Gary Anderson Los Altos CA

Q: I just acquired a pretty original 100-6, BN4 4­seater. The BMIHT certificate indicates it was pro­duced in 1957. I am puzzled because it does not have a ridge in the center of the bonnet, though the bonnet looks like it is the same original paint color as the rest of the car. I had always been told that the ridged bonnet was one oj the distinguishing features of the 100-6s. Is it possible that the bonnet is not original? Do you have any information on this question?

A: Recent research by Bill Bolton and Hans Nohr has surfaced some information on this question, but nothing conclusive. Here's what we know: When the 100-6 BN4 4-seater was first introduced in 1956, the factory parts list shows a part number for the bonnet of 4B1089. In April 1958 the BN6, the 2-seater version of the 100-6 was introduced. The factory parts list for the BN6lists the bonnet part number as 14B 1089 (apparently there was no revised parts list issued for the BN4). When the 3000 was introduced, the factory parts list for the BN7 and BT7 lists the bonnet part number again as 4BI089, the same as the BN4's part number from the 1956 parts list, and the part illustration shows no ridge.

On the basis of this information, we believe that the original 100-6 bonnet did not have a ridge, but that a ridge was added to the bonnet when the BN6 was introduced. When the BN4 was put back into production and produced in parallel with the BN6, the same bonnet, with a ridge, was used on both BN4s and BN6s. (This would explain why your car might not have originally had a ridged bonnet, while later BN4s do have that bonnet.) When the 3000 was introduced, the factory went back to the original bonnet as used in the early BN4s, perhaps as a cost­ saving measure.

There are two complications to this neat theory.

 

First, a Road and Track road test of the "Mille Miglia" model 1 00-6 (the Mille Miglia was what the marketing department called the 100-6 with the new separate intake manifold) that was published in April 1958 shows a 4-seat BN4 with a ridged bonnet, though that particular car would have had to be produced before the BN6 was produced.

 

Perhaps the factory put the new bonnet on a test car with the new engine installed when it made the car available for magazine testing early in 1958.

 

The second complication is that bonnets without the ridge may have been sitting around at the factory or at dealers well past April 1958 and would have been used up, perhaps mixed in with the ridged bonnets.

Q: So what do I do with the car I am restoring for registration with the Concours Registry?

A: Since the information we have above is so ambiguous thus far, if the bonnet on the car is in good enough condition to use, and it appears to have been the original bonnet based on the paint pattems, go ahead and use it. We won't make deductions for either bonnet when used on a 100-6 if the owner believes it was original. For those of you who have no bonnet on your 100-6, or yours looks like a replacement, then the rule of thumb would be that if it is a BN6, use a ridged bonnet. If it is a BN4 produced before April 1958, then use the plain bonnet; otherwise use the ridged bonnet.

And if anyone out there has a 100-6 with a bonnet they are certain is original that doesn't fit this pattern, please write to me and send me the information plus your body and chassis number. This will help us pin down this interesting anomaly.

Austin-Healey Magazine. January 1994