'71 F 100 cam?

B

beekeith

Junior Member
Howdy ya'll. I bought and rebuilt an old truck like I used to haul hay on back in the '70's. It ran smooth but had enough blow-by to blow out the dip stick. It never had a major overhaul 'til now. Torn down, it had one broke piston. The block and all else were good. One new set of pistons ( .040 over ), bearings, valve regrind, lifters, cam, carb rebuild kit etc. and it is up and running again. However, it ran smoother when it had the broke piston in it. I am an ole' diesel mechanic from years ago, so I'm not totally uneducated when it comes to pulling on wrenches. But, add a spark plug and I'm lost. What I see when reading what I can find are things like... "early '71 vs.late '71", "retarded timing gears", " 3 different firing orders ". By the way, I do have the plug wires back on as stamped on the intake. I put all the major parts in from the parts man who's been in business long enough I couldn't tell him much. My doubts began when he wouldn't understand that to adjust the valves, I needed different length pushrods. Anyway, my question is this. Could I have the wrong "stock" cam for my little 302? It seems like it just isn't breathing right. Kind of like a vacuum leak ( my best estimation is that it's not that )......Anybody? Beekeith........... And yes, I keepbees. Lol
 
LOWRIDER said:
Firing order is determined by what camshaft was installed.
Click to expand...
Agreed. If the new cam was in fact for a 351 then the correct firing order will be 13726548. Your engine might only be running on four cylinders with the 302 firing order.
 
Gerry, just pulling your lariat. I bet you thought you were on a Y-Block only site. Easy to forget on this site because everything is together. Or was it one of those Old Timer Moments and /or SoCal Flashbacks? I get them all the time? :eek::eek:

I know very little about SBF's so I never comment when they are the topic. But I do read the thread so I can learn and maybe use some info on a Y-Block
 
Update. I did change the firing order to match Fordors' info. It did make it run worse so that should tell me I don't have a different cam. After repositioning the wires to their original location, the engine seemed to run a little smoother. Imagination? I've got less than a hundred miles so far on it. Maybe the chrome rings just aren't seated in yet? It does still have a little surge as I'm going down the road.
 
You may have the late cam gear. It killed the horsepower and torque on every engine Ford did that to. Makes them pretty anemic. Maybe the dist timeing is different for the late and you're set for the early. I'd think the dist. specs were different between the two.
 
Okay Dave, Considering the late timing gear route. To me, it does seem lacking power. What remedies are available? Would reinstalling the old gear ( but new chain ) be about all I can do? But,there is still that surging thing going down the road. One thing I don't like is the .67 to .167 valve lash they give you on those specs. That seems like such a wide swing compared to some other things I work ( and have worked ) on. I left some of them too loose in my opinion for fear of getting them too tight.
 
Let's consider the lifter adjustment instead. I know Ford has some bass-akwards method to adjust hydraulics on a '71 302 (and many other engines) that use the non adjustable, stand type, rocker stud. When you installed a new cam in your engine assuming it had the same base circle why did you see a need for the longer push rods? If you loosened a rocker, then just tightened it to get to "zero" lash how many turns of the nut would it take to get to the torque spec with an old push rod? I think, but do not know for sure, that they are 5/16"-24 thread so then 1 turn of the nut is just over .040 and 2 1/2 turns is .100 putting you at the bottom of the range of the lifter plunger. If it would take more than 2 1/2 turns then yes, I would see a need for the longer p-rods. The next increment is +.060 and if you installed those push rods if will take fewer turns (and/or increments) of the nut to get proper torque. What I'm trying to clarify is that the lifters are adjusted properly. This seems clear in my head, I hope it comes across that way in print.
 
Good line of thought, Fordors. Let me back up and start over. When the heads came off, they went to a well recommended mechanic who runs his own garage. He said they were good and only needed grinding. Valves and seats and nothing else but that. Now that alone I am thinking would in itself cause the valve lash clearance to be closer. I didn't check the adjustments before tearing it down. But after reassembly, that's where I find some rockers about right and some I think are too loose. I was told by the guy that did the heads that the rocker nuts bottom out on the stud and torque there. Also my "Motor Truck Repair Manual" says the same thing. Assembled as such, the lifters (with valves open) are to be collapsed and the lash is measured there. .067 to .167. Now, I know enough about precision measuring that those Ford engineers have a peculiar sense of humor. And they didn't make it easy to measure because they were bored that day. But my best take on what I see is a full range within the .100 they give you. Some may go outside of that. Now, if what you are saying, I can add the .060 over and let the nut not go all the way down to give me a good uniform lash adjustments across the board? (Uh, heads?) Maybe followed with some lock-nuts to hold the position.
 
The "early" cam gears are available over the counter so you can get a new gear if needed. Crank gear is the same regardless of early or late. You should be able to back trace the part numbers to determine what you really have. "RV" cams were sometimes used, especially for truck applications and one tooth off on the timing can really make a difference in how it runs. Even pros make mistakes. Unless your base circle on the cam has changed, snugging the rocker bolts down should keep them within the spec range so different length pushrods should not be needed. Grinding valve faces and seats only removes thousandths, again, not pushing the lifters out of their range.
 
In the first post you mentioned you needed longer push rods to adjust the valves. If you had installed +.060 p-rods the end of the rocker raises higher and that would require more turns for the nut to get to where they bottom out so that they can be torqued. At the same time you are running the nut down you are also pushing the plunger down in the lifter. If the plunger reaches the bottom of it's travel the next thing that will happen is you will have a valve open should you need to run that nut lower, until it bottoms on the stud, to torque it. A few valves might be open just marginally, enough to hurt the performance. Have you put a vacuum gauge on it?

Did you buy and install the longer p-rods, or did that counterman talk you out of them? If they are in the engine I for sure would put the stockers back in and try that.
 
Yes. Some of my writing may be clear as mud. But on this engine, according to manuals in regards to specs, the rocker nut is tightened all the way down. With the measurement of each valve when it is fully open, the lifter is to be fully collapsed in order to take the measurement .067to .167. Now, about the longer pushrods, I did buy some from another parts house just to have on hand. (My point was when the original parts guy looked at me and said they don't exist, it made me a little unsure of the parts I was getting.) I live far enough out of town that I'd rather have something I don't need than to need something and not have it. When I put some in, they were too tight and I took them back out. They, I believe are in spec, just some of them are on the "max" end of the range than more than half of them. Now about being one tooth off, I'm not gonna put any money on that bet. Seems like every time I try to build something square, it ends up a little more trapazoidal, lol. But, when installing the gears, the centerline of the cam and crank fall in line with the 2 dots on the gears as best as I recall.
 
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