Balance shafts on four cyl. engines?

[Sparky]

I will admit that i dont have much experiance with four-bangers but im starting to look into my future Volvo P1800 upgrade.

 

I did some research, and found the B234f 2.3L DOHC four banger that I think would be a great upgrade to the little P series. but I have a question about it.

 

the engine has two balance shafts on either side near the oil pan driven by a belt. how reliable are these things, and why use them?

 

the Sr20 or Ca18 can live without them right? so why cant this engine? is it a problem in basic design?, kinda like a bandaid fix? from what I understand, they just added a DOHC head to an existing B23 four banger, would adding this head have caused a balance problem.

 

anywho, what im really trying to get at, is WHY a balance shaft? Pros?-cons? I personally dont like the idea, thinking that its just two more things for the engine to spin around.

 

anyone care to set me straight...or just filled my head with info?

 

thanks

[Guest Dan0myte]

Balance shafts aren't required on any 4 cylinder, but the engineers of an engine will sometimes add them to the design for the sake of luxury. Four cylinders are naturally unbalanced and do shake a lot, it's inherrant with the design. The way the crankshaft moves to two sets of pistons (1&4, 2&3) on the expansion stroke causes two distinct movements of the engine block in opposite directions. If timed correctly, a shaft with a large weight on one end can be spun in the opposite direction of the crankshaft, counteracting the shake. Since there's two sets of movement, there has to be two balance shaft to counter each distinct movement.

 

It's a lot of work for them to engineer these things into the block, as it requires extra room to be made for them, extra oiling, and more timing belt usage. The end result is a smooth, 6-cylinder feel to the engine though. Four cylinder engines with balance shafts usually find their way into higher end cars and cars which require a bit of luxury in them.

 

And you're right, a lot of cars with 4 cylinders do not have balance shafts. But these cars are built for sports performance or trucks and will not need a super smooth engine, so a little shaking is ok. That's the other problem with balance shafts is that each one sucks a little power away from the engine. By not having balance shafts, the engine spins more freely and has less parasitic loss. Just remember that balance shafts need oil to spin, so if you remove them, the oil paths will be left wide open and you will lose tons of oil pressure. These balance shaft oiling ports must be blocked if the shafts are removed.

 

So the pros: Smoother engine.... that's about it

 

and the cons: Horsepower loss, Extra weight, Belt that drives them can break and cause damage, Slower reving engine

[Guest Dan0myte]

Just some useless facts,

 

The Dodge Daytona/Chrysler Laser used a 2.2 litre engine in the beginning which had no balance shafts. Later, they increased displacement to 2.5 litres and added balance shafts. Older buyers of the car were happier because the car rode more like a high end car, but performance drivers didn't like it because it sucked away power. The 2.5 litre put into the Caravan/Voyager didn't have the balance shafts, so a lot of people swap this engine into their Daytona's for extra power.

 

The Eagle Talon/Mitsu Eclipse engine had balance shafts to keep it close to the smoothness of it's bigger brother, the Dodge Stealth/Mitsu 3KGT twins. The little belt which drives the shafts is weak though and breaks under high RPM and can cause the timing belt to break, so almost all performance DSMers remove the balance shafts now. It frees about 10 horsepower and the engine loves the extra oil pressure that is freed up afterwards.

 

The Neon SRT-4 has a 2.4 litre, which has a balance shaft setup built into the oil pan. People however do not remove it because Dodge designed the engine with such a huge rod to stroke ratio that the vibrations without balance shafts would be unbearable in a street car.

 

The 2.5 litre in the Nissan Sentra SE-R has balance shafts, and people do remove these because the engine has a decently short rod and good natural balance so it doesn't really need them.

[Sparky]

cool, thanks for the info.

 

I really need to go to the junkyard and check that engine out. the width at the bottom because of the balance shafts my cause some frame rail contact. if that happens than i cant use that engine anyway.

 

Im not sure what the R/S ratio is, I will have to look into that. Im just now doing some in depth research into the Volvo project, so i have a good deal of time to get it all sorted and on paper before I take out the tools and start wrenching.

 

thanks again for all the great info! Gotta love this site!

[datsunlover]

I see the word "Volvo" and I have to pipe up As stated, the balence shafts give a smother running engine, and since most Volvos that got this engine were the higher end luxo' models, you can understand the need for a smooth runner. Not that the 16V engine was a slug though.. I believe it had almost as much HP as the 2.3 Turbo engines Volvo used.

Personaly, I would go with the 2.3 Turbo engine, as they are reliable and for the most part bullet proof. Good strong turbos/engine, and easily modded to get some more HP. I don't know for sure, but I think the 88-89 740 Turbo models were the best motor (stronger internals/block) and I don't think the 16 valve motor was used as extensivly as the turbo... might make parts expensive. You shold try 'www.turbobricks.com' (or some variation of that) Theres lots of good info out there on the web!

[Sparky]

your right about the 16V B23 having as much HP as a the 8V B23T. thats one reason that it is much more appealing to me than the 8V B23T. Im building this Volvo to be a nice Sporty car that rides smooth, and quiet, but can get out of its own way in a straight line as well as through the curves. I have several goals for this car, and one is a smooth FI DOHC turbo engine.

 

I have been looking into the possibilty of getting the B23T block and then just adding the DOHC head, according to all the info i have found, its the same basic block for both.

 

But still, its all up in the air, I have just only scratched the surface regarding the amount of research that I most do for this project. having just drove an RX8, I must say that a rotary would be really cool, but I must build this P1800 using all Volvo parts, the owner must be able to take it to a Volvo shop to have anywork done that it might need. the last thing he wants is to have to take it to some high $$$ guru because the engine is nissan, the brakes are wilwood the rear is S15 and the wiring is full custom.