Your donations help keep this valuable resource free and growing. Thank you.
|
Lazy Rocker Arm |
Post Reply | Page <123> |
Author | |
Ken_Parkman
AMC Addicted Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1814 |
Post Options
Thanks(0)
|
Carefully check the slot in the head. If the rocker is moving around like that the slot is not sufficiently aligning it.
|
|
PHAT69AMX
AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5919 |
Post Options
Thanks(0)
|
Most likely I'm all wet bein' nuthin' more than a dick beater with a keyboard, but...
The stock AMC rocker arms have a slot that is wider and made to "fit" the larger diameter of the stock stepped studs below the positive stop shoulder. So stock rockers slot is "too wide" to use with adjustable no-step 3/8 rocker studs since it creates a situation where with dynamics and with loss of contact the rocker can loose position. Normally yeah it's all ok, and yeah, the stock rocker slot does not contact the stock rocker stud larger bottom diameter, but it is "contained" or "limited" how far out of kilter it can get momentarily in a dynamic situation. I don't know the OD of the lower portion of a stock stepped rocker stud, but... they may work and fit with 7/16" diameter replacement adjustable rocker Studs. For comparison look at the width of the rocker arm slot in a sbc stock rocker compared to it's stock non-stepped stud. Pretty sure the sbc rocker slot is narrower than that of an AMC rocker so the sbc slot coincides with the non-stepped sbc 3/8 stud diameter.
Edited by PHAT69AMX - Apr/13/2021 at 7:25pm |
|
WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5798 |
Post Options
Thanks(0)
|
Phat, what you say makes a lot of sense, most likely just good luck rather than good management that the stock rocker arms work on non-shouldered SBC studs most of the time, or in my case 14 out of 16 times.
I do think it is more of a misalignment issue of that one slot in the head in this instance rather than wear of the slot itself that is the issue, that particular rocker just sits a bit off centre of the valve tip on both heads rather than being centred on the valve tip like all of the others. This is as close as I could get to a direct overhead shot to show the offset on the valve tip when the pushrod is centred in the slot. Scratch the idea of changing the pushrods to run the stock studs, I just rang the local parts shop and it will be $267 for a set of pushrods in the correct length. I am going to try plan B, which is to shim the stock rocker studs up so they will work with the longer pushrods. The idea is to raise the stud up so that the shoulder runs within the slot on the rocker arm, this is how it sits now with the longer pushrods: I can then make a decision over our winter on which way to go for next season as I have some Edelbrock heads I can put on this motor or maybe I can build a new one if finances permit. I'd like to do a bit of port work on the Edelbrock heads before running them. |
|
I've finally given up drinking for good...........now I only drink for evil.
|
|
dkrtgood
AMC Addicted Joined: Jun/27/2011 Location: St Pete, FL Status: Offline Points: 1371 |
Post Options
Thanks(0)
|
My question is why poly locks with positive stop studs? That makes no sense.
|
|
Dave Goodwin
President of Tampa Bay AMC 70 Mark Donohue BBO 390 5-speed 77 Matador Coupe AKA "The Beave" 70 Javelin 360 / Auto - BBG |
|
WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5798 |
Post Options
Thanks(0)
|
Two reasons, one is because pushrods are expensive if you keep having to buy new sets all of the time to get the correct preload and secondly adjustable rockers lets you set consistent preload given that you can't assume all of the valve tips are at the same level when working with 50 year old parts than have an unknown history of repair and maintenance.
|
|
I've finally given up drinking for good...........now I only drink for evil.
|
|
WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5798 |
Post Options
Thanks(0)
|
Well that turned out to be a stupid idea. I now find that the slot in the rocker arm is not long enough and the rocker will be binding on the stud shoulder at maximum lift, which is obviously not a good idea, this is of course compounded by the fact that the push rods are too long. I could grind on the rocker arms to lengthen the slot, but that sort of gets into the realms of two or three wrongs not making it right. Plan C is to install some roller rockers on it, the only issue at the moment is the set I have laying around is 1.7 ratio and that may be pushing the envelope with piston to valve clearance.
|
|
I've finally given up drinking for good...........now I only drink for evil.
|
|
Heavy 488
AMC Addicted Joined: Apr/27/2019 Location: In the Status: Offline Points: 3552 |
Post Options
Thanks(0)
|
You say that you have Eddy heads, maybe a novel idea is to just build it right once instead of just doing it over and over. It's not a top fuel funny car. Lifter preload settings shouldn't cause ulcers. Close is enough. Unless you really like busy work, then just keep going.
|
|
Ken_Parkman
AMC Addicted Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1814 |
Post Options
Thanks(0)
|
High ratio rockers will make no difference (well almost none, maybe .006" or .008") as there is no piston to valve problem at high lift - the piston is 1/2 way down the bore and far away. The problem is 10 degrees either side of TDC, but at that point rocker ratio has very little effect. Duration is far more important for clearance.
So unless it is super tight already you have no concern.
|
|
WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5798 |
Post Options
Thanks(0)
|
Heavy, I hear you, but maybe that is something for next season, I want the next engine to put me in the zone where I need more safety gear, i.e. sub 11.00, so I want to get on top of that first otherwise I only get one run and get sent home to install a cage. The current engine was a budget build, so it has it's limitations in other areas as well. Eddy heads will need porting before running them as well.
Anyway back to the task at hand, it's 1 am here and it is back together with a semi proper solution: Ken, I would suggest that it is super tight, with the 1.7 rockers it has 0.045" @ 7 deg ATDC on the intake and 0.077" @ 7 deg BTDC on the exhaust. 0.180" lift on the intake and 0.150" on the exhaust at these points, so maybe another 0.010" less than what it was before, it's a bit of a weird cam. That's why I was a bit reluctant to go with this option in the first place. I suspect it will either run a PB or go home on the trailer in pieces. |
|
I've finally given up drinking for good...........now I only drink for evil.
|
|
Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6880 |
Post Options
Thanks(0)
|
Ether way, way to go for giving it your best shot.
Have to tell us how the weekend goes for you, makes a great read! Good Luck!
|
|
Post Reply | Page <123> |
Tweet
|
Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |