What can the experts here tell me, regarding my engine number?

I finally managed to remove enough grime so that I could record the engine number in my SIII V12.
However, in the databases, the number doesn’t show up, nor does the suffix.

The complete number is : 7P56200SB
What can be learned from that?

Mine is 7P55236SA
1986 Canadian spec, O² sensors and Cats

What databases are you looking at?

I’m looking at the list of the heritage club, but can’t see anything more than Series III V12 within the ballpark for it’s year of construction…

I reckon engine numbers are related to the build of the engine, so would not give much information on the car itself, except a check of consistency between the engine build date and the car build ?

It’s the suffix SB i am curious about. It is not listed on the official list.

According to http://jaguar.professional.org the SB indicates
S= standard compression
B= grade B pistons and liners.

SD Faircloth www.jaguarfuelinjectorservice.com

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hmm…thanks for the information. As I am not a Jaguar Professional, I suppose that’s the reason why I can get onto the website mentioned?
What does Grade B pistons and liners mean? What is the difference to the other grades?

Fear not. Basically, A and B grading relates to size matching between piston and liner only and in no way describes quality.

I’m also curious, can someone elaborate on the grade A/B pistons thing?

It’s simple enough. Jaguar wanted fit tolerances between piston and cylinder tighter than production machinery of the time could accomplish. So they machined pistons and liners and then measured them, grouping all the ones on the small side as A and all on the large side as B (mighta been the other way around, I don’t remember.) Hence, if you put an A piston in a B liner it’ll be a loose and sloppy fit while a B piston in an A liner will be too tight and might seize. It’s not enough of a difference to make any significant change in displacement, you just gotta keep your A pistons with A liners and B pistons with B liners.

Typically an entire engine is either A or B. A while back we had a member ask about mixing them up. I personally feel one bank being A and the other bank being B would be no problem at all. Mixing them up more randomly might cause some issues, but it might not. Other things such as the injectors are not as closely matched as the difference between A and B pistons and liners.


Note also that for preHe
“L” is low comp ratio - 7.8:1
S standard 9:1
HA high 10:1 (1980 only)