Hard Industrial Chroming of Aluminum, Brass or Steel Cylinders

[PaulHail]

I've thought one of the reasons most high output two strokes have the exhaust ports open at the same time via either one large exhaust port with two additional small ports on top of the rear transfer ports or two large angled exhaust ports that are partially on top of the rear transfers was to have a strong exhaust pulse to get maximum performance from the pipe.

I understand as with all things engine design, everything is a compromise and inter related and that there are advantages of an arched exhaust port such as longer ring life and as you mention potentially less turbulence. And for any given engine, the ideal port shape may be different than the norm.

 

[Rudy Formanek]

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

I tried the alum solution on an aluminum crankcase with a stuck head screw, I felt it corroded the case an destroyed the bearing fits. I came to this conclusion from the change in appearance of the surface of the case, Not extremely scientific but I won't be trying it again. I binned the case.

PS. Acid is gonna eat aluminum, whether HCL or sulfuric or Nitric or Vinegar. I see it liking to eat aluminum preferentially to iron. It's just a more reactive element.

 

[Jim Allen]

Rudy,

We are using two acids (Hydrofluoric & Nitric) , which are mixed together in their concentrated forms, to "etch" # 4032 aluminum cylinders. This is the first step in our chroming process. The cylinder CANNOT remain in this solution for more than 30 seconds at room temperature.

JA

 

[Rudy Formanek]

MACS products used to buy an aluminum "brightener" to dip clean it's aluminum parts prior to brazing. I believe it was a strong HCL solution with some HFL mixed in . We would dilute it and basket seep the aluminum for about 8 min. Rinsing and drying so as to leave the part without residue in the area to be brazed took some planning and fussing.

 

[Jim Allen]

The hard chroming process is not complete without proper honing or grinding of the plated surface. At Aero Precision we use a Sunnen Honing machine & the simple holding fixture shown to quickly hone cylinders round within .00005" & also to the correct taper. Each cylinder is checked during the honing process with a Sunnen bore guage to tight tolerances.

Jim Allen

 

[Jim Allen]

There is one area where a thin coating of chrome can be beneficial when using a brass bushed type connecting rod. The photos show a fixture used to flash chrome plate only the crank pin of an engines connecting rod. This makes the crank pin last forever & the slippery chromed surface helps the bushing to last longer. Since this is only a flashing of chrome (.0001" or .0002" thickness), no grinding or lapping of the chrome is required.

JA

 

[Terry Keeley]

Thanks for the fixture ideas Jim, I swear one day I'm gonna do this to get proper fits on the main bearings.

 

[Jim Allen]

Terry,

At one time we made unhardened steel front ends with chrome plated bearing bores. Grinding the chrome plated bores to size was much easier than machining the tool steel used to the exact (+ or - .0001") size needed for the correct interference fit. We used special clearance bearings in these assemblies with .0005" to .0008" interference fits. Heavy interference fits such as this would wear out the bores in a steel housing that was not hardened. We never tried chrome plating in an aluminum housing, but I think it could be done. We went to hardened steel because of its infinite wear resistance & the very high rigidity of the steel housing compared to aluminum.

Jim

 

[Terry Keeley]

Was thinking of just doing the crank, the bearing fits on CMB cases seem pretty good but the crank just drops in the bearing and can skid.

 

[Jim Allen]

It would appear that even a small amount of interference fit has a positive effect on bearing life & performance in high RPM engines. This is the reason we continue to press crankshafts into the inner races of both front bearings in the Q-40, 29,000+ RPM, pylon racing engines. It is also apparent that polishing of the inner & outer races to a mirror finish with diamond paste, also increases bearing performance in all metal or ceramic hybrid type bearings.

JA

 

[Jack ODonnell]

Terry; That would be the biggest improvement you could make. The rear bearing needs to be a press fit on the crank. j.

 

[Jim Allen]

Terry,

Jack is speaking the truth here. Maybe this is why the rear bearing's inner race is ground on the crankshaft of some very high performance engines.

The accuracy of the fixture you build could make grinding of the crankshaft unnecessary, if a flash plating amount (.0001" or .00015") was applied. This is what was done for the fixture shown. One disadvantage of a chrome bath is it's very poor throwing ability. What this means is that the anode & cathode must be in close proximity to one another & of an equal distance from one another. In the case of a crankshaft the anode (lead antimony) will be on the outside & the crankshaft (anode) will be on the inside. Both pieces must be concentric to each other so that there will not be a larger build up of chrome on one area. If this should happen it will be necessary to re-grind the crankshaft.

JA

 

[Jim Allen]

The two simple fixtures shown, when mounted in the lathe, allow polishing of both the inner & outer bearing races. You will be very surprised at how smooth even ABEC 3 or 5 bearings will spin after doing this. When this is done to a ceramic hybrid bearing.................WOW! One fixture collapses to hold the outer race & the other fixture expands to hold the inner race. Any ball bearing with a snap on cage can be disassembled & reassembled easily.

JA

 

[John Beardslee]

Terry,

Jack is speaking the truth here. Maybe this is why the rear bearing's inner race is ground on the crankshaft of some very high performance engines.

The accuracy of the fixture you build could make grinding of the crankshaft unnecessary, if a flash plating amount (.0001" or .00015") was applied. This is what was done for the fixture shown. One disadvantage of a chrome bath is it's very poor throwing ability. What this means is that the anode & cathode must be in close proximity to one another & of an equal distance from one another. In the case of a crankshaft the anode (lead antimony) will be on the outside & the crankshaft (anode) will be on the inside. Both pieces must be concentric to each other so that there will not be a larger build up of chrome on one area. If this should happen it will be necessary to re-grind the crankshaft.

JA

Hi Guys,

The school district where I taught Machine Tool Metalworking and welding for many years had the good fortune to have Modern Hard Chrome just down the road. My students could have anything they built hard chromed for free. The best was any of their tools they built for their tool box ( and to satisfy old Beardslee) could be flashed 50 millionths and never have to worry about rusting. My own home hard chrome system was a commercial unit with a power supply and a lead lined tank and held about 3 gallons if I remember correctly. I used to do a lot of gun trigger work (thanks to John Bridge) and I would polish the components and then hard chrome and then re-polish and they would look just like decorative chrome but a whole lot more durable. Great work Jim and great information as usual.

Thanks John

 

[Terry Keeley]

Terry; That would be the biggest improvement you could make. The rear bearing needs to be a press fit on the crank. j.

Ya, I was turning the rear bearing blue on my 67 SAW motor a while back...

 

[Jack ODonnell]

Terry; If you have access to a sunnen bore gage check the inter race of your bearing. When the bearing spins on the crank it will heat up and take all of the clearance out of the bearing. I have seen as much as .0005 belly in the race. That takes most of the clearance of the balls. From that point the bearing is dead. J.

 

[Terry Keeley]

Terry; If you have access to a sunnen bore gage check the inter race of your bearing. When the bearing spins on the crank it will heat up and take all of the clearance out of the bearing. I have seen as much as .0005 belly in the race. That takes most of the clearance of the balls. From that point the bearing is dead. J.

I have a pretty good Mitutoyo bore gauge set, not as good as Sunnen but I "think" I can see tenths.

By belly do you mean out of round? After its over heated or when new?

 

[Jack ODonnell]

Terry; The bearing bore will be round. The center of the bore will have a belly in it ( the center of the bore will be bigger than the outer edges ) this will take out the clearance of the assembled bearing. J.

 

[Terry Keeley]

Sorry Jack, not quite following you. Do you mean the outer race?

 

[Terry Keeley]

Thanks for the help Jack, got it!