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Old 04-04-2017, 11:39 AM
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4.2 rear main seal

Hey guys. I have a 90 yj with a 4.2L 200k miles.
My rear main seal is leaking pretty bad, and I will be replacing it and was considering doing the timing set at the same time.
What are your thoughts on using motor flush or oil additive to de-gunk the interior engine before the pan comes off?

Thanks
Jamie

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Old 04-04-2017, 02:38 PM   #2
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What is your oil pressure? Is it low, high, or in spec?

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Old 04-04-2017, 02:46 PM   #3
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I would do it.

There are many products that claim to be engine flush. Some posters here advocate ATF and others say don't do it.
I would search this and any other forum you go to and search "engine flush" for the multitude of opinions you will find.
Then make a decision that you think will work best for your situation.

I have used a BG product for the last couple oil changes with no adverse effects (that I can notice).

Some products that I remember are:
Marvel Mystery Oil
BG engine flush
ATF
Seafoam
Kerosene
I'm sure other posters have other favorites and comments on what I've listed.

I think Seafoam and BG are safe. I'm not so sure about kerosene.

Once you install whatever product you choose, allow the Jeep to run until it reaches operating temp and then for a while longer (I let mine run for about a half hour). Don't drive the Jeep.

Naturally, you will install new oil and filter. While the pan is off, be sure to scrub it well and take a look at your oil pump screen.

I think it's a good idea to do the RMS and timing set at the same time. It makes sealing the timing cover much easier.

Read the instructions for RMS in your Factory Service manual carefully. I forgot to put a speck of RTV between the main bearing cap and block and I have a slight drip. Not enough to go back in, but just enough to be embarrassing.

You might search this forum for "rear main seal" for suggestions on any tips to insure a successful and easy install.

Good Luck, L.M.
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.................................................. ........................
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Old 04-04-2017, 02:57 PM
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Thanks for the advise LM.
MudMagnet, my pressure is about 70 cold, and when warmed up about 15 at idle.
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Old 04-04-2017, 03:23 PM   #5
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Your oil pressure is on the high end (cold). A flush should do you well. I wouldn't recommend it for low oil pressure. L.M. has a good list above. There are different products for different uses. Since you have decent pressure, a mile flush would be the best option. Berryman and Seafoam are probably too aggressive. Marvel's is my favorite mild flush. It's essentially kerosene with some other "mysteries".
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Old 04-04-2017, 03:50 PM
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Thanks for the advise guys. I'm going to start collecting the parts. I guess once I get the timing cover off I will find out if I need the crank sleeve.
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Old 04-04-2017, 05:10 PM   #7
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Check you balancer...mine was shot, I replaced it, water pump and theromostat come to mond as well. II would also buy 2 RMS...there is an edge on it and the 1st time I nicked it putting it back in...needed another one....you can always return it if you don't need it...sucks to stop and have to go get another one...Good Luck!
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Old 04-04-2017, 05:18 PM   #8
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Quote:
Originally Posted by MudMagnetYJ View Post
Your oil pressure is on the high end (cold). A flush should do you well. I wouldn't recommend it for low oil pressure. L.M. has a good list above. There are different products for different uses. Since you have decent pressure, a mile flush would be the best option. Berryman and Seafoam are probably too aggressive. Marvel's is my favorite mild flush. It's essentially kerosene with some other "mysteries".
You think 70 is too high cold? My 4.2 has about 30k on it and 80 is not uncommon when it's cold..
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Old 04-04-2017, 11:26 PM   #9
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X2 on the Marvel Mystery oil
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Old 04-07-2017, 11:36 AM
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Thanks for the input guys. I ordered the timing set and chain snubber, everything else I need is local.

Jamie.
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Old 04-07-2017, 01:49 PM   #11
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See pic 1. Is this where the chain snubber goes that you refer to?
Mine was totally gone when I opened up the timing chain cover. I didn't know anything went there until after I was done. Not having it doesn't seem to make any difference. The tabs on the inside of the cover might not hold it anyhow. They are real worn from a loose chain.

In pic 2, I used the sleeve. You can see where the seal actually wore a groove in the old crank pulley.
Apparently I did it right because it doesn't leak. The rubber in between the inner and outer parts of the crank pulley seemed to be in good condition, so I elected to reuse it.

Just make sure that your distributor is pointing to #1 cylinder (pull the cap and look at the rotor) and then align the timing marks on the pulley and cover to TDC before starting. Pulling the spark plugs makes turning the engine over with a ratchet & socket on the crank pulley bolt easy.

The FSM has good instructions for this job. Either the Chiltons or Haynes manuals (I don't remember which one) has a suggestion on how to center the cover seal without the factory tool. As I remember, you set the cover in place, then put the bolts in place with just a few threads and then install the pulley. The pulley holds the seal centered and then snug up the bolts one by one. Then tighten the bolts. I don't remember if there is a torque value for the cover bolts. I am not a torque nazi, I simply tightened them to "tight but not too tight with a 1/4" drive ratchet.

Good Luck, L.M.
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"Wrangler....It's not just a vehicle, It's a lifestyle".
.................................................. ........................
1987 YJ-4.2L-Standard Shift- Re-manufactured Carter Carb-2" body Lift-31X10.5X15 BFG KOs-190K Miles No back seat.
HEI distributor with computer and all related relays and wiring removed.
12K Badlands winch with dual batteries.
Warn front bumper. Matching imitation Warn bumper on the rear.
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Old 04-07-2017, 02:25 PM   #12
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Quote:
Originally Posted by sccritterkiller View Post
You think 70 is too high cold? My 4.2 has about 30k on it and 80 is not uncommon when it's cold..
Sounds pretty high. Engines aren't my forte but that oil pressure, even cold, is pretty high. It's not too concerning since the idle pressure is normal, but raised my eyebrow.
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Old 05-04-2017, 10:07 AM   #13
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My motor (4.0) experiences high oil pressure when cold as well. And it really doesn't drop a lot when warmed up either.

I've thought about putting Seafoam or Marvel's in, but I'm honestly afraid to. My engine has over 175K on the clock, and I don't want to break something loose and have more problems after the "flush".

What are your opinions about this?

Perhaps I should wait until I'm ready to do the chain, the oil pan and RMS?
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Old 05-06-2017, 03:30 PM   #14
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Every jeep ive owned is around 80 cold and 40 at idle once warmed up
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Old 05-08-2017, 09:35 AM   #15
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Every jeep ive owned is around 80 cold and 40 at idle once warmed up
Well, that's right about where I am. Except it's around 60 when cold, and around 40 warm at idle.

Still afraid to drop any kind of engine flush in there for fear of breaking something.

Back a little more on topic, I thought my rear main wasn't actually leaking, but I found out this weekend that it is. There was a lot of "residue" in the area when I bought the YJ, so I thought it was leaking pretty bad. It's not so bad, just a drop or two on the floor after about 2 weeks in the garage, but still something I'll need to address.
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Old 05-08-2017, 11:44 AM   #16
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I use the BG when I do an oil change. It doesn't seem to hurt anything and perhaps cleared up an occasionally noisy lifter.

I have close to 190K miles. The PO was a responsibly kind of guy, but I think he let maintenance go once the Jeep got old. He owned it from around 1990 to 2013 and used it primarily as a daily driver. I don't think he abused it. His other vehicles were nice.

I think the important part of an engine flush is to run the engine at high idle until it's thoroughly warmed up and don't drive it while the flush is working. You don't want to put any stress on the reciprocating parts while the oil is thinned out. Then dump the oil while it's still warm.
Always change the filter when changing the oil.

I use a NAPA gold filter and 20W40 for my spring oil change and 10W30 for my fall oil change. Just regular dino oil, I think synthetic is overkill for these old tractor motors.
I do a spring and fall oil change because I don't put enough miles on my Jeep to worry about how many miles between oil changes. I have other vehicles that I use for road trips.

Good Luck, L.M.
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"Wrangler....It's not just a vehicle, It's a lifestyle".
.................................................. ........................
1987 YJ-4.2L-Standard Shift- Re-manufactured Carter Carb-2" body Lift-31X10.5X15 BFG KOs-190K Miles No back seat.
HEI distributor with computer and all related relays and wiring removed.
12K Badlands winch with dual batteries.
Warn front bumper. Matching imitation Warn bumper on the rear.
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Old 05-13-2017, 06:51 PM
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Well I have the rear main cap off, but can't drive the upper half of the seal out. Is there a trick, or do I have to drop the crank?
The cost of this is growing, found the damper is shot and wore against the timing cover and the radiator fell apart when I pulled it. The PO was a pos when it came to regular service. ?
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Old 05-13-2017, 10:25 PM   #18
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I used a small punch and gently tapped it until it got it high enough on the other side to grab with needle nose and worked it out....YMMV...
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Old 05-17-2017, 06:31 PM   #19
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I flushed my 4.0 with 20W50 and seafoam and it never hurt anything but idk if it did a whole lot either. I had a Comanche with a 2.5 with very dirty rockers from looking down the oil cap. It was a project and i started it up every day and let it run 10 min and shut it off. I did this for a week or more and then drained it. It came out pitch black and when i went to put oil back in the rocker arms were clean. IDK if that was a good or bad thing because that was a LOT of crud. But i don't think it blocked anything anything up it always ran fine and if anything ran better. You just never know how things like that are going to go though maybe i got lucky.
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Old 05-22-2017, 11:55 PM
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Well got the rear main and timing set done saturday. Turned in to be more parts. Radiator fell apart when pulled, no surprise since it was original.
Damper was shot and the balancing ring slid back and wore a groove in the timing cover. And the timing cover was missing the chain snubbed and it's slots worn away due to slack in the chain, and besides all the neglect from the P.O., he decided to do away with the oil slinger on the crank, so I ordered one as well.
So I threw a new water pump and t-stat while i was in there, also did a a/c delete and picked up a alt bracket from a local yard.
I've put about 15 miles on it since and no leak from the rear main, but did find a half dollar size puddle of dirty oil, I figure it's the trans and will check and top off, but the James bond smoke screen is gone.
Needless to say, my $15 rear main seal job turned into just over $400 and 2 weekends with parts fluids, and can after can of break clean lol.
Still need to reset timing since I have a flat spot at low to mid throttle and the orig damper ring was no where near being clocked correctly when compared to the crown damper from Morris 4x4.
I'll get pics of the timing cover and post when the rain stops.

Thanks for all the advice!
Jamie.
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Old 05-23-2017, 10:03 AM   #21
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snip...

Needless to say, my $15 rear main seal job turned into just over $400 and 2 weekends with parts fluids, and can after can of break clean lol.

...snip
Wait, what? I thought that was how it was supposed to work? I'd think I was doing it wrong if I ended up planning for a $15 part and an hour's work and I didn't spend hundreds of dollars over the course of a couple weeks!!

I'm glad you got it all fixed up!
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