Engine Removal vs Tranny removal

My rear main seal is leaking so bad its not drivable (replaced the $4 oil sending unit and that was a big part of the leak). I know to replace the rear main seal you have to drop the tranny... but I have a rod that bumps on start up.. so I know the lower end is on its last leg (260k miles).. so I'm thinking it might be better to just go ahead and pull the motor and rebuild it.. but money is tight.. .and it would be drivable if I replace the seal..

My question is, how long would it take to drop the transmission. And how long would it take to pull the motor out? I have good tools, and air compressor.. will have to rent an engine hoist..
'87 4.0 auto 4x4...

The rear main seal is a two piece design so you do not have to pull the transmission to replace it.

I saw a writeup on here somewhere about replacing the rear main seal. You can do it still in the jeep, just drop the oil pan and take off the rod and main caps. Remove the crank and replace the seal.

Can you drop the pan enough withe the front axle still in? Looks pretty tricky.. you have to remove the crank to replace the seal though? if you leave the tranny in?

stephenspann27 said:

Can you drop the pan enough withe the front axle still in? Looks pretty tricky.. you have to remove the crank to replace the seal though? if you leave the tranny in?

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on my 87, we unbolted the top of the shocks and undid the motor moun=nts and jacked the motor up a couple inches. its a tricky bastard, but you can get it. the crank can stay in.

You would have to have the tranny out to remove the crankshaft.. becuase of hte flexplate right?

jk333 said:

on my 87, we unbolted the top of the shocks and undid the motor moun=nts and jacked the motor up a couple inches. its a tricky bastard, but you can get it. the crank can stay in.

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you did the rear main or just the pan gasket? Where did you jake the motor from?

No need to drop the crank. Just the rear bearing cap. Search for threads on here. I had to remove/replace the sway bar links to drop the axle low enough to have oil pan off.

ok Ill search.. just having a hard time understanding how you would get the top part of the two piece seal oit with the tranny still bolted up.

If you check around, you'll see quite a few tips and tricks on the RMS job.

I was able to pull oil sump pans on my rigs without lifts just by jacking up the front end and letting the axle hang, although you may have to unbolt the shock dampers to get a little extra (if you do, be careful of the brake lines!) I got the "little extra" I needed by unbolting the transmission mount cushion and using a bottle jack to lift the rear end of the drivetrain just a touch - which was much easier.

The upper half of the seal can be driven out using a small brass or bronze rod (do not use steel! Even hard plastic is a good choice here...) and tapping it lightly with a mallet - the seal is a rubber-over-metal-core design, and you'll just push it out by the core.

Be sure to apply assembly lube to the lower bearing half (inside, where the crank rides) before you put it back in. Results seem to vary on the use of RTV on the ends of the seal half - I don't bother, and haven't had any leaks.

Use the later (1996-up) gasket so you don't have to wrestle with four pieces at once.

The crankshaft need not be removed to service the RMS - I've not had to, anyhow. Worst case is you loosen two or three main caps going forward to give yourself a little wiggle room, and that's about what you'll need.

When you have everything torn to bits, pour out a cupful of clean engine oil. Drop the two seal halves in there, then go for a sandwich. Come back in about a half-hour - the seal lip will be much more pliable and rather less likely to be nicked or scuffed on installation (nothing like having to redo the RMS because you nicked the seal!)

Thanks for the info... would it be a pain to replace the rod/main bearings while I have he pan off? The bump I feel/hear at start up tells me there is at least one worn out bearing.. and I hate to spin a bearing.. damage the crank shaft.. woudl pulling the motor take about 6 hours? If I did it alone.. Just trying to decide if I should fix the seal and keep driving it.. and save for a rebiuld kit.. or just go ahead and take the motor out and wait till I can afford a kit....

stephenspann27 said:

Thanks for the info... would it be a pain to replace the rod/main bearings while I have he pan off? The bump I feel/hear at start up tells me there is at least one worn out bearing.. and I hate to spin a bearing.. damage the crank shaft.. woudl pulling the motor take about 6 hours? If I did it alone.. Just trying to decide if I should fix the seal and keep driving it.. and save for a rebiuld kit.. or just go ahead and take the motor out and wait till I can afford a kit....

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Even bottom end bearings can be done without pulling the engine - or really even the crankshaft. You'll have to loosen the main caps and push the upper halves out (brass rod, again,) but the rods can be done without even doing that much - just do them one at a time, and make sure to lube well (too much is almost enough.)

If you do the mains, loosen all the caps but don't tighten any until you have all seven mains done. However, you're going to need to pull your HD to get some more wiggle room up front - may as well replace that (PM) and the seal behind it (PM) while you're there. The timing cover need not be pulled to do those, unless you're planning on replacing the gasket under it as well.

Thanks again for the reponse. You lost me on the "HD" part.. and is PM the front seal?
I was thinking I might need to replace the oil pump and timing set as well.. Do you know of anyone who has had their pump fail.. or timing chain break or jump time? I mean it does have 260k on it... I just want to replace the most vistal failure prone items right now while I'm on a budget.

maybe I should just do rod bearings. and the rear main...

stephenspann27 said:

Thanks again for the reponse. You lost me on the "HD" part.. and is PM the front seal?
I was thinking I might need to replace the oil pump and timing set as well.. Do you know of anyone who has had their pump fail.. or timing chain break or jump time? I mean it does have 260k on it... I just want to replace the most vistal failure prone items right now while I'm on a budget.

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HD = Harmonic Damper. That big steel/iron wheel at the bottom front of the engine. Should cost $50-60 for a replacement.

PM = Preventative/Periodic Maintenance. "Periodic" maintenance is things like tuneups, lube changes, &c.) "Preventative" maintenance is changing parts that aren't failed or failing, but you're there anyhow.

Sorry - I forget that not everyone speaks the language. If you're at 260Kmiles tho, you're going to be replacing the HD soon. The seal behind it should run about six bucks, and you're going to have it exposed anyhow.

Either way, I'm sure it's going to be cheaper - and easier! - to do now than when it fails later.

You mention a knock. What's your oil pressure been like? Going just by the IP meter, or did you back-check with a decent mechanical gage?

Rear main seal is easy. It's how I got my heep for cheap. $13 seal, and the 95+ 1 peice neoprene pan gasket. Use a brass rod or punch to drive the seal out, as brass won't damage the bearing surface. Check your rod bearings while your under there and if need be, replace them. This is all EASIER if your lifted, otherwise, you have to let the axle go to max droop to get the pan back in. Another trick I used was to zip tie the 1 piece gasket on the sides and corners of the pan to put it in with small zipties. Then once the bolts were started, I cut the ties and pulled them out. All this work can be done with the jeep on a lift or in the air with the pan dangling. With a 6" lift you don't even have to jack it up.

The jeep doesn't have any kind of gauge just a warning light.. the light doesnt' come on when it running, or at low idle.. so it has at least above threshold oil pressure.. I guess I coudl hook up a guage to the new sending unit? or does it requre a different type sending unit?

stephenspann27 said:

The jeep doesn't have any kind of gauge just a warning light.. the light doesnt' come on when it running, or at low idle.. so it has at least above threshold oil pressure.. I guess I coudl hook up a guage to the new sending unit? or does it requre a different type sending unit?

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I have another RENIX full gage pod. To use it, you'd have to swap the temperature sensor (driver's side rear of head) and oil pressure sensor (near base of distributor.) The "sensors" you have now are actually "switches" - a "sensor" gives a variable resistance to drive a gage. All a "switch" has to do is turn a stupid little light on and off.

Change those two sensors, and the installation is otherwise "plug-and-play."

markw said:

Rear main seal is easy. It's how I got my heep for cheap. $13 seal, and the 95+ 1 peice neoprene pan gasket. Use a brass rod or punch to drive the seal out, as brass won't damage the bearing surface. Check your rod bearings while your under there and if need be, replace them. This is all EASIER if your lifted, otherwise, you have to let the axle go to max droop to get the pan back in. Another trick I used was to zip tie the 1 piece gasket on the sides and corners of the pan to put it in with small zipties. Then once the bolts were started, I cut the ties and pulled them out. All this work can be done with the jeep on a lift or in the air with the pan dangling. With a 6" lift you don't even have to jack it up.

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On Autozone's page ( I hate autozone love O'Reilly) they show two different types, a felpro four piece pan gasket, (cheap) and a 1 piece felpro gasket for $16. so I should be able to ask for a '87 gasket.. and just specify that particular felpro gasket..

stephenspann27 said:

On Autozone's page ( I hate autozone love O'Reilly) they show two different types, a felpro four piece pan gasket, (cheap) and a 1 piece felpro gasket for $16. so I should be able to ask for a '87 gasket.. and just specify that particular felpro gasket..

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They used a four-piece cork/rubber gasket 1987-1995, and a one-piece moulded rubber 1996-up. Just ask for the 1996-up - if you ask for one for your year, you get the four-piece pain in the arse.

I don't have the part number handy, or I'd give it to you...