What's new
What's new

Dissolving aluminum with muriatic acid.

Well, I give up on finding a replacement piston, so I took the sharp edge of a carbide blank and pushed off smeared aluminum from the scuffed area, then used a flexible abrasive bar on the skirt and cleaned it up.

Then, I put the lantern tool post in the lathe and put the knurling tool holder in the lantern post.

I then proceeded to knurl the skirt. I went across it twice with slight pressure... it increased the diameter .003.
That made the skirt too big, so I put the piston back in the lathe and laid a file on the knurled area, applied slight pressure, which reduced the diameter just a bit.
Tried it, and it slips in and out of the bore now, with negligible slop. I think it's a win.
View attachment 441782

View attachment 441783

View attachment 441784
I can't wait for the results. I'm concerned about the nursing on a piston skirt. That looks "knurly" 😁
 
Well, there was nothing scientific about it, so there is reason to be skeptical of the results.
I don't really know how much "clearance" is required. If I make it too tight, it might seize again when heat swells it up. But, the cylinder is going to increase in diameter as well, although not as much....so it's got to be a balancing act.
I'll give it some more thought before I reassemble the engine.

P.S.~ The other day, I was attempting to remove the wrist pin from the piston and was having difficulty due to not having a fine point enough snap ring pliers.
I messed around and had it about half out of the slot and had to stop for some reason.
Well, when I returned to finish the job.. .the ring must have been more ready to come out than I thought... it had popped out of there and was somewhere on the dirty floor... so I have to find another.
 
Last edited:
20240601_171313-jpg
20240601_171313-jpg

You don't knurl all the way around the piston.
Just knurl the areas of the skirt 90° from the
wrist pin, where the rocking occurs.

--Doozer

[img]
 
Last edited:
Well, I give up on finding a replacement piston, so I took the sharp edge of a carbide blank and pushed off smeared aluminum from the scuffed area, then used a flexible abrasive bar on the skirt and cleaned it up.

Then, I put the lantern tool post in the lathe and put the knurling tool holder in the lantern post.

I then proceeded to knurl the skirt. I went across it twice with slight pressure... it increased the diameter .003.
That made the skirt too big, so I put the piston back in the lathe and laid a file on the knurled area, applied slight pressure, which reduced the diameter just a bit.
Tried it, and it slips in and out of the bore now, with negligible slop. I think it's a win.
View attachment 441782

View attachment 441783

View attachment 441784
That thing is now minted out! A cereal box base gasket and It will run like new for another 30 years. You won't know it's yours without the piston slap noise. 40:1 and your great grandkids will be using it.
 
Having a swimming pool, I keep a couple of gallons of muriatic acid on hand all the time. Having owned a number of old 2-stroke JetSkis, I've had my share of stuck pistons. As you learned, you can often clean up the cylinder with acid, flush thoroughly with water and baking soda, then hone it.

I looked at Ebay and there are a number of Lawnboy pistons listed. I doubt that there are any new ones, but you might find a good used one.
 
As a general rule with old motorbikes ,if they seize and then free off ,they wont seize again ............Id think your oil mix is a bit lean ...even with super modern synthetic ,a 30 /1 would be max with me.
Concur with this concept. I run non synthetic oils, and 20:1, period. I don’t GAS what the manufacturer calls for, I'm going to have enough oil going through the engine. I have seen problems from not enough oil, but NEVER problems from more oil than the recommended ratio. My 2 strokes do not get babied, most of the time they are operating at WOT once warmed up. Could just as well have an on/off switch for a throttle.

To the OP -- if you can polish the scoring on the piston so there is nothing protruding above the original diameter, I think you could get away with reusing the piston. There may be a bit of knock from here on, but as long as the scoring is not over a big area of the piston it will probably be livable. 2 strokes can take a phenomenal amount of abuse if the are not highly tuned, overheated, or run lean.
 
Its put your junk out week ,and multi car pileups as drivers watch for goodies on the footpath,and jam on the brakes ...a guy is walking past my gate with a near new Honda sp mower ,a rare prize amongst the old broken chairs and setees...............still lotsa rusty old mowers in the junk for the discerning.
 
Still got a commercial lawn boy here, yep parts dont exist for them at all anymore. The one I have here still kinda runs but poorly as it has lost all compression.

They were good little engines, but never lasted long though due to people running them so lean on oil. they were from new supposed to be 24-1 originally.
Definitely wouldn't ever run anything less then 50-1 even with the new oils we have, the base stocks are still the same as years ago.
 
Well, I give up on finding a replacement piston, so I took the sharp edge of a carbide blank and pushed off smeared aluminum from the scuffed area, then used a flexible abrasive bar on the skirt and cleaned it up.

Then, I put the lantern tool post in the lathe and put the knurling tool holder in the lantern post.

I then proceeded to knurl the skirt. I went across it twice with slight pressure... it increased the diameter .003.
That made the skirt too big, so I put the piston back in the lathe and laid a file on the knurled area, applied slight pressure, which reduced the diameter just a bit.
Tried it, and it slips in and out of the bore now, with negligible slop. I think it's a win.
View attachment 441782

View attachment 441783

View attachment 441784
if you have a lathe, why not just make a new piston..... its only molded aluminum.
 
Other than the amount of oil and the leanness, or otherwise, of the mixture, the ignition timing will have a serious effect on overheating (DAMHIKT). If it's over-advanced from worn points, the engine can/will overheat.
 
if you have a lathe, why not just make a new piston..... its only molded aluminum.
Typically pistons are manufactured deliberately a little out of round to compensate for the shape change that occurs when the piston heats to operating temperature. “Cam ground” is the term used. Maybe that is not done on all small simple crude engines but it is a standard practice otherwise.
 
Well, I give up on finding a replacement piston, so I took the sharp edge of a carbide blank and pushed off smeared aluminum from the scuffed area, then used a flexible abrasive bar on the skirt and cleaned it up.

Then, I put the lantern tool post in the lathe and put the knurling tool holder in the lantern post.

I then proceeded to knurl the skirt. I went across it twice with slight pressure... it increased the diameter .003.
That made the skirt too big, so I put the piston back in the lathe and laid a file on the knurled area, applied slight pressure, which reduced the diameter just a bit.
Tried it, and it slips in and out of the bore now, with negligible slop. I think it's a win.
View attachment 441782

View attachment 441783

View attachment 441784
Probably stating the obvious but don't forget to use some assembly lube before reassembling. In the old days we used to put a thin coat of STP on cylinder walls, etc. before putting things back together.
 








 
Back
Top