More 840 head questions...

[Rowdy Rat]

2.19/1.72 was the high performance valve package for rectangular port closed chamber cast iron heads until the 1970 model year when the 291 head was introduced. I don't know where the machine shop came up with a 1.88 exhaust, but I have never seen anything but a 1.72 in a pre 1969 cast iron head.

Your other question is a bit more difficult to answer. Did Chevy start using 291 heads during late 1969 (1970 model year)? I've never seen them on an original car and I've asked several other people who deal with these cars on a regular basis if they had seen 291s and their answer was "no" as well, but they didn't see a reason why it couldn't happen either... Obviously, you're right at the change over point so it is certainly possible.

Two points to add to the discussion...

I recently had a chance to look at a very low mileage 1969 L-71 Corvette at a show in MO. The car was in the 38,000 VIN range (very late build - it started down the assembly line on December 17, 1969) and had a little over 5,000 miles on the odometer. It had 840 heads although I have no idea what the valve size was.

What heads were used on the 1970 L-78 engines (don't have my resources handy)? What valve size? I had heard that only the LS-6 cars received the big exhaust valves anyway... Is this true or just urban legend?

Regards,

Stan Falenski

[Chevy454]

Stan:

According to CBTN, both the LS-6 and the L-78 used the 291 ehads in 1970.

Here is what CBTN (65-69) says about the 2 sets of heads:

840
<UL TYPE=SQUARE>
* This cylinder head was the first big block head produced with a temperature sending unit boss. Very late 1967 cylinder heads would have the boss, but it would not be drilled and tapped. Production of this head began around May 1967 and ceased around May 1969. This head is identical with #3904391 except for the temperature sending unit boss and two accessory bolt holes added to the end of the head.[/list]
291
<UL TYPE=SQUARE>
* This cylinder head is indentical with #3919840 except that it has a tapered spark plug seat, and an exhaust valve seat redesigned to accept the 1.88 exhaust valve. As with #3964290, #3964291 was produced with both "N" and "peanut" series type spark plug seats. This was the last closed chamber square posrt cast iron head produced. It was produced in both plug designs for service replacement, including 1965 through 1969 model years. This was also used in 1970. [/list]
So, does Colvin mean the 291s were ONLY used as service replacements on '69 cars, or that some cars could have gotten them?

[Rowdy Rat]

I get the impression that Colvin is saying that the 291 head replaced the 840 head in production at X date and also became the service replacement for the 840 when that occurred. From the information on the 840 head, Colvin leads you to believe that this date was around May 1969. If that was the case, you should start seeing 291 heads in cars built July-August 1969 as the stock of 840 heads was depleted. Terry's observations from his own L-71 roadster tends to support that...

Fact is that I haven't seen too many solid lifter 1969 Chevys that were built after July 1969... I know that they're out there, I just haven't seen them. This is definitely something that I plan to research. I did find it odd that the late build Corvette that I looked at still had 840s in mid-December 1969. You would tend to think that any 840 heads left in inventory would have been used long before this. I have e-mails out to a few other people on this topic; perhaps they can shed some light when they reply.

By the way, how goes the buildup for the PSMCDR? As I said before, I'm impressed that you've decided to go with the AMA specs for the certified stock class of this event... I hope that you do well!

Regards,

Stan

[Mr70]

I read Alans comment as available as both service replacement and original equipment.
I contacted the original owner of my 1970 L-78 Chevelle which came out of Missouri.He is sure my car came with the 291 heads and are what is still on it today.My Tonowanda engine build date is Sept.15th 1969.Cars Cowl tag date is Oct.24th 1969
Try the guys at www.mortec.com
They have some knowledge as well.

[Chevy454]

I think you guys are reading it the same as I was...that 291s were available late in '69. Now, I am assuming they had the 2.19/1.88s?

What's with all these cars leaving Missouri?! You guys are KILLING me! Go get your own state! j/k

The build up was going great until this head issue came up. All the parts for the short block should be in this week, and will hopefully be put together shortly there after. I thought the heads would be the easiest part of the rebuild, until this thing came up! I really hate to ruin a set of heads because of mis-information! Thanks for the support, Stan, as I am afraid I will need all I can get! I just hope I'm not dead last!

[moparts]

Does anyone have any old GM tech manuals or parts manuals with this head valve info in it???? 69 dated????

Not having any luck finding the 219/172 combination in any parts books under 427 listing. That combo show up under the 396 listings. Rob and I have been comparing the GM by the numbers book with Gm performance parts catalog and my Sealed Power and Perfect Circle parts catalog and are having lots of problems getting information to match.

Now I am not saying that my parts books are always correct (have a whole shelf full of returns to prove that) but it sure seems funny that out of 3 different catalogs that none of them show the 219/172 combo for the 427 engines.

Now with all that being said, and assuming that the machine shop is telling us right,(assume = ass u me) is it possible that some of the late made 840's would have had 188 ex. in them? and how do you prove it??????

[Chevy454]

Well, here is what we have come up with so far. Let us know what you guys think.

The set of 840 heads we found are untouched, and original, and came with 1.88 exhuast valves...absolutely positive of that. They are also machined for BOTH plug types: N and peanut. This was common on early 291 heads, so I am thinking that the heads I have are kind of "in-betweens", or a combination 840/291.

Now, some food for thought. It took me a while of reading to figure out what Colvin meant in his descriptions of the 840 and 291 heads. He states that the production of 840 heads ceased around May of 1969. So, that means they switched over to the 291 heads, which had the 1.88 exhuast valves. He lists the 291 heads as available on the Chevelle, Camaro, Corvette, Chevy II, and Chev/Pass with the L-78/L-72/L-71 in 1969. That makes sense, as both the Corvette and Camaro production ran into early '70(?), and the 1970 L-78/LS-6 Chevelles and the L-78 Novas got the 291 heads. So, why would GM still be making the 840 head in late '69? They didn't...they switched to the 291 head across the entire car line around may of '69. The L-78 Chevelles were made before the LS-6 Chevelles were made, and L-78 Chevelle production ceased when the LS-6 debuted. But, they were still producing '69 Corvette and Camaros! So, you could essentially have a '69 Camaro/Corvette built AFTER a '70 Chevelle/Nova! Right?!

This explains why a lot of parts books and machine shop books only show the 2.19/1.88 combo for '69 cars...GM switched to the 291 heads around May '69, thus "updating" to the 1.88 valve, which would mean the latest combo is the one that the books will show. Another intersting note is that the NHRA shows the 291 head as being legal for 1969, along with the 840 heads. BUT, they only show the 2.19/1.72 combo on the '69 L-72s...why? Probably because the manufacturers had to have thier info submitted and approved PRIOR to the racing season, and GM didn't know about the "update" to the larger 1.88 valve until later in the season.

So, what is my point? Well, it looks like 1.88 exhuast valves were available in 1969 production cars, whether it be on some 840 heads or on the 291 heads. Now, how do I prove that my 840s originally had 1.88s, and who do I prove it to?

[Edited by Chevy454 (06-21-2001 at 01:21 PM).]