lifter pre-load ?
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lifter pre-load ?
89 302 rebuild project. Installing new Comp Cams part #31-255-5, grind #FS XE250H-14 with new lifters and springs also from Comp. Problem is when I put the pushrods in and checked the pre-load I have way too much preload. All I've checked so far was both valves on #1, but they were both about .080-.090" preload. Comp cams instructions say I need .030 but .020-.040 is ok. Do I need to get a shorter pushrod to make my preload come out? If so, where do I get shorter pushrods?
Also, anybody know of a better way to check preload than by making marks on the pushrod with the rocker torqued and then loose using the valve cover gasket surface of the head as a reference--it seems to work, just not as accurate as I'd like to be.
I'm getting anxious to hear this thing run, but I keep hitting these little snags!
Also, anybody know of a better way to check preload than by making marks on the pushrod with the rocker torqued and then loose using the valve cover gasket surface of the head as a reference--it seems to work, just not as accurate as I'd like to be.
I'm getting anxious to hear this thing run, but I keep hitting these little snags!
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From: Crosby TX
You need to measure to determine the proper length of the push rod. Comp Cams and others sell an adjustable push rod to use for measuring. O you can make one by cutting an old rod and welding in a 1/4" bolt an nut so you can adjust the length.
Once you get the adjusable push rod set to the right length, go to any Ford Dealer that carries Ford Performance parts and they should be able to supply the right length rods.
Also I think Comp Cams sells push rods in different lengths.
Once you get the adjusable push rod set to the right length, go to any Ford Dealer that carries Ford Performance parts and they should be able to supply the right length rods.
Also I think Comp Cams sells push rods in different lengths.
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From: Central NYS
Don't know if my '79 302 valve train is different from the '89, and its been a l-o-n-g time since I did mine, but I bought a set of pedestal shims and shimed the pedestals to bring the preload into spec. (I don't remember where I bought the shims, but it may have been from Crane, as I'm using Crane Roller Trunion rockers (no roller on the tips.)
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From: Crosby TX
Here's the procedure for determining Push Rod length from Comp Cams
http://www.compcams.com/Technical/Cu...ML/306-307.asp
http://www.compcams.com/Technical/Cu...ML/306-307.asp
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From: Crosby TX
And here's the link for the Adjustable Push Rod tool.
http://www.compcams.com/Technical/Cu...g/HTML/293.asp
http://www.compcams.com/Technical/Cu...g/HTML/293.asp
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I used to worry about preload, until I finally discovered most engines ran better and quieter out of spec. than they do in spec. I set a 302 up to the preload called for in the book and it skipped like crazy. A foolproof way of checking Ford hydraulics is to assemble the valve train, crank the engine and let the lifters completely pump up. Turn engine off, and at tdc, you should be able to turn every pushrod with your fingers. It should be hard to turn but moveable. A "blue oval" certified mechanic taught me that trick. He say he has NEVER checked pre-load on a Ford the way the book says to. You are actually supposed to use a tappet bleed down tool and check it with a feeler gague if you do it by the Ford shop procedures. He says none of the other mechanics at the dealership do it by the book either, because when you get through it either skips or ticks.
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The lifters are brand new--never been pumped up--so bleed-down is not an issue. If I have too much preload, won't I be putting too much pressure on the cam/lifter? It really concerns me because its not Ford specs, but CompCams specs I'm trying to follow. I figure if I have too much pre-load, the best thing on a list of bad things that could happen would be that the cam/lifter would wear faster. Is that true, or am I just being overly-****?
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Logistics Pro
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From: Central NYS
Originally Posted by M04
I figure if I have too much pre-load, the best thing on a list of bad things that could happen would be that the cam/lifter would wear faster. Is that true, or am I just being overly-****?
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That'd be a little better on the wallet, but I think I'd still cry like a baby if I had to pull the valve covers back off that quick!
I think I can rig up a dial indicator on the push-rod and get a more accurate reading on the pre-load. Ya'll check my logic here.....I think I'd be better off on the lower side of spec pre-load? That way any valve seat wear will bring it closer to spec and the worst thing that could happen would be a little more noise?
Am I looking at that right? For now, until I can get some more accurate readings than by the rather crude method called for in the CompCams instructions, I'm thinking I'll be ordering some .060 under push-rods. I've already spent more than the truck was worth when I started, so what's a few more bucks!
I think I can rig up a dial indicator on the push-rod and get a more accurate reading on the pre-load. Ya'll check my logic here.....I think I'd be better off on the lower side of spec pre-load? That way any valve seat wear will bring it closer to spec and the worst thing that could happen would be a little more noise?
Am I looking at that right? For now, until I can get some more accurate readings than by the rather crude method called for in the CompCams instructions, I'm thinking I'll be ordering some .060 under push-rods. I've already spent more than the truck was worth when I started, so what's a few more bucks!
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From: Central NYS
Originally Posted by M04
I'm thinking I'll be ordering some .060 under push-rods. I've already spent more than the truck was worth when I started, so what's a few more bucks!
Crane Cams carries them under part # 99170-1 for the SBF. Read about them here:
http://www.cranecams.com/?show=brows...-1&showAll=yes
(I am in no way affiliated with Crane Cams - just passing along how I solved the same problem many years ago when I changed cams and milled the heads in my '79 F-150.)
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Crane Cams makes a kit to convert Ford ped. mount to s.b. Chevy type adjustable rockers. I do not have my jegs or Summit book handy, so I cant tell you the part Number. The kit cost about $50.00. In my opinion, its money well spent. I use it on all my mild performance engines. If its a race engine, I would not be using ped. mount heads in the first place. With this kit, You can adjust your preload exactly. I have never had any luck with shims. I have used Cranes shims, Ford Racing shims, and Ford shims. All of them cause the rocker to twist at high rpm. The above kit I mentioned also adds pushrod guides to the head. You do not have to have hardened push rods to run with the kit.
As to your earlier question, the only way I know to measure pre load is between rocker tip and valve ; with the lifter compressed. Any other measurement you make is going to be affected by ratio of the arm. Too much preload = skip. Not enough pre load = tick. Skip will burn valves, ticking will destroy pushrods and rockers.
As to your earlier question, the only way I know to measure pre load is between rocker tip and valve ; with the lifter compressed. Any other measurement you make is going to be affected by ratio of the arm. Too much preload = skip. Not enough pre load = tick. Skip will burn valves, ticking will destroy pushrods and rockers.
Last edited by ga302p; Nov 4, 2004 at 10:10 PM.
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GA302p--I found it in Summitt--that kit is about $90. Can I use the stock rocker arms with that, or would I have to replace them too? If I did that it would be set up like the chebbies that simple-minded folks like myself can relate to, right?
Its not a race truck so I wouldn't hesitate to go with the shim kit if it was just for me to drive--except it will be driven by a teenage boy--ya'll know how that goes.
I didn't really like the idea of having to invest in custom push-rods. Ya'll have given me more options--you guys are awesome--thanks!
Its not a race truck so I wouldn't hesitate to go with the shim kit if it was just for me to drive--except it will be driven by a teenage boy--ya'll know how that goes.
I didn't really like the idea of having to invest in custom push-rods. Ya'll have given me more options--you guys are awesome--thanks!
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The key to whether you can use shims is to look at the geometry of how the rocker contacts the valve stem. (See the photo on the Comp Cams link I posted earlier)
http://www.compcams.com/Technical/Cu...ML/306-307.asp
When the valve is closed the rocker needs to contact the valve stem in the center. If adding shims causes the rocker to contact the valve stem off center when closed, then you will need shorter or longer pushrods to correct the aligment,
http://www.compcams.com/Technical/Cu...ML/306-307.asp
When the valve is closed the rocker needs to contact the valve stem in the center. If adding shims causes the rocker to contact the valve stem off center when closed, then you will need shorter or longer pushrods to correct the aligment,
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Originally Posted by M04
GA302p--I found it in Summitt--that kit is about $90. Can I use the stock rocker arms with that, or would I have to replace them too? If I did that it would be set up like the chebbies that simple-minded folks like myself can relate to, right?
Its not a race truck so I wouldn't hesitate to go with the shim kit if it was just for me to drive--except it will be driven by a teenage boy--ya'll know how that goes.
I didn't really like the idea of having to invest in custom push-rods. Ya'll have given me more options--you guys are awesome--thanks!
Its not a race truck so I wouldn't hesitate to go with the shim kit if it was just for me to drive--except it will be driven by a teenage boy--ya'll know how that goes.
I didn't really like the idea of having to invest in custom push-rods. Ya'll have given me more options--you guys are awesome--thanks!
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