Can a .049 piston be repaired?

balogh wrote:I do not know of any common repair method than replacing the piston from another engine - new 051 pistons are almost unobtanium - cannibalized for spares. Any foreign material used for piston top repair may inadvertently detach from the piston top under the extreme effects of heat and hammering from below by the ball end of the rod,  and do even more damage inside the cylinder.

The 049 piston and cylinder sets - especially #4 - are much easier to buy from either Bernie or Matt, and have the same performance as the #5 in 051 engines.

Balogh:  my feelings, EXACTLY.  


Happydad

I'd say manufacturing a new one would be less trouble, and more successful than any repair.  

Nearly impossible. A lot of the time the piston is pushed out of round when the rod breaks through. On some larger pistons where there is a little more 'meat' on the top of the piston you can press-fit a replacement socket of sorts, but this is even tough and probably would push out of round on its own.

Here is what a replacement .051 piston looks like.
Piston and cage, is made out of high-strength 1045 carbon steel. The piston wrist pin is from a broken drill.
The connecting rod is made from Tempered 2024 aluminum.
The ring clip is made from a bent .032 music wire.

Made the piston parts on my Grizzly Industrial lathe/mill combo.

This is your best bet for a replacement piston.

Great DIY set sosam! I wonder how good the piston to cylinder fit i.e. compression was?

balogh wrote:Great DIY set sosam! I wonder how good the piston to cylinder fit i.e. compression  was?

The match clearance fit was .010 to .020 microns. Though my masters are not certified to what the exact size is?
I'm going off the size that is on the masters (in the box for the Bowers bore gage).
The Sylvac bench mic head I just zero out he anvils together (like a regular mic or calipers)
The Syvac 80 is accurate to 0.001 microns.

I used my Sylvac 80 with the bench mic head and my Bowers bore set.
The Sylvac box can be set to measure each part separately. Channel "A" the cylinder bore / Channel "B" piston dia.
Now the neat thing about the Sylvac 80 there is channel "C".
With channel "C" it will give you the match clearance. Channel "B" minus channel "A" equals match clearance.
One thing to remember is to set up channel "C" correctly. Don't get "A" minus "B" that's the wrong match.
There is a +/- button that would change that to the correct match clearance.

I was able to purchase it from my former job I worked at before I retired.
A good deal for less than 1/2 the price. (about $1,200.00 or so)
They were scraping it out for more precise "AIR" gaging.
The air gaging would measure size, taper, roundness all at the same time.

I do miss some of the equipment I used (hones, grinders, lathes, heat treat furnace, glass beading cabinet).
Had a nice enough boss to let me use the machines (if no production was running on it) to do a little
"government work" as he and I called it.

The mic head can measure up to 50mm


This bore set measures from 6mm to 16mm
head #1 -- 6mm to 8mm
head #2 -- 8mm to 10mm
head #3 -- 10mm to 12mm
head #4 -- 12mm to 14mm
head #5 -- 14mm to 16mm
The three ring sizes in the box are 8mm / 12mm / 14mm

sosam117 wrote:Here is what a replacement .051 piston looks like.
Piston and cage, is made out of high-strength 1045 carbon steel. The piston wrist pin is from a broken drill.
The connecting rod is made from Tempered 2024 aluminum.
The ring clip is made from a bent .032 music wire.

Made the piston parts on my Grizzly Industrial lathe/mill combo.

This is your best bet for a replacement piston.

sosam117:  WOW, beautiful work. so is this how you fixed a hole in the piston? Or is this how you fixed a broken ball socket?  Or did you just start over from scratch? Lessons please.

I have a .010 piston with a suspect ball socket that will not reset. And it is frustrating, because I cannot do anything about it yet. Maybe we should talk again after I get my Grizzly micro-lathe.

Happydad

My biggest concern would be not the piston diameter/clearance but the accuracy of the overall distance from the centre of crank pin to piston crown. I guess the best you could do was measure a known good piston/rod assembly, then correct with shims or case machining.

happydad wrote:

sosam117 wrote:Here is what a replacement .051 piston looks like.
Piston and cage, is made out of high-strength 1045 carbon steel. The piston wrist pin is from a broken drill.
The connecting rod is made from Tempered 2024 aluminum.
The ring clip is made from a bent .032 music wire.

Made the piston parts on my Grizzly Industrial lathe/mill combo.

This is your best bet for a replacement piston.

sosam117:  WOW, beautiful work. so is this how you fixed a hole in the piston? Or is this how you fixed a broken ball socket?  Or did you just start over from scratch? Lessons please.

I have a .010 piston with a suspect ball socket that will not reset. And it is frustrating, because I cannot do anything about it yet. Maybe we should talk again after I get my Grizzly micro-lathe.

Happydad

I started from scratch.
I didn't have a hole in my Cox .051 piston. I snapped off the connecting rod.
I looked around for a replacement, even asked around. No luck.
Some one on the forum here told me to make my own.
How am I going to make a Cox like piston with ball/socket with connecting rod?

Found out from a Aussie friend of the 4 piece piston assembly. Enya does it for their small 049/06/08 and 10 engines.
I had one of these engines!
Took the engine apart and tried to get the piston apart (it wasn't easy!)
Saw how Enya made it and I copied it the best I could.

One Cox .050 piston the other is a Cox .051 piston with a snapped off connecting rod

I think another problem in fabricating the proposed solution may be increase in piston mass (weight) which could affect performance.

However, you can never tell, that rare .051 part or parts engine may show up one day to be snapped up to make a whole engine.

I have an .051 piston with a bent rod that broke when I tried to straighten it. The seller wasn't honest. I've kept it all these years in hopes of maybe one day fixing it. The closest I came to attempt a repair was when someone tried to pull a rod off a piston. Don't remember if he was successful
Does Fox .049 engines have a riveted setup to hold the rod to the piston? Using that setup could save a piston with a hole worn through the top.

coxaddict wrote:  I have an .051 piston with a bent rod that broke when I tried to straighten it.  The seller wasn't honest.  I've kept it all these years in hopes of maybe one day fixing it.  The closest I came to attempt a repair was when someone tried to pull a rod off a piston. Don't remember if he was successful
Does Fox .049 engines have a riveted setup to hold the rod to the piston?  Using that setup could save a piston with a hole worn through the top.  

coxaddict: it sounds-looks like this one above maybe has a groove on the inside of the piston and the retaining ring keeps the assembly in place. Try it.

Happydad, can’t sleep again.  

coxaddict wrote:  I have an .051 piston with a bent rod that broke when I tried to straighten it.  The seller wasn't honest.  I've kept it all these years in hopes of maybe one day fixing it.  The closest I came to attempt a repair was when someone tried to pull a rod off a piston. Don't remember if he was successful
Does Fox .049 engines have a riveted setup to hold the rod to the piston?  Using that setup could save a piston with a hole worn through the top.  

That's the same problem I had. I had a bent connecting rod and tried to straighten it and it snapped off.
Kept it for years just like you. Nothing?
Never got a replacement sleeve/piston.

Until I made my own. It works, but it just doesn't have the speed like the original.

I tried to pull out good connecting rods from bad pistons to try to swap them out with one that’s bent. I made a clamp that holds the piston tight and used a torch to heat the piston socket area up red hot and try to pull the rod out. It ends up destroying the piston and the rod gets stretched out since it gets heated as well. Once it’s bent or broke it’s junk. No way to repair it.

As previous posters stated convert to .049 TD piston/cylinder set and change the carb body to black if it’s a TD.

Yeah, I have a different problem, years ago I purchased 2 new in box TD .049 engines that had red bodies. The boxes clearly shows displacement at .049 c.i.. Would it still be new in box if I changed the bodies to the black one? I'm pretty sure they are Estes era engines so they just used what they had on hand.

I've got a question, albeit academic. Displacement is increased by 4% between the .049 and the .051 by increasing the bore diameter slightly. I'd suspect slightly less than a 4% increase in HP, because piston stroke and fuel passages remain the same.

What is the corresponding HP increase if any?

Hi everyone !

Very interesting topic, I also tried to deal with a similar problem , some time ago I bought a well used .... or rather well abused ... rossi 09.
Its a 1.5 cc very similar to the cipolla junior but  more powerful , unfortunately piston-cylinder coupling was completely gone
It also uses the ball joint system and then I theoretically studied how to solve the problem, the attached sketches are three possible repair solutions.
In the end I chose version N° 2 which is absolutely nothing new as it has been used in many engines such as the Russian VA 049 , a light tightening torque and a drop of Loctite threadlocker et voilà ....now my engine starts and runs like new ..... maybe slightly slower since the new piston group was about 1 gr heavier than the original.
But sooner or later I will try to develop the other two concepts better, the one with the holding clip (N°1)seems to be the most complicated of the 3 in my opinion.
However, it is also the ones that allow easy disassembly but at the expense of resistance over time and at high revs .

Regards

Franco