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Unread 03-14-2014, 09:36 AM   #1
CarolinaYJ
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1989 YJ Wrangler 
 
Join Date: Jun 2013
Location: Fuquay Varina, NC
Posts: 26
Engine rod knock.

I'm needing some solid wisdom here. My 1989 YJ with a 6 cylinder 4.2 started a horrible knocking sound. I'm one of those hopeless newbies who hopes to learn how to fix his rig, but this is way over my head. One of the local shops put it up on the rack and used their stethoscope. The owner said the knock was on the bottom of the engine about 2nd or 3rd cylinder from the front. He said the knock was so loud he couldn't keep the stethoscope on the engine. He says I need a new engine or a total rebuild.
Local shops are charging 2 grand for a rebuild installed (with me giving them the current motor for them to rebuild for the next guy). My wife says that is too much and the Jeep will have to go.
Craigslist is full of people selling motors they've pulled for $200 - $600. But I know enough to worry about why they pulled it in the first place. And how long it's been out and what kind of corrosion may have happened while it's been sitting.

So my need for counsel: Do I try to find a recently pulled used engine and try to convince someone to install it cheaply? Or do I sell it and take the loss with as much dignity as I can?

Thanks for all your wisdom and insight.

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Last edited by CarolinaYJ; 03-14-2014 at 01:41 PM..
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Unread 03-14-2014, 10:19 AM   #2
Que89YJ
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1989 YJ Wrangler 
 
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Location: Detroit, Michigan
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You can use a block from a 4.0 or a 4.2L. Pick and pull an engine. It is cheap and easy. The 4.0l/4.2 is good for about 250K so if you find a 4.0L up to 99 with lower miles on it you are good to go. The swap is pretty easy to do. If the body is in good shape it is a no brainer, do the swap.
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Unread 03-14-2014, 10:32 AM   #3
Que89YJ
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You will need to swap everything over on the intake to the 4.0L if you go that way. It is a very easy swap and you could do it yourself. There are a few people who have never done it before that have taken it on and finished it in a couple days to a week. Including beer breaks.
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Unread 03-14-2014, 01:53 PM   #4
CarolinaYJ
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OK. Sounds great. A neighbor suggested taking off the oil pain and replacing the rod bearings to see if that would help. About a hundred dollars and a couple hours work.

I didn't know the 4.0 was exchangeable with the 4.2. I forgot to mention mine has the automatic transmission. I'll do some more looking around and add a 4.0 in the search. A friend who does restorations of antique vehicles has offered to help. But he'll not be available for 3-4 weeks! I think the YJ is definitely worth the engine swap, it's body and frame are in really good shape with the lightest of rust spots where paint has chipped. No flaking or rust through.
Are there any good links on how to replace an engine? The restorer friend has all the equipment including the hoist. I think a 6 pack and buying him a couple lunches may cover labor costs
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Unread 03-14-2014, 02:19 PM   #5
kb7vlt
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If the rod is knocking there is probably a flat spot on the rod journal now. Replacing the bearings without checking the crank is probably at best a very short term fix.
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Unread 03-14-2014, 03:04 PM   #6
Que89YJ
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Seriously them it's a no brainer. Do the swap.
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Unread 03-14-2014, 05:21 PM   #7
CarolinaYJ
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OK, I'm sold. I'll do the swap. Just gotta get my friend to free up some time while I start the hunt for an engine. I'm right in believing that any Jeep 4.0 is usable? And I can keep my transmission....or should I swap that too?

I really appreciate the knowledge and help here. I've learned a lot by lurking on other people's threads.
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Unread 03-14-2014, 05:39 PM   #8
Que89YJ
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You can keep your trans. Any 4.2 or 4.0 up to 99. If you find a deal on a ax 15 with it you might consider swapping the trans. but the internal slave master combo is what you have. If you get one with an external it is better but a little more involved.
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Unread 03-14-2014, 07:27 PM   #9
plym49
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Not so fast. A simple diagnostic before you drop big coin.

Is the knock times to the speed of the crankshaft, or half the crankshaft speed?

To check: slow the engine down to the lowest idle you can. Now try to surmise if the knock occurs on every rotation of the crank pulley or half as fast.

Same speed = bearing or piston problem.

Half speed = valvetrain problem. Could be as simple as a collapsed lifter.

Shops are motivated to sell you a big coin job. Unless the shop is scrupulously honest, there is no reason for them to go this extra diagnostic mile on your behalf.
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Unread 03-14-2014, 07:34 PM   #10
Old4X
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Quote:
Originally Posted by plym49 View Post
Not so fast. A simple diagnostic before you drop big coin.

Is the knock times to the speed of the crankshaft, or half the crankshaft speed?

To check: slow the engine down to the lowest idle you can. Now try to surmise if the knock occurs on every rotation of the crank pulley or half as fast.

Same speed = bearing or piston problem.

Half speed = valvetrain problem. Could be as simple as a collapsed lifter.

Shops are motivated to sell you a big coin job. Unless the shop is scrupulously honest, there is no reason for them to go this extra diagnostic mile on your behalf.

This.

Plus, the front differential housing can impact the oilpan and dent it. If this happens, you get a horrible knock, in time with the crankshaft rotation.

Rod knock normally comes on slowly, and is quigte noticable starting a cold engine. Once oil pressure gets up, it gets less noisy or goes away depending on amount of wear.

Can you feel the knock on the dipstick tube?
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Unread 03-15-2014, 09:33 AM   #11
CarolinaYJ
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Wow, more information to consider. Here's more details as I can figure them.
Not part of the knock but an additional note - the engine has had an irregular stutter since I bought the jeep. I've replaced the plugs, wires, distributor (including cap and rotor), new fuel pump and EGR. The vacuum lines are a total mess -some dangling, some old and broken, some hooked up but maybe not to the right place.

The knock is not as bad when the engine is cold. In fact, this morning it was hardy noticeable when I started it and ran it for 4 minutes trying to determine whether the knock was at the same speed or half speed. It seems to quiet some when the car is in gear and I have the brakes on. But will get noisy when driving. It is at its worse at about 1500 - 1800 rpm.
The best I can tell, it makes the knock at the same speed as the engine rotation, I confess I'm really ignorant to know how to tell that. I'm one of those guys who is really just learning about engines.
After revving the engine for a while the knock was strong again. I do not feel it in the dipstick tube.
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Unread 03-15-2014, 11:18 AM   #12
RedRockRed
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If you don't believe the mechanic, a get another opinion from a professional. You're probably avoiding the inevitable. You don't say, but I'll guess the motor has 150K or more...maybe a little early, but overhaul time. A used engine is crapshoot. You're already going to take a beating if you try sell with a rod knock. A DIY or local rebuild gets you back to where you were, but adds little to the Jeep's value without a serious warranty in writing. A warrantied crate engine from a commercial rebuilder like Jasper or ATK can add a lot to the rig's value. If you have a lot $$ in the rig, it may be a good choice. Remember, if your motor throws a rod in the meantime, it won't be worth spit.
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Unread 03-15-2014, 12:37 PM   #13
40dog
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You should a compression check.get a accurate oil press reading. I would think if its a rod or main bearing issue it would have spun or or died allready.idk how muc h milage you have put on it since noticing the knock.??. If a bearing is dieing self destruction is daily as it runs so it should get louder or more noticeable every few days depending on use.some will run long term with a bad bearing before giving up.valve train noise is common in mileaged engines. some times a little marvel mystery oil in a tank of fuel and ran Thru a oil change will clean things up and quiet down your valve train.. hate to change a engine if it wasnt positively known that its die.
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Unread 03-15-2014, 03:02 PM   #14
CarolinaYJ
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Red Rock: It's not that I don't believe the mechanic. The reality is without taking things apart, there may be other issues. I just wanted to get a sense from guys who know jeeps inside and out. The mechanic actually told me to sell the jeep and take the loss. A previous mechanic said it was a shift plate, but he just listened to it from 10 feet away. Reality for me is that kicking out two grand for a rebuilt is not an option. I'm currently unemployed, while I have money to live on, that kind of money for a toy just isn't an option. I bought the jeep for $3,500, which I thought was a good deal considering the solid condition of the body. Realistically, I believe my choices are find the problem and fix it, or replace the engine myself with a used one. I know a used engine is not going to raise the value of the jeep. But this is something I hope to fix and hang on to for a good while.
.
40dog: Since the knock started I've probably driven it less than 50 miles (30 at highway speeds trying to get home), and it's idled maybe another 15 minutes while trying to diagnose at different places. The engine has over 160k on it. I compression has been solid. I haven't had it checked since the knocking started. Oil pressure gauge says it's solid. Right where it usually is.

From the wisdom of the collective. It sounds like running it further will just create more damage if it is indeed a rod, or possibly one of the other issues. If I can find a used motor from a trusted source that is likely my option. My car restorer friend is going to a car show in South Carolina and is going to call in some favors to see if some of the jeep guys there can do anything for me.

This is a great community. Thanks for all the help. If anyone else has ideas on how I can diagnose or fix the problem. I'm open to hear more.
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Unread 03-15-2014, 03:12 PM   #15
JWELK
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You can always put a 4 banger in and save some money, then rebuild yours as funds become available.
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