Mancini/HS 1.6 rocker not giving me the lift expected

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Spadman

Spadman

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I installed an MP 2992 nos cam advertised to be .474 lift. Went with Mancini rocker kit 1.6 ratio. The box arrived marked 1.6 and they are grey as expected. I put washers in a hyd lifter for checking and get only .465 lift. The lift directly on the cam lobe is .317, as expected. I have a ball and cup checking pushrod in place with heavy springs so could have a slight amount of flex. Mancini says call Harlan Sharp. What could be the problem other than wrong ratio rocker.
 
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It’s a small block mopar with typical small block mopar pushrod angles. You always throw away some lift. More so if the geometry isn’t correct.
 
With the 1.6 rocker arms I should have seen .507 if perfect. Can geometry lose that much? I’m not even getting the .474 advertised with 1.5 ratio.
 
I usually add 0.030” lift more than I need when order a cam so I get around what I want for the final post geometry influenced lift.
 
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Spadman said:
With the 1.6 rocker arms I should have seen .507 if perfect. Can geometry lose that much? I’m not even getting the .474 advertised with 1.5 ratio.
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Yes it can, and does. Ever measured a W series head? They’re even worse.
 
I measured out the rocker and talked to a Harland Sharp tech. The measurements he gave me are spot on to what I have. He said the checking pushrod with the heavy spring could easily be the problem. I guess I’ll get my cut to fit pushrods done and see after that. The geometry doesn’t look bad at all. Thanks.
 
As you get better lift push rod tunnel clearance becomes a concern so watch for that as well. There comes a point with the effort will yield very little without major surgery.
 
Spadman said:
I measured out the rocker and talked to a Harland Sharp tech. The measurements he gave me are spot on to what I have. He said the checking pushrod with the heavy spring could easily be the problem. I guess I’ll get my cut to fit pushrods done and see after that. The geometry doesn’t look bad at all. Thanks.
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I wouldn't use a checking pushrod with anything other than a checking spring. That's the first thing I'd look at.

Are you 100% sure you're on the base circle when you start your measurements, and also set preload?

What are you using to measure lift? Can you share a pic of your setup? I had to make a big to adequately attach a dial indicator on my heads. Mounts to the valve cover holes.
 
Mean416 said:
I wouldn't use a checking pushrod with anything other than a checking spring. That's the first thing I'd look at.

Are you 100% sure you're on the base circle when you start your measurements, and also set preload?

What are you using to measure lift? Can you share a pic of your setup? I had to make a big to adequately attach a dial indicator on my heads. Mounts to the valve cover holes.
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Yes, started on the base circle and turned several times. The dial indicator was stable. It reliably returned to zero each time as I rotated the crank. Lash was set to zero.

IMG_1706.jpeg
 
Pushrod length affects the valve lift, plus many other factors. The actual valve lift at various points throughout the lift cycle will vary with rocker brand, as David Vizard's testing showed....

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My thoughts on this are that.04 is a pretty good bit off but I still think you should be checking with a checker spring. Those are cheap and easy to install can you do that and get back with us?

I would also compare to a stock set of rocker arms for reference.
 
I had earlier checked with the checker spring, but got rattled when I was rechecking centerline and pushrod length and decided to check it again. Looking back at my earlier notes; what I saw with checker spring; first pass: .486. Lengthened pushrod to max: .504. Shortened to 1-1 1/2 thread: .502. I see now it is definitely pushrod flex. Thanks for your response.
 
Sorry to all you guys for my posting in panic. I hope the discussion was informative to others as well as myself. I should have hit on flex in the checking pushrod right away. Getting old.
 
I noticed that the location of the cup to the rocker arm adjuster changed my numbers.
I saw that getting the least treads out of the rocker arm with the adjuster seemed to help ratio.
Geometry.
What you are calling pushrod flex could be this length change.
 
I ran into this recently with Hughes 1.6 aluminum rockers. I was missing out on over .045 lift with the correct length pushrod and finally saw the difference of the adjuster location to the centerline off the rocker shaft on half of the rockers I received.
Look over your rockers and use a straight edge along the adjusters as a guide.

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mderoy340 said:
I ran into this recently with Hughes 1.6 aluminum rockers. I was missing out on over .045 lift with the correct length pushrod and finally saw the difference of the adjuster location to the centerline off the rocker shaft on half of the rockers I received.
Look over your rockers and use a straight edge along the adjusters as a guide.

View attachment 1716293062

View attachment 1716293063
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:eek::eek::eek:
 
Spadman said:
Sorry to all you guys for my posting in panic. I hope the discussion was informative to others as well as myself. I should have hit on flex in the checking pushrod right away. Getting old.
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No this is definitely an informative post. Beats the hell out of guys asking HP predictions on old *** tired 318's in desperate need of a rebuild lol.
 
Next year we should have sb mopar and bb mopar rockers available, 1.65 and 1.7 in both...rocker arm on shaft, oil thru cup adjuster, roller tip but non roller body. Good for hyd and solid FT, and hyd. roller up to around 480lbs. open pressure.
 
Brian Hafliger said:
Next year we should have sb mopar and bb mopar rockers available, 1.65 and 1.7 in both...rocker arm on shaft, oil thru cup adjuster, roller tip but non roller body. Good for hyd and solid FT, and hyd. roller up to around 480lbs. open pressure.
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The system only lets me hit the like button one time, but your post deserves six or seven. Looking forward to seeing these options.
 
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