The legendary 2.9 Free Floating Rockers


PetroleumJunkie412

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Ok engine experts, here's the newest dumb thing I'm cooking up.

I successfully recreated the 2.9 phenolic intake spacers. Now I want to recreate the Sven Pruitt / Pat Kunz "free floating rockers."

I got my spare heads and rockers back. Finally.

This should be as easy as measuring the gap filled by the springs, applying the Pruitt specs to it, and having a set of the four made, correct?

I'd think that every gap on every set of rocker arms is probably going to be slightly different. Maybe. I have the spare 86TM heads here with arms, and the set of 89TM rockers and heads that are on my truck. The plan today is to measure both and compare.

If you have a 2.9, and the time, could you please take a measurement of at least one of your rocker arm gaps that the springs fill? I want to get a few side by side comparison to see if there is a general measurement that universally applies. I'll post my dimensions below. If any of you have an opportunity, could you please do the same?

As soon as I have a set of dimensions I'm comfortable having produced, the plan is to have these run out by eMachineShop so that others can have them made readily. I'll post the cad files here and see if I can get them in the tech section for all to use.

Let's unearth this relic!



 


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PetroleumJunkie412

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Specs from Pat Kunz:

"Shaft to rocker arm clearance .0025-.003in. (stock is .0013in.) rocker arm bore diameter should be around .7836-.7842in. Aluminum spacer to rocker arm side clearance of .010-.015 for each rocker arm that, that spacer is used with so .020-.030in. for the rocker arms between the pedestals. (stock is 0 clearance between spring and rocker arm, it actually rides up against it)."
 

8thTon

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What exactly goes wrong with the stock spring design?
 

Uncle Gump

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I think what happens are the rocker "walk" on the shaft.
 

PetroleumJunkie412

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What exactly goes wrong with the stock spring design?
Quite a number of things. Gump nailed one of them.

They were a cheap and sh*tty design concocted by Ford.

The springs allow the rocker arms to walk slightly. The other thing they cause is metal galling by exerting lateral pressure on the rocker arms between the arm and the pedestals. Constant uneven lateral force eventually wears the arms in a canted pattern (like my old assemblies) and starts cutting off oil flow to the valve train, and leads to the infamous 2.9 tick.

The spacers create oil galleys in the valve train, and allow oil to free flow through the top end. Word on the street is that they eliminate lifter tick entirely from the 2.9, and allow the engine to come on faster due to less mechanical resistance on the top end.
 

Uncle Gump

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Didn't mean to post that so quick... I wasn't done. They walk and I'm sure the springs fatigue. Doesn't keep things in place so well.

Junkie... I've done this on VW stuff for years. What I know is the spacers we used were not an exact size to position the rockers exactly were they needed to be. They came with shims to do that. It makes producing the spacers far less critical and allows for the assembler to position the rocker exactly were it needs to be. I also know the VW shims were actually valve spring shims. Checking the shaft size and outside diameter of the rocker might yield you some off the shelf valve spring shims that could be used.

EDIT... there is also what junkie said... I was close.
 
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PetroleumJunkie412

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Page from the Sven Pruitt book:

1566740170119.png


I'm guessing the same logic applies to the 2.8 and (ugh) 4.0
 

PetroleumJunkie412

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Didn't mean to post that so quick... I wasn't done. They walk and I'm sure the springs fatigue. Doesn't keep things in place so well.

Junkie... I've done this on VW stuff for years. What I know is the spacers we used were not an exact size to position the rockers exactly were they needed to be. They came with shims to do that. It makes producing the spacers far less critical and allows for the assembler to position the rocker exactly were it needs to be. I also know the VW shims were actually valve spring shims. Checking the shaft size and outside diameter of the rocker might yield you some off the shelf vale spring shims that could be used.
Good idea. I know some of the Chevy guys do this to the 350 small blocks as well. Didn't realize the V-dub builders did.

I *believe* the Cologne V6 rocker arm shafts are a weirdo/orphan size. Would literally laugh my ass off if off-the-shelf spacers fit, especially if the Windsor V8 ones are the correct size.

The 2.9 guys have been chasing this unicorn for years.
 

Uncle Gump

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Everyone needs a little...

Illustration for article titled Fahrvergnügen -The truth


I didn't mean the spacers would fit.... you're gonna have to make those. But the appropriate sized shims might be available.
 

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Ok, but I’ve seen that same spring design in many engines, and it was used for many years. Does it always have this problem? Is it endemic to this design?

My suspicion is that this is another symptom of the oil system design problems in this particular engine - maybe work modifying that?
 

PetroleumJunkie412

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Ok, but I’ve seen that same spring design in many engines, and it was used for many years. Does it always have this problem? Is it endemic to this design?

My suspicion is that this is another symptom of the oil system design problems in this particular engine - maybe work modifying that?
It is endemic to the 2.9, one of the Achilles' heels I'll actually admit to ;brownbag;

Normal joking and 2.9 fanboydom aside, the 2.9's oiling to the rockers, valves, and lifters is p*ss-poor at best. Literally had a brand new lifter start ticking within 20 minutes of first start after my rebuild.

This is the 'known' fix for the oiling issue, and the information on how to construct them has been lost to time.

Gaz's recent (apparently BS) post, and a local machinist failing to get them made has inspired me to just do this one myself and share the results.
 

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Here are some measurements from a pair of '89's. One thing I've wanted to know since reading about these spacers, is what do you do about the gap between the spring clips and the outside rockers? Leaving the spring clips in would defeat the purpose of the project in regards to the outside rockers.

Based on the wear marks where the rockers meet the valve stems, Ford didn't think it was too important to precisely position the rockers. But like Uncle Gump said, shims appear to be a necessity due to the varying dimensions. I haven't looked into this in too much detail, but I assume that the pedestals are pressed on, which is going to have a lot to do with the gaps on either side.

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PetroleumJunkie412

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My old 86 TM heads, rocker shafts installed -

2.055
2.150
2.190
2.031
Shaft diameter at all four spring points roughly 0.880"



Paulos' 86TM Rocker assemblies, not on heads -

2.041
2.148
2.034
2.143


Awesome! Thank you Paulos!!!

Keep em coming guys! Has to be quite a few of us with old 2.9 rocker assemblies laying around, haha.
 

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There is some serious variation with the first two samples.... I see shims in all your futures.
 

PetroleumJunkie412

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Here are some measurements from a pair of '89's. One thing I've wanted to know since reading about these spacers, is what do you do about the gap between the spring clips and the outside rockers? Leaving the spring clips in would defeat the purpose of the project in regards to the outside rockers.

Based on the wear marks where the rockers meet the valve stems, Ford didn't think it was too important to precisely position the rockers. But like Uncle Gump said, shims appear to be a necessity due to the varying dimensions. I haven't looked into this in too much detail, but I assume that the pedestals are pressed on, which is going to have a lot to do with the gaps on either side.
So the pedestals are free floating on the rocker shafts, believe it or not. They feel pressed on due to the spring pressures and galling issue.

Not sure about the spring clips or outside rockers. I can see the utility of aluminum bushing there, though.

My fear with the spacers and shims would be wear. I need to look into how the V-dub guys do this.

Any suggestions Gump??
 


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