How to move rusted pistons in the engine block

Thank you @sfdon for valuable feedback

To support my initial description few pictures from 2021.
Two pistons and crankshaft are out completely. Two left...

Initial condition:
1649795164893.png


After anti-rust agent vinegar is doing it's job:
1649795249839.png


And after draining the soup and a little of cleaning:
1649795343423.png


Once the spring will come I will try to apply Sea Foam Deep Creep for some time and later try to hammer
 
Is the block steel and the piston alu?
If so, then there is a way to chemically dissolve the steel: ask an anodising company.

In order to clean alu prior to anodising, they use a strong acid that will eat steel.
I once had a M6 tap broken off inside an alu part. No problem they said; It came back, nicely anodized, with clean threads and no sign of the broken M6 tap.

It will eat all steel of the block, so also wrist pins, bearings and piston rings.
 
It is not the aluminum alloy pistons themselves but the iron-content rings which are rust-bonded to the iron-content bore wall. The goal
is to get those rings unbonded with no widening or other damage to the slots in the pistons in which they fit (lands).

Yes, repeatedly apply lots of rust buster chemicals and heat. That will weaken but not necessarily undo all of the adhesion.

You want to undo the adhesion first, while not transposing the parts with great force. That invites breakage.

You can try tapping small rotational force on the pistons back and forth, and also gently tap them alternately up and down, doing each tap on a different spot above and below. The goal is to PATIENTLY exert small impacts in all directions so that small granules of the overall rust track between parts are broken and made mobile, until enough of it is broken up that you can try to make transposing progress in one direction, but of course, you can't see this happening. You hope that at some point you can tell that things are moving easier and can dare a slightly harder tap.

caveat: My most recent gnarly rust busting task was a 6 bolt turbo housing.
I succeeded with 5 frozen bolts but the 6th broke close to the flange. Must have lost patience or sometimes the job is beyond success.
 
skk said:
It is not the aluminum alloy pistons themselves but the iron-content rings which are rust-bonded to the iron-content bore wall. The goal
is to get those rings unbonded with no widening or other damage to the slots in the pistons in which they fit (lands).

Yes, repeatedly apply lots of rust buster chemicals and heat. That will weaken but not necessarily undo all of the adhesion.

You want to undo the adhesion first, while not transposing the parts with great force. That invites breakage.

You can try tapping small rotational force on the pistons back and forth, and also gently tap them alternately up and down, doing each tap on a different spot above and below. The goal is to PATIENTLY exert small impacts in all directions so that small granules of the overall rust track between parts are broken and made mobile, until enough of it is broken up that you can try to make transposing progress in one direction, but of course, you can't see this happening. You hope that at some point you can tell that things are moving easier and can dare a slightly harder tap.

caveat: My most recent gnarly rust busting task was a 6 bolt turbo housing.
I succeeded with 5 frozen bolts but the 6th broke close to the flange. Must have lost patience or sometimes the job is beyond success.
Click to expand...
Thanks! I'm with you about the understanding what is a nature of a problem - rings rusted into the cylinder's surface.

I'm totally for trying many small steps trying to broke the junction points.

Heat shocking is one of them. I was not doing this much so far but it looks it will be needed. Probably people burning fuel with oil (to avoid explosion and to longer the time of burning) are causing the cylinder to expand a little and possibly braking the junction ring-cylinder surface.
 
eriknetherlands said:
Is the block steel and the piston alu?
If so, then there is a way to chemically dissolve the steel: ask an anodising company.

In order to clean alu prior to anodising, they use a strong acid that will eat steel.
I once had a M6 tap broken off inside an alu part. No problem they said; It came back, nicely anodized, with clean threads and no sign of the broken M6 tap.

It will eat all steel of the block, so also wrist pins, bearings and piston rings.
Click to expand...
This is very interesting.

Anodising is using sulfurinc acid (the same as in car batteries)

aldari-pl.translate.goog

Aldari - cięcie laserem, anodowanie, ślusarstwo

Anodowanie aluminium to proces elektrochemiczny znacząco zwiększający wytrzymałość tego metalu i jego odporność na korozję. Dowiedz się, jak on przebiega.
aldari-pl.translate.goog aldari-pl.translate.goog

I do have such an acid.

Also vinegar is an acid. That is why it eat all the rust and some of cylinder surface.

It would be great to force it to eat all the rings but probably it would require to seal the bottom of the piston edge to avoid acid to run once any hole will appear on it's way.

Very interesting experiment. Maybe I will look for some aluminum part and dip it into the acid to check whether it will react or not.

Thanks for that Erik!
 
Shock Treatment: you and your BFH (big friendly hammer) need to evenly distribute the force of the blow around the perimeter of the piston to evenly transmit that energy to the ring(s). So, some sort of mandrel between hammer and piston is needed... for instance, a piece of properly sized iron pipe, with smooth end so as not to mar the piston. Then WHAM.

Alternatively, put a plastic bag in the top of the bore, filled with something like plaster of paris (could even use cement mortar). Or, heavily grease the bore and piston top before pouring in in the plaster or mortar. Might even use some fibers such as are commonly mixed into concrete, though the purpose of those is a little different than nthe current need. After (whatever you use) sets a week, it may be hard enough to fully distribute hammer force across the entire top of the piston.

Thing is, these suggestions mostly address freeing the top ring. Clearance between lower rings and piston may lead to breakage of the lands below the top ring.

IT ALSO DAWNS ON ME... that this is a corrosion-of-steel issue. A couple amps through suitable electrolyte may selectively dissolve the rust. Google rust electrolysis. Don't know whether it will attack aluminum at the same time.
 
Dissolvement would be nice as long as it would not harm the piston.

I will check the acid method on some scrap.
 
some links here:

Removing broken screws with Alum bath

I'm in the process of removing a broken off screw using this method and was suprized by the aroma. I was wondering, is the vapor given off by this reaction something to worry about? Should this be done outside or under forced ventilation? I'm not a chemist. Thanks, Eric
mb.nawcc.org mb.nawcc.org

'Alum' seems to be a US word for potassium aluminum sulfate.


this stuff: https://en.wikipedia.org/wiki/Potassium_alum
 
Great link Erik!

It supports anodizing technique to...

(...)make up a saturate solution of alum. You want to dissolve as much alum as your quantity of water will take(...)

Same using sulfuric acid (used in anodizing for example).

I'm really for to try. I have an old aluminum thermostat housing with metal bolt rusted in. Worth to check first. :)
 
My suggestion, is to work from the bottom where rod connects. I assume you're not worried about the rings as that is what is really stuck.
I like the heat the block idea and since you are not saving the block no worries there.
Take a wood 2x4 and fit it round the rod with the most amount of surface area to push on the piston.
With all the soaking and cleaning you have done, just soak again and place 2x4 and hit hard with a 10lb hammer.
It's all about breaking the hold on the rings rusted to the cylinder walls.
Just hope it doesn't break the lands between piston rings but at this point I don't see many other simple ways to remove.
Good luck!
Gary
 
m5bb said:
...
Just hope it doesn't break the lands between piston rings but at this point I don't see many other simple ways to remove.
...
Click to expand...

Thanks Gary. Hammering or pushing with a press is probably the last step.

All above is for how to save the pistons:
- not to deform them
- not to break or expand the slots where the ring as moving

As far as I know engine have had relatively small mileage and cost of used pistons is quite high, so it makes a lot of sense to save them.

If the engine block but would be an easy and secure task I would probably do it but I will try to hit with chemistry and (if still needed) temperature and pressure.
 
So let's back up here.
What's so valuable about these pistons?
Are they Alpina or Hartge or something really rare?
Or are you just trying to save them and the money a new set would cost.
New pistons in an engine would not destroy it's value as to originality.
My understanding is originality includes repairs to keep a car or engine running.

Since you have a few removed you could probably have a brand new set of 6 made that would be the same specifications as the current set.
I have a custom set in my M30 motor. 10.5:1 compression ratio with dished areas for my bigger valves and custom cam.
Pistons around $1200.
That was quite a few years ago.
Here's a set for M30, you spec size and compression ratio, rings and connecting rod pins included. $1300.
store.vacmotorsports.com

CP-Carrillo Forged Piston Set, BMW M30

Crank Type: B30; B34; B35. Bore Size: 89 mm; 89.5 mm; 90 mm; 90.5 mm; 91 mm; 91.5 mm. Compression Ratio: 8.5:1; 9:1; 9.5:1; 10:1; 10.5:1; 11:1.
store.vacmotorsports.com store.vacmotorsports.com

At this point you may have $300 or more in labor in trying to remove two pistons of unknown quality.
Even if you get them out the rings on those two pistons will not be usable.
A set of rings, and you should replace them all would be around $400.

Maybe this is just a challenge and I think we all want to see how you get them out and then if they are even usable.

Just saying..... maybe it's time to move on.

Gary
 
Thank Gary for the message,

The pistons are not too valuable. They are available new from Kolbenschmidt. But they are not cheap anyhow.
I have a loss with this engine. It has been dropped during transportation (professional company). But this is another story.

I'm not in a hurry and yes, this is a challenge.

I'm happy saving some old stuff. Maybe this is out of business case here, maybe not.

This thread is a great example what a great knowledge this forum is full of. So many experienced people, manics with different attitude to old cars (BMW, but not only).

Probably this might be useful for Others, saving Alpina's, Hartge's or others.

I have already learned a lot and I would like to try some ways. sulfuric acid is just eating some aluminum to be saturated with it once I will make and experiment to support Erik's) but not only experience with removal of the rusted bolt or cracked thread inside aluminum.

All I'm doing is building my experience before I will feel ready to start E9 restoration. All the information on this forum are priceless because You are on it Guys!

I'll let you know about any progress on this challenge (let's called it finally as such).

Happy Easter!
 
The good in a bad they are only two our of four to be taken out - this is not M30 engine this time at least. ;-)
 
So, one other simple suggestion I haven't seen here: when I seek to break a rusty bolt loose, I always scrape around the perimeter of the bolt with a pick to remove as much rust as will physically chip off. My thought is that this allows any chemical agent to get closer to the problem.
 
This might also help.

Probably razor could be the tool (due to it's thickness) or?
 
I would use something like the first or third pick in this set: https://www.griotsgarage.com/8-piec...CPLB&msclkid=a4442cfe908912323c164ea44c8b0336

From the top, work down the side of the cylinder and angle the pick toward where the rings are stuck on the cylinder wall, keeping the sharpest part of the pick away from the piston itself. From the bottom, work up the side of the cylinder. The picks are probably not as hard as the piston, but I would think about scraping the walls just in case. Obviously, start gently, first to see if this is going to do any good at all, and then to see the amount of pressure needed to actually get some of the rust off.
 
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