Hard Industrial Chroming of Aluminum, Brass or Steel Cylinders

[Rudy Formanek]

Jim, do you know of any chemical that would dissolve a steel bolt from an aluminum case, leaving the aluminum alone? Rudy

Nitric acid works but you havta be patient.

Have you used this procedure, yourself??

 

[Terry Keeley]

Jim, do you know of any chemical that would dissolve a steel bolt from an aluminum case, leaving the aluminum alone? Rudy

Nitric acid works but you havta be patient.

Have you used this procedure, yourself??

Tries it but got too impatient, it could take a few days from what I've read.

I've got broken taps out with carbide burrs in the mill, start with a small ball nose end mill. For a bolt you could start with the end mill and drill deep enough to use an easy out?

What size bolt are we talking?

 

[Jim Allen]

Terry & Rudy,

If possible, I would like to know where this information originated from. The reason that I'm asking is because two of the necessary solutions needed to successfully hard chrome plate aluminum contain nitric acid. In fact, the last solution, which contains nitric acid & water mixed in a ratio of 1 to 1 by volume, is used as a "stripping bath" before the final immersing in a zincate solution. Even at a ratio by volume of 1 to 1, the nitric acid & water solution attacks the aluminum immediately! Therefore, the aluminum cylinder can only remain in this "stripping bath" for a maximum of "10 seconds"! I have already explained how the amount of time that a cylinder remains in any of three baths used, will adversely effect the chroming process!

Jim Allen

 

[Terry Keeley]

It's all over the net, alum is supposed to work as well...

 

[Jim Allen]

What I see on the Internet pertains to the following: (potassium aluminum sulfate which has the chemical formula KAl(SO4)2�12H2O). It readily attacks the iron component of the steel screw, particularly the threads.


"For that reason, the use of potassium aluminum sulfate to destroy an unwanted stuck steel screw generally is successful only when the other material is brass, copper, bronze or other material that resists corrosion.

It's use is generally a "last resort" as one has to assure there's no other iron or steel components exposed to the alum solution."

JA

 

[Terry Keeley]

http://www.practicalmachinist.com/vb/general/broken-tap-removal-chemical-methods-198135/

 

[Jim Allen]

I think the very last line says something significant doesn't it?

"Tap Removal with Nitric Acid Hot nitric acid will remove a broken tap from Stainless Steel. Use about a 50% mixture of HNO3 (70%) and water. Immerse part in solution, keep hot, about 190 F, just short of boiling for fastest results. The acid will passivate the steel tap, so it is necessary to touch the tap with a copper or brass wire for a few seconds. Vigorous bubbling should start, and in a few seconds, a black precipitate will emerge, with the bubbling stopping, indicating passivation. Touch the wire to the tap again to restart bubbling. This should work in aluminum as well, but has not been tested."

When I return to work next week, I'll post some photos of aluminum cylinders that were sacrificed in an attempt to remove their hard chromium plating.

JA

 

[dwilfong]

If there is no thread locker on the bolt or it was not frozen in place. A left hand drill will work pretty good. Just do it by hand not in a drill press. That way you can control the pressure as it gets a bite on the bolt.

 

[Terry Keeley]

I think the very last line says something significant doesn't it?

"Tap Removal with Nitric Acid Hot nitric acid will remove a broken tap from Stainless Steel. Use about a 50% mixture of HNO3 (70%) and water. Immerse part in solution, keep hot, about 190 F, just short of boiling for fastest results. The acid will passivate the steel tap, so it is necessary to touch the tap with a copper or brass wire for a few seconds. Vigorous bubbling should start, and in a few seconds, a black precipitate will emerge, with the bubbling stopping, indicating passivation. Touch the wire to the tap again to restart bubbling. This should work in aluminum as well, but has not been tested."

When I return to work next week, I'll post some photos of aluminum cylinders that were sacrificed in an attempt to remove their hard chromium plating.

JA

I wonder if it could be something else in the alloy you're using that reacts with the acid?

I used to "mark" the ports on a brass sleeve by dipping the case with sleeve into Nitric acid (70%), didn't leave it long but didn't have any problems with it eating the case.

 

[Jim Allen]

Terry,

I'm not sure what is possible with the aluminum alloys used to manufacture engines. All of the aluminum alloys that may be used (RSP-444, A-357-T6, 4032-T6, 2024-T351, 7075-T6, 2011-T4) in the manufacture of engines contain some amount of iron. The iron is what the nitric acid may react with, much in the same manner that nitric acid reacts with the iron in stainless steels during the passivation of stainless steels. It is definitely safe to say that brass is unaffected even when stronger acids are used such as HLC.

Jim Alen

 

[Andy Brown]

Thanks for all the info guys!

Ken: Never thought of that before but it "kinda" makes sense depending on the play in the rod/wrist pin etc. I might try that even tho the ports will be blocked a little at the bottom of the stroke.

Jim: Thanks for all your numbers for the Nelson and your own design. Those taper numbers for both the piston and sleeve are fairly typical of other motors from what I've measured. Do you relieve the lower part (skirt) of the piston as well?

Jack: Yup! I've messed with stinger size a bit and found gains with smaller diameters but you havta be careful not to overheat the piston!

Here's what I'm talking about from one of my CMB 90's:

It's looking like it's trying to come out of the exhaust port!

The top of the same piston, hasn't been run lean or overly stressed:

Funny, here's a VAC 45 piston with about the same number of runs on it:

Hi Terry

Ken and Jim are both correct about the piston.

The bulging around the wrist pin boss is due to poor piston material as Jim mentioned.

Also as Jim eluded to, cooler internal pipe temps will reduce that bulging.

A quick and simple fix is to work the area around the boss with 400 and 600 grit to get a bit more clearance.

You can do that to the used piston until the scuffing does not show up after several hard runs. Then you will know how much material to remove on a new piston.

The wear at the top of the piston is caused, in part, by the out of balance piston as Ken mentioned. The heavy side of the piston causes the piston to tilt on the upward stroke and snag the top of the exhaust port. Poor material is also part of the cause.

A larger cylinder taper will allow more tilt.

Besides working to reduce the imbalance of the piston, an arched exhaust port with a radius ground and polished into the upper inside edge of the port will reduce the wear at the top edge of the piston.

For everyone following the great information provided by Jim and others on this thread. New records are continuously broken with less than perfect parts and materials so don't loose hope if you don't have access and abilities to take advantage of the information provided.

Our two stroke engines are far from perfected and there are unlimited improvements to be made in all areas of the engine, pipe and fuel delivery systems.

Good boating!

 

[Jim Allen]

Andy,

Your post reminded me of our conversations in the past about piston scuffing. I believe we both thought from the preliminary test done at that time, that higher silicon contents in the piston's alloy would prevent piston scuffing. Later we discovered, after many failed attempts, that the liner's taper when matched correctly with the piston's top taper prevented scuffing. Test with alloys such as A-390, Dispol 250, & Malhe 138 showed that a high silicon piston was not necessary. In tests where the engine was purposely over leaned & overheated there would be no piston scuffing, providing the two tapers were correct. I receive many engines for repair that have been run lean for extended periods of time. Only the cylinders in these engines show any kind of damage. That damage is the cylinder's taper is drastically reduced, but the "wear band" is still visible on the piston. I'm also convinced that the hardness of the chrome plating can also be a key factor. In attempting to get the hardest chrome plating possible, the concentration of the bath, the current density used & the temperature of the bath become critical. An overlooked fact is, hard industrial chrome plating can vary from 750 to 1100 Vickers & still be considered hard.

JA

 

[Terry Keeley]

Interesting info gents, thanks much. I'm anxious to try this RSA 431/444 I have to see if it's any better, that and some lower sleeve taper.

Any idea why CMB (others too I'm sure) would relieve the bottom of the piston as well? Are they hoping it reduces drag?

I can see Jim's point that it would let the piston rock more in the bore, both parallel to the wrist pin and perpendicular to it.

Interesting my 45 doesn't have the same marks, could it be due to what looks like a longer (relative to the bore) piston?

I haven't checked the taper on these...

 

[Andy Brown]

Interesting info gents, thanks much. I'm anxious to try this RSA 431/444 I have to see if it's any better, that and some lower sleeve taper.

Any idea why CMB (others too I'm sure) would relieve the bottom of the piston as well? Are they hoping it reduces drag?

I can see Jim's point that it would let the piston rock more in the bore, both parallel to the wrist pin and perpendicular to it.

Interesting my 45 doesn't have the same marks, could it be due to what looks like a longer (relative to the bore) piston?

I haven't checked the taper on these...

Material expansion is directly proportional to length. A 1.1" piston will grow much more in terms of actual diameter than an .83" piston.

Yet the tendency is to fit them all equally tight in the sleeve.

I have CMB 100 piston that falls straight through the liner. It runs great. Pulls any prop.

Novarossi just learned all of this with the introduction of their 46 marine engine. Those tight fits that work so well in the .21 engines do not work with bigger bores.

You're welcome for the education Novarossi! ;-)

 

[Jim Allen]

I agree Andy. In AAC & ABC engines, a loser fit will allow the engine to turn faster. This is another reason that the piston & cylinder need to be very round, but remain as round as possible at operating temperatures. That wear band is an indicator as to what is happening when the engine reaches it's operating temperature. We use a fairly tight fit on new pylon racing engines with a very fine finish on the chrome. Cylinders are rough honed to the exact taper & roundness with a 61 grit stone. They are finished to a high polish with a 83 grit stone. RSP 444 pistons are finish machined with solid diamond tool bits.

JA

 

[Michael Caruso]

I agree Andy. In AAC & ABC engines, a loser fit will allow the engine to turn faster. This is another reason that the piston & cylinder need to be very round, but remain as round as possible at operating temperatures. That wear band is an indicator as to what is happening when the engine reaches it's operating temperature. We use a fairly tight fit on new pylon racing engines with a very fine finish on the chrome. Cylinders are rough honed to the exact taper & roundness with a 61 grit stone. They are finished to a high polish with a 83 grit stone. RSP 444 pistons are finish machined with solid diamond tool bits.

JA

Thanks for the fit amd finish. Great info everything has to work hand and hand. Great work

 

[Michael Costanzo]

Thanks for all the info guys!

Ken: Never thought of that before but it "kinda" makes sense depending on the play in the rod/wrist pin etc. I might try that even tho the ports will be blocked a little at the bottom of the stroke.

Jim: Thanks for all your numbers for the Nelson and your own design. Those taper numbers for both the piston and sleeve are fairly typical of other motors from what I've measured. Do you relieve the lower part (skirt) of the piston as well?

Jack: Yup! I've messed with stinger size a bit and found gains with smaller diameters but you havta be careful not to overheat the piston!

Here's what I'm talking about from one of my CMB 90's:

It's looking like it's trying to come out of the exhaust port!

The top of the same piston, hasn't been run lean or overly stressed:

Funny, here's a VAC 45 piston with about the same number of runs on it:

Hi Terry

Ken and Jim are both correct about the piston.

The bulging around the wrist pin boss is due to poor piston material as Jim mentioned.

Also as Jim eluded to, cooler internal pipe temps will reduce that bulging.

A quick and simple fix is to work the area around the boss with 400 and 600 grit to get a bit more clearance.

You can do that to the used piston until the scuffing does not show up after several hard runs. Then you will know how much material to remove on a new piston.

The wear at the top of the piston is caused, in part, by the out of balance piston as Ken mentioned. The heavy side of the piston causes the piston to tilt on the upward stroke and snag the top of the exhaust port. Poor material is also part of the cause.

A larger cylinder taper will allow more tilt.

Besides working to reduce the imbalance of the piston, an arched exhaust port with a radius ground and polished into the upper inside edge of the port will reduce the wear at the top edge of the piston.

For everyone following the great information provided by Jim and others on this thread. New records are continuously broken with less than perfect parts and materials so don't loose hope if you don't have access and abilities to take advantage of the information provided.

Our two stroke engines are far from perfected and there are unlimited improvements to be made in all areas of the engine, pipe and fuel delivery systems.

Good boating!

andy,you mentioned an arched exh port. doesn't that also affect the overall timing #'s?

 

[Andy Brown]

Thanks for all the info guys!

Ken: Never thought of that before but it "kinda" makes sense depending on the play in the rod/wrist pin etc. I might try that even tho the ports will be blocked a little at the bottom of the stroke.

Jim: Thanks for all your numbers for the Nelson and your own design. Those taper numbers for both the piston and sleeve are fairly typical of other motors from what I've measured. Do you relieve the lower part (skirt) of the piston as well?

Jack: Yup! I've messed with stinger size a bit and found gains with smaller diameters but you havta be careful not to overheat the piston!

Here's what I'm talking about from one of my CMB 90's:

It's looking like it's trying to come out of the exhaust port!

The top of the same piston, hasn't been run lean or overly stressed:

Funny, here's a VAC 45 piston with about the same number of runs on it:

Hi Terry

Ken and Jim are both correct about the piston.

The bulging around the wrist pin boss is due to poor piston material as Jim mentioned.

Also as Jim eluded to, cooler internal pipe temps will reduce that bulging.

A quick and simple fix is to work the area around the boss with 400 and 600 grit to get a bit more clearance.

You can do that to the used piston until the scuffing does not show up after several hard runs. Then you will know how much material to remove on a new piston.

The wear at the top of the piston is caused, in part, by the out of balance piston as Ken mentioned. The heavy side of the piston causes the piston to tilt on the upward stroke and snag the top of the exhaust port. Poor material is also part of the cause.

A larger cylinder taper will allow more tilt.

Besides working to reduce the imbalance of the piston, an arched exhaust port with a radius ground and polished into the upper inside edge of the port will reduce the wear at the top edge of the piston.

For everyone following the great information provided by Jim and others on this thread. New records are continuously broken with less than perfect parts and materials so don't loose hope if you don't have access and abilities to take advantage of the information provided.

Our two stroke engines are far from perfected and there are unlimited improvements to be made in all areas of the engine, pipe and fuel delivery systems.

Good boating!

andy,you mentioned an arched exh port. doesn't that also affect the overall timing #'s?

Yes Michael. Compared to perfectly straight the arched timing can be a few degrees higher to get similar results.

 

[Jim Allen]

The arched exhaust port in the photo works very well after many test at different angles & arches. Notice that the angle is the same across the entire arch. We also have the same angle cut in the top of the crankcase's exhaust port. We believe that the opening of an exhaust shaped this way creates much less turbulence when compared to a straight exhaust port. In some engines there is also an additional piece added to the exhaust window in the crankcase to smooth the transition from the cylinder's exhaust port at the bottom to the crankcases exhaust window at the bottom.

JA

note: One photo is out of order.

 

[Jim Allen]

This is a photo of what a mild acid (25% HLC) can do to 4032 aluminum when attempting to remove the chrome from the bore. The acid removed the chrome but the cylinder was destroyed.

JA