Novarossi, OS and RB piston Re-Sizing

[izitbrokeyet?]

OK boys and girls, I’m offering a service to resize Novarossi OS RZ .21 and R&B Pistons and sleeves. My price will be $18 including shipping for each piston and sleeve combo . The Price is $29 if you want me to hand lap the piston back into your sleeve. If your P/s is evenly worn without scratches I’ll be able to revive it. If it's scratched.......Please dont send it to me.

I've found when the Piston is Hand-lapped back in it last as long or longer than a properly run-in new P/S.

I’ve been sending mine out for some time to OSRocket and many Buggy guys have been doing this for years now. This has really turned me on to a great way of putting life back into a motor.

I won’t be able to do anything with scratched pistons, or sleeves with hotspots. Soon I expect to be able to do .21 Mac and CMB motors…depending on whether or not anyone uses this service.

Please don’t hesitate to ask me any questions.

KB

 

[Guest]

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...&category=34062

 

[izitbrokeyet?]

That’s pretty nice auction for a toy sleeve die Guest…….now how about some directions……..an hours time, grade 1 lapidary and grade .5 lapidary, and a lapping Jig....

My offer still stands at the stated prices despite some chickenshit whitless posting by another “guest”

Kevin B

and another thing guest.........If you look hard enough on E-bay you might find youself some dignity or maybe a pair of nads....but I doubt you'ld know what to do with either.

 

[Don Ferrette]

Ummm, tell us how you really feel Kev.......

 

[izitbrokeyet?]

getting tired of this guest posting thing <_< does it show?

Especially when it’s not productive, and serves no purpose but to provide a shield to hide behind.

 

[longballlumber]

I am very curious about this procedure you selling. With that being said I have a few questions.

1. How is this "resizing" done with out altering/ruining the chrome plating? Is there some type of heat that is applied during the resizing process?

2. I am going to assume that every P/S set will wear out differently. Do you need the piston with the sleeve to do this process?

3. Basiclly, your putting the sleeve in a fixture and squeezing it. Right? How do you know the sleeve stays circular in shape?

Sorry for all the questions...... Curiousitoy kills the cat.

Mike Ball

 

[Bob Kensill]

The fixtures that I have seen for doing this compress the sleeve. When you make the sleeve OD smaller,don't you lose contact with the block,which also means loss of heat transfer? I have been "swelling" pistons for years and then lapping them to fit the sleeve again. It is not rocket science,but does require time and ability.

Bob

 

[izitbrokeyet?]

Where to start…..I guess I should start with some definitions:

Creep is a permanent deformation in a body caused by strain

Strain is the deformation caused by application of stress

Stress is defined as Force/Area

The process is to apply stress radially (not hoop stress) to the sleeve to induce strain creep. On a brass sleeve 32 MPa produces a normal type of creep curve consisting mostly of transient creep. Transient creep is the first of 3 stages of creep in this type of metal and does not typically have any affects on the ultimate strength of the material. . Brass is known for its high resistance to creep, so when it is induced by the use of a die...... it is equally as hard to Un-do it.

Chrome has a very different Strain/creep curve compared to Brass and would typically be defined as a brittle material because of the shape of this curve and the location of the ultimate strength on the curve. While the Brass sleeve is strained to a point of creep, the chroming on the sleeve is still in Strain mode and is not unlike a passenger when this brass deformation occurs at 32 MPa. So, the chrome is still in strain (non-permanent deformation) while the brass is permanently deformed.

This brings me to the next point:

The Chrome lining has about 10% the Thermal Coefficient of Expansion of Aluminum or Brass. Brass and Aluminum have similar characteristics of thermal expansion. And every time you start (heat your motor up to temp) the aluminum piston expands; the brass sleeve expands at the top and the chrome lining strains to keep up with the Brass sleeve. This expansion is on the order of 10 times that of what is being induced by the tooling die that induces creep into the sleeve.

So, for purposes of this discussion, these materials definitely expand when exposed to heat; but heat is not used to induce creep into the sleeve. In other words, heat makes it move, but the induced creep is maintained thorough the thermal expansion cycle of the materials. In other words: If it’s that shape when it’s cold, it’s relatively close to the same shape when it’s hot. So the answer to #1 is “no”

The answer to #2 is:you need the piston in order to lap the piston back into the sleeve once the sleeve has been pinched. It also helps to have the piston as a reference for quality control

The answer to #3 is you need to apply the stress radially…..that’s why “guest” doesn’t know what the F*&K he’s talking about since the die he has shown doen’t accomplish that. Guest’s die will make a perfect “egg shape”. When I lap a piston to a sleeve, I will typically do a "circular" lap rather than the "Ron Jerome" to make sure the piston is round in the sleeve.

Bob has a very good method to bake a piston and make it swell, then relap it to the sleeve. I also do that to larger motors but it hasn’t been as effective for the little fellers.

I have found that many of the .21 motors that have their sleeve pinched fit better when you put them back into the casting. When the motor is heating up, any slack between the casting and the sleeve goes away when the sleeve is expanding because of heat (again we are talking about less than .001” here)

Hope this answers your question,

KB

 

[Bob Kensill]

You sound like you might just have a degree in mechanical engineering,am I right?

 

[izitbrokeyet?]

actually I'm a structural E....but I still like the mechanics of materials etc.

 

[GTR]

Hi Kevin

So this is what you've been up to hey

I thought you were just designing and building great WOF tunnels.

Are you thinking of expanding this service to include say K&B 45s?

Have you got your new mill yet?

I don't know about 'guest' but I do know Kevin - he takes everything he does seriously and always tries for perfection - he does not spray BS around and is as honest as you can get.

GT - happy to call myself a friend of Kevins becuase I know he puts his rep where his mouth is, and will back it up - unlike some.

 

[longballlumber]

Thanks for the explaination... Your fingers must be tired...

Back to answer #3:

If the die that "guest" showed everyone is not the correct process, what is the process and how is it different than what "guest" was pointing us too...

Also, what I understand out of your answer #3 is, your saying in order for this modification to be effective you really need to lap the piston to the sleeve.

Couldn't you just "break in" the P/S again?

Please understand I am not trying to bust your ball's.... I have just seen this advertised alot on the car side of things, but never talked to a boater that has personally tried it. I am very curious.

 

[izitbrokeyet?]

Hi Gary,

Thanks for the kind words

I have the mill and I've still using it in "manual" mode. This G-code thing is going to take me a while to learn :blink:

heck...I've been working on the "G-spot" for almost 20 years and still haven't learned it.

I purchased a book on "G-code" and it's been laying on the dresser next to my bed.......probably the best sleeping aid I've ever come across. Needless to say I'm only about 5 pages into a 150 page book........this may take some time B)

 

[izitbrokeyet?]

Mike,

On the tooling Die shown on E-bay has a crank on one side with an opening in a “C” shaped clamp. This will allow the sleeve to swell out of the opening in the “C”. The correct die “in my opinion” has a “C” shaped crank that will support the sleeve by overlapping at the opening of the “C”.

I supposed you could could let the end-user run-in your piston sleeve again, but but then the I would have no way of controlling the final fit of the piston and sleeve when it leaves the shop. It pre-supposes that the piston/sleeve fit is round and true and that the end-user will run it in correctly.

I suppose it really boils down to a Q/C issue and a level of completion when the part leaves the shop

 

[izitbrokeyet?]

OK....my fingers are wore out.....no more from me today

feel like I'm writing a novel :blink:

 

[Bob Kensill]

It all comes down to what kind of "fit" you want. Do you want a good running engine or a great running one. When I "build" an engine for a customer,it takes time to get it just right. I have also found that a good fit makes a long lasting engine too.

Bob

 

[TimD]

I have also found that a good fit makes a long lasting engine too.

I agree 100%.

A good P&L fit is something that should be considered desirable IMHO. I think spending the extra dollars to get it hand lapped would be money well spent unless you have the time / patience and equipment to do it yourself.

 

[unclefester802]

Hey Kevin,

Thanx for all the great info you put out there , I thought it was awsome. I just have a simple question for you ( no Steven King answer required ) Can you do K&B 3.5 outboards? I have 2 that I would like to get done before the pond defrosts. If you can please let me know.

Thanx,

Mark

P.S. also how about K&B 7.5 ?

 

[izitbrokeyet?]

Unfortunately, I am unable to do K&B, Rossi, Mac, Or CMB motors. I hope to add the Mac and CMB motors in the near future, but then only in a 3.5cc size.

I don’t have the ability to do any 7.5cc sleeves. You may have good luck with baking the piston and re-lapping it into the sleeve like Mr Kensill said.

Have fun,

KB