1970 Rebuilt Engines/Bored

[Greg F.]

This is my 3rd post in the last 24 hours, so I hope it's ok.

A few of the cars I'm considering have rebuilt motors. Most of them have been bored .030 over but the cam, pistons, etc meet original specs. Is this ok for a numbers matching block or should I stay away? I guess I'm more concerned from the originality/value aspect. Does this hurt the value or is it accepted?

Thanks,
Greg

[William C.]

Re: 1970 Rebuilt Engines/Bored

Pretty normal, as long as they didn't deck the block.

[Greg F.]

Re: 1970 Rebuilt Engines/Bored

What does that mean, "deck the block"?

Thanks for you response!

[William C.]

Re: 1970 Rebuilt Engines/Bored

Many rebuilders as a "Standard" practice will take a small cut off the top of the block surfaces to "true" the top surfaces of the block. This is typically referred to as "decking the block". the problem is it removes the original machining characteristics of the block, as well as the numbers stamped in the block at the engine plant and vehicle final assembly plants to identify the engine to the car.

[Joe L.]

Re: 1970 Rebuilt Engines/Bored

Greg-----

"Decking" the block means machining the block surface to restore it to acceptable flatness. It's sometimes done routinely, and this is unfortunate in the case of Corvettes and other collector-type cars. When it is done, it changes the "broach marks" on the engine stamp pad and, often, removes all or most of the original stamped-in numbers. Obviously, with such collector attention to "stamp pads" this is very undesirable for a collector car and will usually result in decreased value.

If the broach marks appear "straight", then the block has likely never been "decked". If the broach marks are "circular", then it has been "decked".

[Greg F.]

Re: 1970 Rebuilt Engines/Bored

Thanks again. Is it normal to run racing fuel in a newly rebuilt motor if it's .030 over?

[William C.]

Re: 1970 Rebuilt Engines/Bored

Not necessarily, if the original compression ratio was not changed, it should not be required, 93 octane will work fine in most applications. If you are looking at an engine that has been rebuilt, it would be good to look over the builders invoice to the customer to know what was done and what parts were used. Once the engine is apart, too many people can't leave "well enough" alone.

[Phil P.]

Re: 1970 Rebuilt Engines/Bored

mass production has tolerances that have min.max and will inherintaly (sp) produce machineing tolerances that are with in production limits but also could produce an assembly that is at the extreme end of a given production tolerance sorryn cannot end this as 6 13 year old girls want to see hot rods---will be back---phil

[Warren F.]

Re: 1970 Rebuilt Engines/Bored

Greg,

Most engines that have been "rebuilt" usually have an increased bore that is typically .030 over or more, than the "standard" bore. I personally don't like it and prefer the cars to be at their original displacement, ie: 427cid, 454cid, etc. The engine is no longer a true factory cubic inch engine after the machining is done to the bores, unless someone sleeves the cylinders back to stock specifications, which isn't done too often, unless there is some sort of damage to the cylinder.

Most people still refer to a rebuilt engine as the same cubic inch it was before the boring, however that is not accurate.

[Verle R.]

Re: 1970 Rebuilt Engines/Bored

Greg,

I have put some thought into your comments.

I will address your concerns like this.

If the brakes wear out, you will replace the pads so it is safe to drive. By your criteria it is no longer original.

Will you not replace the brake pads, rebuild the master cylinder, replace worn out tires?

Rebuilding a worn engine most often requires the cylinders to be bored oversized. This requires new pistons, rings, inserts, gaskets. If the block is not decked the original stamps are still there and identify the engine. It is still the original engine that has been rebuilt so it can stay in the car and provide more years of service.

A car is only "original" once; when it is delivered by the dealer. After that age and wear make changes.

My personal opinion, and I believe most other people on the tech board, if the rebuild preserves the identifying characterstics, don't worry so much about the internals like pistons and such.

Verle

[Greg F.]

Re: 1970 Rebuilt Engines/Bored

Thanks Verle. I've always heard that, but I figured I'd get the best answer from NCRS. The block has not been decked. I spoke with the engine builder yesterday. He laughed when I asked because he is a corvette guy. He provided the list of parts and the work that was done to the engine (copy of what the current owner has).

Thanks for your reply!

[Verle R.]

Re: 1970 Rebuilt Engines/Bored

Greg,

Don't worry about it, just enjoy the car. Drive it every chance you get.

Verle