Race Engine Forum UK

Following the strip down of my engine I noticed the drilling in the ends of the crank bob weights where material has been removed during the factory balancing of the crank.

From what I have read, I imagine my modern(ish) engine is well balanced at the factory and this has made me wonder if additional balancing is worth it.

But, if I was to go through with it, surely it would be much better to have the factory drillings welded full and then remove material by chamfering the bob weight edges. This would greatly reduce drag.

Any comments would be greatly appreciated.

Ben

You'll gain .1% or so in power and stress the crank thermally by welding.
If you really want to close the holes fill them with some kind of polymer (lots of modern stuff on the market) and then rebalance the crank.

The question is of course what is your application? If its for a road engine that will spend most of it's life below 4500rpm and peak at 6k ish??

My local race engine tuner in denmark balances the crank, fly and clutch together.

TU engines are limited at somewhere between 6500 and 7500 K without problems.

My layman view is if you are going to visit the 7000/8000 rpm mark regularly in a peugeot XU engine then it might be worth balancing. and if it is out of the engine already then hey..why not..but doing that kind of speed in a XU I think will also require at minimum stronger valve springs.

Chris: Golden Rule!

On any rebuild, check/adjust balance of crank and fw by a competent balance professional essential, and maybe clutch too depending on type/balance condition as suppplied (my Helix clutches come pre-balanced and I have never had a problem with them) and engine rpm.

Always, always. Regardless of cost. Imbalance in rotating parts can cause fatal injuries.

No argument on this members, please.

GC

Ok, question answered!

Guy, can you recommend anyone? I am in Gloucestershire.

The nearest company I know are Bassett Down Balancing in Swindon.

Thanks,

Ben

I don't know them personally although I know that they have been going a lot of years. There are some firms I'd never use, they are certainly not among them.

Your protection is only this. You MUST serial number your crank flywheel assembly and insist that this is noted on the invoice and that it is certified balanced in writing.

This is because you may not find out it is wrong till it comes flying out of the bellhousing. Proving the fault was balance is the easy part, it shears the heads off right at the bolts. After that event it is no use in law saying 'they said'...it must be in writing.

I use a guy in Gravesend, have done for years, worth the travel.

GC

Thanks for the tips!
Ben