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  #1  
Old September 30th, 2013, 18:11
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diggerdave diggerdave is offline
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Lightbulb Time to rebuild my motor?

Hey ya'll

Bad stuff happened to my jeep.
First off it's a 97xj 4.0 original stock motor except for an intake and it's got 215k.

Here's the scenario: Left the girlfriend's house upset the other morning and put the pedal to floor. Redlined (which I never do) for a couple seconds. At the first stop sign I noticed a rough idle and drove like a grandma for the remaining couple miles to my house. CEL lit up "misfire cylinder 2" Given the scenario I feared the worst and went straight to the compression gauge in my toolbox. Fears confirmed. 5 cylinders read just over 135psi while cylinder 2 read 80psi.

I'm thinking it's a piston ring and that it's time to pull the motor and have it rebuilt.

This is further than I have ever been into the 4.0 repair realm and wanted to get everyone's 2 cents while I hustle enough money to pay a machine shop so everyone please, pimp slap me with your wisdom and advise!

Thanks
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Old September 30th, 2013, 18:29
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Tim_MN Tim_MN is offline
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Re: Time to rebuild my motor?

What is the budget for repairs, and how long are you planning to drive the repaired Jeep ? No reason not to consider a good used engine from the junkyard.
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  #3  
Old October 1st, 2013, 09:08
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Re: Time to rebuild my motor?

Not quite sure what my budget is yet but I love my jeep and would like to keep driving it as long as possible, another hundred k would be great. My concerns with buying a motor from the junk yard is not knowing the history of the motor. My fear is that I would buy a used motor put it in and find out that it's got a fatal problem of it's own. I'll look into it though, it's at least worth doing some research to see what's available out here..
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Old October 4th, 2013, 14:02
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blondejoncherokee blondejoncherokee is offline
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Re: Time to rebuild my motor?

Did you get 80 PSI dry? whats it like wet? Are you sure its not valves or something?
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Old October 4th, 2013, 14:26
westvirginia24976 westvirginia24976 is offline
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Re: Time to rebuild my motor?

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Originally Posted by Tim_MN View Post
No reason not to consider a good used engine from the junkyard.

This^ If time is on your side, consider buying a rolled or otherwise busted xj. I have done this twice. You get axles, t-case, sometimes good tires, etc... I have less than 500.00 apiece in them. I used the engine out of one and the case from the other. I am about to nab the tranny out of both and swap into my DD's. One jeep had 110k and the other had around 150k. I have enough acreage to store stuff like that though.
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Old October 4th, 2013, 17:19
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Re: Time to rebuild my motor?

Thanks for the input guys! I did two tests both dry and wet both showed 80psi. I wanted so much for it to be a valve!
As for buying a rolled or wrecked jeep I haven't really looked too much yet but if I can find one that would be a great idea. I love to idea of getting extra parts too! I'm getting ready to move across town to a place where I would have the shop space for a few parts/project jeeps so I'll look into that some more and keep my fingers crossed that I can find one..
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Old October 5th, 2013, 05:25
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Re: Time to rebuild my motor?

If it was 80 both ways, It IS a valve, valve spring, rocker etc.
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Old October 5th, 2013, 14:56
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Re: Time to rebuild my motor?

I had thought it was the opposite..Thanks! I hope you're right..that would make my day.. I had a friend who is a mechanic help me out with the diagnosis as I really don't have a lot of experience with engine internals. So, let me recap the tests I did and maybe you can give me a better idea of what my results mean. First compression test was dry just put the gauge on a cranked the motor. For the second test I put a few drops of oil in the cylinder (as per my friend's suggestion) waited a few minutes and cranked the motor again which I'm assuming is what is meant by a wet test. Both tests showed 80 psi and held that pressure (didn't drop pressure after a minute or two)
So if there's anything I'm missing here, or a different conclusion can be drawn from these tests please let me know..as I said this stuff is pretty new to me

Thanks

Last edited by diggerdave; October 5th, 2013 at 15:16. Reason: added more info
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Old October 5th, 2013, 20:44
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Re: Time to rebuild my motor?

A few drops? Or a few good squirts?

Do the squirts and retest. Report back.
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Old October 6th, 2013, 07:55
Shorty Shorty is offline
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Re: Time to rebuild my motor?

Quote:
Originally Posted by diggerdave View Post
For the second test I put a few drops of oil in the cylinder (as per my friend's suggestion) waited a few minutes and cranked the motor again which I'm assuming is what is meant by a wet test. Both tests showed 80 psi and held that pressure (didn't drop pressure after a minute or two)
holding the reading is a sign that your compression tester is good (doesn't leak) or the valve train is completely trashed-- the valves should open and let the pressure out with every revolution.

Quote:
Originally Posted by cruiser54 View Post
A few drops? Or a few good squirts?

Do the squirts and retest. Report back.
best advice^^ see what you've got with a couple good squirts from an oil can.
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  #11  
Old October 6th, 2013, 08:09
O-Gauge Steamer O-Gauge Steamer is offline
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Re: Time to rebuild my motor?

Quote:
Originally Posted by cruiser54 View Post
If it was 80 both ways, It IS a valve, valve spring, rocker etc.
This is exactly correct. The purpose of the oil is to temporarily seal the rings. If the compression does not increase in a wet test, the valves are suspect.

If you wish, you can hook up shop air to the cylinder and then just listen for the leak.

Just make sure the cylinder is on the ignition stroke, preferably at BDC. You can make an adapter out of a spark plug for the air line. Connect the shop air to the cylinder and as suggested, listen. Listen at the tail pipe and at the throttle body. Provided your hearing is up to par (mine is not...) you will hear the air leaking out of the cylinder which will tell you which valve has gone.

Or, just pull the head and rebuild it. It will have to come off for any sort of repair and it makes no sense to only repair the affected valves.

IMO, installing a head from the JY is a waste of money. You could easily wind up right where you are now. Especially if the head is off an engine that sits in undamaged sheet metal.

Just my .02!
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  #12  
Old October 6th, 2013, 10:30
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Re: Time to rebuild my motor?

Thanks for all the advise guys. The wet test I did was indeed just a couple of drops. I will borrow the compression gauge again and do another test with a couple squirts of oil and post up my results.
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Old October 14th, 2013, 10:30
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Re: Time to rebuild my motor?

Update: I've retested everything with much better equipment. Five cylinders show about 150psi. Cylinder 2 shows 90 dry and just over 120 wet with at least a table spoon of oil. I've pulled the head. Cylinder 2 looks healthy with no scratches and I can still see the original hone pattern..I found that my straight edge is bent so I'm taking the head to a machine shop today to see if it's warped. My new plan is to rebuild the motor with new rings, bearings, and gaskets. I'm seeing gasket sets on quadratec from omix (can't find much info on the manufacturer) and I'm wondering if these are worthwhile parts?
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