Volkszone Forum banner

Dynamic Balancing

26K views 17 replies 6 participants last post by  monkey 
#1 ·
Hi People

I want to get a crank+flywheel+pressure plate balanced.

What is the spec that I need to give the machine shop?

P.S. Its a stock crank going into a 1600cc bus engine

Thanks :)
 
#2 ·
balancing a crank is balancing a crank. There are loads of ways to balance a crank, but all result in the same. The object of balancing a crank is to dynamically resolve all forces (both primary AND secondary) and these are all in terms of moments and forces, therefore, a combination of different distances from the centre of the crank and various masses can result in a balanced crank. The aim is therefore to balance a crank with the smallest addition of material (so as to not increase frictional forces inside the engine).

hope this helps
 
#4 ·
Isn't there a recommended spec in grammes/millimetre
In a word - no.

Balancing is exactly what '71 says - ensuring that there are no unequal and opposing forces.

There is no recommended weight - it just has to be 'wobble free'.

This usually involves making all the pistons and rods equal weight, and ensuring that the crank, the flywheel and clutch do not 'wobble' and run perfectly smoothly. The wobble indicates that there is uneven forces and therefore additional wear on the engine.

Contact a shop that balances and they'll explain it.
 
#5 ·
I've found some numbers :)

http://www.aircooledtechnology.com/

"Performance" This spec is for basically stock engines, or for those who want a balance job that will keep their engine from "self consumption". This is recommended for every engine, even stock, and even a 36 horse! The dynamic tolerances are set to .07 oz in. Connecting rods are balanced overall to wihin 1 gram (not end for end) and pistons are balanced to within 1 gram. Budget $100.00 for this service and allow a 3 day turnaround according to our work load

"Intermediate" This is the most used spec, it allows for a well balanced engine, is affordable and provides balance good enough for a sustained 6,000 RPM engine. Dynamic Balance toleranaces are set to .04 oz in and Connecting rods are weighed end to end to within .05 gram, and pistons to within .05 gram This is the most typical state of balance Budget $150.00 for this balance job, and allow one week turnaround time.

"RACE" Our RACE balance is unlike anyone elses, mostly due to the fact that no other shop in the aircooled industry has a balancer that parallels ours! Our RACE balance is good for 8500-9000 RPM engines (I balanced my 2332, 8,500RPM engine to this tolerance)This is the highest state of balance we offer and we maximize the equipment with tolerances of .02 Oz In This balance we take everything to the extremes, and final spins are done in the dark, as flourescent lights interfere with readings (60 cycles) Connecting rods are balanced to .01 gram end for end per set of 4, and pistons to within .01 gram per set of 4. This balance takes alot more time than any other tolerance and is not a flat rate service. Plan on spending $250.00 for this balance service, turnaround time is 2-3 weeks. This is alot of work and is very time consuming.
 
#6 ·
Those specs are from my site.... They are only good if the balancer that is being used is computer controlled and has the capability of breaking balance down into "Ounce inches" (balance in ounces per inch of radius) The old type strobe machines will not break down this way..

Unless you have the ENTIRE ROTATING AND RECIPROCATING MASS BALANCED- YOU ARE WASTING THE MONEY! One imbalanced part can destroy all the balance work.

Also- Ensure that all the parts come back 100% indeed for assebly, if they don't take them back. Those parts MUST be added into the engine the exact way they were balanced together.
 
#7 ·
anyway, it depends on the crank. Having a reground crank, or a second hand one may in itself make it differ from the one balanced in the tech article. It is not just a case of blobing on extra masses in order to hopefully balance it. There is no point either, as stated, in gettin just the crank done. YOU MIGHT MAKE THE ENGINE RUN EVEN MORE 'WOBBLY' THAN BEFORE(due to the interaction of the new balanced parts! Flywheels, rods etc all should be balanced as well in order to acheive a 'balanced' engine.
 
#8 ·
I took my stuff to a guy who does a lot of F1 stuff amongst other stuff.

He insisted on doing the pistons, rods, crank,pully, flywheel and clutch, along with all glandnuts, nuts, washers etc.

I spent a bit of time watching him, it was quite interesting. The pistons and rods were matched by weight . The crank and flywheel and nuts etc were put onto a big machine which span the ran (like you put wheels on when balancing them).

He then proceeded to drill out weight where necessary. I guess this is what Jake's saying. the guy wouldn't do it without all the components and each was clearly marked with what it was and what it was matched to.

http://wwww.vibrationfree.co.uk
 
#9 ·
I had my engine balanced by Oselli in Oxford.....its f**king amazing how smooth it is!
They match weighted the pistons and the rods, balanced the rods end for end, then balanced the crank along with the front pulley, flywheel (lightened) and clutch pressure plate - all marked up so they went back in the order they were balanced. It really is noticeably smoother than an average VW motor.......i reckon its well worth it if you are building the ultimate VW motor (BTW mine is a 1600, too)
 
#10 ·
balancing crank......

You need to do it properly:

crank, flywheel, pulley, clutch(without disc), timing gear, all attached and bolted up.

This is then put on a balancing machine. it is rotated at speed, and the machine tells the operator where to remove material. How much material to remove is dependent on tolerances. Ask for zero. therefore perfect balance.

rods and pistons and balanced differently, by matching weights. For a 1600 motor it is not neccessary.


the better the balance the higer you can rev, without excess 'wobble' damaging the case.
 
#12 ·
It worked out about £160 I think. Maybe £60 for the pistons and rods and £100 for the crank, but he did dress my crank for me as well (placed drive gears etc on it) and did a couple of other bits as well.

Originally I think he quoted £60 and £70 respectively.
 
#15 ·
The crank is the least important and easiest part to balance! It has the smallest radius of all rotating parts..

The worst parts are the flywheel and pressure plate..

I personally balance every engine that comes through my shop, till you have cycled hundreds of jobs you just don't understand.
 
#16 ·
crikey, where was that?
Dude if that was to me..

Vibration Free

The guys names Steve. He'll do a cash deal I'm sure. I've added a link on the VZI suppliers list. It was the 1st VW flat4 he's done. He usually deals with modern racing cars and the odd F1 component

He's probably not the cheapest, but I felt really confident that he'd done a good job - he was insistant that the complete bottom end (like lids says) was balanced. Everything was marked - ie the clutch was marked and the flywheel marked to ensure that the clutch is fitted in the correct fitting.

He warned me that basically getting something like that wrong would negate all his work.

He told me that my engine will 'sing' rather than rasp like the std flat4:D
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top