ok, so im in need of a new crankshaft. i don't plan on changing anything on the engine except the crank. if i buy the exact same one that was on my engine, does it still need to be balanced? i just want to make sure so i know, thanks.

 

yep it should be. Most factory type cranks come balanced to the factory bobweight but they are all different.

 

Too many variations to be exactly the same. Even buying a new set of pistons, there's no guarantee they'll be exactly the same as the old ones or even exactly the same in the same batch. Buying any kind of replacements means it won't have the same balance.

Depending what rpm you regularly spin the engine to, a re-balance may not be necessary but would be recommended.

 

my engine is about 10000 miles old, rpms generally around 1700. (once in a while i will hit the gas). do you think i can install it and be fine enough to drive a few miles to a shop to balance it? oh and (sorry one more question) do you happen to know a ballpark price on what a balancing costs?

 

Balancing cost depends on how much adjustment is needed. Expect to spend around $500.

Keeping the engine at constant low rpms with short medium rpm bursts shouldn't need re-balancing unless the weights are really different.

 

can i measure the two different crankshafts weights on like a scale that people use? lol. oh and do you know how much weight difference is too much without balancing?

 

The throw weights are adjusted to the bob weight of the reciprocating assembly. You need a machine to spin up the crank with the proper bob weight on it then add or remove weight to balance the crank. Adding weight puts a heavier mallory weight into the throws at specific location to balance the weight.

It's just not something a person without a balance machine can do. There are times when the machine is telling you to add weight where there isn't a throw to put any weight. You need to know how to adjust weight to compensate for that.

When I had my engine balanced, the crank was spun up 12 times before the balance weight was absolutely perfect but it's also a race engine spinning well over 7000 rpm.

 

oh no i wasn't planning on adding weight or anything, i just want to know if there is a small enough difference between the cranks for me to get by. or are you saying that the weight can only be measured by the machine?

 

Can you balance a tire by putting it on a bathroom scale? A crank needs to be spun up to see where balance weight needs to be added or removed based on what the bob weights are. It's got nothing to do with how much the crank actually weighs.

 

What is wrong with your current crank?

-- Joe

 

harmonic balancer fell off on my on the highway (someone tightened it too tight i assume) and that falling off caused the crank to be damaged

 

My suggestion to you would be to replace the engine with a used engine, or rebuild the whole thing. I wouldn't try just changing the crank.

What is it anyway? 305? 350?

To balance it, the crank is put on a machine. They don't balance it in the motor, so no you cannot drive to a shop and have it balanced. You also need to take the engine completely apart to change the crank. If you took it apart, I'd have the block checked as I suspect the caps/journals will be shot.

-- Joe

 

its a 305. actually just getting a different engine sounds kind of nice since i wont have to take the whole thing apart.

 

With this economy, you should be able to find a 350, 355, etc for short money on craigslist. strap on a set of L31 vortec heads, an intake and go have fun.

-- Joe

 

thanks for the advice. one last thing though, if i switch from 305 to 350 and their both carb'd, do i need to change anything to make it work? can i just put it in like im doing a 305?

 

A 305 and 350 of the same year are externally identical.