Piston soak method details - real or confirmation bias?

[pasadena_commut]

There are so many piston soak threads, all with slightly different method details. This makes me wonder how many of these method details are "real" (actually affect the outcome of the soak), how many are "confirmation bias" (outcome of the soak is ascribed to this detail but it does not actually make any difference), and how many are somewhere in between. Or maybe there are better methods for these steps which are not in common use? Thoughts?

To slightly limit the discussion, let's restrict it to soaks with Berryman B12 Chemtool, which appears to be the most common solvent for this work at the moment. Also please discuss the mechanics assuming an inline 4 cylinder motor (just to simplify matters.)

Here are some of the details commonly seen in a piston soak method (longer descriptions below)

1. Drainage of a perfectly clean piston
2. Soak times and conditions
3. Position of piston during soak
4. Adjustment of piston position during soak
5. Leave oil in motor or drain it first?
6. Removing solvent from top of cylinder
7. Relubrication of motor before restart

Drainage of a perfectly clean piston. This isn't a method detail so much as a possible measure of the expected end point of the soak. If one took a nearly new motor (let's say after 1000 miles, rings and piston drain holes completely carbon free), set all the pistons at the center of their stroke, poured solvent on top of each piston, screwed the spark plugs back in loosely, how fast would the solvent drain through? "Drained" here means that all solvent has passed the rings except for any trapped in a depression on the surface of the piston. We wouldn't expect to do (much) better than that at the end of a remedial piston soak, although it could in theory go slightly faster since all the oil would have already been stripped from the rings, so wouldn't need to be dissolved away to let the solvent through. Would all the solvent actually drain (as defined above) on all motors, or are there some where the clearances are all so tight that drain times are unreasonably long, for instance, a week?

Soak times and conditions. The solvent is a chemical constant, at least at the moment it comes out of the bottle. However, its viscosity, how well it dissolves oil and carbon deposits, and how fast it evaporates must vary with temperature. So a 1 hour soak on a 4°C day is unlikely to have the same result as a 1 hour soak on a 40°C day. I don't recall reading a single method that disclosed the ambient temperatures (although somebody surely has). There is also the matter of the valves. In the standard soak position (defined above) 2 of the cylinders (those on the compression and power strokes) have all valves closed and are almost a closed system, whereas for the other two one has an intake valve open, and one has an exhaust valve open, and those are much closer to a fully open system. One would expect that the evaporation rate for the "closed system" cylinders would be lower than that for the "open system" cylinders, and ever more so as the ambient temperature goes up.

Position of piston during soak. All the way down, mid stroke, some other point? Does it really matter (once the positions of the valves have been taken into account)? Maybe. The piston tilts when the engine is running, and I suspect that when it stops or is turned slowly by hand the piston is not oriented straight up and down except at top dead center. The piston probably even tilts in different directions (slightly, of course) when it is at the same spot but moving up rather than down. Is this tilt large enough to affect the way the solvent drains?

Adjustment of piston position during soak. Many methods suggest rotating the crank during the soak, but how much and how often?

1. Rotating a few degrees clockwise and then the same amount counterclockwise would leave the valves unchanged but it might reverse the tilt.
2. A half turn would leave all cylinders at mid stroke, but it would rotate states (intake -> compression -> power -> exhaust) changing the valve state of 3 out of 4 pistons and it might reverse the piston tilt.
3. Rotating a full turn would rotate states (intake->power, compression->exhaust, power->intake, exhaust->compression) swapping each piston from "open" to "closed" or vice versa, but not affecting the tilt.

Any of these motions will put some force on the rings relative to the piston. It will also drag the ring on the cylinder surface without the presence of oil (once the solvent has dissolved it all), possibly wearing it abnormally, with the least amount of wear probably corresponding to the least amount of piston travel. After two adjustments the full turn would "balance" solvent exposure seen by each piston, but it would take 4 adjustments to achieve that balance with a half turn, and with the small forward and reverse, balance would never be achieved, with two cylinders always seeing higher rates of evaporation than the other two.

Leave oil in motor or drain it first? Leaving the old oil in the motor during the soak will dilute the solvent into a larger volume of oil - but leave it in the motor. Draining the oil first, and leaving the drain bolt out, will let any solvent which gets past the piston drain out of the oil pan. The immediate difference between these is that the solvent in oil probably won't strip the paint from the bottom of the oil pan on the way out, whereas close to pure solvent coming out the same hole probably will damage surrounding paint. If the crank is turned manually a small amount of solvent dissolved in oil might be moved into other parts of the motor where it could potentially damage seals. The oil pump will most likely not move solvent around the motor if all the oil was drained and the drain bolt left out. Being able to observe the rate at which solvent drains out of the pan could be informative about how the soak is proceeding which would be helpful. It might also let a little dust into the bottom of the motor, which would not be helpful.

Removing solvent from top of cylinder. The two most common methods are to spin the motor with the starter (fuel pump and spark disabled, towel over spark plug holes) and to blow the excess out with compressed air. Other than solvent trapped in piston top depressions, should there be any solvent above the piston after a successful piston soak? Some methods do both, using compressed air to remove any carbon flakes that remained after spinning the motor a few times. Would removing the spark plugs and allowing the remaining solvent to evaporate be equivalent to spinning the motor so long as any carbon left on top was blown out with compressed air?

Relubrication of motor before restart. Adding a little oil to each cylinder before restarting the motor is a common step, said to make it easier for the motor to start and probably decreasing cylinder wear. Would the solvent not also have stripped oil from the bearings, and if so, shouldn't those also be lubricated before start, and if so, how? If the soak was performed with the drain bolt out, and stopped only when no more solvent dripped out, would the fresh oil added to the motor have so little solvent contamination that it could be used for the length of a normal OCI? Once the motor warmed up the small amount of solvent present, very greatly diluted, would be rapidly evaporated and burned in the motor.

 

[The_Jeff]

I leave old oil in so the oil pump doesn't lose prime. I lost prime once on a Saturn SL by leaving it empty for days.

I actually used "Mobil 2" once for the two minute post-soak start and run, just me being cheap.

For me, there has always been a spectacular smoke show. Sometimes (Saturns) the cars run better. Never have I gone from an oil guzzler to nothing at all-- just gone from a quart every 400 miles to one every 650, or something like that.

Your Q&A also doesn't ask about spark plugs-- I reuse old ones for the initial startup. New plugs can come later if it starts running ok.

 

[Skid]

I helped a friend out with a piston soak on his neglected 2AZ (those two words should never appear in the same sentence). I spent almost 6 weeks on the car, a little every day or every other... My lessons learned is simple, never again. Just pull the motor.

 

[Chris142]

I dont think that turning the engine over does anything.

 

[Elkins45]

On an inline four you get a benefit from having the pistons at least somewhat centered if you want to soak all of them at once. There’s no sense in pouring solvent into a cylinder where the piston has stopped at TDC and you lose half the solvent down the manifold thru open valves.

I never did the jiggling between pours and my success rate is 3/3 with the Toyota 2AZ.

Relubricating the cylinders is done to reestablish compression faster, not expressly to protect them from wear. I’ve heard no reports of bearing failure after a soak.

 

[PandaBear]

I did a B12 soak before and here's my observation:

1. Drainage of a perfectly clean piston

I think this is where the "may need 2 applications" come in. Nobody would know but you based on how bad your rings were before, and whether it is good enough. Maybe you will be happy going from burning 1 qt every 1k miles to 1 qt every 3k miles, maybe you will not be and want it to go away completely. The first soak will definitely drain through faster due to more stuck ring and then after the first soak there will be less drain through, etc. My guess is the manufacturer telling you to use 1/4 can per cylinder is a good starting point from their experiment.

I have a bigger concern about soaking a V engine instead of an inline, or a tilted engine soaking unevenly.

1. Soak times and conditions

I think this is where the law of diminishing return shows up. It probably will clean up the most in the first 15 mins then the surface tension holding the solvent would be slowly seep through and break down the critical binding area. I think 1 hr vs 12 hr would be a huge difference and some difference between 12 hr and 24 hr, but from 24 hr to 1 week, 1 week to 1 month, 1 month to 1 year, etc, won't matter much.

1. Position of piston during soak

I don't think it matters, remember the ring may not be all expanded or compressed the same so the piston position will likely not be why more or less leak through. Also at TDC in theory the valve is closed so not much would leak through in the short term. In the long term it would be more about the ring than anything.

1. Adjustment of piston position during soak

I think it has more to do with exercising the ring during those hand cranking that helps blowing and sucking the solvents between the area between the rings and ringlands. Surface tension don't do as well without mechanical agitation by cranking the pistons up and down.

1. Leave oil in motor or drain it first?

Obviously your solvents would have less dirty stuff to go against if you start with a clean oil, but clean oil is not free. If you spend the same money you are probably better off with using dirty oil then buy 1 more can and soak one more time, even with dirty oil. That's what I believe.

1. Removing solvent from top of cylinder

More about hydrolock risk. I am not expecting any extra cleaning power from this as the evaporated solvent leaving loose carbon powder behind won't be staying for long, after a few combustion they would be blown out of the exhaust. It is still good for cleaning if you can remove dirty solvent obviously but that's not my major concern. Dislodged already they won't get stuck back into the ring that fast, certainly not faster than the exhaust stroke blowing them out or combustion stroke burning it off.

1. Relubrication of motor before restart

I have a mix feeling about this. I do think it may help but to be useful you have to add so much oil that you risk hydrolock as well. This is not part of the official instruction, and cranking a few times with the starter would likely bring in enough oil to protect it before scoring the cylinder. Remember most of the scoring is from load and rpm, and if you don't soak all the time you don't get that much damage. If this is a concern I personally would drop a few drop of 2 stroke motorcycle engine oil into the cylinder, or fill that in 2 stroke motorcycle oil in the gas tank with just enough gas and motorcycle oil to run through the start.

 

[4wd]

On an inline four you get a benefit from having the pistons at least somewhat centered if you want to soak all of them at once. There’s no sense in pouring solvent into a cylinder where the piston has stopped at TDC and you lose half the solvent down the manifold thru open valves.

I never did the jiggling between pours and my success rate is 3/3 with the Toyota 2AZ.

Relubricating the cylinders is done to reestablish compression faster, not expressly to protect them from wear. I’ve heard no reports of bearing failure after a soak.

Yep, said this many times - a boxer ? Wellll …
A great time is when it’s time for new plugs anyway …

 

[PandaBear]

I leave old oil in so the oil pump doesn't lose prime. I lost prime once on a Saturn SL by leaving it empty for days.

I actually used "Mobil 2" once for the two minute post-soak start and run, just me being cheap.

For me, there has always been a spectacular smoke show. Sometimes (Saturns) the cars run better. Never have I gone from an oil guzzler to nothing at all-- just gone from a quart every 400 miles to one every 650, or something like that.

Your Q&A also doesn't ask about spark plugs-- I reuse old ones for the initial startup. New plugs can come later if it starts running ok.

My old plugs came out looking like it was dipped in black paint, I would definitely use some old spare plugs to crank and run first. I think it refused to start for like 15 mins of cranking (with cool down rest time in between) and until I took the plugs out to find them looking like tar. New spare plugs go in and they finally crank after about 5 mins.