Thread: Engine problem

Originally Posted by Fivefingerdeathpunch

It's not about being TTY or any of that stuff.
There are three basic reasons for line boring the main bearing and cam bearing bores in engine blocks. One is to restore worn, out-of-round or damaged bores. If an engine overheats or loses oil pressure, one or more bearings on the crankshaft or camshaft may seize and spin. The resulting damage to the bearing bore must then be repaired by either machining the hole to accept a standard sized bearing or an oversized bearing.
With main bearings, a worn, out-of-round or damaged bore can be restored back to standard ID by grinding or milling the mounting surface of the main caps, bolting the caps back on the block, and then cutting the holes back to their original dimensions.
In the case of worn, out-of-round or damaged cam bearings in an engine block, there are no removable caps. The only option is to enlarge the bores so new oversize cam bearings with a larger outside diameter (OD) can be installed.
Reason number two for line boring a block is to restore proper bore alignment – a process which is often called "align" boring (or honing if a line hone is used instead of a boring bar). As rigid as an engine block might seem, there is actually quite a bit of residual stress in most castings. As a new "green" block ages and undergoes repeated thermal cycles, the residual stresses left over from the original casting process tend to distort and warp the engine. This affects the alignment of the crankshaft and camshaft bores as well as cylinders. Eventually things settle down and the block becomes more or less stable (a "seasoned" block). The bearings as well as the crankshaft and camshaft journals gradually develop wear patterns that compensate for the distortion that has taken place.
Additional warpage can occur if the engine is subjected to extreme stress (like racing) or overheats. If the original crankshaft or camshaft is then replaced without align boring the block, it may bind or cause rapid bearing wear. Likewise, if you’re building a high performance engine with close tolerances, you don’t want any misalignment in the main bores or cam bores.
The third reason for line boring or honing a block is to correct or change bore centers or bore alignment (as when "blueprinting" a high performance engine). The camshaft and crankshaft should be parallel in the block. If they are not, line boring can correct the misalignment to restore the proper geometry. With performance engines, there may also be a reason to change the centerline of the crankshaft or camshaft slightly to alter the piston or valvetrain geometry.


This is really why, once the caps are removed you are now in a way ruining what was once a properly aligned motor.

The way I read that is that line boring is required and bearing bores need aligned before bearing shells are installed into an engine that has had distress...
Please explain, what does this have to do with removing and reinstalling bearing caps in an engine without distress as along as you follow the correct procedures for installing the caps such as torque procedure. The information quoted above doesn't explain why removing and reinstalling a cap would cause misaligned engine bearing bores. Caps are specific to the block/rods they are mated with and machined together. It only says line boring should be done for replacement work or rebuild work which I agree with. But simple replacement or inspection of bearings and nothing else I am not convinced is wrong or risky to the life of the engine.

Don't get me wrong here, I do not want to harm my engine. I want it to last as long as possible trouble free. I think it would be stupid not to look at a couple of bearings and decide if its worth installing in the car without new bearings. Please explain further why a 3800 is different than any other motor. I have done this same thing with other engines and had zero problems. Are there any reputable references that you guys know about regarding this?