My engine is a '79 345. It was low mileage, but I opened it up for a minor problem and ended up rebuilding the whole thing. I have another thread on my project I started: "345 rebuild, quench, compression, cam".
I recently measured what changes, if any, might be required in my pushrod lengths to ensure my lifters will have the correct preload. I have new eptwi ha855 lifters, a new isky 190156 cam, the block decked, and head work. I had hoped I would be able to use my oem prs as is and still be in the range of good lifter preload (.050-.075 ideal) since the new cam is .030"smaller in basecircle radius than the oem and the head gasket is thicker which I had hoped would balance out some of the machine work. I was wrong.
After checking all pushrods and all locations, the best I could do requires pr that is .054” shorter to get .075” lifter preload. So I sent a pr that I used as my “standard” to smith bros for them to make me new ones with specified amount shorter.
However, I have since noticed a discrepancy (trying to hide my frustration here) in the design dimensions of the lifters and pushrods.
Please see the attached photo for an explanation.
The oem lifter has a ball end based on a spherical diameter of ~.390” with a flat on it of ~.160” dia. For oil collection and to keep pr surface pressure on an outer ring on the lifter so it rotates with the lifter.
The oem lifter has an annular ring surface about .040” wide where the oem ball end rides. It also has a relief in the center for oil collection.
The rocker arm cup is ~.390” spherical with an oil passage in the center (the pr flat allows the oil passage to be free to pass oil).
The oem pr ball end rotates and nests perfectly in the oem lifter and oem rocker.
However-the new ha855 lifter has a.375” diameter spherical cup with a chord across its chamfered mouth of .350”. As you see in the photo of the radius gage (also .375” diameter) on the pushrod end, the oem pr .390” dia ball end will have only a line contact around the lifter cup at the contact location shown. Surely, a bad design waiting for damage instead of smooth area break-in.
This also produced a problem in accurate pr length assessment, since a .375” pr ball end will sink into the new lifter all the way, but the oem pr ball end will be .011”to.013” shorter (measuring virtual length to end of ball without flat, or same flat).
So….a “correct fit” would be a pr with an oem .390” dia. Spherical surface ball end with .160”dia. Flat on the oem rocker end (the flat for oil passage), and a .375” dia spherical surface with a .160” dia. Flat on the ha855 lifter end (the flat is still needed to ensure the pr rotates with the lifter and not just pirouettes in the center, not just for oil collection).
I would rather not have to be an engineer. I assume the eptwi ha855 lifters are manufactured by johnson? What is the cup pocket radius of the “other” manufacturer? Is it made more like the IH oem which appears to be able to accept both .390 and .375 in its cup, or is it also .375”?
I don’t yet know what smith bros will come up with. Are IHOnly north’s prs’ ball ends based on a .375” sphere or a .390” like the oem? And, do they have the requisite flats?
This issue might not seem important since the engine will run in any case with a doable lifter preload, but if it’s wrong, it’s wrong for a reason…eventually.
Please comment. Thanks.
I recently measured what changes, if any, might be required in my pushrod lengths to ensure my lifters will have the correct preload. I have new eptwi ha855 lifters, a new isky 190156 cam, the block decked, and head work. I had hoped I would be able to use my oem prs as is and still be in the range of good lifter preload (.050-.075 ideal) since the new cam is .030"smaller in basecircle radius than the oem and the head gasket is thicker which I had hoped would balance out some of the machine work. I was wrong.
After checking all pushrods and all locations, the best I could do requires pr that is .054” shorter to get .075” lifter preload. So I sent a pr that I used as my “standard” to smith bros for them to make me new ones with specified amount shorter.
However, I have since noticed a discrepancy (trying to hide my frustration here) in the design dimensions of the lifters and pushrods.
Please see the attached photo for an explanation.
The oem lifter has a ball end based on a spherical diameter of ~.390” with a flat on it of ~.160” dia. For oil collection and to keep pr surface pressure on an outer ring on the lifter so it rotates with the lifter.
The oem lifter has an annular ring surface about .040” wide where the oem ball end rides. It also has a relief in the center for oil collection.
The rocker arm cup is ~.390” spherical with an oil passage in the center (the pr flat allows the oil passage to be free to pass oil).
The oem pr ball end rotates and nests perfectly in the oem lifter and oem rocker.
However-the new ha855 lifter has a.375” diameter spherical cup with a chord across its chamfered mouth of .350”. As you see in the photo of the radius gage (also .375” diameter) on the pushrod end, the oem pr .390” dia ball end will have only a line contact around the lifter cup at the contact location shown. Surely, a bad design waiting for damage instead of smooth area break-in.
This also produced a problem in accurate pr length assessment, since a .375” pr ball end will sink into the new lifter all the way, but the oem pr ball end will be .011”to.013” shorter (measuring virtual length to end of ball without flat, or same flat).
So….a “correct fit” would be a pr with an oem .390” dia. Spherical surface ball end with .160”dia. Flat on the oem rocker end (the flat for oil passage), and a .375” dia spherical surface with a .160” dia. Flat on the ha855 lifter end (the flat is still needed to ensure the pr rotates with the lifter and not just pirouettes in the center, not just for oil collection).
I would rather not have to be an engineer. I assume the eptwi ha855 lifters are manufactured by johnson? What is the cup pocket radius of the “other” manufacturer? Is it made more like the IH oem which appears to be able to accept both .390 and .375 in its cup, or is it also .375”?
I don’t yet know what smith bros will come up with. Are IHOnly north’s prs’ ball ends based on a .375” sphere or a .390” like the oem? And, do they have the requisite flats?
This issue might not seem important since the engine will run in any case with a doable lifter preload, but if it’s wrong, it’s wrong for a reason…eventually.
Please comment. Thanks.
