After years of infrequent short trip driving, and less frequent moderate trip driving, I am going to daily drive my 87 van to a job site 45 min away.

I'm sure there's a ton of carbon and gunk built up in the top end.

I was thinking I would put MMO in the spark plug holes, let it soak a couple days and burn it off. (possibly repeat every other weekend for a while).

What would be the best position to clock the crank to get all 6 pistons as close to level as possible?

(I'm sure this is like a 3rd grade math problem, but I keep drawing blanks).

Thanks in advance.

There is not likely to be one spot where all the pistons are at the same height.
jus sayin....

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-MattMan
LEANED & MEAN

You're probably going to get a lot of varied and conflicting advice for this question.

If it were me, I wouldn't bother putting MMO in the cylinders unless the engine has been sitting without running for a long time. If you've been changing the oil on a regular basis and your spark plugs look fine, I wouldn't worry about it. I think you'll burn off anything you're likely to burn off the first time you take it on a long highway drive, regardless of additives.

Instead I'd focus on checking all the obvious stuff and doing any maintenance you might've (understandably) put off over the years since you weren't relying on it to get you to work. Does the vehicle have any issues or symptoms while driving now?

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

This sounds crazy to me. If the engine is running OK, just a normal long drive without any special stuff will help it.

Plus, if you put a tad too much oil in, you could bend stuff like connecting rods.

And most of the MMO would be gone within a few combustion cycles anyway.

Personally, I find MMO as useless as t*ts on a boar-hog.

There are upper cylinder cleaners, like Lucas or BG 44K, that people in the trade use to help remove combustion chamber deposits. I'd be more inclined to use one of those though I remain unconvinced they do much.

Trickle plain water down the carb, while at a fast idle (About 1500 rpm). Just pour at a speed that does not stall he engine. The flash steam will clean any carbon.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

It won't hurt to use an upper cylinder cleaner. Make sure it has drained before you attempt to start or it could hydro lock. MMO won't hurt the motor oil but the oil is best changed when using some of the other cleaners, some will clean as well as carb cleaner. This was good practice on flathead motors once a year or so, as those can coke the rings which can lead to broken rings and piston lands.

Just put it in the gas tank and drive it.

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Official Cookie and Mater Tormentor.

I like MMO to un stick rings, and maybe it could help break down carbon.
Occasionally I remove the spark plug from the 73 Wheel Horse Kohler Rader 8 motor,
put a couple of pumps of MMO from an oil can and let it set overnight..

In your case, if you think it will help, well it certainly can't hurt.

I would,
* with a cool motor, remove all six spark plugs,
** using a pump oil can, put three maybe 4 good squirts of MMO in each cylinder,
*** just bump the starter, not a full revolution, just a few real short hits to help distribute the oil
**** let it set overnight
***** next day, spin the motor over and re install the plugs
****** repeat as desired

the MMO you add to the chamber will leak past the rings and be in the crankcase by morning
with the stock pistons being .160 or more down in the hole, and another 60cc's of room above
the top deck, I would not worry too much about having enough fluid in the cylinders to lock the engine,
but spinning the motor without sparkplugs after setting overnight, will eliminate that possibility.

adding to the fuel, as mentioned above is another good method.
I like to use a healthy dose of MMO in the fuel after engine rebuilds
to help lube the upper chamber during the initial run in- break in period,

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Around 1980, my father bought a 63 Dart GT 2DR HT. It had a bad Slant Six engine, so he found another and put it in. It was a 170 that came from who-knows-where. When he went to start it, it cranked over fine but wouldn't start. The carb was fine, so was the ignition. But it had absolutely zero compression. The rings were stuck, apparently. He put oil in the spark plug holes and got it to fire. It ran with zero horsepower...it was like it took every bit of power it had just to spin 700RPM. But, after an hour or so it ran a little stronger, then the next day it ran a little better, and so on. After a few days he was able to drive it, slowly, then faster, then after a few days it became his daily driver for the next 10+ years. It ran fine, just like a 170 should run. Didn't use oil, either.

At some point, he bought a used Chrysler 5th Avenue and the Dart sat. After a couple years of sitting, we decided to start it up and...it had zero compression!

I would put Kano Labs Kreen in the oil and fuel then drive it. With Kreen in the oil you can overfill it by a pint and when the oil level is back down to normal change the oil.

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Joshua

This.

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If it was easy, everybody would be doing it.

It runs fine apart from the choke not really being adjusted (put in one of those aftermarket adjustable automatic ones. Never really got around to dialing it in.)

It hasn't been sitting undriven, and it is otherwise maintained. (arguably more maintained than driven).

It had run rich for a while (original choke modulator failed-open. It took a while to notice.)

I get black (not blue at all) smoke at startup.

Fresh oil turns black, quickly.

I am concerned about built up carbon creating overheating problems.

Kreen and/or water probably a better idea.

Thanks for all replies.

I have a 1974 225 in garage that I will throw a gasket set (less head) and a timing set and install temporarily while I rebuild original motor--likely next winter.

In the meantime, just want to get to work without overheating or damaging the block/crank/head. It was my dad's motor, and I'd like to be able to keep it.

I would suggest fixing the over rich condition first, or you'll reinstall the carbon deposits you get rid of. Plus, the excess fuel that doesn't burn off tends to wash the oil off the cylinder walls and dilutes the oil. Been there, learned the hard way on my V8 wagon. That engine packed it in at only 88K.

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If it was easy, everybody would be doing it.

Less useless than Marvel Mystery Oil: bacon grease, as it seems.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I will agree with SSD here,,
Any additive is a ‘helper’ not a fixer,
You need to get the tune right on the motor,
Then work on enhancements.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8