More Engine Tech Tips:
Valves and Camshafts


Valve Adjustment

Scott Blystone: "My stock 3B has been rough for a while. Recently it had to be tuned real rich to keep it running and now it loads up plugs. Vacuum at manifold is shaky and about 17 psi. Anyhow, compression is 120,90,120,90 front to back. Oil in cylinder made no difference. Is it possible my valves only need a gap adjustment or is there something really wrong? When valves are responsible for low compression is it typically intake or exhaust? Can this repair be done in vehicle? How deep do I tear down? What parts do you replace while you're at it? I hear no valve rattle at all, but engine lacks power. Anyone who has done a 'valve job' on an F4 for similar reasons, please let me know what you encountered and any other details."

Ed Wilson: "Valve adjustment can be done just by removing the two valve covers, top and side. Replacement requires removing the head as well, but both are fairly simple without removing the engine. The only special tool you will need is a valve spring compressor. And be sure to use a good gasket sealer, such as Permatex #2 or a high temperature silicone when replacing the covers."

Joel Kamunen: "Adjust the valves and find out if it will run any better. It will only cost you the price of the gaskets to find out. Usually the exhaust valve goes first because of the heat of the exhaust flowing past it."

Valve guidesBen: "Does anyone have any experience replacing valve guides in an L-head motor or the block on an F-head (I assume they are the same). I have found out if they are bad you end up with a carb full of oil."

Eric Lawson: "I've always just taken the block to my local machine shop and had them do this. It doesn't look too hard to do -- a "punch" with a shoulder on it, with the shoulder slightly smaller than the bore into which the valve guide fits, and either a press or a hammer looks like it would do it. Be careful... gouging the bore in the block for the valve guide would be hard to fix."

Scott Blystone: "From looking at it and the manuals, it appears that the exhaust valve cover is held on by the PCV valve bell bolt and the stud that holds the throttle linkage. Is this really IT???"

Adam Charnok: "Yes, that's it. I've had mine on and off many times (trying to get the valve adjustment right). I find, just like a valve cover, you don't want to overtighten the 2 bolts. If you do you might get a leak. Plus take note of how the linkage comes off, to make putting it back on easier. If you don't do it right, the pedal might stay to the floor unleashing all the forces of the mighty Hurricane."

Jim Sammons: "Just another little piece of advice: besides the rag to catch errant parts, have a magnet ready also. And use some heavy grease to keep the valve spring retainers in place when you are installing them on the valve stem. Otherwise they almost always fall off before you can back off the spring compressor."

After repairing a broken exhaust manifold, Bob Christy could hear that his engine needed some valve work. However, he was receiving conflicting information: "One place says that the valve clearances are .016 of an inch for the intake and .018 of an inch for the exhaust valves and the other place is reverse of that. Also, I'm not sure if I actually know how to adjust valves."

Scott Blystone said: "I set both intake and exhaust valves to .016 of an inch. Take both valve covers off and remove the plugs. Rotate the engine by hand until a cylinder is at top dead center. The valve should be loose. Put a wrench on the tappet adjustment nut and turn until the .014 gauge will rattle but the .108 won't go in. Tighten down the locking nut against the adjustment nut. I usually run through all four valves twice as sometimes they move after you tighten them down. While it's a bigger pain to do the exhaust valves, they need it the most. Since you have just replaced your manifold, it will come off easily and you should get it out of the way to have room to work. Remember to take compression readings before and after the job so you can see the improvement. If the valves were way off, you may need to lean out your mixture a bit when you are through. Adjust the valves with the engine cold."

Austin provided the following information: "Cold clearance: intake valves .018 of an inch; exhaust valves .016 of an inch.

Valve Work

ValvesChuck came to the Bulletin Board looking for some advice on some valve problems that he encountered. "I have a M38A1 that is running low compression in the #3 cylinder. I was wondering what a ballpark figure for dealing with just the #3 intake valve would run? I know that all should be done, but the other three run at 100%."

Ed responded: "Well, it's always the #3 on these, isn't it? I went through the same thing myself; everything was fine when I bought the Jeep except for low compression on #3. I towed the Jeep down to my local motor guru after having first removed the head myself. They found that the #3 intake valve guide was broken and the valve bent. Replaced the guide and valve and ground ALL of the intake and exhaust for $200, including parts. I went home the same afternoon and put the head back on and now it runs like NEW. My advice is if you are going to do it, do them ALL; it will cost very little more than doing just one. That way you can be absolutely sure of your motor for a long time. Also, if the motor does not have hardened valve seats put them in now, while the engine is apart."

Jake recommended an option if the valve was merely frozen: "This might work for you if the valve is just stuck. We have had good luck at the garage for years using this mixture. Take one part ATF, one part brake fluid and one part paint thinner. Take out the spark plug and add the mix into the cylinder. Turn the motor over by hand 8-10 times and then let it sit for a day. Then roll it over with the starter."

Ed Wilson related his experience: "Several years ago, I had a burnt #4 exhaust valve in my F-head. I replaced it in my driveway one afternoon without doing anything to the other valves. I put it in, lapped it and stacked it all back together. This worked very well for four or five years. You can do a lot of valve work with the head off of an F-head, but in my experience, you don't have to."

Camshaft Bearing Clearance

Dan inquired: "Considering that three of four cam bearings have no replaceable shells, what choice does one have to tighten up the bearing clearance on the cam? Also, how far can you realistically exceed the specifications listed in the manual without losing too much oil pressure?"

Maxx responded: "Years ago, if the block webbing wore out where the cam rides, they scrapped the block. Then it was learned that if you have a good machine shop align bore it and install small block Ford 302 CID V-8 cam bearings, it will perfectly match the cam journals and solve the problem permanently."

Meanwhile, MrBob posted: "A friend and I are rebuilding an F-134 engine from my 54 3B. While ordering a rebuild kit for the engine, the representative for a very well known supplier of Willys parts said there should be only one bearing for the camshaft. My engine has four. He said someone must have added the additional bearings and that they do not supply any other camshaft bearings for the F-134 powerplant. They measure, in inches, as follows, front 2.185, center front 2.116, center rear 2.055 and rear 1.622. The big bearing is stamped, Clevite and SH-69. Do any of you have experience with this situation? Do you know where I might be able to buy the bearings I need. We removed all those bearing while taking the engine apart.

"Actually, there were three bearings, not four as I stated above.

Maxx again was on the ball: "MrBob, there is a possiblility someone bored out the block and installed Ford 302 cam bearings, a common fix when the cast surface wears down. ID & OD dimensions of the Ford bearings, cam journal measurements and snap guage & micrometer will confirm what you need.

"The back three cam "bearings" were not true bearings. Only the front one. They were cast iron. The kit you recieved should only have one bearing. Order a set of Ford V8 302ci cam bearings. They should not cost much and will likely answer your questions."

MrBob: "Thanks. That helps very much. Hopefully the fix applied to our engine is the one you describe."

Copperswilly: "Only on CJ3B.info can you get help like that!"

Oldtime: "Judging from the camshaft bearing overall diameters that you have supplied from your camshaft it appears to me that #2 and #3 cam bearings were turned undersize about .005". # 1 and # 4 appear to be standard. I can't very well give an exact determination because your calipers and mine could vary by perhaps as much as .002".

"So evidently your engine has been previously rebuilt. Seems the cam bearings had noteable wear which is a relatively rare occurence for these engines. I might suggest that you measure all your cam lobes to check them for wear as that could be most critical. These cams are nowadays seeing excess wear. This is likely due to the 1970's reduction of anti scuff agents in motor oil.

"Here are the cam specs from the service standard booklet:

"Remember micrometers and calipers can vary as much as .002 from one to another. So like I say it appears your # 2 and # 3 bearing were turned down in diameter.

"If your block has been bored to accept bearing shells then you will have to reinstall new babbit bearings. The new babbits must obviously fit both the line bored block and the camshaft bearing dimensions.

"Only if your cam lobes are shot will you need a new or replacement camshaft. The maximum diameter of the camshaft intake lobes will measure approx 1.390". The maximun diameter of the camshaft exhaust lobes will measure approx 1.540". If your lobes vary by more than about .030 from my given maximum specifications then I would scrap that camshaft. This is only an approximation taken from my personal experience. I currently know of no specified tolerance to reference for this data."

Skidog64 commented, "I just finished rebuilding an F134 that had a cam bearing problem. The cam had seized in the block at the second bearing. I used the old cam to make a boring bar that I then set up on my milling. Rebored the second bearing .100'' oversize. Machined a new bearing out of good quality bronze (660 or equivalent.) In the inside of bearing made a small circular groove for better oil distribution. Installed in rebored block with loctite 609. When installed don't forget to drill the oil hole. To do this remove small plug outside of block at each bearing that you worked on. If those Ford bearings don't work out find a good machine shop to help out. You can also buy an oversize camshaft and finish grind the bearings on the cam after you install those bearing. It's easier to get the right tolerance this way.

MrBob: "Here are some measurements from my camshaft: lobe heights, front to back

  1. 1.485
  2. 1.347
  3. 1.360
  4. 1.488
  5. 1.485
  6. 1.352
  7. 1.352
  8. 1.479"

Skidog64 "My understanding of your problem was those camshaft bearings fit in the block. If you have a doubt about those fits, change the camshaft. Lobe dimensions are for the performance buffs. Work on getting those bearings (bushings in the block) the way they should be. Buy a new cam and get the engine up and running."

Oldtime: "Skidog64, thanks for your commentary on the bronze bushing insert. It's all good advice. I am attempting at this point only to help MrBob decide whether his cam is worth reusing or not. MrBob still has to deal with the oversize bore in the block regardless of what cam he uses. We are not at this time concerned with optimum valve lift specifications. We are not attempting to gain performance at this time. These cams simply do at times wear out."

"Mrbob, these camshafts do seem to vary from one to another. They don't always appear to have the same grind specifications. Your camshaft seems very questionable to me because of the seemingly low lift. Yet I believe in always reusing serviceable used components.

"So far I can advise you that numbers 1,4,5, and 8 are your exhaust lobes. You indicate only a .006 variation among those lobes so that appears to be a serviceable variation from one cylinder to the next.Numbers 2,3,6 and 7 are your intake lobes. Here your variation from lowest to highest is .013". Still probably O.K.

"But your cam appears to have notably different specifications than the ones I have measured (both new and used references.) Perhaps your cam is very worn or the grind is just different. So in order to determine your grind lift I need to know what all your lobes measure at the narrow dimension (side dimensions.) Then I can advise youwhether to scrap it or reuse it."

MrBob replied, "Here are the camshaft lobe measurements, narrowest point, from front"

  1. 1.152"
  2. 1.145
  3. 1.155
  4. 1.150
  5. 1.152
  6. 1.152
  7. 1.150
  8. 1.145"

Oldtime: "Let's see now... first we will subtract the first set of lobe numbers that you posted from the second set of numbers you posted:

  1. exhaust 1.485 - 1.152 = .333 - .016 (tappet adjustment)= .317" valve lift
  2. intake 1.347 - 1.145 =
  3. intake 1.360 - 1.155 =
  4. exhaust 1.488 - 1.150 = .338 - .016 (tappet adjustment)= .322" valve lift
  5. exhaust 1.485 - 1,152 = .333 - .016 (tappet adjustment)= .317" valve lift
  6. intake 1.352 - 1.152 =
  7. intake 1.352 - 1.150 =
  8. exhaust 1.479 - 1.145 = .334 - .016 (tappet adjustment)= .318" valve lift

"Service standard specification for the Exhaust valve lift should be .351". Service standard specification for the Intake valve lift should be .260".

My humble conclusion: I won't even bother figuring the more complex intake specifications. Why not? Your exhaust valves do not come up anywhere near to service standard. This cam has evidently been inappropriately ground down and should be considered at scrap value. The exhaust valves just simply are not being lifted high enough with that ground down camshaft.

"Generally camshafts are good for one rebuild but seldom for two rebuilds. Your F-134 is on its second rebuild and this cam has been altered significantly from service standard specifications. You will need to purchase either a new or a good used camshaft. Then you will need to re-bush your bored block journals to correctly fit the cam bearing journals."

Skidog64 Keep the block, work on it! Make sure those bushings (in the block) are to fit with cam. Oil pressure, clearance betweem elements are all related. Keep the clearance low and you will have better oil distribution. Remember: one oil pump, many bearings to lube.

MrBob concluded, "Thanks guys, looks like a serviceable used camshaft is the direction we will go."

Thanks to all the contributors, and to Ed Wilson and Doug Hoffman for editing. -- Derek Redmond

See also Rebuilding an F-head Engine, Page 3: Installing the Valves and Camshaft.

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Last updated 16 January 2009 by Derek Redmond redmond@cj3b.info
All content not credited and previously copyright, is copyright Derek Redmond