Balance Shaft - What is this?

Overall, I would never remove or disable the balance shaft just for the hell of it. It's worth having IMO. Only when it inhibits power, should it be removed and that would be when you must use a double timing set which would be if you're going to run a moderate to aggressive cam requiring something more than 105lb valvesprings. Not many of us fall under this catagory.

^ Agreed. I think disabling the balance shaft would cause more vibration than most would consider acceptable, and possibly damaging engine mounts. In one published source, it says an odd-firing V-6 (without balance shaft) had such prominent harmonic vibrations that it actually destroyed an engine dyno connected to it.

I have driven several 3800 cars with no balance shaft and would not do it to a street car. If you are making a big cam build, and a double roller is required, well do what you have to do, but that's where I draw the line on my DD. I did not like the vibrations at all. I considered them unbearable, considering I want a luxurious feel to my vehicle. The non-BS cars I drove also had uncomfortable additions like poly engine mounts and such, which didn't help the feel any. Perhaps our engine/trans mounts can absorb more of the shake.

I don't believe a double roller chain is required until you get into the stage 2 level and above cams. The XP and S1X I have seen many many run with a single roller and no detriment or longevity issues. I'm not sure what timing chains they recommend for those cams though. I would guess it depends on your desired RPM limit and valvespring rate.

Thanks for all the info guys. The balance shaft stays and i just need to inspect my chain and tensioner to see if they are worn and at minimum just replace tensioner and put a quality chain on it.

i read somewhere that a balanced crankshat would cancel out the vibration problems associated with the B.S removal
anybody heard of that?

Our crankshaft is balanced, but that's no enough on a 90º V-6. we need the balance shaft also. Some 60º V-6s can get away without the balance shaft.

That's one of the disadvantages to chopping off two cylinders from a V-8 back in the day. Sure saved a lot of money for GM over the years, though.

just read an article over @ ZZperf, and they recomend removing it.they claim NO damage to the engine,and it increases high RPM performance.

From Wikipedia:

While an inherently balanced V6 engine would have either 60 or 120 degrees angle between the two banks of cylinders, many current V6 engines are derived from older V8 engines, which have a 90 degree angle between the two banks of cylinders. While this provides for an evenly spaced firing order in an 8 cylinder engine, in a six cylinder engine this results in a loping rhythm, where during each rotation of the crankshaft three cylinders fire at 90 degree intervals, followed by a gap of 90 degrees with no power pulse. This can be eliminated by using a more complex, and expensive, crankshaft which alters the relationship between the cylinders in the two banks to give an effective 60 degree difference, but recently many manufacturers have found it more economical to adapt the balance shaft concept, using a single shaft with counterweights spaced so as to provide a vibration which cancels out the shake inherent in the 90 degree V6.

The ZZPerf and others talking about pulling the balance shafts from the 3800 have the luxury of not having to warrant the work of those who take their advice. It won't blow up the engine immediately if you do it - but anything setting up permanent vibrations versus this tradeoff (~10 HP) well, with the other 240 horses available I think it's not a bad tradeoff at all.

I agree with radomirthegreat Link that removing the balance shaft isn't really a performance modification. I'll go further to say that if I was driving a car for more than weekend fun I wouldn't do it, and that as long as you're going to do it consider replacing the timing chain if your mileage is up there, say 150K plus. Also, referring to comments in the link, seriously consider replacing or reinforcing the engine mounts if you do this, to deal with the vibrations. I am not saying the engine will shake itself apart, just that it *will* shake and with weak mounts you're not going to get as much of the 10-15 horses that you supposedly gain to hit the wheels, some will go to hitting the shaker.

I agree with Albert, though there really isn't any physical danger to the engine. These 231" engines originally had neither the balance shaft, nor the "split-pin" crankshaft... I remember looking at one idling in the mid-70's, and I couldn't believe how much is shook back & forth on it's big, loose motor mounts.

It became much more civilized with the introduction of the split-pin crank later on, which made it "even-firing", and the balance shaft finally gave it "Buick smoothness".

You can remove your exhaust system for a few HP, too, and it won't hurt the engine - but you wouldn't want to live with it.

Eldo wrote:

I agree with Albert, though there really isn't any physical danger to the engine. These 231" engines originally had neither the balance shaft, nor the "split-pin" crankshaft... I remember looking at one idling in the mid-70's, and I couldn't believe how much is shook back & forth on it's big, loose motor mounts.

It became much more civilized with the introduction of the split-pin crank later on, which made it "even-firing", and the balance shaft finally gave it "Buick smoothness".

You can remove your exhaust system for a few HP, too, and it won't hurt the engine - but you wouldn't want to live with it.

When I installed a custom, T304 stainless exhaust the noise/drone was not terrible but the constant vibration played hob with the car's electronics, loosened a connector -- nothing terrible critical or irreversible but truly a nuisance. When I sold the exhaust to another Riv owner it was modified a little before reinstall to get rid of the first harmonic created by the downpipe-resonator link--among other things put in a flexpipe IIRC. This is why I mentioned if you're gonna remove the balance shaft you want to check the motor mounts. What I did not say is that you'll end up filling them with urethane (3M window caulk) because the Riv's little gumband OE mounts are not going to last all that long with an unbalanced 3800.

The original 231... another thing I don't know is what crank grind was on those compared to the current 3800, for instance. And finally, that engine has an inherent imbalance that without a balance shaft can't be hidden.

By the way, 231 cu. in volume will hold about one gallon of water.

Albertj

albertj wrote:

By the way, 231 cu. in volume will hold about one gallon of water.
Albertj

Wow, that's funny... Turns out that 231 cubic inches is exactly 3.785 liters, or 1 gallon!
(Fascinating, Captain.)

you could call the sc 3800 engine "gallopin' gallon"

Naah.

Albertj

The urinals in many public restrooms say "3.8L per flush". I can't help but think of the 3800 every time use a facility!

Quote :

Also, referring to comments in the link, seriously consider replacing or reinforcing the engine mounts if you do this, to deal with the vibrations. I am not saying the engine will shake itself apart, just that it *will* shake and with weak mounts you're not going to get as much of the 10-15 horses that you supposedly gain to hit the wheels, some will go to hitting the shaker.

And here exists to whole reason for using a balance shaft. In the past, GM has actually used extra soft mounts on unbalanced engines to reduce the vibration levels in transferred to the chassis (ex: Vega 1.4L). What they found was the softer mounts wore out more quickly, causing an even greater problem. So, they use the balance shaft in some engines not only to smooth out the vibration, but to extend the life of softer mounts. Imo, you would not want to run "firm" mounts without the balance shaft. The amount of vibration may not be damaging to the engine, but it could rattle the car enough to damage interior components (think electronic solder connections, interior panel fasteners). I would guess it would be quite loud and intense for the driver as well. But I haven't tried it, so can't be sure. Maybe test it out and report the results?

I have driven an L67 W body car with a bigger cam, no balance shaft and poly mounts all over it. I did NOT like it for use as a DD car. It was fast, but clearly marked the difference to me for a street built motor vs a motor built for racing. In a street driven car I wouldn't go for a cam bigger than the S1X or XP cam, as that's the threshold at which they want double roller chains, which means no balance shaft.