VW/Porsche factory balanced (crank) good enough?

bcrazy

An engine builder ones told me this:

"No one can balance a vw crank better than vw, so there is no need to have it balanced again"

So is this true? I guess if vw is good, Porsche would be good too?

More specific, should i send my 74mm stock counterweighted porsche 912 crank with flywheel to get it balanced? Or did the factory do a good enough job? (Redline will be 6500 rpm)

67SQARE · Posted: Tue Dec 22, 2009 5:00 am Post subject:

Have the flywheel, pressure plate,crank, and pulley done as a set. Better safe, than sorry. Balancing will increase longevity, as well performance and smoothness.
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perrib · Posted: Tue Dec 22, 2009 6:47 am Post subject:

Jake Raby · Posted: Tue Dec 22, 2009 7:41 am Post subject:

Pure bullshit.

The balance equipment that was available when the VW was new was incapable of attaining the balance tolerances of today's equipment. See my site for dynamic balance info and a peek at a modern balance machine.

On top of that without balancing the crank you have no way to fully know if some idiot hasn't tried to balance it in the past and screwed it up.

The person who told you this is stuck in the 1960s, so your best off not listening to anything he tells you. His days of effectiveness are probably long gone and complacency has set in.

Balancing the crank only is virtually worthless, cranks themselves have the smallest diameter of any component in the dynamic mass so ensure the entire dynamic mass is balanced and indexed as a unit.
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nextgen · Posted: Tue Dec 22, 2009 8:15 am Post subject:

I agree with Jakes extensive experience in engine building. To simplify the balancing story, the Flywheel, Crank, Crank Pulley, Pressure plate should all be assembled and balanced together on the machine. If you just balance the Crank you may actually have created a greater imbalance when all are assembled.

When I had my engine balanced the guy used a punch with his logo to make alignment marks on each part, to be used to realign when I reassembly all the parts.

He was so precise that he shimmed the springs on the clutch pressure plate to release the pressure on the plate. He said this allows me to install the plate in the flywheel and easily center it in the flywheel. He said this helps to prevent me from misaligning the plate from hitting the edge of the flywheel and shaving metal off the flywheel, which can cause even that much of an imbalance.

I don’t care if you have a 35hp or 260 hp engine, I believe nothing is more important then balancing. It is a very satisfying improvement you can feel.
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craigman · Posted: Tue Dec 22, 2009 10:21 am Post subject:

I believe that balancing the pressure plate with the assembly is a bad idea.
Just me though.

Jake Raby · Posted: Tue Dec 22, 2009 10:29 am Post subject:

Why is that? The pressure plate is a dynamic component. It is affixed to the flywheel and doesn't change index with engine operation.

Historically they have been more out of balance than any other component in the dynamic mass. Today we see pressure plates that are elliptical and as much as 17 grams out of balance right out of the box.
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craigman · Posted: Tue Dec 22, 2009 10:39 am Post subject:

i don't doubt their out of balance.
The problem i see with balancing it as a whole unit is, what happens if you need to change the clutch/pp for some reason? Then your no longer in balance. So what do you do, take apart the whole engine and rebalance after each clutch change?

Jake Raby · Posted: Tue Dec 22, 2009 10:48 am Post subject:

Thats easy and its why I recommend balancing a second unit at the time the unit is balanced.
OR
If the unit is balanced on a modern machine the replacement pressure plate can be easily matched to the prior assembly due to the file management system within the machine
OR
The pressure plate is the LSST component that is to be balanced/ added to the assembly. Due to this the balancing of the pressure plate WILL NOT imbalance the engine if the balanced pressure plate is removed and replaced any more than it would have been if the original pressure plate had not been balanced.

There are many ways to attack this situation, forethought is the key- as always.
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Jake Raby
Raby Engine Development
www.rabyenginedevelopment.com
"I've never given anyone Hell, I just told them the truth and they thought it was Hell"

jfats808 · Posted: Tue Dec 22, 2009 10:52 am Post subject:

I dont know about the clutch, but i know some shops will balance a pair of pressure plates to the same assembly and include it in the kit. Im sure you will have to request it.
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craigman · Posted: Tue Dec 22, 2009 10:54 am Post subject:

Ahhh,, nice to know! Cool

nextgen · Posted: Tue Dec 22, 2009 11:44 am Post subject:

As for the main topic being no one can do it better then the factory. Well if you read the Official work shop manuals they actually allowed several grams of intolerance and if I remember correctly the weight of a quarter was the reference used. When you have it balanced it has been done as close to zero intolerance as you can get..

Also you can be sure the factory did not balance all the parts bolted together as a unit.

As for the clutch pressure plate getting damaged and worrying about the new part not being balanced to the unit. My engine has 100k on it and the same pressure plate, actually the pressure plate was from a bus and who knows how many miles were on it.

But if you are a drag racer or really intend on torturing the engine OK get a spare balanced at the same time. Other wise I would not even give it an extra thought.
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Jake Raby · Posted: Tue Dec 22, 2009 12:05 pm Post subject:

Yeah.. The allowable differential in pistons can be as much as TEN GRAMS per set of 4!!

My spec is one half of one gram differential in the entire set to include pistons, rings,wrist pins and retaining clips all measured as a unit.
_________________
Jake Raby
Raby Engine Development
www.rabyenginedevelopment.com
"I've never given anyone Hell, I just told them the truth and they thought it was Hell"

nextgen · Posted: Tue Dec 22, 2009 2:51 pm Post subject:

Yep!! A quarter weighs 5.6 grams, so you say 10 Grams, wow!!

In my head I see a quarter glued on to two pistons of a set of four, that is crazy bad.

I think it is something nuts like that with rods too!!!
_________________
email: [email protected]
The TYPE IV UPRIGHT CONVERSION MANUAL
BEETLE MAGNETIC DEFLECTOR SHIELDS
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nsracing · Posted: Tue Dec 22, 2009 3:47 pm Post subject:

nextgen · Posted: Wed Dec 23, 2009 6:43 am Post subject:

Relax, I know the details, I said"To simplify the balancing story". I was trying to explain as simple as possible the parts have to balanced in conjuction with each other to get the best results.

Thanks for jumping in and giving the exact process.
_________________
email: [email protected]
The TYPE IV UPRIGHT CONVERSION MANUAL
BEETLE MAGNETIC DEFLECTOR SHIELDS
LETS TALK DUBS https://www.youtube.com/results?search_query=joe+cali+ghia https://letstalkdubs.libsyn.com/ep-200-joe-cali-ty...qI3xJTCzjs

nsracing · Posted: Wed Dec 23, 2009 11:13 pm Post subject:

WE do NOT want to mislead the flock now, do we? Very Happy

thepadawan · Posted: Thu Dec 24, 2009 3:38 am Post subject:

here to beat the dead horse.

last 2 type 1 engines I have done have been out over 50 grams,

one was 30 grams heavier in the nose then the rear

the other had a very weird heavy web, it litterly looked like someone for got to grind off a chunk of material between 1st and 2nd bearing.

I had a new set of H-Beam rods in hand that were off by 20 grams end to end as a set. one was perfect, one was 5 grams heavier in the tail, one was 8!!! grams heavier in the wrist pin (wonder what that would have done for the piston rings LOL). the other was 6, but still to close for percision racing products in my mind.

every part you get should be balanced, and anything you order that says is balanced should be checked LOL. Id rather waste 150 dollars in checking, then waste 2000 plus on being cheap.

just a side note just had a brand new c/w crank magged because I was concerned by some of the new equipment rolling out of brand name companies, and the BRAND new crank has a crack between the number 2 rod journal, So far I am waiting on a return from the company on what they want to do.

nsracing · Posted: Sun Dec 27, 2009 11:41 pm Post subject:

Well if it is a new crank, then they can swap for another one. Of course there is not guarantee on the next one. Might be worse or not.

That much unbalance on the set of rods? Pistons too? That is a lot of weight.

thepadawan · Posted: Mon Dec 28, 2009 1:11 am Post subject:

now imagine they are all fighting against each other at 6-7 thousand RPMS....

recieved my call back from that company, they will NOT be exchanging with me, as its been past 30 days since I have recieved the product, and it wasnt sent to them for inspection? WTF?


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