Early Slant 6 Rebuild

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chinze57

Push Button tranny and a Slant 6 that'll never die
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Hey y’all, it’s getting to be about time to rebuild my slant 6.

I’ve recently developed a leak at the rear main seal, and my mechanic doesn’t think it’s worth having replaced until the engine is rebuilt. A little history on the engine, I know the previous owner who knows the owner before him. Neither of them ever had it rebuilt, and the guy who had it before me (an idiot) probably only ever did one oil change in the 5+ years he had the car. It was in bad shape when I got it, so I’ve known this was coming.

Is this something I could fairly easily do myself or is it something that would be best done by someone with experience?

I live in Georgia, near Atlanta, so if anyone knows someone who does quality work on a /6 around here please let me know.
 
Hey y’all, it’s getting to be about time to rebuild my slant 6.

I’ve recently developed a leak at the rear main seal, and my mechanic doesn’t think it’s worth having replaced until the engine is rebuilt. A little history on the engine, I know the previous owner who knows the owner before him. Neither of them ever had it rebuilt, and the guy who had it before me (an idiot) probably only ever did one oil change in the 5+ years he had the car. It was in bad shape when I got it, so I’ve known this was coming.

Is this something I could fairly easily do myself or is it something that would be best done by someone with experience?

I live in Georgia, near Atlanta, so if anyone knows someone who does quality work on a /6 around here please let me know.
To get to the rear main seal on a slant you will need to drop the oil pan.
To get the oil pan out if you are working on an A body you will need to at least remove the motor mounts and tilt and lift the engine up.
After doing all of that, trying to get the top half of the seal changed, trying to get the oil pan re sealed, while working on an engine in chassis,,, is a lot of effort without a great chance of success.
I would pull the engine to change the rear seal, or wait and change it when the engine is rebuilt.

It would be worth the time to do a quick investigation as to why it is leaking oil,,,
Did some of the oil pan bolts get loose?
Is there excess / non vented pressure in the crankcase from a plugged PCV system or road draft tube?
Has piston ring blow by got so bad that the crankcase vent system can’t keep up?
Is there thrust bearing worn and the crank end play is out of specification?
 
Hey y’all, it’s getting to be about time to rebuild my slant 6.

I’ve recently developed a leak at the rear main seal, and my mechanic doesn’t think it’s worth having replaced until the engine is rebuilt. A little history on the engine, I know the previous owner who knows the owner before him. Neither of them ever had it rebuilt, and the guy who had it before me (an idiot) probably only ever did one oil change in the 5+ years he had the car. It was in bad shape when I got it, so I’ve known this was coming.

Is this something I could fairly easily do myself or is it something that would be best done by someone with experience?

I live in Georgia, near Atlanta, so if anyone knows someone who does quality work on a /6 around here please let me know.
 
Buy the book " how to rebuild and modify slant six" by Doug Dutra. Well worth it even if you don't rebuild it yourself. I was always told, "if you want something done right, do it yourself". Lots of good help on this site. Have at it.
 
To get to the rear main seal on a slant you will need to drop the oil pan.
To get the oil pan out if you are working on an A body you will need to at least remove the motor mounts and tilt and lift the engine up.
After doing all of that, trying to get the top half of the seal changed, trying to get the oil pan re sealed, while working on an engine in chassis,,, is a lot of effort without a great chance of success.
I would pull the engine to change the rear seal, or wait and change it when the engine is rebuilt.

It would be worth the time to do a quick investigation as to why it is leaking oil,,,
Did some of the oil pan bolts get loose?
Is there excess / non vented pressure in the crankcase from a plugged PCV system or road draft tube?
Has piston ring blow by got so bad that the crankcase vent system can’t keep up?
Is there thrust bearing worn and the crank end play is out of specification?

The oil pan is sealed tight. The leak is coming right at the bottom of where the engine and transmission meet.

As to why it’s started leaking in the past 2 weeks, no clue. I’ve been driving with this motor for about a year now. I had a ton of maintenance done when i first bought the car, which included new timing, new oil pump, new valve cover gasket and oil pan gasket, etc. And have had one tune up done and done another myself. But it’s not a very fun leak, I lost a quart of oil in ~2 weeks. Previously i went almost 2 months before i was noticeably down (not even a quart, maybe half a quart), And by then i was due for An oil change. But now it’s leaking like a sieve.
 
The oil pan is sealed tight. The leak is coming right at the bottom of where the engine and transmission meet.

As to why it’s started leaking in the past 2 weeks, no clue. I’ve been driving with this motor for about a year now. I had a ton of maintenance done when i first bought the car, which included new timing, new oil pump, new valve cover gasket and oil pan gasket, etc. And have had one tune up done and done another myself. But it’s not a very fun leak, I lost a quart of oil in ~2 weeks. Previously i went almost 2 months before i was noticeably down (not even a quart, maybe half a quart), And by then i was due for An oil change. But now it’s leaking like a sieve.

Then, I would pull up the timing for the engine rebuild and fix the rear main seal when the engine is redone.
That will save you the couple of hundred dollars that you will pay someone to just change out the rear seal and you stand a much better chance of the work being done correctly with the rear seal being changed with the engine out of chassis.
 
Are you certain it’s motor oil? Sudden huge leaks don’t happen that often to the main seals. Transmission seals, especially in manuals will let go on a guy...
 
I'm doing the bottom end on mine right now.

VIXEN MOTOR REPAIR.jpg
 
Are you certain it’s motor oil? Sudden huge leaks don’t happen that often to the main seals. Transmission seals, especially in manuals will let go on a guy...
It’s definitely motor oil. Haven’t had to put in any trans fluid in a year, it’s still got plenty. But ran low on motor oil 2 weeks after an oil change. Oil pan is tight and back oil drain plug is tight
 
Rusty, are you changing out the rear seal? I believe you are changing the bearing but not pulling the pistons and rods,,,

Yes. It had the old rope seal. Dang right I am changing it. lol And I did leave the pistons in place since I'm not pulling the head. I just yanked the crank out, cleaned it all up and put new bearings in it.
 
It will be good for another 50 years!

Probably. That's actually what I'm counting on. Last compression test, it had 155-160 on all six so the top end is great. It doesn't smoke a lick. So the ring seal is good. With the new bearings, oil pump and timing set it should be golden. Remember when I keep saying I "might" leave it a slant? Yeah. That.
 
Probably. That's actually what I'm counting on. Last compression test, it had 155-160 on all six so the top end is great. It doesn't smoke a lick. So the ring seal is good. With the new bearings, oil pump and timing set it should be golden. Remember when I keep saying I "might" leave it a slant? Yeah. That.
Don’t want to get the original post off track, but you may want to do valve seals if they are OE.
 
Don’t want to get the original post off track, but you may want to do valve seals if they are OE.

I looked at them when I did the valve adjustment. They are soft and look pretty new.
 
If the compression measures fine, the engine doesn't need a rebuild and you would risk f'ing up your engine. All oil seals and gaskets can be replaced from outside with the engine in the car, except for the head gasket (usually an overheating issue from coolant loss). It is a pain removing the oil pan, but after that the rear seal isn't hard to change. It isn't like new cars which require removing the transmission and flexplate (since they slide over the crankshaft to seal better). It is the same PN as used in the Hemi engine. I haven't seen the rope seal that Rusty mentions. Perhaps that was original, but my 1964 had the 2-part rubber seal.

While in there, insure that the tapped holes in the aluminum seal holder for the oil pan bolts weren't stripped by some gomer (common). Now is the time to fix that with a Heli-coil insert. Indeed, that could cause the oil pan gasket to leak right where the rear crank seal would leak. Insure those bolts are tight and don't torque beyond the spec!. If they are stripped, you might be able to screw a stud in the holes to reach unmolested threads, then a nut, or use a slightly larger metric bolt for now until some day you have the oil pan off to fix it right. I used a better silicone oil pan gasket (Real Gaskets of TN) since getting that pan off is a hassle.
 
If the compression measures fine, the engine doesn't need a rebuild and you would risk f'ing up your engine. All oil seals and gaskets can be replaced from outside with the engine in the car, except for the head gasket (usually an overheating issue from coolant loss). It is a pain removing the oil pan, but after that the rear seal isn't hard to change. It isn't like new cars which require removing the transmission and flexplate (since they slide over the crankshaft to seal better). It is the same PN as used in the Hemi engine. I haven't seen the rope seal that Rusty mentions. Perhaps that was original, but my 1964 had the 2-part rubber seal.

While in there, insure that the tapped holes in the aluminum seal holder for the oil pan bolts weren't stripped by some gomer (common). Now is the time to fix that with a Heli-coil insert. Indeed, that could cause the oil pan gasket to leak right where the rear crank seal would leak. Insure those bolts are tight and don't torque beyond the spec!. If they are stripped, you might be able to screw a stud in the holes to reach unmolested threads, then a nut, or use a slightly larger metric bolt for now until some day you have the oil pan off to fix it right. I used a better silicone oil pan gasket (Real Gaskets of TN) since getting that pan off is a hassle.

The rear main seal cannot be replaced from the outside and if his has the old rope seal like a lot of them did, that's a major source of contention with an oil leak.
 
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