I was wondering if anyone could tell me what month in 1968 that GM started producing the 186 heads for the Z28's. I ask this because I thought it was August but just saw a head on eBay that I would swear says F 25 8 (or June 25 1968) on it. Take a look at this casting and you will see what I mean. If this is correct, did GM start casting the 186 heads 2 months earlier than than they starting building Z/28's for the early 69 model year?

JUNE 68 DATED 186 CASTING (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&category=33617&item=2464170779&sspagename=STRK%3AMEBWA%3AIT)

If so....somebody slap me cause that contradicts the old rule of the heads must be dated within 30 days of an engine build. (lol)

Ive seen june 68 186 heads before..ive never heard of a 30 day rule..?? Gm made 1967 corvette 427s in june 1966,usually june is the changeover date for the following year production parts...not 30 days before.....1968 427s came out in june 67 also.

One of the heads is dated 69 but the other one looks early. The rules on date codes are not fast and firm. I have seen some VERY strange date codes on 186 heads. Wish I had taken a picture.

Those heads were not originaly from a Z/28 or LT-1 but might be from a lower performance model. Those are factory small valve heads. They were not originaly 2.02/1.60" valves. The chambers do not have the big valve unshrouding cut.

-Mark.

An interesting point: One casting number/date is into the head. The other is out of the head.