance. This resonance causes stress beyond what the crankshaft can withstand, resulting in crankshaft failure.

 

To prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft. The damper is composed of two elements: a mass and an energy dissipating element. The mass resists the acceleration of the vibration and the energy dissipating (rubber/clutch/fluid) element absorbs the vibrations.

 

Additionally the energy transferred from the piston to the crankshaft can induce as much as 2 degrees of twist in the crankshaft, which has many follow-on effects on all engine elements that require adequate timing such as valve opening, cam timing, ignition timing etc.

 

Over time, the energy dissipating (rubber/clutch/fluid) element can deteriorate from age, heat, cold, or exposure to oil or chemicals. Unless rebuilt or replaced, this can cause the crankshaft to develop cracks, resulting in crankshaft failure.

 

Performance enthusiasts have been known to remove harmonic balancers, usually when the balancer is attached to the crank pulley, deciding that they aren't necessary and their mass reduces the performance of the engine. However, this is unproven and potentially very risky because the danger of damage to the engine from the vibrations the damper is intended to prevent is too high.[citation needed]

 

Certain cars, however, do not come equipped with an external balancer on the crank pulley, and as such, can have the pulley replaced with a performance oriented product which counter-acts these resonance frequencies.

 

Any good Roger?

Edited by ntc

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Hi Neil,

 

the extract from Wikipedia which you have posted verbatim is simplistic, not particularly accurate, and very possibly originated in some USA 'performance harmonic damper' maufacturer's publicity blurb . . . . .

 

Torsional oscillation is what the damper is there to control. Torsional oscillation was a terminally limiting problem in the early days of 6 cylinder engines, and in triples for that matter, even more so in straight 8s, to a lesser extent in V6 and V8 configurations, and latterly a major factor in V12 and V16 engine design. Lanchester and Royce in their separate ways pioneered the solutions to the vibration induced, and to the crankshaft breakages.

 

Four cylinder inline engines do not suffer to anything like the same extent from torsional oscillation, hence crankshaft dampers not having been a regular feature of 4-pot engines. Mitsubishi (Colt) pioneered the re-introduction of counter balance shafts as a means of minimising vibration in larger 4 cylinder engines, Porsche quickly followed suit, but through the 50s, 60s and 70s 4-bangers generally made do without crankshaft damping. Audi ploughed a different furrow by developing 5-cylinder engines, as a compromise seeking to include the better features of 4s and 6s without the downsides.

 

The rotating masses on the front of the crankshaft on 4 cylinder engines generally existed for other purposes than damping - driving timing chains, pulleys or fans. They may have had some modest effect on overall balance, but I'd suggest that was not a significant design parameter.

 

For a succinct explanation of crankshaft priorities, Hillier takes some beating, as ever - 4th edition or later reflects the advances of the late 70s and the wider adoption of crankshaft damping techniques. It can be interesting to compare the 1st or 2nd editions with later versions, most illustrative of the detail of automotive engineering evolution.

 

Cheers,

 

Alec

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Guest ntc

Yes Alec it was an extract to try and explain to Roger ;) removal of the the existing rubber bushed mounted / balanced fan with a non harmonic front pully is not a good idea

Edited by ntc

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Hi Neil,

 

the original TR fans have a balancing facility, sure, but that is limited. The rubber bushing on the mounting comes into its own when one or another fan blade is distorted or damaged, minimising any resultant vibration input from imbalance. Considering the relatively small masses involved, influence on oscillation of the crankshaft mass is pretty minimal in any event. A conventional harmonic damper is a hefty chunk of high-density casting, precision machined, and of a mass sufficient to exert an influence on that of the crankshaft. A TR fanblade of the traditional sort exerts negligible forces in comparison.

 

In any case, we are talking about a 4-cylinder crank achieving usually no more than 5500rpm in normal road use, which implies that a damper is not strictly necessary - and given the nature of the crank bearings, such additional fitment potentially a liability unless very carefully designed and applied to an equally carefully balanced engine.

 

There is no good reason why a fan should not be removed, replaced with an equivalent mass steel washer, in effect, retaining the fan hub extension if so desired.

 

Cheers,

 

Alec

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From what I learned, dampers participate thru their weight in the equilibrium of the complete rotating gear. They tend to cure vibrations caused by unbalance.

The matter of resonance is another thing. Resonance can be seen as a microscopic vibration, more related to the way the engine is built and rotational speed than to basic desequilibrium in weight. This will occur even in a balanced engine. Equilibration will improve it but can't suppress it. That's where a harmonic damper may help.

Lightening the flywheel also impacts resonance. As I've been told, you can't remove any weight but have to act according to certain rules. Some classic specialists even devised math formulas to figure the precise authorized weights and wrote abacuses for various engines. I've seen one of these but I don't know if it's solid science or shop witchcraft.

I know for example that the A7 crank suffers severely at 2300 rpm, although it can manage 6000 rpm while the standard TR4 engine has two resonance zones at 5200 and 5800 rpm. So either you drive at 5000 or 6000 rpm but you don't keep loitering in between.

 

All the balancing magic work aims at suppressing vibrations and displacing resonance to seldom used rpm figures. For example, changing the 5200 rpm resonance to a 6200 rpm one. Of course, if you want a race engine, you have to find another zone. And logically, the more bearings, the less vibrations, the sturdier the engine. That's why my 122S 5-bearings engine went easily to 7500 rpm with just a good cam, large valves and well-done balancing. But I kept the heavy flywheel and damper to dispense from working "in the dark" about the resonance zone. Total weight is irrelevant, what matters is rotational neutrality.

 

Isn't that fun?

 

Badfrog

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Thanks chaps, it was only a simple question!! :blink:

 

Here are some facts -

 

the forces imparted by the piston on the big-end/crank web are shear (cutting)forces

The #4 big-end/crank web failures are caused by tensile (pulling) fatigue forces

The forces on the main bearing/crank web are torsional (twisting) forces

 

However, the damper helps against torsional forces but there have been none/very few main bearing crank web failures.

 

The #4 big-end/crank web failure is very possibly caused by poor machining of the big-end/web radius leaving a stress raiser behind to develop into a crack many years down the line.

 

There are/were thousands of these cranks in dailly use, each doing 100,000+ miles but only a comparative few have failed, some with the mechanical fan some without, some raced but most not.

 

As BrianC stated it is a complex struture. But the metalurgy (crack structure) is easy to read.

 

However, as it is a mine field with little data to support one way or the other then Niel's suggestion of the damper is worthwhile if only to put ones mind at ease.

Have I got a damper - no. 120,000 miles without one and my own theory keeps me happy :)

 

Roger

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I see two possible explanations;

 

1) by sheer luck your crank/rod/flywheel system is neutral.

2) The PO had the system re-balanced without the damper.

 

But then, I'd really like to see a pic as I don't see how you did bolt the original pulley on the crank. Did you just use the central part with the clevis pin plus shorter bolts ?

 

Badfrog

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