COmpression ratios for Series2 a

[conjames]

Hi,

Apparantly there are 2 Compression ratio motors available in the series 2a.
7:1 and 8:1.
Can anyone tell me how you can identify which one you have?..

[d@rk51d3]

Once the 8:1 came out in the early 80's, the heads were cast with a rectangular boss, roughly in line with the carby.

The boss was stamped with either a 7, or an 8, designating the compression ratio, or left blank to designate 7 also.

If you don't have the rectangular boss, then it's probably a 7 too.

[JDNSW]

Correct. The square boss is between two headbolts on the top of the head between the rocker cover and the carburetter. If it has no boss it is 7:1, and if it has no number stamped on it or "7" it is 7:1, and if there is an "8" stamped on it it is 8:1. Note that the number may not be stamped very clearly, and you may need to polish it with wet and dry to see it.

This assumes that the head has not been ground to increase C/R without remarking. The earlier head casting does not reliably have enough metal to safely grind to 8:1, but some of them may have been reground successfully to give the higher ratio, or even more. (I would be cautious about going over 8:1 unless you are running exclusively on LPG or are happy to use high octane unleaded).

John