16 replies to this topic

[Chris11K]

Hi All,

 

We have a romac harmonic balancer that we're trying to install. Is there a mini specific tool that we need? Had a look online couldn't find anything related.

 

Any suggestions? Anyone that has one installed?

 

Cheers,

 

Chris

[nicklouse]

If designed for an A series engine it should fit just like the original.

 

never having seen or heard of Romac it is hard to understand the problem.

[mad4classics]

Looks similar to factory part.

https://www.norndaau...Cooper&series=-

As such should't think it would need special tools???

Edited by mad4classics, 12 August 2022 - 08:03 AM.

[Spider]

You usually need a puller to remove them but they fit up like a stock item.

 

never having seen or heard of Romac it is hard to understand the problem.

 

Good Aussie stuff, very high quality. Sold all around the world.
 

[whistler]

I think Romac were a rubber or metalastic manufacturing company of late 60's/70's making 3rd party products for cars.

 

It's possible they were the manufacturer of the Mk1/2 seat rear height adjuster that just slipped onto the rear base tubular frame to lift the back of the seat.

Edited by whistler, 12 August 2022 - 08:31 AM.

[Spider]

Owned by Nornda Automotive these days;-

 

https://www.norndaautomotive.com.au/

 

https://www.norndaau...product/70.html

 

[nicklouse]

You usually need a puller to remove them but they fit up like a stock item.

 

never having seen or heard of Romac it is hard to understand the problem.

 

Good Aussie stuff, very high quality. Sold all around the world.
 

So just fits like the original.

 

if the OP is having issues it could be catching on the woodruff key. And may need a tickle with a file.

[Chris1275gt]

Ok hands up, what does a harmonic balancer do and where does it go.

[Compdoc]

Its attached to the front pulley and helps smooth out engine vibration.

Edited by Compdoc, 12 August 2022 - 11:40 AM.

[Spider]

Ok hands up, what does a harmonic balancer do and where does it go.

 

Not wanting to sound a smarty here but the correct term is Harmonic Damper. The term 'Balancer' here is a slang name.

 

In short, it stops the Crank from breaking for being twisted back and forth.

 

We tend to think of the action of an internal combustion engine as being smooth and even over a full cycle (2 turns of the crank for a 4 stroke), however, its anything but. On the firing Stroke, the Crank Big End Pin is subject to an impulse, not too different to say a hammer blow driving a peg in to the ground. Cycle after cycle, this sets up a twisting vibration in the Crank which is referred to as Torsional Vibration. That's the first part.

 

Putting that to one side for a moment, everything physical has a Resonant Frequency, this isn't some vibration that the items makes itself, but a (usually) critical frequency (of vibration) at which it amplifies itself exponentially and can feed on itself to cause the amplitude to grow even bigger. I'm sure at some point you've walked on a plank of wood and felt it sag and spring back as you walked across it, if you walked at a certain speed, you could get it to sag and spring back further, growing on itself. That it a Resonant Frequency of that plank of wood. As a side note here, for this very reason, in WWII German Solders were told to only ever walk across bridges, never march across them as the regular beat of the feet marching could hit the resonate frequency of the Bridge and bring it down. There are also multipals of this fundamental resonant frequency which will have the same effect, but usually less so, these are referred to as a Harmonic of that Fundamental Resonant Frequency.

 

Just like the plank of wood, Crankshafts too have a Resonant Frequency, which if we were to run the engine on that Resonance it can be very destructive to various parts of the engine, in particular, the Crankshaft, often resulting in the Crank cracking and breaking, on an A Series Engine, this nearly always occurs between the Centre Main Journal and the 2nd Crank Pin. Off hand the Resonate Frequency of most stock A Series Engines occur around the 6000 RPM mark, give or take and so harmonics occur around 3000, 1500 and 750 RPM. Lightening bottom end components, usually raises these frequencies.

The function of the Harmonic Damper is to reduce the effects of these harmful Resonant Frequencies from the Crank. Often, the cause of a broken crank isn't a bad crank or a poor regrind, but a failed harmonic damper. The common dampers are quite simple in construction and have a hub that mounts to the nose of the Crank, a rubber that has particular properties on to which is mounted an outer rim that has mass. They fail when the rubber looses it's properties and this can usually be picked up when the outer has spun a few degrees on in relation to the inner hub. I always put a Mark across the inner and outer so I can see at a glance if it's moved at all.

 

Hopefully this gif will work, this shows how a crank is twisted back and forth in operation. This is torsional twisting and as it occurs at regular frequencies depending on RPMs and how much BEMP (cylinder pressure) is being made in the cylinder, it becomes a torsional vibration in crankshafts

 

This graph shows the how much torsional vibration a crank can get with and without a Damper

 

 

[Chris1275gt]

Thanks for that Spider. Next question : I can’t find any mention of a damper in my Haynes so Is the damper an upgrade?

[nicklouse]

Thanks for that Spider. Next question : I can’t find any mention of a damper in my Haynes so Is the damper an upgrade?

I am sure it should but which section would be the question. The S engines had a two piece damper and all the 1275 A had them and I think all the A+ had them.

 

my Haynes shows a picture of the Pulley only versions as fitted to the small bore engines. There may be a comment in the supplement part for the damped version.

[Spider]

Thanks for that Spider. Next question : I can’t find any mention of a damper in my Haynes so Is the damper an upgrade?

 

The 850 and early 998's (to about 79) didn't have them, just a pulley. In standard form, which they did make Torsional Vibration, it wasn't deemed enough to warrant a Damper being fitted. For what ever reason, they deemed then necessary from 79-ish on. In all the Special Tuning Bookletts, the factory advocated the fitting of a damper from the very smallest of tunes.

The very early 1100 engines also had just a Pulley and no damper, but they soon started fitting them !

Most likely in the Haynes book, they probably just call it a 'pulley'. Having just written that, I have a look in one Haynes manual and it make no reference to even as much as a 'pulley'.

[OzOAP]

If designed for an A series engine it should fit just like the original.

I have fitted a few. Like most parts these days fitment can vary.
3 parts have to be compatible. Pulley, crank and woodruff key.
Remove key and make sure pulley is a nice slide fit onto crank, then make sure key fits the pulley nicely. Refit key to crank and it should fit together.
This can take a while but the job is done properly.
On Small Block Ford engines I build, the harmonic balancer/pulley needs a tool to fit and remove. The A Series should just be a nice 'slide' fit.
KAD do a fluid damper in 2 sizes. One for steel, (Arrow), cranks, one for std ones. There is a slight difference in size.

Edited by OzOAP, 13 August 2022 - 05:23 AM.

[Ethel]

I like the  kid on a swing analogy:

 

If they throw their legs out & lean back in time with the frequency of the swing they go higher. A crank damper does the opposite by "swinging" its mass out of sync with the crank.

 

Every crank would fatigue eventually, but it only really enters the realms of probability if the engine runs for extended periods where it harmonises to amplify the bending. That's much more likely on a competition car that's constantly driven flat out. It also became more marketable if the engine didn't shake your fillings out, probably why they spent the extra pennies on putting one on the A+