That might be the reason the piston got stuck. The cup dissolved and worked its way between the piston and the bore.
Get the right tools, don’t improvise before you destroy the engine.
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Standard “disposable” tea cup. (Maco, as it happens). Probably is PET, which life is really too short to try and dissolve with solvent worked down the very tiny plastic filled gap between piston and block.
IOW I don’t think thats going to work, though I thank you for the thought.
Keep them coming. There may be a diamond in the coal.
Pet doesn’t dissolve in most common solvents, Google says this
(43,44) PET is soluble at room temperature in pure TFA and HFIP, as well as in a mixture of these solvents with DCM. The polymer quickly dissolves, leading to colorless transparent solutions.
I don’t know what’s in gasoline but I would not use any plastic parts in an engine as it probably contains all kinds of stuff that may dissolve or degrade plastic.
Is it’s ps (polystyrene) then gasoline dissolves it fast.
I believe dcm stands for dicholoro methane, which is used in paint strippers. I don’t know what those other solvent stands for.
Don’t think so. No petrol residues remain, and I doubt this plastic will be affected by petrol anyway, though I ought to test it, I suppose.
I think it jammed because I didn’t realise what was happening and carried on stubbornly hammering it a bit too long.
Re “don’t improvise”, dont think you are quite getting into the spirit of the thing, and/or you’re attacking my religion, though I AM quite likely to destroy the engine and that WILL annoy me quite a lot, only-myself-to-blame stylee.
I should seek out specialised piston-plastic-cup-unjamming tools?
In TAIWAN, the Land of Eternal Unobtanium? Hmm…
I just googled piston ring compressor. It looks like a metal sheet and 2 band clamps. You can buy both items very easily in taiwan.
All I can think of now is take the crank case off, and hammer the piston out from the other end.
Or you can attempt to hammer on other pistons in the engine to cause the stuck piston to go up. I don’t know what risk this carries.
Edited because it appears to be a metal sheet, not rubber
Piston ring compressors are either (a) a spring steel band with a clamp, (Ｕniversal/Adjustable) or (b) a steel shallow cone of the right size for the piston. The last time I did this, several decades ago, the standard improvisation was a big hose clamp, which I tried and couldnt get to work, so I bought the tool. You can probably buy it in Taiwan, too, but I’ll probably never use it again.
More recent improvisations are cable ties, which I tried and couldn’t get to work, and a split bit of PVC pipe, which I’ll try when/if I get the piston out.
You can get band clamps, and sheet of metal. But I don’t see how you can’t get a piston compressor. I mean lots of auto mechanics around here.
Do you know any auto mechanics where you could borrow tools from?
Hammering likely wouldn’t work, but I did think of turning the crankshaft with a long lever.
No good because of restricted access to the end of the crank shaft, and because the crank pin cant be lined up with the big end bearing.
Yesterdays problem. And maybe tommorrows. Today’s problem is a very stuck piston.
(I really wouldn’t expect a mechanic to lend tools. Its not how they make a living)
I was thinking of retail. The good Ktown tool shop has a big variety of greases, but (with one possible exception) they are all possibly dodgy (in some cases possibly deeply dodgy, given the obvious fakery on the packaging ) local brands.
From a quick look at your links, pretty much the same applies.
The possible exception was some 3M Lithium bearing stuff which no one (including 3M’s website) had ever heard of, but which hopefully isn’t fake, since I bought some. Cartridge only, which is inconvenient and leaks. I brought some Moly stuff in the UK, and GL3 manual transmission oil in Japan.
Some CPC filling stations sell greases which are probably OK and if I was doing it again I’d just get that, but they only sell GL4 transmission oil, not GL3.
Its Taiwantown
Bottom of the conrod not really very suitable or accessible for BFH application, and it and the crankshaft blocks access to the underside of the piston for anything wide enough to not pose a risk of punching through it.
I made a collar to protect the crank pin from further flailing about (split ring of PVC pipe.)
Then I put the bottom of the bearing carrier back on.
I made an excessively robust protector for the bottom of the bearing carrier, (PVC pipe, with an aluminium pipe inside it, filled with chopsticks hammered in tight)
I made some sleaves for the sides of the big end, from longitudinally split pipe, in case it hung up on the bottom of the cylinder and or scratched it on the way up.
I got my smallest bottle jack and pushed on the underside of the big end.
NOTHING
Pushed harder, lifting up the block (engine mounting is off at the front)
The block ended up maybe a foot higher. This was a bit stupid since gravity is a constant, but the tension from the other engine mountings probably er mounted quite a bit
NOTHING.
So PLAN B
Aluminium BBQ dish formed to the protruding piston top, full of pre lit charcoal, and blown to red heat with a blowpipe. Much horrible abrasive ash blowing around.
For maybe a couple of hours. Quite toasty.
This would perhaps attract comment from passers by in The Yook (or from people who’s expensive cars were parked alongside) but all DIY car work is equally weird and alien to Taiwanese.
NOTHING
OK, mosquito happy hour approaches. Time to pack it in, but still quite a lot of hot charcoal.
Quench with water
BANG!
Whole piston and quite a lot of the conrod pops up through the block.
I think it was probably held in place by thermal expansion and it was differential cooling that shifted it.
No obvious damage to bore or piston, though of course there might be distortion, or damage caused by jacking up the block so high (and then dropping it) that I don’t know about yet
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Cockup
Seemed like a good idea at the time
(and I still think it might have worked with a bit better execution, though I might not risk it again)
Pushup
Cookup
Popup
The problem there is that’s not how a piston ring compressor works, it stays outside the bore of the cylinder and the rings slip from one constrained space to the other. (If there ever appears to be overlap it’s simply due to chamfering of the cylinder opening.)
Yes, cut slightly too narrow so drawn in and jammed up.
Cut the same diam as the bore, might have been OK, though maybe too thin/flexible
They make steel ones sized to the bore that work in this way, though thats not the standard DIY type…
Maybe next time use something thick like PVC pipe
As I said above. That’s a recommended improv on the Internyet, but I hadn’t seen or thought of it at the time.
The protective collar for the crank pin (seen in pic 2) is sort-of-similar and worked well
This could be the source of a future problem. The highest temp rating I’ve ever seen for an aluminum head/block is 390deg. Charcoal fire temp ranges from around 200deg to >2000deg, depending on availability of oxygen. As long as the coals were just sitting there all mellow-like you’re probably fine, but if you were going at it with a bellows there could be a problems later. (Not even going to comment on the water quench…)
ETA: looks like a cast iron block though, and it would have sunk heat away pretty well from the piston, so even if the piston was aluminum all may be well? 
I don’t know, the problem might be with localized heating in the wrong part, but aluminum is very conductive and it’s very hard to heat aluminum locally with anything short of acetylene flames. I seriously doubt it got to 2000 degrees as this would require you go at it with bellows and it would have melted the aluminum long before. But I don’t know if the smoke caused any damage.
A heat gun would have worked to soften the plastic and allow removal.
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Sure. I think I already acknowledged the risk of distortion, but whaddyagonnado?
An engine with a stuck piston in it is a dead engine.
I think I got it quite a lot hotter than I probably needed to. The idea was to melt the jamming plastic, but it doesn’t look like that happened, and I think it was the quench that shifted it.
However, combustion temperatures go quite a lot higher than 390C, (but of course are more controlled) and I think this is a cast iron block.
The CB20 engine (this is a CB22 which I have no documentation for) is described as a integral cast iron block and there is no cylinder liner replacement procedure in the manual.
OTOH I did find some mention of Charade cylinder liners (of interest given the strange bore damage in cylinder 2) available from PRC, so either thats just your standard search engine lying scumbaggery, or there’s another (later) version of the engine.
I suppose I could put a magnet on it.
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