Engine balance question...

[Sandst4rm]

Hey all, just got my big series 1 back from the machine shop.

Balanced rotating assembly with 040 pistons rings and Spool H beam conrods. New balancer and they did something to the flex plate i think.

I asked them to replace the balance shaft bearings am unsure if they did or not cause it wasent on the invoice HOWEVER.
If i fit the balance shaft like i want to. (I dont think they modified it in any way) wont it make the balance WORSE? Since the overall weight of the rotating assembly has changed???

 

[losh1971]

I see no downside in removing it. I would either leave it out or just remove the drive sprocket. The BS is not needed.

 

[Skylarking]

I’ve understood that engine balancing was something done in engines of old because the manufacturing tolerances were a lot rougher back in the day. For example differences in piston e weights would be a big measurable difference. In comparison, modern engine components are much more accurate these days with parts batching making component tolerances even tighter so “balancing” isn’t a thing these days..

Having said that, a balance shaft itself takes away more of the inherent unwanted harmonics that would still exist in some engine designs (I4, v6, etc) even if the rotating assembly was itself as balanced as much as is possible. In that context you’d think the balance shaft itself would also need its counterweights trimmed to better match the newly balanced motor…

The fact many say that v6 balance shafts aren’t needed in road cars is confusing to me knowing manufacturers are cheap bastards and wouldn’t include bearings, balance shaft and gears & chains unless such was actually done for improved NVH reasons, a consideration that’s not relevant in race motors for example….

 

[MikeC]

The V6 cylinder configuration is inherently unbalanced. The three cylinders in a row causes a primary imbalance- balancing the rotating assembly won't fix that..
The V6 wasn't used in the days before balance shafts- leave it out and the engine will want to rock end to end as each piston approaches TDC. I'd keep the balance shaft but a lot of people on JC seem to have to removed them over the years with no ill effects.

 

[Sandst4rm]

Yes i know why its there thanks guys
I want to use it

concerned if it would make it run WORSE than removing it entirely cause it might put things FURTHER out of balance

 

[Immortality]

Balance shaft - Wikipedia

en.wikipedia.org

This goes into a lot of detail about various V6 configurations.

V6 engine - Wikipedia

en.wikipedia.org

The balance shaft doesn't change the "balance" of the rotating assembly itself but it's there to cancel out a weird harmonic caused by the cylinder configuration.

Early V6 motors were really bad for it because it was literally a V8 motor with the 2 rear cylinders removed but still in a 90° configuration. Then in the 80's they developed the even fire V6 with the offset big end crank pins but still 90° V6 with a balance shaft (and crap harmonic balancer) and finally GM went to the 60° V6 (the best V6 cylinder configuration) with the Alloytec.

And this one a full history of the little V6 that could (Buick)

Buick V6 engine - Wikipedia

en.wikipedia.org

To the OP, speak to the engine shop who did the work because engines can be balanced to different bob weights and these are changed on the V6 motor depending on if you intend to run with or without the balance shaft so its' best to find out how it was balanced.

 

[Immortality]

I’ve understood that engine balancing was something done in engines of old because the manufacturing tolerances were a lot rougher back in the day. For example differences in piston e weights would be a big measurable difference. In comparison, modern engine components are much more accurate these days with parts batching making component tolerances even tighter so “balancing” isn’t a thing these days..

Having said that, a balance shaft itself takes away more of the inherent unwanted harmonics that would still exist in some engine designs (I4, v6, etc) even if the rotating assembly was itself as balanced as much as is possible. In that context you’d think the balance shaft itself would also need its counterweights trimmed to better match the newly balanced motor…

The fact many say that v6 balance shafts aren’t needed in road cars is confusing to me knowing manufacturers are cheap bastards and wouldn’t include bearings, balance shaft and gears & chains unless such was actually done for improved NVH reasons, a consideration that’s not relevant in race motors for example….

All engines are "balanced" to a degree. Factory balance tolerances on production engines are a lot larger than for lets say blue printed race car engines.

But... then there are some really well known engine builders that say balanced to what? You could balance a engine perfectly but then when it's running you have this pesky stuff in the crankcase (oil) that tends to stick to parts which will change the balance of the parts in a running motor. One engine builder said +/- 2 grams is fine due to this fact (I'd need to find the source to confirm).

I'm sure if you compared a brand spanking new VN/VP and compare it to what we drive today (VN/VP) then that brand new car will probably drive "smoother" but then how smooth would that VN compare to a brand new VE alloytec? I guess it comes down to what people expect and or what you are used too. The Alloytec V6 motors don't have balance shafts so there are cases when clearly it's not required.

On the VN manual models there is a large weight hung off the end of the tail housing on the manual transmission because of the weird vibrations that motor had (with the balance shaft fitted) that would be felt in the transmission as well as a huge weight welded to the clutch fork (I believe the clutch fork would rattle against the bellhousing at certain rpm's).

I removed the balance shaft, fitted a proper harmonic balancer and combined with new engine mounts it was the smoothest I had ever had it (I can't compare to a brand new VN however). I also removed the mass off the back of the T5, why drag extra weight around?

 

[Sandst4rm]

Won't mine be blueprinted anyway when done?

It's had a RA balance, new cam bearings, block acid bath, tunnel checked and 040 grind to match brand new pistons, 030 grind on all crank journals, main caps checked, new conrods, new rings gapped to spec, new pistons, new wristpins, new ACL main bearings and conrod bearings to fit 030 that I will check with plasti gauge, getting new timing kit, have new timing tensioner S1 specific, new oil pump kit, new welch plugs, new lifters and pushrods, new double valve springs and stem seals due to age, new rockers if the roller ones i have my eye on work; at 1.7 ratio, every seal new, have new balancer, flex plate checked, *new balance shaft bearings I hope they did them at least, cam checked and gears checked.

Heads are recon already but is a NOS situation as had been sitting many years in engine shop storage; evident by plastic wrap disintegrating.
Considering having acid bath on them and reface due to the plastic being stuck to the face so i had to sand off with 1500 grit.
Also someone painted the runners on one of them without masking and the other is OK, obviously done at different times by different workers.

by my understanding that is pretty much blueprinted.

 

[losh1971]

BS' are just another thing to cause a rattle.

 

[losh1971]

If you haven't had them done already and you have the budget get those heads ported slightly. Engine builder spent about four hours cleaning up the ports on mine and doing bowls and it made a decent difference in torque and it smoothed up the power delivery after it was done.

I can't explain it well but for me it was like when I had my crank blueprinted on the two stroke race bike. Tt just reduced a lot of the vibrations when pushing the pedal hard. Basically on the VR it just pulled a lot more smoothly and just felt nicer.