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  #1  
Old 09-02-2009, 06:59 PM
Mr_Mopar Mr_Mopar is offline
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Default Valve Geometry PROBLEM!! HELP!

Hello. I am having valve geometry problems.

I am rebuilding a 273 with a mechanical cam, solid lifters, I put a comp cam with a 468 lift. I did not buy new pushrods or lifters, because the engine was rebuilt recently by someone else and they looked practically brand new and did not have any wear on them. I assume they are stock applications. I have heavy duty valve springs and stock adjustable rockers, stock valves. I did shave the head 10 thousandths, but I do not know if the person before me decked the block. I assume that it's not because I didn't see any marks on the deck?

Problem: When I turn the engine over by hand, when the cam lobe is at the top of its rotation, the pushrod is pushing the rocker the whole way up and hitting. There is no adjustment left because I have the adjustment the whole way out and the cam is almost at it's fullest point. What do you think I should do? I did not know what to do, because I don't know if I should buy different pushrods, shims, or lifters? I held the pushrods that I have next to a set of for-sure stock 273 pushrods and they practically the same length. There might have been a hair difference, but not enough to change my problem. Please, anyone, let me know if you have had this problem, what to do, and where to buy the parts!

Thank you in advance for your help!
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  #2  
Old 09-02-2009, 07:24 PM
crisser crisser is offline
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Old lifters on new cam?

I`m not sure what the problem is by your description but, it sounds like you need shorter pushrods. Might want to see also if the pushrod seat on a stock lifter is at the same depth as a Comp solid.
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  #3  
Old 09-02-2009, 10:47 PM
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JVMopar JVMopar is offline
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I guess I don't understand what's hitting. Is the retainer hitting the valve guide, valve hitting the piston, or what? You shouldn't have changed the valve geometry that much with that small of a cam. I think I read somewhere that you gotta cut the guides down with cams over 0.450
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Old 09-02-2009, 11:20 PM
Billydelrio Billydelrio is offline
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If the cup on the pushrod is hitting the rocker arm, you may be able to pull the cup off, shorten the pushrod and press the cup back on. Or, get a set of shorter pushrods.
Decking the block and head could cause what you are experiencing, but so can a longer than stock valve stem, very deep valve seats, large base circle cam, hydaulic lifter on solid cam, and other things.
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  #5  
Old 09-03-2009, 04:42 PM
John Kunkel John Kunkel is offline
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I'd bet the problem is a larger than original cam lobe base circle, shorter pushrods are the only practical solution.
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  #6  
Old 09-04-2009, 01:46 AM
rusty duster rusty duster is offline
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There's only one size push-rod and that is the size that fits. If the cup is hitting the rocker,and it is just a small amount you can grind the rocker for clearence.THere is also push-rods with different size cups. Call Smith Brothers and tell them the problem your having.They can hook you up with a better push-rod that fits.
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Old 09-06-2009, 07:35 PM
MerrittRacing MerrittRacing is offline
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I would say that I would make sure that the timing gears are correct, if the cam isn't off in any way then use a pushrod lenght checker and adjust it to where the rocker is right on the valve tip, measure how ling the length checker is and thats what pushrod you need. Also, I would definitely put a new set of lifters in that, not good to run old lifters on a new cam.
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Old 09-07-2009, 11:59 AM
gwaii gwaii is offline
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Make sure your solids are actually solids and not hydraulic.I wouldnt run the old lifters on a new cam,go to the manufacturer of the cam and get the lifters that match the cam there maybe a difference in the inside depth of the lifter,also you may have to get the pushrods that are for the 340 t/a engine as they are shorter and what you would use to run a hyd cam and lifters with the adjustable rockers if i remember correctly.
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Old 09-08-2009, 05:24 PM
TeamDart TeamDart is offline
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Maybe this would help to finding the proper sized pushrod....

This is how I do it. I do the final check with the full valve train assembled and the heads torqued. P/R's are the last thing to be installed. Here I'm doing an initial check making sure the rockers are in alignment, not too high on teh stud, yada yada.
Mock up the head, cam in the engine. Measure your full valve lift at the retainer, making sure you've got the lash taken into consideration.


Next, rotate the cam until you're at exactly mid-lift. Using a small square, (and check to make sure it's square) align the center of the trunnion and the center of the roller tip with one edge, and look to see that the other edge is parallel with the valve stem. Not almost parallel, and not close, but dead nuts parallel. It's pretty easy to see with a machined surface. Because of the rocker ratio, it doesn't take much change in P/R length to change this either.



You can see here I'm not exactly centered on the two trunions with the one side of the square, but it's hard to take a pic with one hand and hold the square with the other and keep things in place. It takes a little bit of patience to look at one, then the other, adjust the pushrod, re-set the rocker, and do it all over again until you get it right, but once it's done, it's done. Remember, if you're going to do this, every time you change the adjustable P/R length, you have to re-set your lash.

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  #10  
Old 09-08-2009, 06:09 PM
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pishta pishta is offline
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I doubt the base circle of the cam is actually larger, that would make little sense as the additional lift on a cam that already has lobe crowns that are very close to the bearings can only be achieved by lowering the "floor" or base circle. I bet your lifters are the culprit, but if you milled .010, you might be able to shim the entire rocker shaft with the appropriate shims that allow oil to continue to be routed through the pedestal. I have some original 273 pushrods, Ill get a measurement tonight from tip to tip of cup (easiest to measure) I thin kthey are a tad off from the 70 340 pushrods.
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  #11  
Old 09-12-2009, 04:51 PM
Mr_Mopar Mr_Mopar is offline
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Hello. I am getting back to everyone. I appreciate all the advice and insight. I did order a different set of lifters and shorter pushrods. My factory pushrods are 7.497 and I needed the 340 TA pushrods that are 7.342. It did fix the problem, so thank you all. It wasn't as big of deal as I thought. This was just the first 273 that I have ever rebuilt. I wouldn't have had this trouble, but all the tech people at comp cams said this cam would work with factory rockers and factory pushrods. Thanks again.
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