Balancing the crank and flywheel

[Nico86]

Just to be sure before bringing a crank for balancing, what do you put together?

Crank + flywheel + pressure plate + clutch disc + cam gear + pulley, do you mount all the shims, spacers and gaskets ?

Is there any special thing to take care of I'd have to tell to the machine shop ?

[Fastbrit]

Just the crank, flywheel and pressure plate will do – maybe the crank pulley but most have little effect.

[Harry/FDK]

Incl. crankpulley.

[kingsburgphil]

If you ever feel you might need a new or heavier pressure plate, have one balanced now. 

[Nico86]

Thanks for the infos guys   I have a Berg crank pulley so it's already balanced, but it will not cost much more to have a look a it.

And about the mounting "hardware" (washers, spacers, shims and endplay shims, woodruff keys, cam gear, gaskets...) do you assemble everything as if the crank is in the case, or it's not necessary?

[Diederick/DVK]

i had the crank assembled - i think.
i bet you that with a DPR crank the only adjustment will be made to the pressure plate. a DPR crank = immaculate!

[Nico86]

Yes I have a DPR crank with a DPR flywheel. I have a Kennedy stage 1 pressure plate and the Berg EQ pulley, everything is supposed to be balanced, but it's safer to check it mounted I guess.

[javabug]

Ask the shop doing the work.

[Diederick/DVK]

sure you gotta check everything mounted together! i didn't mean otherwise.

[Nico86]

So it means I'd have to set the endplay before balancing? Or am I going crazy about balancing shims and washers 

[kingsburgphil]

If you ever feel you might need a new or heavier pressure plate, have one balanced now. 

In my own situation, I acquired my car with a KEP1 and a Black Magic disk. We replaced the BM disk
with a Dual Force disk to save the trans and help drivability, result, not enough pressure plate. If I
step up to a KEP2 P/P obviously it wouldn't be balanced to the motor.  IMO,  Buy two/balance two 
I'll shut up now.

[John Maher]

You should supply crankshaft, flywheel, gland nut, pressure plate, clutch bolts and washers, crankshaft pulley, pulley bolt.
Also install gears, spacer, woodruff keys and circlip on the crank. They have a significant effect on crankshaft balance. Balance the crank without them and you'll create an unbalance when they're installed.

In the event you may want to fit a replacement flywheel or clutch pressure plate at a later date, have parts balanced individually and together.
My procedure is to balance the crank (complete with gears, keys etc) by itself. Then fit the flywheel and carry out any corrective work to the flywheel alone.
Next the pressure plate. As before, correct any unbalance by working on the pressure plate only. And finally the pulley etc.

Some places will balance everything as an assembled mass. This is quicker and easier but can cause problems if you need to replace anything at a later date eg clutch pressure plate. When the entire crank/flywheel/clutch/pulley assembly is balanced as a single unit, an out of balance pressure plate may well be correcting an equal and opposite unbalance in the flywheel or crankshaft (or combination of both). Fitting a new 'balanced' pressure plate would upset balance of the whole rotating assembly.
i.e. you have a group of individually unbalanced parts that can only work as a group when bolted to other unbalanced parts.

When the parts are treated individually, a replacement balanced clutch can be supplied by mounting it to a 'properly' balanced crank and flywheel, saving the customer the trouble of pulling the motor apart for a full rebalance.

Balance tolerances: ask what tolerance the balancer is working to and whether that tolerance is suitable for the application or not. Nobody can balance to zero. Not even F1. That's why we have tolerances. For a high performance street engine I work to 4gm inches (4gm 25mm), i.e. there is no greater unbalance than a mass of 4 grams at a distance of 25mm from the centre line of the crank. That's equivalent to 1 gram at a distance of 100mm from the crank centreline. 6gm inches is probably more than adequate for most street stuff. For high rpm race engines I use a tolerance of 2gm inches (2gm 25mm). That's equivalent to less than half a gram on the outer edge of the flywheel.

[Diederick/DVK]

elaborate and informative as always, john! thanks

[Harry/FDK]

x2

[Nico86]

Thank you guys and thank you John, now I know everything. 

[henk]

little question about balancing.
after we had the crank,flywheel,pully and pressure plate balanced we saw that the flywheel was not running staight when we mounted it on the crank.
it seems that the flywheel was not perfect flat where you mount it to the crank,so at the dowel pins.
the movement was to big to leave it like that so we machined the flywheel so it is runnung straight no when it is on his place on the crank.
my question now is,do i need to balance the flywheel again or should i be ok as there is no real material been taken away?

henk!!!

[Bruce]

That is what I saw with my engine's parts after I got them balanced.
I went back to the shop that did the balancing to ask.  The guy said he always puts a dial indicator on every flywheel to ensure it's running true before balancing, and that my flywheel did run true.  Later I determined the runout I saw was while I was setting the endplay and not torquing the bolt all the way.  Once the bolt was the proper torque, all was well.

If your balancing shop didn't notice it was wobbling, and you've now fixed it, you must send it back for rebalancing.

[henk]

hallo,

they did notice the wobbeling but they  thought that it was just the starter theeths that where not straight due the hardning of them.
so with sending it back do you mean the whole assembly(crank,flywheel,...)?

henk!!!

[Bruce]

.... do you mean the whole assembly (crank,flywheel,...)?

yep.  they have to attach the flywheel to something to spin it.

[henk]

ok thanks for your info.

henk!!!