Cylinder Boring and Honing

[HarahanAutoParts]

When dealing with a machine shop having your cylinder resized you should be aware of the difference in machines doing the procedures.

On boring engines, there are three types of boring bars that are generally used, the portable bar, one that sits on the deck of your block and centers with fingers in your old bore, on a regular rebuild this is a good way. The only problem with the portable bar is it sits on the deck to hold down. Is the deck straight? Will the new bore be perpendicular with crankshaft? On a regular rebuild this is an acceptable way for refinishing.

The second type of machine is a bar that sit on a table, while the block sits on a bar in the main bearing saddles. The boring bar is generally an airflot design that will float easily from one cylinder to another. This type of bar still use centering fingers to align in the old cylinders, but remember, the old cylinders have wear that has to be contended with while centering. This type of system is much better than portable as it will bore perpendicular to crankshaft saddles.

The best type of bar is The CNC vertical mill with the performance block fixture that uses two bars to attach block to machine, one through cam tunnel and one through main bearing saddles to perfectly aliagn bores over centerline of main bearing saddles. In most applications ( actually all racing application) we can follow original blueprint design on bore spacing without having to worry about the present cylinder wear.


What ever above system being used a most important consideration is the amount of bore left to be honed, .005 to .007 thousants need to be left in bore for finish honing to get down to the base metal in bores.

Honing of bores is as important or even MORE important than the boring operation to maintain correct cylinder leak down and control oil consumption.

The above procedure was for V configuration blocks, straight 4cyl and 6 cyl require a different procedure for attachment.

More on this subject in our next thread.

[MntlKase]

Wow this is good information. C&F Automotive actually has my block\new pistons and crank right now for a bore and rehone. When I go pick my stuff up friday I think ill ask em what process\machine they used just to see their faces and to know exactly how my shit was done. Thanks for offering the information

[RyansQuick6]

I've heard something about having to bore and hone in a manner dependent on what the engines operating temperature will be, in order to compensate for expansion and things like that. It sounds somewhat plausable, but it also teeters on that fine line of myth and reality.

Is there any factual basis to it? I've heard it a few times, but never thought to see if there was any truth to it.

[HarahanAutoParts]

There are a few people that will finish hone (not necessary when boring) using a liquid (water or oil) at engine operating temperature to simulate the actual running condition of the block. I personally do not know of anyone in this area that does this procedure. The most important thing in the process of honing (performance application) is using a honing/deck plate on block at the correct torque poundage for the fasteners using. Remember, different fasteners require a different torque as well as different lubricant on fasteners would require the same. If possible we also torque main bearing saddles as well.
Two other considerations are important as well.
#1 The bores should have .005 to .007 of material removed from bores to get down to the base metal of bore.
#2 The bore needs to be round and straight when finished. This procedure sounds easier than in real life but a shop using a Dial Bore gauge can check correct cylinder size. It is very,very difficut to check bore from top to bottom using "inside mikes".