Piston balancing?

[twentyeight]

I'm rebuilding a 1Z with ALH pistons to go into a Eurovan. I neglected to have the machine shop weigh my pistons, so I'm dealing with it now. If I balance all of pistons (sans pin) and swap pins around I can get the whole piston/rod assembly within 300mg, and 1/4 & 2/3 will be identical.

Charts at the end of the page here: http://andrewclink.com/projects/thebus/rotating-assembly

1) Can I drill the underside of the piston between the pin bosses to lighten them? Can I get 3 grams out of them there?
2) Can I switch pins or are they a matched set in terms of fitment? These are brand new .5 oversized Nüral ALH
3) Is this worthwhile, or am I close enough without messing with it at all? It'll probably spend most of its time around 2600-2700 (66-68mph).

 

[oilhammer]

I've never messed with balancing these on any engine build I have done, because they are pretty heavy to begin with being chunky diesel parts, and the engines don't spin very fast. Think of any differences in terms of a percentage of the total piston weight.

On gasser engines I have always had our machine shop take off some of the inner skirt underneath to get them closer.

Others will chime in with their experiences.

 

[twentyeight]

When I added up the assemblies for 1&4 vs 2&3 they were within 700 mg of each other. Even 6 grams difference is 0.4% of the total weight of one assembly, and 0.1% of all four assemblies.

I also was told that the pins can't be swapped even on new pistons.

So all in all, I just went ahead and installed them. I haven't torqued the rod caps to yield, so if someone tells me my dog is going to catch fire before the head arrives I'll pull them back out. Otherwise, I'm satisfied.

 

[bobbiemartin]

I would say 1 gram is not bad, even 2 would be OK. 1/2 gram if you are racing. If you didn't balance the rods, I wouldn't worry about 2 grams high to low.

 

[blimo]

Matching Piston Weights

You can take weight off by removing casting flash & casting marks underneath the piston.

You can also remove sharp edges on the inside edges of the skirt, and pin bosses. For more serious weight loss, you can remove material symmetrically by rounding off the bottom sides of the pin bosses.

Once you have finalized your ring clearances, you need to add the rings + pistons + wrist pins + pin retainers and match total weights (you may be able to chamfer inside edges of wrist pins to drop a bit of weight, too).

Top and bottom ends of the rods should be made to weight the same, as should the total rod weights.

 

[DieselCecil]

Speaking as a former, professional engine builder:

1. If you haven't balanced a set of pistons before take them to a shop and let them do it.....right. If you take metal off the wrong area you're gonna REALLY regret it. What's it going to cost you - $25-$30??? But no one with their head screwed on straight will drill a piston to balance it. Drilling produces sharp corners that will lead to fatigue and breakage.

2. You NEVER balance just the pistons, you balance the pistons, the rods (one end at a time) and rod and piston together. THEN you balance the crank with the combined weight of the rods and pistons so your entire "rotating assembly" is balanced. REALLY balanced! Otherwise you're just blowing smoke up you-know-where!!!

3. And if you don't balance the crank why balance anything else?

4. You NEVER swap parts, leave out something (like the wrist pins) and balance it. If you do how "balanced" do you think it's going to be?

Get it done right, or don't even do it. You can get a V-8 balanced at a real shop for under 4150, so what's a 4 banger gonna cost you?

 

[DieselCecil]

FYI - About 30 years ago I read that ONE ounce out-of-balance will produce several pounds of counter-force!!!

Now how important do you think balancing is? Even on that 3000 rpm engine?

And another thing about diesels - in all the reading I've done on automotive forums over the past 10-18 years NO ONE says a thing about porting the heads!!! I guess they all think that just because they have big thing on the engine that blows air into it they don't need to port the head?

My response to that is have someone wrap their hands around your throat and see how good you can breathe!!!!............even if they blow down your mouth!!!!!!!

You can have a turbo that huffs 100 psi, but if your intake and exhaust ports aren't opened up to let the air FLOW, you're just wasting your time.

Bottom lie is - "psi" doesn't mean "volume".

 

[oilhammer]

Actually, people HAVE done head porting on TDIs, and found that there is little to be gained, because the amount of extra material that can be removed before you go into the water jacket is very little. At least on the engines that have both intake and exhaust ports on the same side of the head.

Given that you can TRIPLE the output of an 8V 1.9L TDI 4 cylinder with a 100% stock casting on the cylinder head, and run into trouble with clutches and axles being able to handle the power as well as having a tough time getting that power to the ground through only two wheels, I'd say that messing with the cylinder head isn't going to do much and isn't worth the effort.

Also, unlike domestic V8s with designs from before the space program*, VAG's modern engines are very well balanced from the factory by using extremely tight tolerances in the manufacturing process and "batch assembling" of the components. Our machine shop is always amazed at how well matched the components are on a run-of-the-mill engine produced by one of the world's largest car makers even after that engine has allowed the car to cover some 1/4 million miles. I've dorked around with quite a few Pontiac and Chevrolet V8s in my younger, dumber years, and none of them were build so tight as the VAG engines.

*I do realize, that while the Pontiac, Oldsmobile, Buick V8s are long gone, the Chevrolet V8s that were currently have in new(er) cars is indeed a thoroughly new design and shares virtually nothing with the old design. Those are pretty good engines.

 

[p0wer]

Actually, there is quite much of benefits on TDI head porting and better cam when doing it right, that´s not big effort either ( we have lots of places doing it here for few hundred euro ). Depends what you are heading too. You will not see 300 or 400hp outputs easily with unmodified cylinder head, also bigger turbos spool up much faster and you can use bigger compressor without stall because of better flow too. But on these 200hp engines with small turbos, benefits are just almost nonexistent.

Piston balancing on quite stock TDI ( below 200hp ) isn´t any benefits i can say. When you rev up to 6500-8000rpm, you could count for this issue too. For example, haven´t seen any importance on ~400hp 6000rpm engine yet. But when you change pistons and rods, you should be sure they are quite same weight than original ones are.

 

[Digital Corpus]

To the OP, here are my adventures with a newer generation piston in an older generation block:
http://forums.tdiclub.com/showthread.php?t=402877
http://forums.tdiclub.com/showthread.php?p=4391194
Be advised that I've mixed and matched the wrist pins. Due to where the weight is, you won't find that much savings from the aluminum on a piston so I'd advise lightening a wrist pin to compensate. The con rod will 'view' the mass reduction the same way.

 

[twentyeight]

Thanks! I've read both of those

I was considering balancing the wrist pins and will likely do so when the build continues. That seems a lot safer than modifying the piston itself. However, it's currently on hold because it appears that the machine shop ruined my block.

 

[bhodgkiss]

There is so much info here on porting heads Im not sure where you've been reading...and lots of people showing gains.

My engine felt much better after porting. No dyno results, but revs more easily and reduced smoke for the same fuel.
Ive also done the same tunes for people with the same hardware mods but with no porting, and I've had to back their fuelling off to due smoke....

Also, an ounce out of balance (28g) will easily gives lbs of counter force, that's just maths

Edit: Hold on, the guy above has been banned from this forum? I did see lots of his silly postings....

 

[john.jackson9213]

Edit: Hold on, the guy above has been banned from this forum? I did see lots of his silly postings....

Likely several somethings he said on the Dieselgate thread. Noticed a few people there not playing nice got banned.