71 -Sanity Question - to rebuild or not to rebuild

[Peter B.]

Everyone,

I have a 71Convertible. It runs GREAT. The engine is an unrestored original (from what I can tell), here are my questions that I need guidance on...

> How do I really know that the engine is an un-restored original? Are there some markings?

> It runs great, should I rebuild? I think it is more valuable leaving it as an un-restored original. Is this true?

Happy Holidays

[William C.]

Re: 71 -Sanity Question - to rebuild or not to reb

To Pharphrase some Philosopher who was a lot smarter than I am, "If it ain't broke, don't fix it"

[Duke W.]

Re: 71 -Sanity Question - to rebuild or not to reb

It can be very difficult to determine if an engine is still original Flint-built or has been rebuilt if effort was expended to maintain original appearance and major visible parts. Low true mileage is often an indicator, and there are still vintage Corvettes out there with less than 100K total miles and often the original untouched engine.

One dead giveaway can be the head gasket thickness, which is offen increased on pre-'71 engine rebuilds to "lower compression", which is not necessary with today's premium unleaded fuels.

Such does not apply to the post-'70 engines since they were ALL designed to run on 91 RON unleaded fuel, which is equivalent to today's 87 PON, but "engine builders" often use thick head gaskets on these low compression engines, lowering compression even further.

The head gasket thickness can be determined by sliding feeler gages between the block and head on the stamp pad or the driver's side - whichever is most convenient based on the accessory configuration.

The OE head gasket should measure about .018" thick, and since the GM service gasket after about 1963 was thicker, an .018" gasket is a good indicator that the heads have never been off.

If the engine runs "great" it probably doesn't need any major work, however, a compression or leakdown test can validate subjective impressions.

As these engines age and accumulate mileage, oil consumption can increase, and if it exceeds one quart per thousand miles, replacing the valve seals, which is a fairly simple task, will often reduce oil consumption, signficantly.

Duke

[Patrick H.]

Re: 71 -Sanity Question - to rebuild or not to reb

Don't touch it.

If it uses oil, check out the valve stem seals. Else follow Bill's sage advice.

Patrick

[Harmon C.]

Re: 71 -Sanity Question - to rebuild or not to reb

Peter

The best way to find out about your car would be if you could attend a NCRS chapter's monthly meeting with your car and ask someone to take a look at it. If you post a city and state someone may offer to stop by and take a look. One good book to buy would be the 70-72 Corvette technical information and judging guide sold on this web site. It will answer many of your questions.
Lyle

[Jeremy D.]

Re: 71 -Sanity Question - to rebuild or not to reb

Leave it alone, and drive it like you stole it. And check to see what the engine stamp pad says. It's on the passenger side, right at the front of the cylinder head. If it's blank and looks like it's been machined, your block has been decked, and your motor HAS been apart. If it has a squabble of numbers & letters (some of which should be the same as the last 5 digits of the VIN number of the car)you're probably in good shape. There's great info on how to decipher the jumble of numbers and letters on the stamp pad in the NCRS Technical Information & Judging Guide for '70-'72's.

And if it has the three letters "CGZ" stamped on the engine pad, send me a private email and we'll talk!! LOL!!(CGZ is the engine code for "LT-1", a high performance solid lifter engine option. If you have one of those, you are in a whole different ballgame!

[Peter B.]

Re: 71 -Sanity Question - to rebuild or not to reb

Jeremy

I saw that there were the numbers on the engine exactely where you said they would be. I could not write them down, I was trying to work on the steering (I will post another question about a problem I have on that). Never the less, the numbers look un-touched. It runs great and really does not burn any oil. I have had the car since 1998 and I bought it from a Germany Engineer who was setting up the M-Class Mercedes plant in Alabama. He was done and returning to Germany and selling the car. He had it for about 4 years and I know he did not rebuild the engine. I will get back to you on what the stamping says to see if you can decifer it. Thanks again for the help.

By the way, yes, I love driving it like I stole it. I put about 1000 miles on it per year and I love driving it. If you dont mind, check out my new posting on this site regarding my steering issue if you can offer some help.