I recently purchased a Jasper 351w that has 5,000 miles on it with the casting of E9 or 1989. I plan to install Comp Thumpr cam kit Summit Racing part number K35-600-4. I am trying to determine if I will need custom push rods before I get too deep in the install. Is there anyway to tell before hand? I also plan to use the factory rocker arms which are pedistal mount I think "right?" If that makes a difference. Thanks for the help!

 

Yes, pedestal mount rockers. I don't think you're going to need new pushrods. The higher lift cam has the same base circle and is simply moving the valve further. If the cam was more radical, it might matter? Don't take my pushrod advice as sure truth, it's just based on what I've been reading lately.

Is this a carb truck or EFI? The 107 LSA won't work with EFI...

 

It is def going to be carbed. Using a dual plane Summit Racing intake and a 750 cfm vaccuum secondary electric choke Summit Racing carburator. Also going to run Hooker longtube headers. Nothing crazy just a daily driver with what is probably an over sized cam, but hey it is what I had laying around.

 

I think you'll be disapointed in the "***** Thumper." Nice rumpity-rump but everything I've read about them points to being useless in these trucks.

If you're set on installing it, ok, but I would invest in a pushrod checker to determine correct pushrod length. The base lobe is usually ground down allowing for a higher lobe lift so lifter pre-load may be off if using stock pushrods.

With pedestal rockers you won't have to worry about valve train geometry if using OEM stamped steel rockers.

Be sure to degree the cam for proper cam timing, too.

 

I think it is just the Thumpr because it has the smallest amount of lift in the Thumpr series I believe.

 

Well this is the mis-statement of the year. the whole combination of parts affects the geometry, using the factory rockers will not in themselves guarantee the geometry will not change.

 

Indeed. I can think of more outrageous (mis) statements that make mine look like cotton candy.

Would you not agree that pushrod length determines lifter preload?

Would you not agree that rocker pedestal and rail rocker shims (if needed) determine geometry using roller rockers?

So, how would you determine what's the proper valve train geometry using stamped steel rockers at zero lift, half lift and full lift if (noting that stamped steel rockers slide over the valve stem), any mark (sharpie, mechanic's blue, etc) on the valve stem would be obliterated?

I agree with you on the fact that valve train geometry is a combination of lifter preload, pushrod length and shims if needed on roller rockers but correct lifter preload using stamped steel rockers would render good valve train geometry automatically.

 

No, it will not. Just because you think that the geometry cannot be checked due to your assumption that the rocker slides across the valve stem does not automatically make the geometry OK. He's changed the cam and the lift specs, so he will need to check the geometry if he want's to guarantee that it's not so far off as to dramatically shorten the life of the valves and the guides.

 

Any machining of the block deck or head mating surface will affect pushrod length, as will valve seat machining if valve stem length isn't altered to compensate. If the cam you use isn't ground on a small base circle(is a retrofit cam) then it should work with the pushrods you have but measure to be sure. I'd also question the carb choice, in general that 750c waaay too big but it could be made to work with a serious downsize in the jets, with stock heads this motor will not make more than 275hp at about 4500rpm so a 550cfm would be plenty. That last point also weighs in on the cam choice, yes a nasty high duration cam will work as in the motor will run but something with much shorter duration would actually make more Tq and Hp.

 

My question was: So, how would you determine what's the proper valve train geometry using stamped steel rockers at zero lift, half lift and full lift if (noting that stamped steel rockers slide over the valve stem), any mark (sharpie, mechanic's blue, etc) on the valve stem would be obliterated?

What's not true? The fact that any mark on the valve stem to check proper geometry would be obliterated? Can you not answer that question?

Apparently not. In the picture below of a stock 429 head, it seems that I also can't apparently see the ball berrins or needle berrins on the OEM stamped steel rockers which allow the rockers to "SOMEWHAT ROLL(S) ACROSS THE TIP OF THE VALVE STEM."
The wear pattern on the valve stem is 0.1530" and on the rocker (measured linearly) is 0.3800" That 0.2270" difference seems like quite a bit for a rocker that "rolls" over a valve stem despite it having a minor arc.




429 stock head, valve springs and rockers.




.....but correct lifter preload using stamped steel rockers would render good valve train geometry automatically.

Jeez, those poor Ford UAW boys must have had a bear of a time checking each engine for proper valve train geometry, with all the different cams in the different engines that came off the assembly line!

I never said the geometry can't be checked using OEM stamped steel rockers...

Again, I feel for those UAW boys who had to check each engine..... . Yes, if the geometry is way off, it will wear out the valve guides sooner. But, OEM rockers and lifters are very forgiving with the 0.185" of lifter plunger travel and rocker to valve stem tolerance. But, there is always lateral/side to side forces in play with OEM rockers producing more friction and, thus, wear on the guides...as opposed to roller rockers.

Another question since I brought up roller rockers: Do you think roller rockers should start rolling at the inboard valve stem, roll to the middle and then roll to the out board side of the valve and back during one rotation of cam lobe/lifter travel?

 

[QUOTE=Filthy Beast;16598176]My question was: So, how would you determine what's the proper valve train geometry using stamped steel rockers at zero lift, half lift and full lift if (noting that stamped steel rockers slide over the valve stem), any mark (sharpie, mechanic's blue, etc) on the valve stem would be obliterated?

What's not true? The fact that any mark on the valve stem to check proper geometry would be obliterated? Can you not answer that question?
you don't measure the marking, but the missing portion.
Apparently not. In the picture below of a stock 429 head, it seems that I also can't apparently see the ball berrins or needle berrins on the OEM stamped steel rockers which allow the rockers to "SOMEWHAT ROLL(S) ACROSS THE TIP OF THE VALVE STEM." Are you blind ? Look at the tip of the rocker. It's not flat. It's curved, just as I mentioned.
The wear pattern on the valve stem is 0.1530" and on the rocker (measured linearly) is 0.3800" That 0.2270" difference seems like quite a bit for a rocker that "rolls" over a valve stem despite it having a minor arc.




429 stock head, valve springs and rockers.




.....but correct lifter preload using stamped steel rockers would render good valve train geometry automatically.



Jeez, those poor Ford UAW boys must have had a bear of a time checking each engine for proper valve train geometry, with all the different cams in the different engines that came off the assembly line!
really ? how many different cams were used in the 429 ? The ones that were used didn't have that wide a variation in lift specs, in which the OP proposes to use in picking that Thumper cam
I never said the geometry can't be checked using OEM stamped steel rockers...
you implied that the geometry couldn't be checked and more than once. (see your statements above)
Again, I feel for those UAW boys who had to check each engine..... . Yes, if the geometry is way off, it will wear out the valve guides sooner. But, OEM rockers and lifters are very forgiving with the 0.185" of lifter plunger travel and rocker to valve stem tolerance. But, there is always lateral/side to side forces in play with OEM rockers producing more friction and, thus, wear on the guides...as opposed to roller rockers.
we're not talking about a pure OEM combination of parts here.
Another question since I brought up roller rockers: Do you think roller rockers should start rolling at the inboard valve stem, roll to the middle and then roll to the out board side of the valve and back during one rotation of cam lobe/lifter travel?[/QUOTE]

The pattern should be pretty much centered on the valve stem tip. Where it starts and ends up is a moot point. Do YOU know where it starts and ends ?

 

Next time you have an engine assembled to where you can observe the action of the rocker on the valve stem, get someone to rotate the crank slowly and watch what happens between the rocker tip and the valve stem. You will clearly see what I'm talking about. And I'm also going to guess you think the cam lobes slide across the bottom of a flat tappet lifter too ?

 

Thread hijack of the century... calm it down you fellas.

To the original poster, I would follow the directions of the cam manufacturer. If it says original valve gear is fine then use your original valve gear.

Hell, I've gone one better and looked up the specs for the Thumpr 279 (part 35-600-4) and it says you need replacement valve springs... thats it.

I'd put the cam in with new valve springs, do the valve seals while you are there (may as well) and boom, you're in business. Make sure the rockers are contacting the existing wear pattern on your valve tips and you are good to go.

- boingk

 

Really ? This is a forum to discuss things. Chill out.

 

So, again, how would you determine proper valve train geometry using OEM rockers? The fact that any mark on the valve stem to check proper geometry would be obliterated. Can you not answer that question?

One measures the missing portion??? How can you measure something that's not there? Is that like measuring the quantum decoherence of a collapsing wave function? Or dividing by infinity?

Yes, indeed, it is curved. I'm glad you mentioned it as I never would have known.....and the valve stem tip is flat. A portion of the rocker slides over the valve stem tip leaving a mark on both. The rocker position is noted at zero lift, half lift and full lift with attention paid to its position at half lift. Doing some math and noting the net valve lift, the rocker's optimum position should be 90 degrees from the pushrod at half of the cam's net lift. Also, at half lift, a 90 degree angle should be between the valve tip and rocker centerline... or center of the rocker's rotation.

And, if OEM rockers rolled across the valve stem, as you insist they do, wouldn't they have a different name? As in "roller rockers?

I never said the geometry can't be checked using OEM stamped steel rockers...
Again, I never said, nor implied, geometry can't be checked using OEM stamped steel rockers. Maybe you're blind and have trouble comprehending the written word. I see no statements I previously made (above) that states that. Quote me where you see it?

Do you think roller rockers should start rolling at the inboard valve stem, roll to the middle and then roll to the out board side of the valve and back during one rotation of cam lobe/lifter travel?

"Well that is the mis-statement of the year." While a centered pattern is desirable, it is not often the case. At half lift, 90 degrees from the rocker's centerline and proper math, the roller tip could be any place on the valve tip as long as it doesn't roll off.

Where it starts and ends is not a moot point as one is watching and noting where it starts and ends at different cam lobe lift. Anyone with a dial gauge and a pair of eyes could see that.

Matter of fact. How else would it (the lifter) rotate around as the cam lobe is imparting its information? The lifter's foot is convex which allows a rotation as it slides over the cam lobe. If it "rolled" it's nomenclature would be a "roller lifter" on a "roller cam."
Imagine that!