Re: Valve marks on head

Posted by Sherlock On 2017/6/16 17:21:09

Given the plug data and looking at the '30 -'32 Service Parts List, it is clear the head presently being used on my 740 is 1932 or later. It uses 14mm plugs which were used from '32 to '36. It is stamped HC which corresponds with the 1932 high compression head (as opposed to low compression head) as set forth in the Service Parts List.

The SP List carries the same part #s for 1930 and 1931 384 c.i.d. heads, but the numbers for 1932 are different. Therefore, I am given to believe the heads are not interchangeable.

The 1932 (or later) head fits on the engine, so there must be something else about it that doesn't work. Perhaps the HC engine has a smaller chamber with a lower dome. This might account for the valve marks.

Whether the marks are a result of incompatible head design or over-planing, I guess the simplest solution would be to just use the spare head which has the correct size spark plug holes.