Freeing up a seized piston

Need help finding information or parts for that old machine in your shed? Someone in here will know!

Moderator: Moderators

outforfun
C grade participant
C grade participant
Posts: 27
Joined: Tue Sep 10, 2013 7:51 pm
Club: WDTC
Bike: 2002 Sherco 290

Freeing up a seized piston

Postby outforfun » Thu Apr 20, 2017 7:57 pm

Hi everybody.

I have a seized TY175. There has unfortunately been water in the air intake when it was sitting. As a result the piston has become 1 with the barrel. I have separated the barrel from the base and the big end and mains feel OK so far.

HOWEVER, the piston is convinced it's not going to let go of the barrel. I put diesel/tranny fluid in the combustion chamber before I dismantled it, this sat for about 3 weeks. I've delicately used the oxy (not wanting to melt things) and Yield (a higher quality WD40 type spray) and a hammer and a block of wood. No luck.

I was hoping some of the gurus might have an idea.

The piston is about 2/3 up towards TDC.

Cheers, Don.



David Lahey
Champion
Champion
Posts: 2976
Joined: Thu Jun 05, 2003 7:01 pm
Club: CQTC Inc, RTC Inc
Bike: Many Twinshocks
Location: Gladstone, Queensland

Re: Freeing up a seized piston

Postby David Lahey » Thu Apr 20, 2017 9:57 pm

Here are a few ideas:
1 No matter how good it feels, the big end bearing is sure to be corroded so a new conrod kit will probably be needed, so cut through the conrod with a hacksaw, then degrease the whole cylinder and piston and trickle phosphoric acid so it runs down between the piston and cylinder. This will dissolve the rust from the rings and dissolve the corrosion from the piston which will free it up. Don't get any on the cast aluminium part of the cylinder

2 If you want to try and reuse the conrod, drill a circle of holes through the crown of the piston near the OD to remove as much of the crown as possible, so you can then use a reciprocating saw through the hole to cut through the gudgeon pin on both sides of the conrod. Then there are lots of options for getting the piston remnants out.

3 Again if you want to try and recover the conrod, hang the bike up somewhere, suspended by the cylinder so the weight of the bike is pulling on the piston/cylinder fit. Keep up with the yield and heating and cooling and the wooden block over a period of a few weeks (my dad showed me this way when I was a kid on a 1937 Norton engine that had been sitting full of water for about 20 years at the back of a beach).

4 Another idea is to load up the piston/cylinder fit using tapered wooden chocks under the cylinder so that there is load on it while you hit the piston crown (instead of the hanging up thing)

5 Fit the cylinder back in place and fasten it there and apply torque to the chankshaft one way then the other repeatedly until it starts moving. When it starts moving down the bore, chock the cylinder higher and higher until the piston comes out the bottom.

Yield works much better on its own rather than mixed with diesel and ATF


relax, nothing is under control

outforfun
C grade participant
C grade participant
Posts: 27
Joined: Tue Sep 10, 2013 7:51 pm
Club: WDTC
Bike: 2002 Sherco 290

Re: Freeing up a seized piston

Postby outforfun » Mon Apr 24, 2017 9:53 am

I had a win!!!

The diesel and tranny fluid didn't work while the engine was in one piece. However after removing the head, in the space on top of the piston I filled it with the Yield. I checked yesterday, and the Yield had mostly disappeared. It had been soaking for about a week and a half. So I took to it with a copper drift instead of the hardwood block.

In the process the top of the piston broke out as it is domed, this gave me better access to the crown with my drift. I added blocks of wood under the barrel and working it up I managed to get it out. No severe rust etc, so maybe just a rebore to the next size up? Not yet measured but I hope it's that simple.

So leaving Yield to soak past the rings and rust/corrosion is a fix if you have the time to leave it alone.




Return to “Twinshock & Classic Trials”

Who is online

Users browsing this forum: No registered users and 2 guests