273 hydraulic cam/pushrod/adjustable rocker combination.

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jh66cuda

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Just in the process of swapping out my intake with a LD4B on my 66-273. I decided to do some preventive maintenance and check the rocker arm adjustment. The engine has and Melling 23203 hydraulic cam (specs below) with Melling MPR-155 push rods and adjustable rockers. To my surprise there was very little preload on the lifters and most were set a zero lash. Also noticed that there were a couple push rods that appeared to be bent. After removal it looks more like the top cup wasn't on straight. I did some digging and the MPR-155 should have an over all length of 7.342, mine measure 7.186. I also attached a picture of where the push-rod travels through the head, a couple of the rods that appeared to be bent were actually hitting on the head.

Any thoughts or ideas would be greatly appreciated.




  • IMG_0698.JPG
    IMG_0699.JPG
  • Advertised Exhaust Duration: 298 deg
  • Advertised Intake Duration: 288 deg
  • Basic Operating RPM Range: 2800 RPM
  • Cam Type: Hydraulic Flat Tappet
  • Computer Controlled Compatible: No
  • Exhaust Duration at .050 inch Lift: 224 deg
  • Exhaust Valve Lift: 0.466 in
  • Exhaust Valve Lift with Factory Rocker Arm Ratio: 1.50 in
  • Intake Duration at .050 Inch Lift: 214 deg
  • Intake Valve Lift: 0.444 in
  • Intake Valve Lift with Factory Rocker Arm Ratio: 1.50 in
  • Lifter Type: Hydraulic
  • Lobe Separation: 112 deg
 
Usually bent pushrods are a side effect of valve float. May want to pull your lifters and check for scuffing or irregular wear. Check rockers for lateral movement, may need re-bushed, replaced. Get a pair of adjustable length checking pushrods, set up rockers with 1-1/2 threads showing from under rocker, install set-up and adjust pushrod length for around .020-.030 of lifter preload. Check at least all four corners of engine, cylinder number 1,7,2,8. Bear in mind lifters preload usually between .020-.060, so you have some leeway. Order pushrods set for that length or get a cut to fit set, if available, your preference.
 
Those adjusters look well down lower than normal, so short pushrods makes sense. How are you measuring the pushrod length? Top of cup to end of ball, or bottom of cup to end of ball?

That's not a ton of lift so that would be less likely to cause the pushrod to contact the hole. But, the short pushrods and the resulting adjuster position would move the pushrod over towards the side of the hole where your pix shows contact, so that could be the reason for the bending.
 
One other thing to check with checking pushrods in place at proper adjustment is the reason for the recommended 1-1/2 thread showing out of bottom of rocker. The middle of the tip of the rocker should be centered on the middle of the valve tip at 50% camshaft lift.
 
Those adjusters look well down lower than normal, so short pushrods makes sense. How are you measuring the pushrod length? Top of cup to end of ball, or bottom of cup to end of ball?

That's not a ton of lift so that would be less likely to cause the pushrod to contact the hole. But, the short pushrods and the resulting adjuster position would move the pushrod over towards the side of the hole where your pix shows contact, so that could be the reason for the bending.
I measured overall length, top of cup to bottom of ball. Just wondering if some one had previously shorten them for some reason.. according to melling they should be 7.342..
 
jh66',
Mr Ellison & nm9 have You covered .
I am chiming in to validate their observations,
-from experience- (lol).
LOL ! destructive experience.
 
That's the old 68 340 cam specs. A powerful cam in a 273.
 
I have found a lot of these pushrods are bent out of the box most people don't check new ones I've sent many back they say its from over pressing the ends on the tube and bending them
 
Those adjusters look well down lower than normal, so short pushrods makes sense. How are you measuring the pushrod length? Top of cup to end of ball, or bottom of cup to end of ball?

That's not a ton of lift so that would be less likely to cause the pushrod to contact the hole. But, the short pushrods and the resulting adjuster position would move the pushrod over towards the side of the hole where your pix shows contact, so that could be the reason for the bending.
I agree with the adjusters being screwed in lower then normal but they are all over the map as well. Kinda the reason for mr to look deeper and check adjustment. Pic is of #1 and 7
IMG_0701.JPG
IMG_0700.JPG
.. see attached pics.
 
I measured overall length, top of cup to bottom of ball. Just wondering if some one had previously shorten them for some reason.. according to melling they should be 7.342..
OK, more often measurements are from ball tip to bottom of cup, but it can vary. Melling shows it being measured in this fashion in the document below, so they are even shorter than you think, something like 7.080" if measured from ball tip to bottom of cup....!! Almost seems like the wrong pushrods are in there.....or they were indeed shortened, maybe for a higher lift cam at some point? The crooked cup at top may be caused by poor cutting techniques.
https://www.melling.com/wp-content/uploads/2017/03/push-rod-identification-chart.pdf
 
Hummmm.... the exposed threads do not look so bad from that angle. Those adjusters are not stock so I was probably fooled on the depth. Some variation in the exposed thread is to be expected.

Have the heads been milled on this engine? Or the block deck milled? That could explain some of the pushrod length situation.

Also, if the valves are longer than stock and/or are excessively sunk in the heads, that would push the pushrod ends of the rockers downward and put the pushrods close to the hole as shown in your pix and cause the pushrods to be shortened.
 
OK, more often measurements are from ball tip to bottom of cup, but it can vary. Melling shows it being measured in this fashion in the document below, so they are even shorter than you think, something like 7.080" if measured from ball tip to bottom of cup....!! Almost seems like the wrong pushrods are in there.....or they were indeed shortened, maybe for a higher lift cam at some point? The crooked cup at top may be caused by poor cutting techniques.
https://www.melling.com/wp-content/uploads/2017/03/push-rod-identification-chart.pdf
If measured from ball to bottom of cup they are 7.026. Where do I go from here? Any ideas? I have had this car for 7 years and it doesn't matter what I touch I come across crap like this. I appreciate the help.
 
Hummmm.... the exposed threads do not look so bad from that angle. Those adjusters are not stock so I was probably fooled on the depth. Some variation in the exposed thread is to be expected.

Have the heads been milled on this engine? Or the block deck milled? That could explain some of the pushrod length situation.

Also, if the valves are longer than stock and/or are excessively sunk in the heads, that would push the pushrod ends of the rockers downward and put the pushrods close to the hole as shown in your pix and cause the pushrods to be shortened.
Unfortunately the engine was done before I purchased the car. from the documentation I have it was bored .040 over and the heads were ported. so kind of a Pandora's box.. lol
 
Those don't look like factory rockers to me. Locknuts?

Also the pushrods for factory solid / vs hydraulic are different, wondering if you looked up the wrong dimension. I don't know what they are, offhand.

"If I can get to it" I had a running 318 using original 273 hydraulic adjustable pushrods and could measure them, later..............
 
I’m finding 7.25 listed for pushrod length for adjustable rocker and hyd lifter
 
Those don't look like factory rockers to me. Locknuts?

Also the pushrods for factory solid / vs hydraulic are different, wondering if you looked up the wrong dimension. I don't know what they are, offhand.

"If I can get to it" I had a running 318 using original 273 hydraulic adjustable pushrods and could measure them, later..............
Yea I know that the adjuster are different then stock, just not sure why?
 
I'd measure the installed spring height at this point. Stock is 1.685" from head to bottom of retainer. See what that dimension is to start to see if the valves are set up right, and to see if the rockers may be at an 'off' angle.

As for knowing the head and block milling, if it is not known, then it would have to be partially dissassembled. No the first time weird things are found in an engine...unfortunately.
 
I have 7.389 in mine with stock rockers.
Edit: With a stock cam

Alan
 
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If your longer pushrods still hit the head, you’ll need to move the rockershaftsup and backwards.
(Backwards meaning towards the cam.)
 
I have a 318 with same set up, adjustables with hydraulics. Cam is almost identical to yours, not that it matters.

I took .010 off the head and about .080 off the deck. KB167 piston .004-.006 below deck with .028 head gasket.

Pushrods are 7.060 long. The custom pushrod set was around $200.

Also, one of the heads, I had to elongate the holes where it passes thru the head. It was hitting same place as yours. Precision machining, casting, was not a priority for dodge way back then. Not impressed.

I have to either elongate the holes on my intake manifold or have it machined .030 per side due to misalignment on intake bolts.

If the threaded bolt holes are low (alignment) in the intake manifold holes, your heads or block,or both have been machined like mine is.

If your intake was machined as well, there won't be a misalignment, a stock manifold would reveal the truth.
 
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I have a 318 with same set up, adjustables with hydraulics. Cam is almost identical to yours, not that it matters.

I took .010 off the head and about .080 off the deck. KB167 piston .004-.006 below deck with .028 head gasket.

Pushrods are 7.060 long. The custom pushrod set was around $200.

Also, one of the heads, I had to elongate the holes where it passes thru the head. It was hitting same place as yours. Precision machining, casting, was not a priority for dodge way back then. Not impressed.

I have to either elongate the holes on my intake manifold or have it machined .030 per side due to misalignment on intake bolts.

If the threaded bolt holes are low (alignment) in the intake manifold holes, your heads or block,or both have been machined like mine is.

If your intake was machined as well, there won't be a misalignment, a stock manifold would reveal the truth.

SO after looking a little closer at the push rods they have definitely been shortened. Some of the cup tips weren't pressed in correctly or the rod wasn't cut squarely. I like the idea of setting my new intake on the deck and inspect the bolt alignment... I think i'm going to buy a set of pushrod checkers just to double check length is.
Appropriate you information. TY
 
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