Authenticating one-of-a-kind cars

Many carmakers have programs where you supply a collector car's serial number and they tell you what equipment it was built with. Some go farther, allowing collectors to match component serial numbers to the build record, thereby establishing the originality (or not!) of those bits.

How do you determine originality when you have a car from a one-off carmaker who is long out of business?  Check out this 1969 Iso Rivolta, onstage with Mike Brewer and Wayne Carini at a show last year.  Alex Turner from Robison Service is in the driver's seat, and the car is from the Boch collection in the eastern part of the state.

1969 Iso Rivolta IR340 @RobisonService 

Iso built cars between 1963 and 1974.  There are several books on the marque and some databases giving basic details of most cars but there is no comprehensive database of serial numbered components used in specific vehicles.  For that, we must use a combination of investigation and judgement.

The starting point is the serial number tag under the hood.  As you can see the tag on this car is simply screwed on, and with non-matching screws we know it's been off the car. How to tell if it's original?

We compared this tag to photos of other tags in the catalogs of auction companies who sold similar car in recent years.  Auctions are often a resource for rare car photos.

The tag looked right, and the chassis number matches what's stamped in the chassis below it.  That's a good sign.  How to tell is the stamping in the body is original?  The best way is to remove the paint and look.

On the left you can see the shock tower to which the serial number tag was affixed.  The stamped number is clearly the original number in that spot; any alteration would leave traces on the bare metal.  So far, so good. We can be confident IR 830782 is the number this car was built with.  But there's more!  Look to the right and you see another number: *260*782*TN.

A bit of research revealed that the chassis assemblies were made in one area, and then welded to bodies crafted in another plant.  The body plant used die stamping to produce smoothly curved panels for the exterior. The chassis assembly is a lot cruder, and you can see that where the chassis and body are joined.

The *260*782*TN stamping is on the body while IR 830782 was stamped on the chassis.  The last three digits, 782, tell me the body and chassis were destined to be joined from the beginning, and this is a further sign of originality.

Now we move onto the engine.  Iso used Chevrolet engines, sometimes in stock form and sometimes modified.  They made two versions of the Rivolta, with this example being the higher powered IR340. This is the engine in the Rivolta in our shop.

There are two casting numbers and a serial number that have significance.  At the driver's rear there is a casting number, 3892657.  A Google search will reveal that this citing number denotes a 1967-era high power 327 block, and that's why we'd expect to find, if the engine were original.

On the other side of the block there is a cast date stamp which decodes to November 1967

Then we have the serial number stamping ahead of the passenger side cylinder head.  

There are two numbers stamped in that area.  The first - *1198* matches the engine number on the serial number tag.  The second number, V 0430 HT, should mean the engine was assembled at the GM Flint engine plant (V) on April 30 (0430) and the motor is a 350HP 327 (HP).

However the appearance of the engine pad is different from how GM usually did these, and the GM number is also curious because it is hand stamped and these were usually gang stamped. The 1198 is stamped in a different type because it was stamped at Iso in Italy. Removal of paint and a close look revealed that this area was surfaced and restamped, presumably by Iso. Why? That is still a mystery.

There are casting numbers on the cylinder heads dating them to 1963. The intake is 1967 and other components decode to the months after the manifold.  That suggests Iso bought and warehoused a supply of performance parts and put them on the fast cars.  Did they buy shorts blocks to build out in Italy, or take complete engines and strip them down for modification? We don't yet know.  

This is the correct cast iron thermostat housing for a 350HP 327:

This is a the correct 42 amp external regulator alternator from that period. It is right for the car? We will see . . . the date codes are sandblasted off so it's probably not original.

These "circle N" bolts and tabs are the original exhaust manifold hardware

This is an original GM Winters aluminum performance intake, from the 350 horse 327 parts bin back in 1967.  Very rare today.

All the evidence suggests this is the original engine with most of its original parts.

Some parts are missing now, or have been substituted with more modern pieces. We had to search out distributor, carburetor and other small parts with the correct date codes. To determine what parts to use we worked with vintage GM parts books and the experts at Tracy Corvette to see what Chevrolet would have recommended for the car Iso was building around their engines. 

If this was an over-the-counter short block the numbers generally started CE, and not V. We are trying to determine if Iso bought a complete custom engine for this car, or just a short block and performance parts. 

In addition to Corvette engines, Iso used GM transmissions.  This car has a Muncie M-21, a famous box from back in the day. We can identify the box from the tag number, and the casting numbers. The tag contains a few clues, in addition to the stamped numbers:

Note how clean the tag is. No sign that it was repeatedly straightened and re-bent, as you see on 99% of these transmissions.  Could this be totally original and unmolested?

In the photo above you can see there are no scuff marks from loosening and tightening the bold, and the bolt itself has the correct SBC casting numbers, as do all the other bolts on the cover. I will give very high odds this is a rate, totally original box. The part number identifies it as a close ration box most often used in the 427 Vette. The casting makes in an early 1968 model year, which matches the rest of the GM parts on this car.

GM engines and transmissions are identified and authenticated by a mix of stamped and cast markings. One thing I am often asked (on many cars, nit just GM) is how you can tell if a number was restamped.  Look at this shot of the date number on atransmission body:

What I've done is use contrast enhancement to show the grain in the cost metal.  If this number had been ground off and restamped we wold see the depression, and the grain of the casting would change. This is an original number, flaws and all (what looks line a half-stamped E at the end is actually an inspector's mark).   

The transmission appears totally original. It is a once-year-only part, an M21 used with the L36 big block engine for model year 1968. It would be a good match for the modified L67 327 in this car. The date code above decodes to May 7 1968 production.

For all this data I should thank Ron Lovelace at Tracy's Corvettes who decoded all these tags and marks. His knowledge of these things is remarkable.

There are other signs of originality on small parts.  Here is a shot of the assembled engine bay when we received the car:

You can see the Chevy engine, a GM alternator, an ATE brake booster and master cylinder (as used in the Mercedes 280SL) along with a number of Delco relays and European fuse boards and wiring.  The modern HEI distributor and wires stand out, and we will change them to the original period parts.

The air filter is not obviously original; my first guess was that it wasn't.  But look closer:

Under the lid, beneath a layer of soot and grease, the original GM print survives

And on the edge of the lid, the stamped part number is an ISO part number.  Very cool, that.

The fuse board is a generic European part of the day, and the relays are a mix of American Delco and European. The wiring colors seem to follow American conventions more than Italian.

Everything we can find says this Iso Rivolta is remarkably original, retaining all its major components 51 years after leaving the factory.  We feel a sense of pride, determining that through detective work, since there is no other way to do it.  We look forward to bringing this fine car to a higher level so its owner can put it on the show field next season.

Till next time
John Elder Robison
J E Robison Service
Springfield, MA, USA
413-785-1665