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.