Need advice on balancing my ABY with new pistons please

[YELL MAN]

Hello, After many years of enjoying the S2 she was starting to get a bit crusty especally the suspension and around the engine bay so I took her off the road with the intention of giving her a basic refurb. I intended to clean up and paint the engine block too while I was at it and things snowballed as they do.

She was a bit smokey before I took her off the road so I figured I would strip the bottom end and check the rings and bores, I had to rebore engine to the next size up due to the cylinder wear being at the maximum limit. I decided to fit FCP pistons since I couldn't find standard oversize pistons anywhere and figured if I was going to the bother of fitting them I may as well fit FCP rods as well, Definatly overkill as the car is only homefried but it's here now.

I realise that the rotating assembly will need to be balanced with the new pistons so I contacted Basset Down Balancing and I was informed that they cannot balance a engine fitted with a dual mass flywheel, plus I was a bit concerned that my original front puller/damper is past it's best as it has a wobble and there is a fair bit of corrosion which I assume Basset won't want to touch as I got the impression if the part isn't perfect they won't want to touch it.

My original intention was to just replace the damper with a Fluidampr which arrived the other day and looks great, then get the crank zero balanced to suit but I was informed that it needs to be knife edged and I am worried that by doing this on a car thats only running a homefry (so about 270hp) it will ruin the characteristic of the engine, especially if I have to go down the single mass route.

I am trying to decide what to do.

I have read about some folk not rebalancing the engine with new pistons and rods and getting away with it but it seems like a risk.

If I get her rebalanced I will have to go single mass it seems, so I assume it would need to be a 3B as anything lighter probably would be less than ideal or am I wrong in worrying about a light flywheel on a low power S2?

It is possible that the damper can be used but considering I can't just nip in to Basset Down since I live in Shetland I won't know till I crate it all up and send it down the country and if not then is it worth knife edge zero balancing or trying to source another standard damper that seems to be nearly unobtainable.

Can anyone share any thoughts on my predicament

[K Simmonds]

You'll want a 7A or 3B flywheel though an NG one can also be used with some basic mods for the sensor pick ups.

I hope whoever did your re-bore matched each piston with a specific cylinder as the tolerance's are very close and pistons can vary in size by a couple of thou.

I would absolutely balance all moving parts, it's not actually that hard to do rods and pistons yourself if one is reasonably mechanically competent, though the crank and flywheel are specialist jobs. I'd watch some YouTube vids to learn how to do it yourself.

I don't see why the crank need's to be knife edged, were you given an explanation as to why this need's to be done, it'll be expensive and I don't see the need, though happy to be proved wrong.

Have you had the exhaust valve guides renewed whilst it's apart? Depending on mileage these will probably be quite worn, their not expensive to change in the grand scheme of things.

[YELL MAN]

Basset Down Balancing seemed to say that to zero balance the crank it had to be knife edged due to the amount of material that had to be removed to acheive it. I am no expert on the matter so I am simply going be what I was told. The only reason I would zero balance would be to use the Fluidampr which as I mentioned I assumed could be done without knife edging. It's always possible I have missunderstood what the balance company said though.

The head has had a complete refresh and skim as is the block when it was rebored. Precision Engine Services did the work.

[K Simmonds]

Basset Down Balancing seemed to say that to zero balance the crank it had to be knife edged due to the amount of material that had to be removed to acheive it. I am no expert on the matter so I am simply going be what I was told. The only reason I would zero balance would be to use the Fluidampr which as I mentioned I assumed could be done without knife edging. It's always possible I have missunderstood what the balance company said though.

The head has had a complete refresh and skim as is the block when it was rebored. Precision Engine Services did the work.

Well, Basset Down are an excellent company with a very good reputation so I'd follow their advice, even if is going to be expensive, Audi cranks are extremely well balanced from new, but as I said I would follow their advice, they won't want to do it for no reason. On the plus side it should make the engine a little more free revving to as the webs cut through the oil in the pan more efficiently, plus the crank will be lighter weight.

Precision Engine Services are also a great company so I'd have full confidence in their work.

[YELL MAN]

Well quality work is never cheap and thats the way it should be . I am just worried that if I do get the knife edge crank that it will make the engine hard to live with. It might be excellent however, but I don't have any way to know myself as I haven't had the chance to try one thats been done.

[K Simmonds]

You should like it, as I said if anything it'll rev a little more freely, the only downside is the cost, but if needs to done then so be it.

[YELL MAN]

Thanks, that helps put the mind at ease a bit. , Once she is up and running again I might have to look into getting a bit more power installed. on that note does anyone have a good 3b flywheel for sale?

[K Simmonds]

No worries, sounds like your going to have a cracking engine!

[YELL MAN]

Hoping so. once the engine and running gear is sorted she's getting a respray and I'm going to takle the headlining and door cards as they are starting to show thier age too.

[SteveH]

I think you will locate a 7A flywheel easier than a 3B as they are broken for parts more often. You could look into a Fidanza or similar off the shelf single mass flywheel if you can't find a second hand item. I wouldn't worry about having the crank knife edged. BDB are correct that it's the easiest way to zero balance the crank and it will make the engine far more responsive in combination with a single mass flywheel. BDB are not who they used to be though as the business was bought from the original chap some years ago. Did they provide you with any prices for zero balancing?

[YELL MAN]

There is a few 7A flywheels on Ebay at the moment but they all would require a good clean up and definatlly a skim of the friction surface.

I do see a flywheel for sale at Ultra Performance Engineering but it's 6.1KG so maybe too light for my needs? Camn anyone advise on it?

The cost of the Knife edge so long as the website is accurate is £380+Vat.

[SteveH]

I'm assuming the £380+Vat is for the knife edge, zero balancing with all components? I guess that's not bad if it is. They used to charge £200 + Vat to zero balance a crank.

[YELL MAN]

Yea I thought that was a fair price considering it's such a specialist job.

[newsh]

A warning, you will hear the straighter cut 6 speed gearbox through the solid flywheel which is annoying. I changed a very good 6 speed out thinking it was knackered before I worked out what was going on. Still annoyed about that!
Read the 5 speed page on the BD site, AFAICT it doesn’t say you have to knife edge, it’s only if you want it converted to neutral balance.

https://bassetdownbalancing.com/five-cylinder-car-engine/

This allows you to rev the engine more which IMHO is a complete waste on a stage one tune where the fun is between 3-4k.
FWIW we never balanced the crank when we changed my rods, just the rods to each other and end to end and the pistons to each other.
The crank is balanced within itself as are the flywheel and damper.
My car makes 450hp and 450 ft/lbs and is smooth where I drive it, in the midrange. My all original Avant was a little smoother at the top end but that had the DM and more soundproofing so not really like for like.
If I was building a race engine I might go the whole hog and send it to Basset (who are among the best of the best)
If you want to retain the plush feel of your car then keep the DM

[YELL MAN]

I am just concerned that if I bolt it back together there may be a vibration and it would be a major hit to moral to have to take it all apart again. Saying that though you may be right and it would be fine. The only way I would be able to keep the Dm flywheel would be not to get it balanced.