302 Chevrolet Engine Build

[Greg Reimer 7376]

Interesting. I will check this weekend for the water temperature boss and the threaded hole. Winder if these came on a 327 350 horse or even a '68 325 horse 327. When did the screw in studs and push rod guide plates come along?

[Greg Reimer 7376]

Well, curiosity being what it is, I got back out there and checked. No coolant temperature switch hole,no provision for one. I checked the other two pair of cores I have, none there either. I then went into the trailer, opened the hood on my race car, no temperature switch holes or boss for one on them either. Now, heads made in 1968 had them, as the 3917290 and the 3917293 castings, which are '68 only, do have a plug or a water temperature switch opening. Seems that '68 was the year stuff like that started changing.

[killintime6968]

My 69 Z28 was built in late May 69 and has screw in studs and guide plates. Not sure on the date codes on the heads though.

[Greg Reimer 7376]

Well, according to the NHRA Tech Bulletin pages, 462 heads are only legal on the 67 Z/28. There's several other accepted heads, which carry over into 68 and 69, but the 68 and 69 cars don't show a 462 head as being legal. The 69 cars had the later casting with the bolt holes for accessory mounting brackets, because 69 was the first year for the long water pump and brackets mounted to the heads and block instead of the exhaust manifolds. All Z/28 engines had the 2.02 intake/1.60 exhaust valves, but the OEM 67-68 heads had no boltholes. 67 Z's were so rare anyway, it's very unlikely anybody is going to find a set,originally.
In the summer of 1980, I wrapped up my days of working in dealers and one of the last jobs I did there was to put a rear main seal in a very nice low mileage 67 Camaro SS 350. Camaro was the only Chevy in the lineup that got the 350, and when the pan was off, I noticed it was a 2 bolt main block but it had a steel crank. I've wondered, since it was a one-off combination if that engine that year only was a small journal 350.That would have been before the changeover to the large journal engine division wide the next year.

[Hacksaw]

A 67 z had 462 or 291 heads and the 68 z had 291 castings. Of course your results may differ. LOL

[Mark Yacavone]

Are you guys thinking that guys like Tony Pizzi and Ben Wenzel, Durbin and Sartwell, Wheatley Bros. etc, were breaking rods back in the 70's?
How about all the 283's that would leave the line on the mat back then, with an even smaller rod? I realize the Z pistons were heavier, with the dome, but Mike said they would be lightening them.
This is a street and strip, but mostly street build.
I'm sure the Chevy rods will be fine.

[Dwight Southerland]

Yac-
Leaving “on the mat” back then is not the same level of strain as the sustained 8000+ rpm runs of today’s cars. Secondly, we broke a bunch of rods back then, too! And if you break a rod in an engine today, it’s way too expensive to consider taking a chance.
There were only three small journal rods - early 265, ‘57-‘62 265 & 283, and the ‘63-‘67 283 & 327. There ware no special high performance forgings. The solid lifter ‘65-‘67 engines sometimes got “green” rods which meant they were magnafluxed before they were machined. All these rods are 50+ years old today. Do you want to trust them for a $10K engine?
Head casting numbers changed due to engineering changes that had nothing to do with port design. 462 changed the combustion chambers, 291 made allowance for closed crankshaft ventilation with open slots between the push rods, and 186 had the provisions for bolt holes in the end.
Just a bit of history.

[MAURICE BLENDHEIM]

Early 1967 Z/28 cylinder heads were "462", Late '67 castings were "291" with no temp sender provision. Early 1968 Z/28 heads were "291" with introduction of temp sender and late 1968 castings were "186". Screw in studs and guide plates ONLY came on Performance Optioned small block engines with factory installed 2.02 & 1.6 valves. All the above mentioned heads were also available with 1.94 &1.5 valves and came with NO factory installed screw in studs and guide plates, "291's" may have an un-drilled lug for temp sender. The 1967 Z/28 connecting rods (3864881) were a regular production rod, that utilized a press pin. The floating pin was a late 1968 Z/28 introduction. Hope this helps... MB.