[1966Lemans]

Hope some of you engine experts can help... My old worn out 400 has always had a lifter tick, since I've owned it (19 years). Recently, I had the valve covers off, and I decided to make sure they were all torqued to 20 ft lbs. One thing that's weird with my engine is that someone, long before I owned it, replaced one stud with a screw-in stud... the old one must have pulled out. That stamped rocker looks different than the rest (although still stamped) and has what I think is a pinch nut. Anyway, I always thought that that rocker was probably the one that ticked. So, for that one rocker, I didn't try and torque it. I just snugged it a little more (maybe a 1/2 turn). I drove the car for 20-30 miles, then I noticed the engine starting to miss. When I listened in the garage, it "seemed" like the tick had gone away.

So, I took the valve cover off again, and that "odd" rocker had jumped off the valve and pushrod and was sideways. The end of the pushrod was somewhat mangled... not "too" bad, but not usable. So, I want to buy a new pushrod, and try to adjust that valve in the "adjustable valve train" manor. Here's the issue... I looked up (in the Ames catalog) the stock pushrod, and it says they should be 8.694 inch. But from measuring this one, it seems like it was probably a 8.875 inch rod (taking into consideration the messed up ball end). So, what do you guys think? Should I order an 8.694 or a 8.875 ???

Thanks!

[1966Lemans]

By the way... this 400 was probably a 290hp out of a big car, so it should have the lowest performance cam in it (I don't know for sure). I think it's a '68 400 YC code with the 75cc #15 heads (press in studs).

[steve25]

There was only 2 times that Pontiac used the 15 casting number, once in 68, and once in 70.
Both take the standard 9.130” long. Push rod,

The 67 400 2 bbl motors and all other cid motors from 66 on down took a 8.694” long push rod, but for these details.

A early 67 big car 2 bbl motor would have had 143 casting number heads and used the 8.694” long push rod.
The early big car 4 bbl motors would use the very rare 061 casting heads that used the 9.130” long push rods.

Since you where running the motor with the rocker kicked off then before you put it back together you had better try real hard to look down at that lifter and confirm that the plunger has not extended all the way and popped the round wire C clip out that holds it in place.

[1966Lemans]

I got some more information... I was TOTALLY wrong about the fact that it was converted to a screw-in stud. It still has a pressed in stud, and it doesn't look like it's higher than any of the other studs (so hasn't pulled out). So, basically someone put a different rocker arm and different pushrod in "for some reason". And it's been ticking ever since. I need to locate a proper Pontiac rocker and pushrod. I'll also try and look down the bore, and see if I can see anything, relative to the lifter C-clip. I'll pull one of the other pushrods, and measure what it has on the good cylinder.

--- Jay

[1966Lemans]

OK... the neighboring intake valve has a 9.130" pushrod. So, I think someone really jurry-rigged that rocker/pushrod with some non-Pontiac parts. I'll buy a new 9.130" pushrod and correct stamped rocker for a 3/8" bottleneck. I assume Ames probably has them?

[steve25]

Be sure to look at the bottom side / flat side of that rocker arm nut.
I have seen quite few that had cracks extending out from the center to the perimeter due to being tightened up beyond the 20 ft lb spec, and when they are such they do not hold there adjustment .

[Kenth]

Rocker and push rod for 1968 400:

https://www.rockauto.com/en/moreinfo...t=5656&jsn=445

https://www.rockauto.com/en/moreinfo...t=5648&jsn=451

[steve25]

If you unbolt the push rod guide plate you can see down into the lifter valley much better and you will also be able to confirm the new push rod has made it into the lifter plunger seat.

[1966Lemans]

I ordered the Ames ones, before I saw that Rockauto post. The Ames rocker comes with a new nut. I looked down the pushrod hole, and didn't see anything unusual. I put an extendable magnet down there, and got some metal grit out... probably from the ball end being damaged. The only weird thing about the Ames pushrod is that they list the nominal length as 9.165, instead of 9.130, but I assumed Ames knows what they're doing

[steve25]

In my Ames catalogue they list the N512 push rod as being 9.145”.

[1966Lemans]

Cool (9.145)... on the the amesperf.com online lookup, when you pop-up "detail", it says 9.165, but it's probably just a mistake on the online catalog... N512 was the one I ordered.

[1966Lemans]

Follow up... the old rocker was obviously for a 7/16 stud... it dropped to the bottom of the stud if not supported by the valve and pushrod. When I assembled it with the correct rocker (for 3/8 bottleneck) and the 9.130 pushrod, everything seems to work great. It's definitely not missing on that cylinder anymore. Before I go out and thrash on it, I'm changing the oil to Mobil 1 15w50 with some STP. That should help out those old lifters. Thanks for all the suggestions and help!

[steve25]

Great news to hear and it’s also good that you stuck with it and just did not walk away!

Be sure that rocker stud is not gouged Around where the rocker slot resides, if there are it may snap off at that point if loaded enough.

Just for future reference, Lucas oil stabilizer is a more modern formulation and as such a better product then STP.

[1966Lemans]

Oh, cool... thanks for the tip. I grabbed some STP "high mileage" when I picked up some Mobil 1 15w50 at Walmart... next time I'll try the Lucas additive. Thanks!

[Dragncar]

I run Lucas in everything I own. Never blown up a engine or even spun a rod bearing in my life.
That said, seen a lot of cams broken in as a kid with nothing more than STP. It has some zinc in it.

[johnta1]

the old rocker was obviously for a 7/16 stud.

They all are for 7/16" stud. (lower part of stud)

The rocker arm rides on the lower part of the stud which on a bottleneck 3/8" stud is 7/16". The difference is the nut holding the rocker on, 3/8" needed in your case.

[Kenth]

Originally Posted by 1966Lemans

Oh, cool... thanks for the tip. I grabbed some STP "high mileage" when I picked up some Mobil 1 15w50 at Walmart... next time I'll try the Lucas additive. Thanks!

15W50 does not flow well until engine is at 250°+F and added STP will only make it worse.
It will take longer for this syrup to reach out were it´s most needed, expect ticking lifters at cold starts.

Why not use standard 10w30 API SF mineral oil prescribed by the manufacturer (GM / Pontiac) for use at normal engine temperatures?
Is your engine completely "high mileage" worn out?

[1966Lemans]

I don't really know how old the engine is, but it's safe to assume it's got a fair amount of mileage. Whoever replaced it (greater than the 19 years I've owned it) probably pulled it out of a big car in a junkyard. I typically use the 15w50 Mobil 1 in the summer, and 10w40 in the winter.