roller tip to valve stem contact

[46flattie]

Long story, but an engine guy suggested I try running roller rockers in my 401 w/o machining the pedestals down by compensating with longer pushrods. I have been running this motor for several years w/o much trouble. I have it apart for some other maintenance and am again looking at my rocker arm geometry with this set up. Technically the roller tip should be centered on the valve stem. By eyeball it looks pretty good, however when I ink up the valve stem and check contact area I am slightly off-set towards the intake. Maybe 10-15%. Should I have any big concerns, or keep on keeping on?

[tufcj]

Optimally, there should be as little movement of the roller on the tip of the valve as possible. The slight offset won't hurt anything as long as the roller isn't contacting the valve keeper and the pivot on the rocker isn't contacting the stud. If it's been running OK that way, let it go unless you have the heads off for other machine work. The only down side I see is that the longer pushrod has more chance of flexing under the pressure of the open valve.

Bob
tufcj

[46flattie]

Thanks for your input. Roller is nowhere near the keeper, and the rocker arm pivot "slot" does not touch the stud or nut, Running trickflow 5/16" rods, etc....so I think I'm good. I have the heads off to repair a burnt valve, so I thought I would revisit this. I do plan to re-check push rod length after the heads are done though.

Thanks!

[46flattie]

Sent my heads in to have a the burnt valve replaced and the rest checked over. Shop found all the exh valve guides to be junk! THe worst he's ever seen! While these were completly rebuilt about 8 yrs ago, they really do not have many miles on them. Intakes are all good. Makes me think the original shop did not replace the the guides as they said they had....

Anyway, while these are at the shop, I am considering having the pedestals machined down...I have seen posts that indicate 0.25" + guide plate thickness. Is this correct or is is it dependant on other factors? Am I wasting $? The old set up seemed to be fine and I assume had nothing to do with the exh guide failure as the intakes are all good.

Thanks for any input.

[tufcj]

Are the holes already machined out for 7/16" studs? Generally, .250" shorter on the pedestals + the thickness of your guide plate (usually .125"), so about .375 total from the pedestal.

It will mean getting new shorter pushrods and re-checking geometry. It could be the offset and longer motion of the rocker that wore your exhaust guides. It can't be that much extra cost if the heads are already apart, and it couldn't hurt to get it closer to factory geometry.

Bob
tufcj

[46flattie]

yes, I drilled and re-tapped for 7/16 studs...and that is what I was thinking. Appreciate your input!

[46flattie]

Sorry to beat this to death, but I had to know where .25"+guide thickness comes in...so I mocked up stock vs. my crane rockers/studs and find the difference between the center pivot points are approx. 0.25". Can anyone confirm that I am on the right track with my theory? Just want to cover my bases before removing metal!

Also, K8600 summit cam....this 401 is in a Jeep CJ-8, 33's w/3.73 gears. I like low-end torque and 5000-5500 rpm is plenty high enough for me. any opinions on their cam set quality? any other options anyone else can recommend?

Thanks again!

[tufcj]

The .250" measurement came from the 70-early 73 heads that came from the factory with individual rockers. Those heads (casting numbers 291-C, 090, 993) had guide plates built in (the pushrod holes were oval) and 7/16 screw in studs. There was just a comparison measurement between the pedestals on the early heads and the later bridged heads.

The 8600 is kind of small for a 401. AMC engines like to breathe. I ran an Edelbrock Performer in my 360 powered Jeep (t-18, Dana 300, 4.88 gears, 37" tires, 80:1 final ratio). It pulled hard right from idle, but would fall flat over 4500 RPMs.

Bob
tufcj

[46flattie]

The .250" measurement came from the 70-early 73 heads that came from the factory with individual rockers. Those heads (casting numbers 291-C, 090, 993) had guide plates built in (the pushrod holes were oval) and 7/16 screw in studs. There was just a comparison measurement between the pedestals on the early heads and the later bridged heads.



Makes sense and matches what I calculated. Thanks for the explanation! Still thinking about cams, I have run both the edelbrock performer and the summit k8600 in my 401. I felt I lost some low-end w/the 8600, certainly gained some mid and upper range though.

[46flattie]

Ok guys, need more advise on this subject....got my heads back, while the shop had them I had the pedestals milled down as discussed above anticipating it would make my existing roller rocker arm geometry better. What a mess....makes it worse for re-using the same Crane energizers #11746 1.6 ratio as before ...I have to run the rocker up a long ways on the stud to get what I had before for roller tip to valve stem contact pattern, which was not great (slightly inboard of center towards intake). If I run lower on the stud where I should be the contact area on the stem is WAY inboard! I have come to the conclusion that while they are advertised for AMC V8 applications, they are not right. As if the rocker arms are too short - pivot to tip

I have come to the conclusion that I need a good AMC V8 application rocker arm...So any recommendations on roller rocker arms? I am considering Hardland Sharp S4004 or the Scorpion...both in the adjustable stud style.

[tufcj]

I looked at that part number on Summit's site. I don't know how Ford/Chevy/AMC could be covered by one rocker. Chevy rockers are known for being too short from pivot to tip for AMC use. Ford applications are much closer, but sometimes the slot is too short and the rocker hits the stud when the valve opens. I'm running Crane Gold rockers (35750, I think) on both of my 390s, using 70 heads (291C) and .100" longer than stock pushrods. Harland-Sharp are very good, I believe MC sells the Scorpion rockers right here at the Bulltear store.

Bob
tufcj

[46flattie]

Bob,
Thanks for all your replies, they have been very helpful!

Talked with both Harland Sharp & Scorpion this morning. They both indicated their rocker arm sets are the same body as Ford. However, Harland Sharp said they do an additional chamfer machining operation the relieve the bottom of the rocker arm in the slot area for the stud due to AMC rockers typically sitting lower on the stud. Scorpion rep could not or did not indicate either way, even when quizzed if the do anything different for AMC applications. Both reps indicated chevy is too short for AMC.

I was very impressed with Harland Sharp guy....he knew his shit...I mentioned the S4004 part # and he rattled off application & how much spring (pressure & diameter) I could run for that application (way too quick for pulling it up on the computer), was very familiar with the manufacturing process and application differences, all made in the USA including sourced materials,etc., etc.

Thanks again...I'll keep you posted. Been fooling around with Jeeps & AMC v8's for most of my life and still learning!

[tufcj]

I lived in the mid-west in the late 70s/early 80s. Mud bogging was big. I built class compliant AMC engines for mud boggers, along with other makes. I've always been impressed with AMC engines. I had a 304 in my Jeep, bored .030", flat top pistons, and 1.94/1.50 valves, rods shot peened and crank nitrided, I revved it to 6500 all the time. Lots of guys were convinced I was running a SBC before I would open the hood and show them an AMC engine.

Hope you get the rockers worked out.

Bob
tufcj

[46flattie]

(((((Quote Originally Posted by AMX69PHATTY View Post
I have a '69 343 block fitted with a 3.44 stroke 304/360 crank.

Now I have bought the Harland Sharp 1.6 AMC Rockers.
To make the geometry come out correctly with them
I've had to go back to "standard" Studs, 1-3/4 long
and 7.700 long Pushrods, shorter than '69 stock at 7.748.
Could maybe go even shorter, but two problems arise,
The Rocker gets to close to the Stud Hex
and run out of threads on the 1-3/4 Studs with the Poly Locks.
Both sets of rockers are 1.6 ratio.

So there is definitely a difference in Rocker Geometry
when using SBC dimension rockers versus AMC (Ford) dimension rockers.

Probably no surprise to most folks here but I am,
and I have it all to owe to BullTear and this Forum.

Allow me to say THANKS to all the helpful folks here.
END QUOTE)))))


I found this thread elsewhere on here and wanted to include this info in my thread. Thank you for this post!

As I am too in the process of ditching Crane energizer "AMC, Ford, Chevy" rockers and installing Harland Sharp 1.6 rockers on my 401....just finished checking pushrod length....I also came up with 7.700 and also found that I would like to go slightly shorter, but have the same issue with rocker arm to stud clearance. I am running ARP studs which have the shortest hex. I suppose we could have machined the pedestals down more to improve this....I believe we took off something in the 0.280 range, will have to double check.

At any rate your set-up gives me some confidence in my measurement!

My valve stem pattern is damn close to being perfectly centered to being slightly outboard...