Engine Balancing

[pgp001]

I am now rebuilding my spare 1098 engine and have borrowed a Jones & Shipman grinding wheel balancing jig.
Having sat the crank, flywheel & clutch assembly on it, there is around 13 grams worth of magnets required on the rim of the flywheel to statically balance the whole assembly.

Does that sound excessive, or should I even bother drilling the flywheel to remove that amount of metal. ?

Any thoughts please before I start drilling.

[Banned User]

Balance the crank first, then add stuff. There’s no point in balancing the whole lot from the off.

[pgp001]

The crank is actually OK. Its just when adding the fly wheel I get the 13 gram figure, even adding the clutch does not significantly change that, so I deduce it must be the fly wheel.
I have just had it refaced and a new ring gear fitted, so anything is possible.

My question really is... Should I be worried about 13 gramms or just leave it be.

Phil

[Banned User]

Personally I’d want it spot on. If it’s measurable then it’s correctable.

[philthehill]

Unless you are prepared to balance the whole lot there is little point in just balancing the crankshaft and flywheel.

You need to balance the pistons, the con rods (overall and end for end), the crankshaft pulley (damper if fitted) and the clutch cover.

The crankshaft, flywheel, clutch cover and crankshaft pulley/damper should be balanced as one assembly and marked so that the assembly can be stripped and rebuilt in exactly the same orientation without effecting the balance.

Static balance is a start but you do need to balance the crankshaft assembly dynamically (at rotational speed) to get the best out of balancing.

For equalizing the weight of parts I use a Salter digital scales capable of measuring in increments of 0.5 gram.

Below - using the digital scales for balancing and equalising conrod end weights.

100_2253.JPG (1.35 MiB) Viewed 1672 times

To achieve dynamic balance I farm out the process.

[pgp001]

Hi Phil

I am doing all of the above, I think my scales are the same os yours as well.

Static balancing is all I am intending to do, and not bother spending money on dynamic balancing, it is only a road going engine and static balancing cannot hurt and it is something I can do myself.
It is debatable wether it will make much noticable difference, but I will get some sense of satisfaction from doing the best job that I can on it.

What I am unsure of is just how far to go with the static balance of the crank/flywheel/clutch/damper pulley assembly. Currently 13 grams of magnets at the flywheel rim makes it balanced.
Compared to the overall weight of the assembly 13 grams is miniscule, and I have no idea how it will affect the engine when running, will it even be detectable at normal cruising revs ?

Phil

[philthehill]

Thanks for the reply.

Refacing the flywheel and fitting a new ring gear should not effect the balance to any degree if at all.

If you can accommodate those 13 grams so much the better. As they say 'every little helps'.

Static balancing is good and yes it does cost money to dynamic balance the crankshaft assy. As you state that it is only a road engine therefore anything you can do to balance the engine components will improve the running and reduce the vibration factor.

If you have not already considered it - fitting a damped crankshaft pulley to a 1098cc engine works wonders.

Phil

100_2018.JPG (1.16 MiB) Viewed 1655 times

[pgp001]

Phil

I took your advice from quite a few months ago and obtained said pulley

Phil

[philthehill]

Very good

Oselli did the dynamic balancing of my 1380cc/1400cc engines and yes it was not cheap.

Below is their price list for balancing.

http://www.oselli.com/service/engineering/balancing

[Rust bucket]

Sorry to butt in on your conversation.....when I rebuild my engine just for road use I had the flywheel lightened and balanced and also fitted a damper pulley the other end, works well.

[Banned User]

Rusty Bucket, do you know how much weight was taken out of the flywheel?

[Rust bucket]

If I remember correctly it was 6kg as standard and the engineer reduced it down to 4.5kg.

[Banned User]

7kg is standard, but either way it’s a worthwhile reduction. Thanks.

[philthehill]

In the Car and Car conversions booklet Tuning BMC Sports cars there is a cross sectional diagram with measurements for lightening the BMC 948cc flywheel. The measurements are also applicable for the 1098cc flywheel.

Car must be taken when lightening a standard cast flywheel as the flywheel if excessively lightened can at high revs explode with devastating consequences.

It is recommended that flywheels lighter than the standard ex factory weight are made from steel.

[Banned User]

I’ve got that drawing Phil, my machining chap has recommended not taking off as much as he would for a saloon, as it could have an adverse affect pulling away fully laden.