Do you have to re-balance crank when you oversize pistons?

BrianF3D

Member
Joined
Jun 23, 2019
Location
Cleveland, Ohio
TDI
Jeep XJ 1.9 swap WIP and 2014 JSW tdi 6 speed
New here forgive me for my ignorance.


Is it a general rule of thumb to re-balance your crank when you do oversize pistons?


Have ALH block and getting .20 over nural ASV pistons.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
No, a balancing of the rotating assembly (which would be EVERYTHING that is spinning... crank...pulley...flywheel) is typically done with race engines that are spinning at super high RPMs.

Rule of thumb with VAG engines: the specifications and tolerances from the factory are VERY good, right out of the box. The TDI is far to slow spinning not to mention fat and chunky to worry about anything beyond what the factory already did when it balanced your crankshaft when it was manufactured.

You just want to make sure the four pistons weigh the same, and the four rods not only weigh the same but are the same length (this is why VAG batch builds rods, and stamps them with a number, so when they grab X number of rods for an engine, they grab them from the same bin so they all have the same number).
 

BrianF3D

Member
Joined
Jun 23, 2019
Location
Cleveland, Ohio
TDI
Jeep XJ 1.9 swap WIP and 2014 JSW tdi 6 speed
So ill have the pistons assembled with conn rods balanced at the machine shop. that was a fast answer thank you.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
I would not even bother with that (assembled). If the 4 rods are the same, and the 4 pistons are the same, then the 4 assemblies will be the same. And these do not have any pressed in wrist pins or anything, they are floating pins with circlips, so nothing special that you'd need a press fixture to install them.
 

Mongler98

Top Post Dawg
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Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Just weigh each part and match them up as best it can be so the sum of each set is close enough. TDIs dont rev very high, there really no need to do any additional balancing other than matching.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
For the sake of sanity, weigh the old ones as well, try and match the weights to each cylinder that they came out of.
 

Festa

Veteran Member
Joined
Aug 14, 2016
Location
South east uk
TDI
Vw t5 van
I got the rotational stuff balanced on my 5 pot pd and it did rev quicker. However I didn't balance the stuff again since I now have oversized pistons but instead I've removed just over 22 grams from the new pistons which are now lighter than my old pistons by 2.5 grams. It saves adding heavy metal back onto the crankshaft to account for the heavier pistons. I also have forged rods which are 90 grams lighter than the oe rod so I guess that running lighter you can remove more material from the crankshaft.
 

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
For the sake of sanity, weigh the old ones as well, try and match the weights to each cylinder that they came out of.
no
match opposing cylinders

1,3
2,4
or
1,2
3,4
depending on which pistons are closest in weight

when one goes up the other of the same mass goes down
crank gets balanced neutral
rods get matched same as pistons

I've done it both ways, tossing an engine together with stuff untouched and then later on taking the time to balance the stuff (took a lot of metal off one of the pistons to get them right)
Same engine, same everything, just had to cut the pistons for lower compression so took the time to balance everything. It didn't make a noticeable difference.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
no
match opposing cylinders
1,3
2,4
or
1,2
3,4
depending on which pistons are closest in weight
when one goes up the other of the same mass goes down
crank gets balanced neutral
rods get matched same as pistons
I've done it both ways, tossing an engine together with stuff untouched and then later on taking the time to balance the stuff (took a lot of metal off one of the pistons to get them right)
Same engine, same everything, just had to cut the pistons for lower compression so took the time to balance everything. It didn't make a noticeable difference.
Yea, 100% with that, that's basically what i meant.
 
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