OK I have a 350 small block in my rod now out of a '79 truck. I'm trying to save some space between the radiator and motor. I would like to know I can change the harmonic balancer to a smaller one that I have off a 283 small block. The balancer on the 283 is about a 1/4 of the size in thickness. I've gotten two opinions on it and was told it will work because the motor is internally balanced. Has anyone done this or know if it will work? The 283 motor is from a 70's, maybe like 60's nova.
usually won`t be a problem, there are a few aftermarket ones for the 350 that are very thin like the one you want to use, so, i don`t think thickness is really an issue....
Yes it will absolutely work.We do it all the time to put 350s in early chevelles.You have to,or get to use the short water pump then
The balancers will interchange but will still have the same final length. All the difference in thickness only happens on the backside. If you don't already have a short water pump, you can gain space with it and matching pulleys.
Watch out for the timing marks on the balancer. The early and late Chevs balancers had TDC marked at different spot. You will need to buy a "timing tab" bracket for the older balancer (it bolts on using two timing cover bolts). When mixing and matching, it would be best to verify TDC and then use the appropriate timing tab.
I wonder why chevy went to the expense of adding all that metal to the torsional damper when the increased the stroke of the crankshaft to 3.48"? Must be a good reason...they didn't make things more costly if they didn't have to.
Ive always been told not to put an early (small dia.) balancer on a larger displacement engine if you plan to rev it. Probably wont hurt on an engine thats babied, but not a good idea if you plan to flog the snot out of it. Like Squirrel said, balancer diameters increased with displacement for a reason. When the power output of some engines increased, the balancer diameter also increased.
This is due to the increased harmonic vibrations. Increasing the size of the damper increases the inertia. The more inertia the better the ability to dampen. Now of course there are high end limits as well. Obviously you cant stick a 500 # damper on the crank.
If you remember they added a larger balancer when the '64 365hp (and 375FI which was the same engine just adding the fuel injection) came out. This was to dampen a harmonic vibration that occurred above 6,000 rpm which this engine easily reached even in production form. Harmonic vibrations occur at multiples of the lowest harmonic i.e. a harmonic vibration that occurs at 2,000rpm will occur again at 4,000 and once again at 8,000. or in the case of the 327 at 3,000 (approx.) and again around 6,000. In drag racing you pass through the rpm ranges so fast that it doesn't matter if you have a more massive balancer (thus you see the use of smaller mass balancers on high RPM drag engines) but in oval track and road course (this also includes street driving) you can spend longer periods at smaller rpm ranges and a harmonic vibration will tear an engine apart if left unchecked for too long. Frank
Thanks for the insight Frank. Chevy put the bigger dampers on all the 350s, street motors included. I wonder why they did that? Could it be related to the switch to cast crankshafts at the same time? or that combined with the longer stroke? Did they expect all their 350 engines to eventually be used in race cars?
Don't forget to leave enough space for a fan. Aren't all 350's internally balanced? The damper in your case is just a mounting suface for the crank pulley, so any internal balance damper should work.
400 was the only sbc in 1979 that was not internally balanced. Crankshaft and bearing life is a separate question.
I use the smallest lightest balancers on my race motors (circle track) and spin 68-7200+. They are all well balanced though
thanks for all the input, the main reason I wanted to go with the smaller dampner and short water pump was to have enough room for an electric fan.
Aren't all 350's internally balanced? The damper in your case is just a mounting suface for the crank pulley, so any internal balance damper should work. BINGO. That's why, if you use a 350 block and aftermarket stroker crank, you must use a 400ci balance damper
If you go to this website and pick out a fan, click on dimensions and a new page will appear that gives you the exact dimensions with drawings. Not all, but most have dimensions available. Click here: The Fan Man
The damper is NOT just a mounting surface for the crank pulley. A damper is actually TWO things. The center, or the hub, is normally used to mount the crankshaft pulley. The outside ring is the "damper". It is a "resonant" device that is intended to cancel out the torsional vibration (twisting) that the crankshaft experiences due to the inertial forces of pistons changing directions in milliseconds, combustion impulses, etc. That rubber polymer which bonds the hub to the damper ring is designed to flex near or at the same frequency the engineers calculated the worst crankshaft harmonics to be. So is it a good idea to interchange dampers? Probably not, but it is done all the time, and most engines that it is done on survive without incident. By the way, an engine with PERFECT dynamic balance still has torsional vibration when it is running. One more point. The dampers on the externally balanced engines provide the two functions mentioned above, but also provide a third function. Think of it as a "wheel weight" (along with the flex plate balance weight on the other end of the crankshaft) to help balance the rotating assembly.
This is unlike an internal balance configuration where the harmonic dampener or flywheel do not contribute to the balance of the crankshaft and are not required to be installed when the crankshaft is balanced.
The front mounting surface of the balancer will be the same on any of the sbc balancer. If you have room for it I'd leave it and just put the short pump and correct pulleys on. That will mean you also have to move the alternator to the drivers side (US) of the engine or buy special brackets for the right side with the short pump. Guys usually swap to the smaller balancers for clearance between the balancer and the crossmember on some vehicles. Or as stated by a couple of the guys previously for rotating weight reduction. I've seen central Texas dirt trackers just run the hub but that is pretty iffy for anything on the street.
Other than the flex plate and the damper playing a role in the dynamic balance of the rotating assembly, it is EXACTLY the same. Do not confuse "harmonic balancing" with "rotating assembly" balancing. They are two completely different things. I don't know who first started calling the harmonic damper a "harmonic balancer", but they sure have caused a lot of confusion with what the real role of the damper is.
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