RRussellTx - 1974 Commando 850 Project

RussellTx said:
I'll try anything at this point!
I just have penetrant in there at this point.

I rigged up a little contraption to put some steady pressure on it and now I'm going to have a pint...
What could go wrong?

contraprion.jpeg

contraprion.jpeg

  • Media owner RussellTx
  • Date added

with penetrant.jpeg

with penetrant.jpeg

  • Media owner RussellTx
  • Date added
Click to expand...
I always use heat with penetrating oil, the magic temp being about 300F to make press-in bearings and such come free (gas BBQ is my friend). But that's steel surrounded by aluminum so it's a different kettle of greasy fish and chips, expansion-wise. I wonder if a bag of ice, or dry ice on the piston tops while heating the barrels might persuade them to part company? Aluminum reacts to temp pretty radically compared to steel so perhaps it may contract? Dunno just guessing.
 
RussellTx said:
I'll try anything at this point!
I just have penetrant in there at this point.

I rigged up a little contraption to put some steady pressure on it and now I'm going to have a pint...
What could go wrong?

contraprion.jpeg

contraprion.jpeg

  • Media owner RussellTx
  • Date added

with penetrant.jpeg

with penetrant.jpeg

  • Media owner RussellTx
  • Date added
Click to expand...
Looks a good idea..

You can strip the head in the meantime. Can you see RH10 stamped on the head just a bit back from the exhaust rocker cover on the timing side?
 
Last edited:
johnm said:
Looks a good idea..

You can strip the head in the meantime. Can you see RH10 stamped on the head just a bit back from the exhaust rocker cover on the timing side?
Click to expand...

I'm going to keep everything in chunks as I tear it down until I get a handle on things. I don't like everything apart and spread out any longer than is needed. I confuse easily...

It does have the RH10 though. What does that mean?

Head Marking.jpeg

Head Marking.jpeg

  • Media owner RussellTx
  • Date added
 
RussellTx said:
I'm going to keep everything in chunks as I tear it down until I get a handle on things. I don't like everything apart and spread out any longer than is needed. I confuse easily...

It does have the RH10 though. What does that mean?

Head Marking.jpeg

Head Marking.jpeg

  • Media owner RussellTx
  • Date added
Click to expand...
RH10 is the correct head for your model of Commando.

It's also generally accepted as the best Commando head with good porting as original and also usually safe from cracks and leaks.
 
Those pistons are probably not going to be used again anyway since It looks like you'll need to bore the barrels out to the next size up. (I had an engine that I got from a junk yard back in the 80's no telling how long it had been sitting outside- I tried a bunch of stuff with no luck, until drilling, but then once it was off the bike and I was able to get it set up in an arbor press, it let go under a bunch or pressure & with a really surprisingly large spark I might add). - I never would have had any success otherwise. Cj
 
Mine was locked up just like yours. I soaked mine down with diesel fuel for awhile, put it in fourth gear and rocked the rear wheel back and forth many times. Finally it broke free. Soak it and rock it, soak it and rock it. Rock it with vigor, put some oomph into it. Good luck.
 
Corrosion E X P A N D S

OP, heat the cylinder. Block the heat gun up pointing at it.

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The Industrial Master "D-Series" Heat Gun

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Drink a beer.

Then a second one.
 
You have a great idea. Many of the above suggestions will help. The only thing I can add is to have patients. And get more beer
 
Schwany said:
Looks like a quick flip is out of the question. :)

Welcome to the dream. Do not add up the receipts.
Click to expand...
Nothin quick about this project!!

Day 2 of the soak...
Elevated the front end to get it level to cover the entire top of the pistons.
Mixed up the fun colored AFT/Acetone concoction.
Topped off the cylinders.
Unscrewed the nuts on the bottom of the barrel to push up on the fins.
Got my favorite English Beer...

Day 2 of the soak.jpeg

Day 2 of the soak.jpeg

  • Media owner RussellTx
  • Date added
 
RussellTx said:
Nothin quick about this project!!

Day 2 of the soak...
Elevated the front end to get it level to cover the entire top of the pistons.
Mixed up the fun colored AFT/Acetone concoction.
Topped off the cylinders.
Unscrewed the nuts on the bottom of the barrel to push up on the fins.
Got my favorite English Beer...

Day 2 of the soak.jpeg

Day 2 of the soak.jpeg

  • Media owner RussellTx
  • Date added
Click to expand...
I'm def a fan of SS beer, I remember buying my fave 'old brewery pale ale' at the Liquor Barn in Monterey CA in the early 80s when I was stationed at the Presidio of Monterey language school. Drinking that beer was like going from the Monkees to the Beatles, it really opened my eyes, well, before it closed them.

Oh, as usual, mdt-son makes a great point, he knows his shnit. I have used phosphoric on many things, especially tanks. Take proper care and it'll get things done for you.
 
RussellTx said:
Nothin quick about this project!!

Day 2 of the soak...
Elevated the front end to get it level to cover the entire top of the pistons.
Mixed up the fun colored AFT/Acetone concoction.
Topped off the cylinders.
Unscrewed the nuts on the bottom of the barrel to push up on the fins.
Got my favorite English Beer...
Click to expand...
I knew that it was going to be some serious effort from the first pic. Good thing you got it for the cost of trailering it home or wherever it got trailered to.

I seldom drink beer these days. It just makes me fat.

This is my after 5PM fuel of choice in 2024.

RRussellTx - 1974 Commando 850 Project
 
I've had several seized pistons very much like yours, and they've always freed off eventually, following soaking in penetrating oil, followed by regular attention with a wooden block and a medium sized hammer. The shock loading seems to be key, but your setup looks good
Time & perseverance...
 
B+Bogus said:
I've had several seized pistons very much like yours, and they've always freed off eventually, following soaking in penetrating oil, followed by regular attention with a wooden block and a medium sized hammer. The shock loading seems to be key, but your setup looks good
Time & perseverance...
Click to expand...
I’d say use both, shock and constant load…

Get a drift in there and apply some shock whilst it’s still under constant load.
 
RussellTx said:
Pretty sure it's not coming out without pulling the motor at this point.
Click to expand...
If you can afford to put 2 weeks aside then first clear out all the grounds and debris and then soak the piston tops with ATF/Acetone mix. Then over the following 2 weeks daily use a long wrench to the crank nuts to attempt to rock the crank back and forth, topping up the ATF/Acetone mix as needed. Occasionally let all the fluid disappear or wipe it out and then apply heat to the piston tops before again rocking the crank. Once it starts to move slightly it is only a short time before the pistons are free.
 

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