Hi Y’all,
I’m sorry if this has been covered but I couldn’t find the answer.
I think I’m having a cam issue. The engine is in a 1986 F250. I measured the lift as best I could with a magnetic dial micrometer while turning the engine. I got measurements between .272 and .282. I think that looks low. The engine runs fine, maybe a little underpowered, at least until two lifters collapsed. I am in the process of replacing the lifters.
I looked in the service manual and it only states the lift as .2600 for intake and exhaust. I’m not sure what that means. Is it the minimum lift, max lift, nominal lift? I have been looking for specifications as well as cams and I don’t think there is such a thing as a cam with .260 lift. Someone told me the OEM specs are .444 intake and .450 exhaust. That sounds good but what duration? Also, where did that info come from? I’m not trying to be difficult, but just telling me what the OEM specs are doesn’t convince me. The largest Ford dealership in a four county area is nearby and they can’t tell me what the cam specs are. There are a lot of specifications that go into cam selection, and I don’t know any of them except the firing order.

The shop service manual indicates a cam lift of .260. How is that when my original cam with 86,000 miles that is in the engine measures .272 to .282 lift?

 

Cam lobe lift (0.260") multiplied by rocker ratio(1.6) equal valve lift (0.416"). At this age the cam could have been changed but production tolerances could also explain your discrepency.
What the manual doesn't show is valve timing and duration and that is what influences the powerband more.. although compression ratio and head flow capacity also factor in.
This is a low compression(8.3:1) smog era motor with undersized heads and a poor cam so not surprising it is underpowered, all that can be changed though... there is a ton of untapped potential in this engine. The stock cams are not well documented but here is a chart with a bit more data, you likely have the 351-2bbl not the 351HO

 

Thank you Sir. That makes sense. It sounds like what I really need to do is install a set of solid lifters and measure again, this time at the end of the valve stem. My goal in all this is determine if my cam is worn and needs replacement. Also, my measurements could be suspect as measuring the movement of the end of a pushrod while leaning into the engine compartment trying to make the magnetic dial gage fit all the while turning the engine with a ratchet might result in a questionable measure. One additional question though, and this displays my ignorance of the system, is when a cam producer lists lift as .xxx, is that the actual rise above the base line on the cam itself or is that the measure of the valve stem movement, guessing that the rocker arm ratio is taken into consideration? Because, if so, then that would make sense when the Summit racing answer was the cam lift is supposed to be .44 and .45. I’m a little surprised that the shop manual has such limited information on the cam other than it works by turning. Even the book on how to rebuild your small block Ford engine doesn’t really cover the cam much.
Thank you again. You are wealth of knowledge and I appreciate your willingness to help guys like me.

 

Aftermarket cams are listed by lift at the valve, with the stock rocker ratio.

I wouldn't get too hung up over your measurements being right on with the book. Production tolerances can be larger than they should be sometimes. What I'd be more concerned about is whether they're all relatively close to each other (ie: you don't have a lobe going flat).
Also, I recently had a lobe get wiped out on an original 351w cam (all stock motor). I would SERIOUSLY consider a zinc additive or a high zinc oil if you're not already using one.

 

Thank you Sir. I think my accuracy could be better so I’ll probably measure again. The readings I got were all between .272 and .282. But, trying to measure the movement of a wobbly pushrod could result in inaccurate readings.
As far as the zinc goes, one of the few tidbits I learned from Motor Trend TV was about the zinc in oil and as a result, all my old vehicles use Amsoil with ZDDP additive. I think it’s ZDDP but it could be a different terminology, but the idea was the zinc. I change the oil in my truck every 3000 miles or every year, whichever occurs first.
Apparently, I’m the only person messing with engines that didn’t know how cam lift is reported. Sorry to make a pest of myself but I appreciate the forum readers patience with me while I learn.

 

Not a pest at all.
I'd never berate someone who's genuinely searching for knowledge.

BTW, ZDDP is an acronym for the compound in oil that the EPA so lovingly decided we didn't need any more. It's a compound of zinc and phosphorus. Often times it's just simplified to 'zinc' by us laymen.

 

Zinc dialkyl-dithiophosphate (ZDDP) is a very effective anti-wear additive, but it produces ash when burned, which can jam up piston rings and other tight-tolerance parts, like bearings. It also poisons catalytic converters when it's unavoidably burned in normal engine operation. EPA did not explicitly ban ZDDP, but its detrimental effects on modern engines and emission control systems forced auto manufacturers and oil producers to look for alternatives, such as molybdenum based additives.

Ever since I learned of roller cams in the 70's, I've always cringed a little when thinking about how flat tappets worked. I now have much easing of mind after converting my last flat tappet engine to roller tappets (and cam, of course).

And yes, most cam manufacturers today list lift at the valve, taking into account the factory rocker arm ratio.

 

Hi Y’all,
I am finally getting around to reassembling the engine. I have the lifters preloaded with oil and I have assembly lubed everything and changed the oil. I have the pushrods and rocker arms ready to torque but that’s where I had to stop to ask a question of y’all. I have two references, he How to Rebuild Your Smallblock Ford book and the Ford shop manual. I use both for reference. The rebuild book has a lot of tips and techniques that are a great aid to the puzzle of rebuilding. The shop manual is, well, the shop manual. It’s more clinical and not much on tips and techniques. The question I have is both books have different crankshaft turn amounts for aligning the valves for rocker arm torquing. Below is a pic of the rebuild book and a pic of the shop manual.



This is from the shop manual.

This is from the rebuilding book

Both books adjust the same valves at each turn of the three turns. The shop manual steps, 1: #1 TDC, #2: turn crank 360 deg, #3: turn crank 1/4 turn. The rebuilding book steps, 1: #1 TDC, #2: turn crank180 deg, #3: turn crank 270 deg. At each step the same valves are supposed to be fully closed.
My question is which of these do you think are correct? I suppose I could just tighten and torque all the rocker arms and rotate the engine and check the torque every few degrees. However, that is not the recommended method. An alternate method is to just make sure each piston is at TDC in the firing order. I’m not sure how to do that, so I’m stuck with either the shop manual turn method or the Rebuilding a Smallblock Ford method.
What method do y’all use?
Years ago I rebuilt , actually helped rebuild, a Smallblock Chevy 350, and we only torqued the rocker arms all at the same time. The engine ran great. This engine is proving to be a little more picky.
Thank you for your help.

 

it works out the same, there are multiple valve that are closed at any one time so there are short cuts. In fact the valvetrain in these motors is non adjustable so if the machining has been done correctly and the first couple rockers torque to spec when they are supposed to you can usually skip all the other steps and just torque them all down without turning the crank to close valves.

 

Thank you for your reply Sir. I have been thinking about this and thought that if I turn the crankshaft 1/4 turn I should get the next cylinder in the firing order at TDC, then two full turns later it should be back at TDC for #1. But then again, like you said, backyard mechanics have been just torquing them all down at once and the tough old engine just takes it and keeps ticking. I went through all the trouble to get a sharp pointed needle to load up the lifters with oil, then to see them pressed in, slightly, and the oil squeezed out when the crank turns makes me wonder why I did that. I see multiple crank turns the next time I get to work on the truck to get the rockers torqued at the right time. I’m a little confused by the whole description of the turning crank valve up thing. I think the next time I’m in the garage I’ll check the firing order thing. I just want to eliminate a possible weak link in a possible noisy lifter event when I get the engine running again.
Thank you again for your reply.