piston fit

[NeilLickfold]

I realise this is an old thread, but just wanted to mention that when I trim pistons, I set the compound slide on an angle of about 1/2 to 3/4 of a degree,depending on the amount of taper per side required for the crown. Mostly I use 3/4 of a degree per side.

I trim the piston parallel till it fits the desired height from TDC or from the top of the liner plus that of the estimated crown chamfer. So if it has a 0.100 inch crown taper and the finished fit is 0.280 inches from the top of the sleeve, I will trim it to 0.380 inches. To achieve this diameter, I move the compound slide backwards, which in turn makes a very small amount off the X axis. I turn using a pcd tool with a 1/64 corner rad, and use canola oil as a cutting fluid. After each pass, I initially clean with denatured alcohol and then with break clean to remove any oil residue. I monitor the amount of shift up the liner to the amount the compound slide has been moved backwards. The final fitting is actually achieved when the crown taper is applied. So some pistons will have 0.090 crown tapers while others may have 0.110 tapers, and of course you will get the odd one that is right at the 0.100 taper length. The fastest engines have always been ones that did not require any lapping, so I do not lap Ali pistons to size, they are always finished turned. The feedrate for the surface finish I use is 0.001 inch per rev which is very slow. I finish turn normally at about 590 to 680 rpm, mainly as that is the smoothest rpm of my lathe and I do not get oil going everywhere.

Hopefully this may be of interest to someone else down the road as well. A very good condition spindle with less than 0.0002 inch runout is a very big advantage when trimming your own pistons.

Neil

 

[Terry Keeley]

I realise this is an old thread, but just wanted to mention that when I trim pistons, I set the compound slide on an angle of about 1/2 to 3/4 of a degree,depending on the amount of taper per side required for the crown. Mostly I use 3/4 of a degree per side.

I trim the piston parallel till it fits the desired height from TDC or from the top of the liner plus that of the estimated crown chamfer. So if it has a 0.100 inch crown taper and the finished fit is 0.280 inches from the top of the sleeve, I will trim it to 0.380 inches. To achieve this diameter, I move the compound slide backwards, which in turn makes a very small amount off the X axis. I turn using a pcd tool with a 1/64 corner rad, and use canola oil as a cutting fluid. After each pass, I initially clean with denatured alcohol and then with break clean to remove any oil residue. I monitor the amount of shift up the liner to the amount the compound slide has been moved backwards. The final fitting is actually achieved when the crown taper is applied. So some pistons will have 0.090 crown tapers while others may have 0.110 tapers, and of course you will get the odd one that is right at the 0.100 taper length. The fastest engines have always been ones that did not require any lapping, so I do not lap Ali pistons to size, they are always finished turned. The feedrate for the surface finish I use is 0.001 inch per rev which is very slow. I finish turn normally at about 590 to 680 rpm, mainly as that is the smoothest rpm of my lathe and I do not get oil going everywhere.

Hopefully this may be of interest to someone else down the road as well. A very good condition spindle with less than 0.0002 inch runout is a very big advantage when trimming your own pistons.

Neil

All good info, I'm gonna try my hand at re-chroming liners and making pistons again one of these winters.

What lathe are you using?

 

[NeilLickfold]

My lathe I use for pistons is an old Myford Super7, but I have reground the spindle shaft, and blued the taper bearing to the reground spindle.

Fitted new rear Angular contact bearing pair.

In order to have the lathe at it's maximum concentricity, it can not run in the high gear mode. The heat build up although slight, will cause a bind of on the front taper bearing. I redid all the slides as well and made M8 X 0.5mm screws and nuts for the cross slide and compound slide. I changed out the original metric dial for the imperial 0.100 inch dial, so now reads 0.01mm on diameter for every 0.001 dial increment. I don't always have the fine pitch screws installed, only when setting up to piston crowns or fitting heads and things like that. For general work I often change out the fine for the original screws and dials. More recently I have replaced the single phase motor for a 3phase VFD. I really like the VFD as it is easy to dial up or down the rpm. In conjunction with a micro switch, I can screwcut and make it stop to better than 0.1mm(4thou) stop. The wind in and reverse back,recut. This is really useful for internal threading especially if you have an undercut or small run out area. My other lathe is currently undergoing the VFD and motor conversion.

Neil

 

[dwilfong]

Do you set the tool stand compound at 45deg and use it to make a move on the piston to cut the OD?

 

[Terry Keeley]

Myford 7 is a sweet machine so I'm told, especially with the improvements you've made.

I just got my hands on an Emco Super 11 in great shape and am going to use a Pratt Bernerd collet system that came with it to hold the stock.

Can I ask what material you're using? Also would you have a number for the PCD inserts you're using?

I have some 30% Si Dispal 226 left but I also hear from Jim Allen that RSA-444 is a good choice.

 

[NeilLickfold]

Myford 7 is a sweet machine so I'm told, especially with the improvements you've made.

I just got my hands on an Emco Super 11 in great shape and am going to use a Pratt Bernerd collet system that came with it to hold the stock.

Can I ask what material you're using? Also would you have a number for the PCD inserts you're using?

I have some 30% Si Dispal 226 left but I also hear from Jim Allen that RSA-444 is a good choice.

I am currently using a ccmw09t304 MD220 , it is a md220 grade pcd insert with w 0.4mm radius from Mitsubishi. Not sure what the USA designation is sorry.

Mine is flat on top, but am looking at getting a positive top rake insert, but it requires another holder that I currently do not have.

The piston materials I trim are re heat treated Mahle 18% si from Mercedes truck pistons, RSP company RSA-444.

I have some Dispal 226 and some Dispal 224, but have not trimed any of those since I brought the pcd insert yet. I used to just use a ground edge insert for Aluminium , but always used the 0.4mm radius. Those were the ccmt304 but not sure of the grade, they were not a coated insert, but that was 15 years ago.

The 444 is a very good piston material in deed, just it is expensive. When you break it down to the fact it is the heart of the engine, the material price become not so important compared to the performance gain and life.

Neil

 

[Jack ODonnell]

Neil; What type of sleeve material are you using with the RSA 444 material and what kind of fit are you using with the 444 material. J.

 

[Terry Keeley]

I am currently using a ccmw09t304 MD220 , it is a md220 grade pcd insert with w 0.4mm radius from Mitsubishi. Not sure what the USA designation is sorry.

Mine is flat on top, but am looking at getting a positive top rake insert, but it requires another holder that I currently do not have.

The piston materials I trim are re heat treated Mahle 18% si from Mercedes truck pistons, RSP company RSA-444.

I have some Dispal 226 and some Dispal 224, but have not trimed any of those since I brought the pcd insert yet. I used to just use a ground edge insert for Aluminium , but always used the 0.4mm radius. Those were the ccmt304 but not sure of the grade, they were not a coated insert, but that was 15 years ago.

The 444 is a very good piston material in deed, just it is expensive. When you break it down to the fact it is the heart of the engine, the material price become not so important compared to the performance gain and life.

Neil

Thanks for sharing, I see this article mentions your insert: http://www.forgacsolaskutatas.hu/innovacio/microCAD_Delphi_ENG/

Are you using coolant of any kind?

I have some positve rake inserts a toolmaker buddy gave me: http://www.iscar.com/eCatalog/Family.aspx?fnum=1682&mapp=IS&app=28&GFSTYP=M They cut harder materials like HD17 sintered tungsten very well but are not PCD.

Found this holder: http://www.mscdirect.com/product/details/09829318

Now to find some RSA-444...

 

[Jack ODonnell]

Terry; Unless you are making your own sleeves, the 444 material does work to good on std brass. J.

 

[ABC PROPS]

Jack is correct on the standard brass.

Too soft

But BeCu Sleeves Heat treated is a nice match

Also

Forging of the 444 material makes for a better part

Jim

 

[Jim Allen]

There are several cylinder alloys that can be used successfully with RSA-444 T6 aluminum. Aluminum alloy #4032-T6, B-1 #360 free machining brass & B-2 #544 phosphor Bronze. At Aero Precision we presently are using the #4032 aluminum alloy for cylinders in the Nelson Q-40 & Q-500 engines. Mechanical design of the cylinders lip is critical for upper cylinder stability & upper cylinder heat transfer. All machining, chroming, honing & fitting is done on site at Aero Precision. When using different alloys, there must be a change in the cold fit crunch of the engine. According to the finish on the chrome we have found that, in general, to tight of a fit will make the engine run slower. A fine type of finish on both pieces, with the correct fit, will make the engine run faster, much longer! The ability to machine fine finished pistons round within .00005" & finished honed cylinders with the same tolerance (checked with a Sunnen bore guage after honing), makes fitting of these engines a "piece of cake"! There is no mention of the amount of cylinder taper or piston top taper necessary, which varies with the engine's stroke & bore. However, it can be said without any question, that this cannot be accomplished with any type of non-embedding lapping compound, emery wet or dry papers, or without the use of precision machinery.

Someone mentioned heat treated Beryllium Copper as a possible alloy for cylinders. Which alloy is being used for this purpose? Is the alloy finish machined before or after the heat treating?

Jim Allen

 

[ABC PROPS]

The BeCu is close to what I make the props out of.

A modified 275 CT

I have cast oversized Sleeves before for different engines applications

Cast - Rough Machine and Grind

Heat Treat

Finish grind and Hone

Plate

Final Grind or Hone

The nice thing about this Alloy is after proper Heat treating(Salt or Glass)

You can get close to Rockwell 45C

As Cast we at B88 or close to

and it plates very nice

Machine up some small wax prototypes or make a mold for wax injection

Or I can Print a mold On my 3D Printer if you have a CAD file

and i can cast some off to play with

This Material is also great for EDM die sinking ( I hate Graphite)

 

[Jim Allen]

The BeCu is close to what I make the props out of.

A modified 275 CT

I have cast oversized Sleeves before for different engines applications

Cast - Rough Machine and Grind

Heat Treat

Finish grind and Hone

Plate

Final Grind or Hone

The nice thing about this Alloy is after proper Heat treating(Salt or Glass)

You can get close to Rockwell 45C

As Cast we at B88 or close to

and it plates very nice

Machine up some small wax prototypes or make a mold for wax injection

Or I can Print a mold On my 3D Printer if you have a CAD file

and i can cast some off to play with

This Material is also great for EDM die sinking ( I hate Graphite)

Hi Jim,

This is very good information. All the brass & bronze alloys are easy to hard chrome plate. Even though we have finally figured out how to chrome the aluminum, it is still "A PAIN IN THE ASS" & it doesn't allow for any mistakes. Thanks for the valid information on what to do. Now you have me wondering about what would happen with other non-casting alloys such as a pre-hardended #172 beryllium copper?

Ja

 

[Brad Christy]

Jack,

I have been using RSA 431 for years with very good results. Honing the OEM sleeve to remove previous wear and fitting the new piston to it. Easy peasy. There are many who will vouch for these pistons. When I contacted RSPTech for my material, I asked for the 444. They indicated the 431 was the material of choice and I went with it. Ancient history.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

 

[Brad Christy]

Jim,

If you want to go with BeCu, look into MoldMax High Hard. It is a 172 BeCu variant that is developed for various specific applications, and is pre-hardened to about 45 Rc. I am currently machining some parts out of it. It doesn't come without it's challenges, but it machines well enough. You can forget about tapping it unless you've got a lot of time to burn. Thread milling is the only way to go. I don't see this as being a problem with sleeves, though, so it's probably not really even worth mentioning. It seems to be very stable while removing large sections from it, so sleeve ports shouldn't distort it any.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

 

[dwilfong]

Scott Bouchie makes them from 4032.

He made me a set from this hard micro fine material from Holland. Don't quit remember what it was.

But on the large bore 1.01 eng thy did not hold up.

Thy where to brittle and the skirts would break at the ex side.

My be on the smaller size eng it is not a problem but on the big bore stuff I can tell you it dose not work.

Had 5 pistons made and thy all broke.

With the 4032 no problems and the seat up really fast. Also thy grow as you heat the eng up and make a better seal.

Down side thy don't last long if you like to run on the lean side. The expansion from the heat needs to be kept the same as one hot run and it starts to seat to this size.

So if the eng temps are maintained it last longer.

And thy lap in just fine with lapping compound.

The hard stuff forget it dose not work trying to lap them in..

Gust what I have found from running my boat...................

 

[NeilLickfold]

Are you using coolant of any kind?

I use cooking oil as a coolant, what ever is cheapest and thinnest seems to work well.

As for fit and liner material, it all depends on the engine type and liner taper. With the 4032 F3D liners about 0.260 inches from the top of liner or about 0.07 inches BTDC. With the 2.5cc speed liners, not sure if they are BeCu or a Bronze, but they are about 0.025 to 0.030 depending on if it is a hot weather engine or a cool weather engine. With the brass liner of 2.5cc sport glows, non piped, I set them at 0.06 inches BTDC or in most rossi type 0.16 from the top of liner.

As for a source, you can buy the 444 from Rob Metkemyer in Holland MB engines. Mike may even sell a small amount , but you will have to ask him nicely if he has any to spare. Did I mention it is expensive but well worth the money though..

Neil

 

[Jim Allen]

Jim,

If you want to go with BeCu, look into MoldMax High Hard. It is a 172 BeCu variant that is developed for various specific applications, and is pre-hardened to about 45 Rc. I am currently machining some parts out of it. It doesn't come without it's challenges, but it machines well enough. You can forget about tapping it unless you've got a lot of time to burn. Thread milling is the only way to go. I don't see this as being a problem with sleeves, though, so it's probably not really even worth mentioning. It seems to be very stable while removing large sections from it, so sleeve ports shouldn't distort it any.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

Hi Brad,

Are you stress relieving the RSA 431 before final machining? When Henry & I tried to use this alloy in place of RSA-444, it would continue to grow in the engine, even after stress relieving it at 405* F for 5 hours. I think Jack tried to use it also. Maybe he will comment on his results. I have tested different alloys over the years including A-390, Dispal-250, Mahle-138, RSA-431 & RSA-444. The 444 alloy works in any size engine if the piston's top taper & the liner's taper are correct. It does not require any type of stress relieving! It Is the alloy used in all the Nelson Q-40 & Q-500 pylon racing engines produced & sold world wide at Aero Precision Machine. It has very high wear resistance, does not grow at elevated engine temperatures encountered when running lean, will not scuff & it machines to a mirror finish at spindle speeds of 4,000 RPM with PCD coated cutting tools.

Jim Allen

 

[Brad Christy]

Jim,

Heat treating and/or stress relieving has some positive benefits, but it's definitely not a requirement. I had been making them for quite some time before I started baking them, and I no longer bake them at all. I have learned how to machine them so that nearly all the stress is relieved in the process, and the heat cycling they go through during break in finishes the job. 21's through 1.01's.... No difference.

The PCD inserts are the only way to fly. Standard carbide works for a short time, but the silicon in the alloy wears it away too fast and tolerances are impossible to hold for more than a cut or two. PCD seems to last forever until you do something stupid with them. Ask me how I know............

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

 

[Ken Retallick]

Interesting stuff!

I have been making pistons for engines from .21 to 1 cube for a few years now.

I have been using RSA 431 T6 with great results. The T6 heat treatment for this alloy has only been around the last 3 or 4 years, (could be longer)

no need to heat treat them.

As for machining them PCD inserts are the only way to go. Also TiB2 coated endmills are great in this material.

If machined correctly there is no need to lap them in with any abrasives.