4.2L stright 6 puking Oil out dipstick

[Lister]

Picked up an 81 Laredo that has been sitting in a field for a number of years. PO said they ran the engine a year or so ago. What I did: New battery, new oil, cleaned and gapped spark plugs, bit of WD40 in each cylinder through the spark plug hole, new fueld filter, new gas.

Engine was started with the air filter off and the rear vent tube and plug from the air filter on the valve cover off.

When it started it sounded really rough like there was a hammer bouncing around inside. It was a regular interval sound. After several starts and running it at high RPMS for a bit, got out and there were several litres of my nice fresh oil which appeared to have come out the dip stick tube.

I did a compression test and front to back got 140, 140, 150, 160, 127, 117. Is the 117 bad enough that it would cause back pressure to push the oil out as it did?

I did not check the PCV as I figured with the above noted vent tube out of the valve coiver, it was not a cause.

Youtube for reference. Skip to 1:04 for when it first fired and 2:02 for the higher rev run.

https://youtu.be/aK056MjZHiI

[Mars]

if it's been sitting wouldn't hurt to put some marvel mystery oil in your cylinders let it soak a while, could have a stuck ring that could cause blow by. Also check your timing, backfiring through the carb is not bad gas. Great way to bork your power valve and maybe cause a fire. I've never seen one blow out out of the dipstick, is it like under actual pressure?

I'm far from an expert, perhaps someone with more experience could chime in.

[Ristow]

sounds like the firing order is off to me.

[Lister]

Thanks. I'll try/check both of these things.

[Lister]

Thanks for the tips. Plug wiures were not correct on the distributor. Unforntunately there were some very bad noises internally. Engine is going to need to be pulled apart, or tossed aside for the Engine swap i was planning for the spring.

[tgreese]

Which transmission do you have? Go 4.0L HO with MPI.

[Lister]

It has the 4 speed, but I am already set on a V8. Need to have the rumble

[tgreese]

It has the 4 speed, but I am already set on a V8. Need to have the rumble

The factory 4-speed in that Jeep is barely adequate for V8 power, IMO. There were some 360 2V FSJs from this era with a variant of this 4-speed, but those transmissions have taller gearing than the sixes. And they are not plentiful. There are a lot of differences between inline 6 and V8 models of these Jeeps. Installing a V8 in a FSJ equipped with a 6 is not straightforward - using the existing transmission at its current location, a V8 will interfere with the firewall. Jeep used a different transmission for the V8 that moves the engine forward - search - lots of old posts about this.

The 4.0L HO can be a very tidy swap in a FSj that currently has a 258. The factory Mopar/Bosch multiport fuel injection is excellent, and you'll get significantly more power, better economy, and improved drivability with the factory MPI setup. No tuning, turnkey starting, outstanding reliability, excellent trail performance.

[Lister]

Thansk Tgreese. Just at the preliminary research stage so this is good info!.

[yossarian19]

Also - power is not so limited as you might think with an I6.
You can use the 4.2 liter's crank & rods (if savable) and a 4.0 block, you get 4.5 liters stock bore or 4.6 / 4.7 with a 0.030 or 0.060" overbore.
There is also a guy, Boostwerks Engineering or similar, who is working on a turbo manifold for the 4.0
Then there are supercharger setups for the 4.0, too.

Don't be afraid of the 4.0 - wouldn't be hard to make one walk all over a stock 401