Took my GX head into the machine shop for a rebuild. Valves will be recut and valve seats will be replaced. What angle is recommended for the valves? This head will be going on an A15 block that is for street use. Intake will be dual Hitachi's coupled with GX exhaust manifold. Thanks.

All A-engines came from the factory with a 3-angle valve job. The recommended angles are:

Quote:
Also note all A12/A14/A15 came with unleaded valve seats

many aussie speedway backyarders shave the crap out of them while racers
that are smarter in the USA and here angle shave them so ports are steeper
and valve angle is closer to 18-20 degrees open up the pushrod passages
to avoid any issues and use quality custom pistons for high comp

Peter Zekert can help as well with hints and tricks and also pistons

Go to page 6 of of the following line; it has a nice diagram.

http://www.datsuncherry.ch/PDF/Rennteile75.pdf

Hmm ... the 1974 racing guide
Quote:
The 1981 guide:
Quote:

I notice some typos in the original specs in Post #2. Have corrected them

The seat width is (as I understand) a compromise between good flow (narrow width) and good heat transfer (wide seat). So exhaust valves need a wider seat contact area. And so do hotter engines

As to why the racing engines used a 1-angle exhaust valve seat while factory engines got 2-angle exhaust valve seats, I am baffled

The 45-degree cut used in 1974 may have been to make it easier on machine shops. The factory used a 45°30' cut, and later racing used a 48.5(!) cut, so a plain 45 might not be optimum. The slight difference between seat angle and valve angle (interference angle) helps with initial fit and may help with longevity

Here is the 1981 diagram, which I take to mean 48.5 + 48.5 = 97 degrees (if this is incorrect please let me know -- maybe the Competition document has a typo)

Attach file:

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  Renteille81 valve seat.jpg (31.01 KB)


  Backcut.jpg (44.04 KB)

Thanks for the information guys. Is the valve angle the same for all of the various A series cylinder heads?

As far as I know, the valve angle is 45 degrees 30 seconds for all As

If you are fitting new valve seats, you can make them whatever angles you want. I'd go with the proven 60° + 45° + 30°, maybe even pay extra for a 5-angle job (75 + 60 + 45 + 30 + 15)