Hello from England

[OldSwartout]

Sorry about the space hogging in the previous post. Something happened to the site when I was writing it.

Fixed it for you.

[BridgeBrit]

Why thank you! Much more tidy.

[steve]

Nice to see you on here Stella and good luck with the BS 50 - I'm enjoying your enthusiam with this 'new' bike!
I'm also in the UK (south Bucks) and have a couple of 350s...my GTO is will be on the road in the next few weeks after having had a full engine rebuild...nearly finished thankfully!
My partner has a place in Lymington so I get to go along to Sammy Miller's place every now and then...I don't think he was having a bad day when you saw him, fairly normal from what I've seen!

Steve

[BridgeBrit]

Hi Steve,

Thanks for your post. Pretty cool to be at the end of your rebuild! Congratulations! No mean feat and i am completely envious. And it's also great hearing about more and more Bridgestones here in old blighty, too.

Others have shared your Sammy observations too, but hey, the man is a legend. He has actually helped spur me on. I'm driven by the idea of riding round to his museum when my 50 Sport is finished. However, first I still have to free a siezed piston. It was day two today and it got a little ugly. I fear it may be welded in but ironically everything else looks okay. The gearing seem sound, magneto looks immaculate, carb is all complete and just needs a clean, there doesn't seem at this stage to be anything else seriously wrong apart from the fixed piston. Gentle hitting with a hammer has led to less gentle hitting and it hasn't budged at all. Figure the piston is shot anyway so am wondering if it can be drilled out? Sounds severe and will cost more parts but I don't know what else to do. (Yes, I know this is what happens if you are stupid enough to buy a bike with a seized engine but it's only a 50cc, surely it can't be that bad.)  If anyone has any ideas I am definitely interested in hearing them. Top of the cylinder is off, bottom of the cylinder is disconnected from the exhaust and the cylinder and piston move up and down when you move the wheel with the gear engaged. I leave the cylinder bathing in WD-40 every night but the level never seems to go down. It is seriously jammed.

But I'm not discouraged! :-)

Thanks y'all.

Stella

[Sno Jet]

Hi Stella,  I was looking through an old magazine "Classic Motorcycle Mechanics" and they had an article on stuck pistons.  They start out by soaking in diesel or something else, as you are doing. 

The next step if that does not help would be to apply a little heat with a hand torch and gently tap the piston, up and down with a wooden mandrel. (USE CAUTION AND REMOVE THE FLAMMABLE LIQUIDS FIRST FROM THE BORE AREA!!)  Your goal should be to move it only a little and not force anything.  You can always go back to soaking again if need be.  They warn about forcing the piston down past the bottom skirt of the cylinder as this may cause CRACKING of the bore.

They recommend using something to hit on the outer rim of the piston so that the piston does not want to go sideways.  Your goal is for the piston to uniformly go straight up or down the bore!

You have to be patient or you will end up ruining the cylinder.

If all of this does not work, they say drilling multiple holes thru the top of the piston MAY loosen some of the forces holding the piston in.  Be careful in drilling so you do not hit the bore and also cover everything up so pieces to not fall into the case.  And don't forget the eye protection thru all of this!!

In the end, you will most likely need another piston at the very least.  If the cylinder bore is damaged, you would either need to have it fixed or replaced.  Hope this helps.  Good luck

[BridgeBrit]

Thanks Sno Jet, that's really helpful! Had to remove the fuel tank to make space to operate today though and had some spillage so I'd better make sure that is absolutely cleared before torching. It makes sense using heat to expand the cylinder although I guess that needs exceptional care with cast iron.

I've just been googling the problem on the internet, too. Has anyone ever used oxalic acid to remove a stuck piston? Found a forum that recommended it. It seems an effective rust destroyer and that looks to be the problem inside my cylinder given the pitted appearance of the piston head and shards of rust inside the cylinder. I have heard of using oxalic acid to treat corroded fuel tanks but have never heard it being used for stuck pistons, although it sounds logical (if the fuel tank treatment works.) Not sure though if I have to prevent the acid from going into the crankcase also though. Another site recommended patience and frequent reapplying of penetrating oil. That sounds like a lesson.

Thanks again Sno Jet. I shall definitely investigate that further.

Kind regards,

Stella

[Sno Jet]

Hi Stella, Patience and thought are most important at this point.  Once you bring out the heavy artillery, there may be no going back!

[BridgeBrit]

Hi Sno Jet,

Yes, I think that is absolutely the case. It's only a couple of days. I'm going to go backwards a little and just keep using the penetrating oil. Eventually it would have to seep through (I hope.) I don't have any time constraints so can afford to take it slowly.

Thanks. Good reminder.

Stella