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Unread 05-02-2011, 05:47 PM   #1
Plyj
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1990 YJ Wrangler 
 
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New Lifters - Old Cam??

This coming weekend, I'm installing a completely rebuilt '98, 4.0L head (with Port/Polish) on my '87 4.2L block (no idea how many miles are on this since it was a replacement for the original 4.2L in my '91 YJ).
I've done everything by the book thus far (new everything for the head, exhaust headers, rocker arms, valve stem sleeves & seals, springs & shims, pushrods, intake manifold, etc.) and was planning to install new Crane (flat tappet hydraulic) lifters.
Then I read something that said I should "always" replace the camshaft if I replace the lifters. Sounds like a pant-load to me but I'm a software guy... not a mechanic.

Anybody got an opinion on this?

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Unread 05-02-2011, 05:51 PM   #2
4.7stroker
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I have plenty of opinion on that, a smart software guy would do a internet search to find the answer. This old wrench has already done it for you though so all you have to do is read the links in my sig.

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Unread 05-02-2011, 05:54 PM   #3
OOXTEME
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If your that far into it i would do a cam to. But ive also been told that if your goin to redo the whole top end you better do the bottom end also. With all that being new on the top the compression will increase causing more force on the old weaker bottom end. my buddy did that to a 454 in his baja and after about 10 mins he blew it up...
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Unread 05-02-2011, 06:35 PM   #4
shaggyjim
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I had a lifter go out on me at 80,000 miles and replaced them all but kept the same old cam the YJ came with. I've never had a problem with them and they were Napa lifters.... I have just under 185,000 on the Jeep now. I however don't think it would be wise to use old lifters on a new cam. Still if you have it out and all the head work done why not upgrade the cam aswell?
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Unread 05-02-2011, 06:48 PM   #5
Plyj
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Thanks for the advice...
I did the web search and that's how I came up with the "pant-load" theory. Your links were interesting but I didn't see anything that sounded very convincing. I always run the COMP Break-in Oil Additive (contains lots of zinc) during every oil change and spring pressure on these engines is only about 90 lbs. The engine never has (and never will) see 3000RPM.

I rebuilt the bottom end last year since I had to replace a rear main seal... replaced the mains while I had it open and installed Chrysler high capaity oil pump at same time.
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Unread 05-02-2011, 06:53 PM   #6
MLJeeper
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If you had a single lifter go bad, would you replace the cam and all lifters? No and neither would a mechanic. There is an outside chance that the wear pattern on the lobe could damage a new lifter and cause a bad chain of events, but it would be rare. I mean the cam lobe and lifter do develop a matching wear pattern. But its obviously more critical to use new vs old lifters with a new cam. the break in of the cam itself is the most critical. If i was in your position, i would just throw in new lifters and roll on.
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Unread 05-03-2011, 06:06 PM   #7
4.7stroker
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Hey it is your money you spend it how you like. Me I love to see it when "smart" people have to do the job twice because they wanted to cheap out on a repair.

Your opinion may vary.

Dwayne
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Unread 05-04-2011, 08:08 PM   #8
laybackman
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An engine is made up of parts nothing magical about that. It is all about clearances and wear, or lack thereof. I would inspect the wear on the bottom of the bad lifter. If there was little to no wear I would swap out the bad lifter and be done with it. If the lifter was so worn that the bottom was concave then that engine needs a complete rebuild.

NOTE: Usually when factory lifters are shot so is the factory cam since the surface of the cam lobes are not flame hardened.
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Unread 05-04-2011, 10:38 PM   #9
Alabamaranger
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If you are not having a problem with the cam, you can replace the lifters. If you have one bad lifter due to gunk or something, it be crazy to replace a good cam. Lifters do go bad which does not mean the cam is bad.
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Unread 05-05-2011, 12:22 AM   #10
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Quote:
Originally Posted by Plyj View Post
This coming weekend, I'm installing a completely rebuilt '98, 4.0L head (with Port/Polish) on my '87 4.2L block (no idea how many miles are on this since it was a replacement for the original 4.2L in my '91 YJ).
I've done everything by the book thus far (new everything for the head, exhaust headers, rocker arms, valve stem sleeves & seals, springs & shims, pushrods, intake manifold, etc.) and was planning to install new Crane (flat tappet hydraulic) lifters.
Then I read something that said I should "always" replace the camshaft if I replace the lifters. Sounds like a pant-load to me but I'm a software guy... not a mechanic.

Anybody got an opinion on this?
One more time (fact and experience, not opinion...)

New Cam + New Lifters = OK.
Used Cam + New Lifters = OK.
New Cam + Used Lifters = BAD.
Used Cam + Mixed Lifters = BAD.

"Mixed" means that, if you want to reuse a conventional flat tappet, you MUST put the tappet back ON THE SAME LOBE YOU REMOVED IT FROM. Full stop.

I qualify that using "conventional" - I recall seeing lifters with composite feet that you're supposed to be able to change on lobes, change between camshafts, &c - but I have no experience with these and therefore cannot comment.
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Unread 05-05-2011, 12:30 AM   #11
Peter Nuss
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I'm not following your plan too well here.

Changing the mains and adding an oil pump is not rebuilding the bottom end. You still have rod bearings down there, and cam bearings, if the mains are worn the rods are also. Never mind the wrist pins and pistons and rings. The high volume pump will masked a sloppy lower end for a while but, it's not rebuilt because your oil pressure rises or you add zinc to your oil. You have an engine you don't know history or mileage on, so chasing symtoms and spending a little at a time is only extending the life of the engine till the next issue down the road.

You did a port and polish job on a head that will never see 3000 rpms???? You must have had a good reason for that, but, I can't see it. Replaced all the parts in the head, for good luck I guess. And now you want to save money on a cam? I'm getting this right so far, I hope. Yeah, sure you can put in new lifters on an old cam. People do this with evidently no problems, and I have done it also with an engine I knew the history on and had low mileage. But, this will only again extend the life of your engine a little further, any new part will, but, after spending alot more money to do it the way you are going, you still will not have a long term dependable rebuilt engine. A piece meal approach to engine rebuilding is a hit or miss deal.

Sounds like you have a nice head and upper valve train, I'd make the bottom end as good as the top and take a break from Jeep wrenching for a while. Good luck with your choice.
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Unread 05-05-2011, 05:00 AM   #12
oldtime_ironman
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Technical explanation, if I may: Cam and lifters is usually a matched set, for life. You can put new lifters on a used cam, but its kinda half-assed way to do it. Under no circumstances should you put used lifters with a new cam, nor mix up which used lifter came from which hole.

The reason why is these parts all "wear in" to each other when the engine is started for the first time. So that particular cam with its lifters in each particular position, can only work together in that way for life. Literally they "mated" to each other. If old lifters are mixed up in the order which they came out, then they and the cam will literally grind each other to pieces. You can get away with a complete set of new lifters on an old cam if you're in a pinch, though I don't like to do it. Comp Cams is a good brand name, they been around quite a while.
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