Is balancing and line boring an engine really necessary?

[Silly Seville]

Hey Guys...

I'm looking for the opinions of those who have more experience with this subject than I, and would like to hear first hand accounts of your results. My issue is this; I'm having another SBC 350 rebuilt, and have encountered a number of different machine shop owners who disagree with each other on what is the proper way to prepare an engine for rebuild.

Several shops say that line boring (aligning the mains) of the crankshaft are unnecessary, while others say it is a "must do" procedure. Then I hear that weight balancing the rotating assembly is very important by some, while others say it's not important unless building a very high rpm engine. Basically, the impression I'm getting is, the mom & pop "redneck" shops are suggesting I slap the engine together without align boring or balancing, while the high dollar "NASCAR" builders say that if I don't have those things done, I am glutton for punishment due to the severity of the marine duty cycles.

Is there a DEFINITIVE answer to these two questions? Is align boring the mains, and balancing the rotating assembly of a MARINE engine totally necessary, or just padding the shops bill?

Your thoughts, experiences and suggestions greatly appreciated, since the above procedures add $500 to the machine shop bill.

 

[achris]

Re: Is balancing and line boring an engine really necessary?

Just my experience....

I have never had an engine line bored, but I have never had a bearing spin to make it necessary.
I have always had engines balanced. Even a 'slow revving' marine engine. The other process I would look at having done is to check the 'deck heights'. That is, the height of the piston at TDC against the top of the engine block. It's more common to be done to a diesel, but any engine would benefit. What that does is to ensure that the compression on each cylinder is the same. IMO just as important for a smooth running engine as balancing...

There you have it.... My navel...

Chris.......

 

[04fxdwgi]

Re: Is balancing and line boring an engine really necessary?

Like Chris said.

Line boring normally on a perfomance engine or if old crank came out looking bad w/ bad bearings, not oil related.

Deck height should be done on all engines, usually. (I do) It also assures the block deck height is parallel with the crankshaft line.
This ensures even compression across all engine holes.
Seen the decks off A LOT on some engines, making the comression all over the place. Some too high (ping), some too low (low power).

Ballancing on ALL engine rebuilds. The rotating assy (Crank, rods, pistons, rings, rod bearings, vibration damper, flywheel and timing chain gear) all need to be ballanced in relationship to each other, or the life expectancy of a rebuild and smoothness of engine will not be good.

 

[Bondo]

Re: Is balancing and line boring an engine really necessary?

Ayuh,.... Line borin', 'n deckin' the block gives ya a solid baseline block to build in,...

Balancin' the rotatin' assembly is money Well spent on Any motor gettin' rebuilt....

 

[Silvertip]

Re: Is balancing and line boring an engine really necessary?

The auto engine rebuilders and Mom/Pop rebuilders that say line boring, decking, and balancing are not necessary say that because an auto engine rarely sees 4800 rpm and when it does it is for a couple second blast getting onto an expressway or passing grandma to show her how she should be driving. A marine regularly sees much higher rpm for long periods of time so as long as the engine is being worked on, these extra steps are well worth the money and you will be rewarded with a much better engine.

 

[gm280]

Re: Is balancing and line boring an engine really necessary?

I'm for doing all those things if you have the funds available. I have had engines balanced with every rebuild...period! Line boring and decking are more of the same issue in equalizing output power from each cylinder. Another good building issue is to have the heads CC’d as well. Make each combustion dome equal in volume by CCing them too. Your total goal is to try and make every cylinder perform equally in every respect. Then each cylinder contributes equally to the total power output and no one cylinder is pushing another along so the power is use as output power. So, yes, do all those things and anything else to help with equalizing all cylinders AND reducing internal friction. That is what all engine builders are seriously trying to achieve... I’d rather have a lower HP output engine completely balanced and all cylinders equal then an unbalanced high HP engine that is fighting itself to perform. Guess which one will crap out first...?