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Balancing
garage19 - 19/11/03 at 11:56 AM

If I fit oversize pistons to my zetec engine do you think I should get the crank assembly re-balanced?

zetec - 19/11/03 at 07:27 PM

Have you fitted new pistons? I'm not sure that you can to a 2ltr. Even if it is a lower capacity I suspect it would be more cheaper to get a good s/h engine. I had a single big end bearing fail and that was going to cost nearly £200 to sort. A Ford replacement half engine is only £500.

Zetecs are so cheap now that if you have anything major go just get another.

mad4x4 - 20/11/03 at 01:18 PM

I was told once that a well balanced Crank will allow the engine to rev higher.

Don'y know if its true.

ned - 20/11/03 at 01:42 PM

From my understanding there are various reasons of changing the pistons including lower compression for turbo'ing a zetec or higher compression to tune a n/a version. or just to replace a knackered one, or overbore.

Getting the crank balanced IMHO is a good idea. not sure it'll allow the engine to rev much higher than it normally would, but it should rev more safely as there should be less forces trying to pull the bottom end apart which is what would eventually happen on an unbalanced bottom end in a race/high revving scenario.

the above is probably a little OTT for a road car though, depends what you're trying to achieve really...

Ned.

darren(SA) - 20/11/03 at 05:29 PM

neds right,
you prob won't feel any diff at all, as the cranks nowadays are so well balanced.

But I would agree that it is always a good idea to balance as much as possible, believe it or not i had my pistons 'balanced' as they were all slightly different weights (as per factory supplied,a few grams out).

garage19 - 20/11/03 at 05:32 PM

quote:
Originally posted by ned
From my understanding there are various reasons of changing the pistons including lower compression for turbo'ing a zetec


Clever Flanders knows what I'm up to and has explained it before i could get
there.

The pistons I'm using are actually slightly larger forged pistons out of a Vauxhall engine.
They have a lower deck height and there fore will drop the CR for turbocharging!

Just wondered if they were a different weight to the stock items would i have to change the weight of the corresponding crank journals accordingly?

Ned is also right in saying that a balanced item will rev higher without pulling itself apart due to unbalanced forces acting on it.

Peteff - 20/11/03 at 08:07 PM

As long as all 4 pistons are similar you shouldn't need to do anything to the crank. It's better to weigh the conrods and pistons as an assembly rather than seperate items and if you need to lose any weight you can do it while you stress relieve the rods by taking any rough edges off them.

yours, Pete.

Stu16v - 21/11/03 at 12:05 AM

quote:

It's better to weigh the conrods and pistons as an assembly rather than seperate items


I'd have to disagree with your usually superb guidence Pete....

A 'proper' balancing session would see the pistons balanced separately, and the conrods balanced end to end. Each rod would be weighed at the big end, whislt supporting the little end, and the heaviest three brought down to the lightest weight. Then the same is done to the little end. In theory at least, you end up with four perfectly balanced rods and pistons when assembled.

P.s. If you are turbocharging, I doubt you will have the need to rev the engine as hard as you would in normally aspirated form....




HTH Stu.

[Edited on 21/11/03 by Stu16v]

Ben_Copeland - 21/11/03 at 09:09 AM

Yep, if your turbo charging, the revs tend to be lower than NA. Due to the turbo's power band being lower.

Oooo Stop nicking Vauxhall Engine bits Though i should feel proud

Peteff - 21/11/03 at 09:53 AM

I mean someone who is doing the job at home with a basic setup, not an engineering shop with dynamic balancing equipment and all the whistles and bells. If he is going to do a full blueprint on the engine I'll agree with you but if he isn't taking the crank, flywheel and front pulley to be balanced as well it's all a bit aesthetic.

yours, Pete.

Stu16v - 21/11/03 at 10:31 PM

If you have the measuring equipment accurate enough to do balancing in the first place, then it will be accurate enough to do the pistons/rods separately IMHO.
But as you say mate, it's all a bit aesthetic if the crank/flyweel/pulley isnt being done too......


Regards, Stu.

david walker - 22/11/03 at 09:02 PM

quote:
Originally posted by darren(SA)
neds right,
you prob won't feel any diff at all, as the cranks nowadays are so well balanced.


Yeah, maybe true to a degree, but a comment that does not apply to X'Flows, Pintos and few Zetecs!

To answer the original question, No the crank won't need balancing and unless you having it done profesionally leave the rods, pistons and everything else alone.