Stihl 024 air leak

[ihatesaws]

On 04/07/2023 at 10:06, openspaceman said:

Nikasil is a deposit on the aluminium that is only about 20 thou thick so rubbing or honing is only really to scratch circumferential micro grooves to hold oil.

 

The big thing is to remove all the aluminium which has been picked up from the piston and melted onto the bore with chemicals and only lightly hone after.

 

 

 

Other experts say that you can ruin your cylinder with acid and if you manage to go through your plating with sandpaper then it was rubbish anyway.  I tried some more caustic soda on the line to the right of the exhaust port but it doesn't seem to do anything.  The black area under the exhaust can't be felt.

 

Out of curiosity I put the chinese cylinder on the meteor piston to see what compression I'd get and it's 140psi as well.  I'd say the gauge is right because the super is 170psi on the gauge and I can feel alot more resistance from its starter cord.  I figured that if the damaged oem cylinder is going to wear the piston and the rings then I might as well use the chinese cylinder as there is no damage in that.  It's practically unused.  Anyway the saw is going again.  It's idling and it's cutting although with maybe a little less power that with the oem.  Not sure yet.  Will have to run it for a while and see how it is when it's hot.

[openspaceman]

2 hours ago, ihatesaws said:

Other experts say that you can ruin your cylinder with acid

Well I am no expert and I use caustic soda gel and place it with a cotton bud, it takes ages and repeat applications but gets there. I don't think it reacts strongly with nickel

Edited July 5, 2023 by openspaceman

[spudulike]

Acid or alkali will react with aluminium to form oxide and that helps getting rid of the transferred aluminium. Once the black oxide has formed, you remove the oxide with abrasive paper and add more chemical until it stops fizzing and the plating looks clean.

From the wear to the piston, I woulds say that the black patch of oxide is proud of the bore hence the wear occurring. I would stick with the OEM/Meteor option and see if a few hours use will bed it down.

[openspaceman]

12 hours ago, spudulike said:

Acid or alkali will react with aluminium to form oxide and that helps getting rid of the transferred aluminium. Once the black oxide has formed, you remove the oxide with abrasive paper and add more chemical until it stops fizzing and the plating looks clean.

From the wear to the piston, I woulds say that the black patch of oxide is proud of the bore hence the wear occurring. I would stick with the OEM/Meteor option and see if a few hours use will bed it down.

I don't know what the blackness is but it may be some pick up from the rings or some species of metals in the aluminium alloy.

 

When you dissolve the aluminium pick up with caustic soda it turns it to sodium aluminate which is soluble, so it can be washed off. The fizzing is hydrogen being given off by the reaction.

 

Aluminium oxide is insoluble in water

[spudulike]

The black looks like the residue left when you use acid on the aluminium transfer. The black usually comes off with a bit of rubbing with emery but wouldn't do any more of this unless the black part is a high point.

[openspaceman]

15 hours ago, spudulike said:

The black looks like the residue left when you use acid on the aluminium transfer. The black usually comes off with a bit of rubbing with emery but wouldn't do any more of this unless the black part is a high point.

I never felt comfortable using acid so haven't experience of it.

[spudulike]

I had 5L of brick cleaner left for me by the previous owner of my old house, with a decent amount of HCL in it, it seemed rude not to use it!