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Seems like this would be an easy question to answer, but the forum archives & Google present some conflicting info. Simply put, what's the stock push rod length on a late 70's SBO? My shop manual says 8.265", some sources agree. Most manufacturers claim 8.234", and that number also gets tossed around here. I plan on checking a few used ones just to satisfy my curiosity (tomorrow when I have access to a longer caliper).
The difference in those numbers is about the difference in thickness between the factory .017" steel shim head gaskets and the thicker aftermarket composition head gaskets.
Well, this may explain a problem I had when installing a cam in my 71 350. I got the aftermarket stock type grind cam and ordered new pushrods. When assembling engine I had a bunch of clearance. I figured it was because of the reduced base circle of the cam. But now if original pushrods were 8.265 and replacements are 8.234 then that is a difference of .031. Then use .043 gaskets instead of .017 and that would make another .025 for a total of .056. Am I figuring this right? I had to use the adjustable pushrods I bought from Mondello.
The difference in those numbers is about the difference in thickness between the factory .017" steel shim head gaskets and the thicker aftermarket composition head gaskets.
I wonder when Olds went to a thicker gasket? I pulled down the '77 Shop Manual and it also lists 8.265" like my '79 Cad manual I've been using.
Well what Ken said seems backwards to me. If head gasket is .026 thicker, then pushrods need to be that much longer, not shorter.. Right???... I don't think that "Olds went to a thicker gasket". I think the thicker gasket was what was supplied by the aftermarket (Felpro,etc.) . I hope Joe P weighs in on this, I am going to look in my factory 71 shop manual and see if I can find the length of factory pushrods in there also.
Since I'm not certain the full attached document is viewable to everyone, I'll simply embed the pertinent Section 4.4 material:
Valve Train: 1964 Type "1" heads used different rocker
arms and pushrods which are 8.235” long. 1964-1965
Type 1A and 2 heads (442 and B04 Police) used
pushrods that are 8.3125” long, because of their
rocker/pedestal setup that was used in that head only.
"1" series heads have a different angle of attack for the
pushrod hole because of the 45 lifter angle of attack on
the early blocks. Thus, these heads would have to have
the pushrod holes bored out to 0.562" to make sure the
pushrods do not bind in the hole when mounted on 1966
and later blocks (engine casting codes "2" or higher).
1964-67 Type 3 Heads used pushrods are 8.400” long,
and used the typical stamped steel rockers and
aluminum pedestals. Starting in 1968 all small blocks
used 8.2656” length pushrods. In 1986 the 307 changed
to roller lifter cams with a much longer lifter requiring
7.718” length pushrods. 307 and 350 Diesel blocks that
used the 0.921" diameter roller lifter that is longer which
calls for the 7.718" length pushrod.
Starting in 1968 all small blocks used 8.2656” length pushrods with flat tappet camshafts through 1984, plus the 1985 307 VIN 9 (442) engine only.
In 19861985 only, the 307 VIN Y (along with all 307s starting in 1986), changed to roller lifter cams with a much longer lifter requiring 7.718” length pushrods. 307 and 350 Diesel blocks that used the 0.921" diameter roller lifter that is longer which calls for the 7.718" length pushrod.
Fixed that for you. Adding a bit more context as 1985 was a messed up year. Most 307s in 85 had roller lifters, but there were those 3000 442s that came with flat-tappets.
Oh, and an edit- there were 2 types of SBO V8 flat tappet "modern" 8.2656 pushrods I am aware of. The earlier versions, part 398687, through 1979 (I think) with the smaller ball ends, and the later versions that used larger 0.375" ball ends, part number 22505582. This was coupled with corresponding matching size rocker arm ball cups. Earlier rocker arms were part number 401384, while the newer versions were part number 22505583.
Last edited by 69HO43; May 13, 2022 at 08:29 AM.
Reason: additional info about push rods and rockers
Fixed that for you. Adding a bit more context as 1985 was a messed up year. Most 307s in 85 had roller lifters, but there were those 3000 442s that came with flat-tappets.
Oh, and an edit- there were 2 types of SBO V8 flat tappet "modern" 8.2656 pushrods I am aware of. The earlier versions, part 398687, through 1979 (I think) with the smaller ball ends, and the later versions that used larger 0.375" ball ends, part number 22505582. This was coupled with corresponding matching size rocker arm ball cups. Earlier rocker arms were part number 401384, while the newer versions were part number 22505583.
Oh Man, this is clear as mud... and guess what? I found another strange issue. Apparently the 70 and 71 service manuals have a typo regarding pushrod length. I have 3 factory shop manuals, 1970, 1971 and 1975. The 70 and 71 manual lists the pushrod length for 350's as the same as the 455's. The 75 manual lists 350 and 260 pushrod length as 8.265- Wow.....
Having the same exact issue, All i see are "stock" length 8.234 " listed. With every thing new, stock, they clatter like a solid lifter cam. I have Trickflow 8.25" pushrods coming and hope it corrects my issue.Does anyone have a number for the "longer" OE pushrod like TRW or?
This has really turned into a can of worms, though I'm glad I asked. Ha! For what it's worth, Edelbrock suggests BBC pushrods with their cam, claiming an 8.285" length. GM p/n 14075629. Haven't verified the length, nor ball ends.
Being my valve train is stock, I think I'll put together a set of used Olds PR's, after a cleanup and dimension check. What I don't quite understand is why all of the replacements are 8.234"?
That makes sense, with the smaller base circle cam and thicker head gaskets, using the longer BBC pushrods. It sounds like the ideal length. Interesting on the pushrod lengths in the 70 and 71 CSM. I forgot to look in the "Bible". It shows, even it can be wrong on occasion.
Just make sure if you go the BBC pushrod route, you only buy 2 sets of INTAKE pushrods for non-roller cam. I'd still get a pushrod checker and measure to be sure. The BBC typical intake push rods are 8.28", but the exhaust pushrods are an inch longer at 9.25" due to the valve geometry. They make 3/8" and 5/16" diameter pushrods, so there's that to consider as well. For BBC rollers, they lopped off 3/4" from the length.
If you're going all out performance, get custom rods made.
Don't quote me on this, but I think all stock BBC flat tappet push rods came with 5/16" ball ends, so if you use them in your olds, you'll likely need to use the smaller cup "early" rockers.
According to the 75 manual I posted above the 455 pushrod is 9.570 and the 350 is 8.265. 9.570 would be way too long for a small block, wouldn't it? Over 1.300 longer??
UPDATE !! The .030 longer pushrods are perfect. installed them tonight and car runs and idles nice with a nice quiet valve train. Will update after some miles.
A few more statistical datapoints to muddy the waters. Looks like I need to get a measurement tool; unfortunately 8" seems to be the limit of readily available ones (including Amazon). May have to fab my own if I want to get this thing assembled in the next day or two.
First pic is of the new BBC intake PR as recommended in the Edelbrock cam instructions. 8.285". ~0.030 longer, so no surprises there.
Second pic is a used rod from one of the three SBO's around here that I've torn down. It's either from a 403, or one of two '79 350s, so all late 70's. I was expected 8.265 by the manual, what I got was 8.234(ish). Most of the others were similar, +/- a few thou from wear. Hmm.
The third pic really makes me scratch my head. It was also part of this group... Careless rebuilder?
Thanks Eldo for the follow up. I see now I misread about the BBC (big block Chevy) pushrods. I thought I read big block Olds, which of course would be over a inch too long. So the big block Chevy intake pushrods you used on all 16? That is great, really good info. Thanks
Greg, that's the plan. These are Sealed Power RP-3182. Guy on eBay sells them by the set from bulk stock quite reasonably.
Perhaps this will help others.... With Edelbrock cam and matching lifters, stock rockers, FelPro headgaskets and no milling, I took a random selection of the old PR's and measured lifter pre-load (checked on both heads). They all came in between 0.010 & 0.018. I repeated the test with the RP-3182's and had between 0.038-0.042. That sounds pretty good to me.
Trickflow, the cylinder head people sell 8.25 length chrome moly. Summit has them in stock. had them in three days, all good. Sorry for the delayed response !
