"Growing a Piston"

[Jerry Wyss]

Thanks Rod, Iguess there really is "more than one way to skin a cat",,hope my cat doesn't see me typing this

I did notice "one" thing about the "Oven Growing" method,,The piston pin "fell" into

it's hole. I couldn't feel any movement in it when secured but it's not possible to feel a 1/2 a thousands with your fingers anyway. I'll have to keep "tabs" on this area now cause the pin went in there way too easy :unsure:

 

[dave roach]

This is why you do'nt heat the piston.

 

[james irwin]

Jerry,
Believe it or not, the pipe cutter will restore the piston but you can over do it so easy.My cutter has been modified, it has been sharpened to remove the small flat that is on most wheels. This allows for a much lighter groove.

If you elect to do this, do it very carefully and lightly. You will have to break the piston back in slowly but you actually can run the piston a couple of more weekends.

However, you will find that this trick is only good for a short time and will

have to be done again. After the second groove job, I typically scrap the piston.

REMEMBER I SAID: You can really screw up quick if you are not careful!

Carl,

You can really get after those grooves in a piston if you have a helical lap to bring the piston back to size.[www.helicallap.com]I have a set of 3.5,7.5 and 11CC external laps and have been resizing pistons for years and then re-lapping them to fit the liner.

The re-lap job will last for one hell of a long time.Maybe not as long as a new P&S but dam close to it.

In fact I have a personal piston in a motor that I have done 5 or 6 times and the motor just gets easier to 2 stage.I don't know why,it just does.I suspect it has something to do with reduced drag but I don't really know for sure.

These laps are not cheap and they take some getting used to.Learning what lapping compounds to use is the learning curve.

When you get done wash the piston in the dishwasher with Cascade to get rid of all the laping compound in the aluminum pores.Just put a piece of wire through the wristpin hole and securely wire it on the rack in the dish washer.

The beauty of this process is the piston does't need to be perfect.I have taken siezed pistons.cleaned them up in the lathe with some 600 paper,re-cut the oil rings and then expanded the piston with the cutter and re-lapped it in to fit.The motors run great.

Carl is right,be careful and keep the cutter in the grooves when you are expanding them.

Carl,don't be to quick to go to the trash with those pistons,I'll gladly take them off your hands.

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ROD ,,, YOU ARE #2 AFTER ME , HE HE NOW WE HAVE GIVEN AWAY ANOTHER ONE OF UOR SPEED SECRETS . O WELL . HELL I CANT DRIVE ANY MORE ? MIGHT AS WELL GIVE IT TO SOME AND LET THEM GO WITH IT ,

 

[6cuda6]

Guy's cutting grooves in piston for expantion is nothing new....years ago they use to knurle the skirt section of car pistons to decrease cylinder clearance...worked o/k...

The only question i have about the heating deal is technicaly don't you harden the piston??? As well wouldn't this make it more brittle??? How do you control the expantion so the piston remains it's proper shape???

 

[Jerry Wyss]

Guy's cutting grooves in piston for expantion is nothing new....years ago they use to knurle the skirt section of car pistons to decrease cylinder clearance...worked o/k...
The only question i have about the heating deal is technicaly don't you harden the piston??? As well wouldn't this make it more brittle??? How do you control the expantion so the piston remains it's proper shape???

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Mr. Cuda, I would rather think you were "annealing"(sp) the piston rather than hardening it, hence it expands. I ran the motor 7or8 tankfulls today and it still has the "pinch" where it needs to be,,besides that, it has never ran as fast than it did today,,so it MUST work

 

[6cuda6]

Thanks for the info Jerry...i'll pile it into my folder so i can perform the same some day!!!

 

[Geraghty]

Guy's cutting grooves in piston for expantion is nothing new....years ago they use to knurle the skirt section of car pistons to decrease cylinder clearance...worked o/k...
The only question i have about the heating deal is technicaly don't you harden the piston??? As well wouldn't this make it more brittle??? How do you control the expantion so the piston remains it's proper shape???

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Knurling a piston skirt to get rid of piston slap is completley different than restoring compression which is what we are doing with this process.

In this process the taper in the liner remains constant and the piston is mechanically expanded to restore the compression fit. Slight deformation of the piston during the groove [oil ring] cutting means nothing.That is why I use the helical lap to make the piston absolutely round again.

The aluminum in the pistons we use is high in silicon content and piston strength is basically unaffected by baking.I have never found that baking worked as well as grooving and lapping.In fact I can't honestly say that I have never found a baked piston that retained its restored fit for very long.

 

[Foolwitools]

Hi temp baking to "grow" a piston,

It doesn't work in northern Illinois...........

I took several pistons( some of which could be easily identified as "cast" pistons),

measured some then,the fit others in cylinders.

After 30 min. at 500 deg.F, no measurable change. the pistons compared to their before and after fit to thier cylinders seem to be the same, if not worse.

--------------------------------------------------

for those truley interested in this subject..................

I am privelaged to have as one of my customers Mr. Ezra Kotzen. Ezra is (at 85 years old) one of the most knowlegable persons in the US in the field of metal casting.

Ezra retired 2 years ago ( at age 83 ! ) and is as sharp as they come.

Being that Ezra is still very much interested in his craft, I will carry any questions to him. I'm sure that he will be happy to answer them, and I will post the answers here.

Remember:the better question you ask, the better answer you get...............

Bob the Fool :blink:

 

[VansRacing]

Guy's cutting grooves in piston for expantion is nothing new....years ago they use to knurle the skirt section of car pistons to decrease cylinder clearance...worked o/k...
The only question i have about the heating deal is technicaly don't you harden the piston??? As well wouldn't this make it more brittle??? How do you control the expantion so the piston remains it's proper shape???

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Knurling a piston skirt to get rid of piston slap is completley different than restoring compression which is what we are doing with this process.

In this process the taper in the liner remains constant and the piston is mechanically expanded to restore the compression fit. Slight deformation of the piston during the groove [oil ring] cutting means nothing.That is why I use the helical lap to make the piston absolutely round again.

The aluminum in the pistons we use is high in silicon content and piston strength is basically unaffected by baking.I have never found that baking worked as well as grooving and lapping.In fact I can't honestly say that I have never found a baked piston that retained its restored fit for very long.

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Rod,

I have always grooved the piston and worked from there and somehow got the fit I needed but... I am always up for a new gadget to drag to the pond (like I don't already have enough...LOL) But I want to know more about your helical lapping tool. Where do I get one? I'll give it a go and see what find of fit I can make using your method.

-Carl

 

[Tim_Duggan]

I did notice "one" thing about the "Oven Growing" method,,The piston pin "fell" intoit's hole. I couldn't feel any movement in it when secured but it's not possible to feel a 1/2 a thousands with your fingers anyway. I'll have to keep "tabs" on this area now cause the pin went in there way too easy :unsure:

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Jerry,

Just between you and I

That area has always been a problem area on those pistons. They wear in the pin boss part of the piston worse than any other engine I've ever seen. I think they are a low silicon content piston too.

Tim.

 

[Geraghty]

Rod,

I have always grooved the piston and worked from there and somehow got the fit I needed but... I am always up for a new gadget to drag to the pond (like I don't already have enough...LOL) But I want to know more about your helical lapping tool. Where do I get one? I'll give it a go and see what find of fit I can make using your method.

-Carl

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www.helicallap.com

 

[VansRacing]

Rod,

I have always grooved the piston and worked from there and somehow got the fit I needed but... I am always up for a new gadget to drag to the pond (like I don't already have enough...LOL) But I want to know more about your helical lapping tool. Where do I get one? I'll give it a go and see what find of fit I can make using your method.

-Carl

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www.helicallap.com

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Thanks Rod! I'll check into it.

-Carl,

 

[Jerry Wyss]

Tim_D and Fool W/tools,,The piston "Grew",,Make No Mistake Of That. Besides Bob,

It was 675deg! and the whole process took over 4 hours to "cool down". There was no evidence of "Slack" from the big end of the rod and up while locked at "full

pinch" (or "nip") near TDC. The engine has had 8 ,8 ounce tanks run thru it with

"pinch" still near TDC where it had "None" before I sent the pistons thru this process. Also when I remove the sleeve and go to re-install it, it's a Bear to get it the piston started into the sleeve again during assembly,,In the past it has Never been difficult in that area. This engine was new with break-in and one race of 5 heats before I "grew" them,,after the 8 tankfulls with the piston locked in the "pinch" near TDC I now have a "slight" amount of "slack" in the flywheel,,probably due to the "piston pin" hole being enlarged along with the piston, this may Or may not be a problem,,I'll just have to keep an eye on it like I said before.

 

[Tim_Duggan]

I know how I can fix all the piston issues Jerry - BILLET B)

 

[Jerry Wyss]

I know how I can fix all the piston issues Jerry - BILLET  B)

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I wonder if it would be worth it , making a piston has to be pricey. You know how the P/S fit is in these motors, and when you throw a .005in shim under the sleeve the "nip" goes bye,bye. Gawd, after all the time and effort it took to get my head buttons made, I'm a little leary about goin' thru that with Pistons I have a good "seal" with the one in the motor now and I "grew" another along with it as a back-up,,but growing them doesn't insure that they're round :unsure:

 

[Foolwitools]

......................... Bake the piston at the highest heat setting (500o) for a couple of hours.  Turn off heat and let the piston cool naturally. You'll need to break in the piston again. Good luck.

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Jerry,

This is the sorce of my confusion. I'll try again..........

Bob the Fool :blink:

 

[Jerry Wyss]

Hey Bob, I thought "cooking oven" temp like Jack was saying "might" be a little low on temp to do a "good" job,,so I went to one of my friends where I knew there was a "small ceramics" oven that could go much higher. I don't know if this is the "best" way to go, cause of the "enlarged" piston pin hole,,I didn't expect that I thought the "pin" would be harder to get into it's place. If the "slack" I feel now in the flywheel is due to the loose fit of the pin , well this is only gonna get worse due to the "annealing" of the piston in the heating process. The slack is only "very slight" right now, but it's a easy thing to check each time the engine's run. The pin "fit" could be tightened up by using a "punch" and a small hammer in the "right"

spot with the "right" amount of force to keep the pin snug in its hole I 'spose :huh: