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291c Heads |
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AMXAL 
AMC Nut 
Joined: Feb/19/2012 Location: IL. Status: Offline Points: 324 |
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 Topic: 291c HeadsPosted: Apr/03/2012 at 9:22pm |
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Great info everybody...but I need some help, am building a 74, 401 for my Javelin, had the engine freshened up and changed the pistons to give 10 to 1 compression, the heads were given a 3 angle and new Crower springs to match the cam, I just bought some Scorpion 1097 pedestal mount roller rockers, seems the pushrods are short, still using the stock ones 7.90 I believe, I did not mill the heads but had them cleaned up and flattened, builder said the stock rods were good but that was before I went to the Scorpions, what pushrod length will work? Anyhelp is appreciated
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73hornut
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Joined: Jul/03/2007 Location: Southern Oregon Status: Offline Points: 3130 |
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Posted: May/21/2011 at 9:47am |
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I was considering scorpians, but after a google search, there were quite a few negative forum post for these developing cracks.
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71 Javelin
74 Gremlin 79 Spirit AMX Rogue Valley Rumblers Like Us on FB https://www.facebook.com/groups/1602825606650796 |
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GREM
AMC Apprentice 
Joined: Feb/12/2011 Location: Colorado Status: Offline Points: 46 |
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Posted: May/21/2011 at 3:20am |
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so here goes...
I'm a rookie on a mission here...I'm going to keep asking questions till I get it right. I can't afford to make mistakes so I swiped a diagram from one of the fantastic links provided above; & added the letters A thru D to it, with some more questions having to do with "stack" measurement. I read both links multiple times before understanding the theory but need confirmation. Never was any good with engineering terminology  ...I can visualize pics better so here goes... A= HALF the diameter of the roller B= valve stem height above top of spring retainer C= difference between top of retainer & center of trunnion (BTY both are clearly marked on the Scorpions) D= Angle & centerline of rocker stud So if I'm seeing this right starting from lower to upper I would lay a straightedge up the yellow line represented by D & at the same time lay a straightedge flat across the top of the spring retainer. The resulting measurement gives us measurement C. From the top of the retainer to the top of the valve stem measurement is B From the top of the valve stem to the center of the roller measurement gives us A A+B+C= stack That right?  |
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69 ambassador 390
Supporter of TheAMCForum 
Joined: Nov/22/2009 Location: Peoria, AZ Status: Offline Points: 3539 |
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Posted: May/06/2011 at 10:51pm |
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YUP!!!!!
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Steve Brown
Algonac, Mi. 69 Ambassador sst 390 84 Grand Wagoneer 69 Cougar XR7 65 Fairlaine 500XL 79 F-350 Super Camper Special |
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GREM
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Joined: Feb/12/2011 Location: Colorado Status: Offline Points: 46 |
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Posted: May/06/2011 at 10:25pm |
Great information! I've got a much better understanding of the importance of stud height & pushrod length now when using roller rockers. No more bench racing for me... the next pics will be of the motor on an engine stand with one of the 291's torqued on over a used (squished) head gasket along with a layer of clay on a piston. A couple of superglued hydraulic lifters will be in place as well as a pair of 10lb weak valve checking springs on one cylinder for the purpose of checking everything! With the adjustable pushrod I'm going to assume that the procedure stays the same as far as checking valve to piston clearance...that being with valve closed...0 backlash. Turn the crank by hand two or more revolutions. Once adequate clearance has been verified I then use the procedure above to re-adjust the adjustable pushrod for final length. Am I getting close? Thanks, Grem |
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tsanchez
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Joined: Jul/09/2007 Location: Arizona Status: Offline Points: 4303 |
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Posted: May/04/2011 at 1:00pm |
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Basically you want the roller to begin it's travel just barely to the intake side of the stem and to roll across the center and when at maximum lift for the roller to be in the same position on the stem where it started. While it goes through the full range of travel it should have a very tiny sweep pattern on the top of the valve stem.
To do this you can simply measure. The best resource for this is here:
And a old article that explains it right
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tsanchez
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Posted: May/04/2011 at 12:45pm |
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Grem that is opposite of what comp cams says and is also wrong.
I wrote this on the other amc forum and just copied it, so some might not apply.
Well to be short, there is not a perfect rocker for all groups, being that the rocker stud and valve are at different angles it creates a problem when a different lift is used or when a different length valve is used. Different lifts makes the point of pivot higher or lower on the stud which is in turn closer or further from the valve center. The best geometry is the rocker with the least amount of sweep for the lift and centered on the valve tip and the pushrod side with the least amount of sweep but since that is dreaming most of the time just getting the sweep minimised on the valve is best and where it ends up on the valve tip is of minimal concern as well as what happens on the pushrod. Wayyyyy too much effort is used to get the roller centered on the valve tip when most of the time that makes the geometry horrible. Also valve geometry has NOTHING to do with deck height or pushrod length, the geometry is on the head you just have to figure what pushrod to use for the geometry you need not the other way around.
My opinion, you may have different results  |
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69 ambassador 390
Supporter of TheAMCForum
Joined: Nov/22/2009 Location: Peoria, AZ Status: Offline Points: 3539 |
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Posted: May/04/2011 at 11:37am |
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Yes, The pattern should be centered on the tip. Two things to consider. You can acheive this pattern with a lower fulcrum and a short push rod or a higher fulcrum and a longer push rod. Valve length cannot be adjusted so the two things you are dealing with is fulcrum height on the stud and pushrod length. What you are doing is moving around two of the three points on a triangle with the valve tip being the one that you cannot move. You want to set up the rocker so a straight line drawn from the valve tip to the push rod cup results in the least angle of deflection between the lifter cup and the rocker cup(pushrod pushes with least angle). You also want to make sure you maintain the rockers rated ratio in the length between the two bottom sides of the triangle. This is why it is so important to have the correct rocker arms and not just the correct ratios. The distance between the valve and the stud and the stud and the point where the pushrod intersects the rocker is different far all engines of different makes. A Chevy rocker is not a Ford rocker is not an AMC rocker. The fulcrum depth below the tip and the cup as well as the overall length of the rocker will be different for all also. You could have a rocker that is 10" long across the top and one one side of the arm would be 6.25" and the other would be 3.75" and you would have the same 1.6 ratio. If you are truly using AMC rockers then you will just need to set the pushrod length and be done with it.
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Steve Brown
Algonac, Mi. 69 Ambassador sst 390 84 Grand Wagoneer 69 Cougar XR7 65 Fairlaine 500XL 79 F-350 Super Camper Special |
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GREM
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Joined: Feb/12/2011 Location: Colorado Status: Offline Points: 46 |
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Posted: May/04/2011 at 12:34am |
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I received the two sets of adjustable studs yesterday & had a chance to play with them enough to visualize how the whole roller rocker thing works. I think the SBF set will work best as they have the most adjustment; but I have a few more questions to ask first; since the heads aren't mounted to a block yet.
I'm trying to get my head wrapped around this & in my mind after mocking these up, it seems that initial adjustment should be set up with the roller more towards the exhaust side of the valve stem with the valve closed. As the pushrod opens the valve it seems to me that the roller will travel closer to the center of the stem & at midway valve opening, the roller should be positioned in the middle of the stem. As the valve opens all the way the roller should be positioned closer to the intake side of the valve stem; then everything reverses going back the other way? Am I close in my thinking?  |
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GREM
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Joined: Feb/12/2011 Location: Colorado Status: Offline Points: 46 |
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Posted: Apr/29/2011 at 1:48am |
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Thanks all! Very good info!
I've been doing some research on the geometry involved in roller rocker setups & how important all the different components are when setting up a valve train. I went into this swap blind but I'm starting to see the light; & how all the moving parts have to be matched for the purpose intended...in my case a Gremlin weighing less than 3,000 lbs. The donor motor is a 390 from a 1968 AMX rebuilt & balanced about 5,000 miles ago. The only thing I know about the cam is that it's a "Blue Racer Performance Cam" that Summit used to sell which I believe was manufactured by Crane. At idle with the stock square port heads it has a pretty good lope. It comes on strong around 1500 & flattens out just above 5000 with stock springs & stock hydraulic lifters. I plan to keep this cam & lifters. When I dropped off the heads to the machinist he needed to know what the lift on the cam was. As near as I could figure it was somewhere between .478 & .496... so that's what he used for base when replacing the springs. I'll be using an Edelbrock Performer intake & an Edelbrock Thunder series AVS 650 carb jetted for altitude. I ordered two sets of ARP rocker studs today from Northern Auto Parts...just in case. One is the SBC part# 134-7101 & the other is the SBF part# 134-7104. The valve covers I plan on using are original Edelbrock Aluminum Finned ones. I don't know if they are taller than stock so maybe someone can set me straight. The Scorpion box was calling out to me tonight so I couldn't resist. I had to see how they looked so I mocked them up with the stock AMC studs until the ARP ones arrive. The last pic shows the spring specs taken from the box of springs now on the 291c heads...    |
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tsanchez wrote: