escargot

I understand how V and H (opposed) engine configurations are balanced by having cylinders fire in the right order...

However I don't understand how some people can have their engines balanced. Does this only involve balancing the crankshaft, or is there more too it? Shouldn't it come balanced perfectly from the factory? Is there more to balancing an engine?

A friend of mine has a father that was stationed in Berlin during the cold war. He had an MG that he drove around, and eventually the vibrations got to be such a problem that he took the engine to go get balanced. He said some crazy German perfectionist had it for two days, and when he got it back it was the most smooth running engine he's ever had the pleasure of driving. He now owns a 2002 Mercedes C280, and he still thinks the MG was smoother. I understand much of this might be the fast switch from vibration to smooth, and his love for that car... but how does one balance an engine so perfectly!?

-Mike.

paulroad

They were all out of balance. It was all cranshaft, and pushrods... (no overhead cams). this was all at the bottom of the engine and the cylinders on top of them.

It has very little to do with the firing order and more to do with the weight of the crankshaft going around and the pistons occilating back and forth. TWO OPPOSITE MOVEMENTS, causing all kinds of vibrations.

IE: Cyl 1 Fires at 12 o'clock, cyl 3 is at 15 minutes past, cyl 4 is at 12:30, and cyl 2 is at 12:45. They all stay 45 degrees appart from each other. BUT, at the opposit end is the cam shaft, pushing the pistons. The weight of the cams is not always equal to the weight of the piston. Add to this the force of combustion.. the explosions of gas and you have even more out of balance problems.

The MG you spoke of, most likely had weights added to the cams, (or some metal removed)... kind of like balancing your tires.

In the 70's, Mitusibishi solved the problem with an often used device called the COUNTER BALANCE SHAFT.. Trademarked as THE SILENT SHAFT ENGINE... it was a secondary cam shaft with weighted cams, that was powered by the engine and, it rotated in a direction, opposite the engine. and was sequenced to "balance" the vibration of the engine itself..very succesfully.

Now we have overhead cam engines, this too balances todays power...

I hope I was clearer than mud....

sportQ

for the 944 motor.

A400

Unless you mean the cam pushing the pushrods via the buckets I am completely lost. My machines have the crankshaft pushing and pulling the connecting rods which are connected to the pistons via gudgeon pins in the skirt. What type of engine are you referring to?
Rod

paulroad

The CRANKSHAFT cam not only pushes the pistons up and down, but they also push on the "push rods" these pushed on the rocker arms, (see-saw) which in turn pushed open the valves.

All the action came from the crankshaft.

A400

Thought you meant the camshaft was actually pushing the pistons??

paulroad

<center><img src="http://pictureposter.audiworld.com/63674/engine.jpg"></center><p>
This is a conventional NON Overhead cam engine.
It does use a valve cam that connects to the push rods, etc.

There were also older engines.. primarily 4 cylinders that did not have the secondary cam shaft. In this cas the push rods went all the way down to the cam on the crankshaft.

cuatrokoop

4cyl's tend to need a good sized vibration damper or harmonic balancers to make them "vibration free" from the factory. To balance an engine would be time consuming at the factory, and not worth the additional costs. A balanced engine is one that has had its crankshaft counterweights balanced to match the attached piston/rod combo (done dynamically, material removed). They do rev smoother, with much less vibration than a stock engine. This is true for ANY reciprocating engine.

MikTip

Did you know, only a rotary engine can be perfectly balanced? ;O)

A400

This must be a language problem. I cut my teeth on these engines and cams dont push pistons, even in your pic. Which is exactly like all the ford gas engines I grew up on. Never heard of a crankshaft cam??
Rod