Hard Industrial Chroming of Aluminum, Brass or Steel Cylinders

[Brian Spitzer]

Jim,

It looks like the Mic you're are using has a resolution of .000050 , correct? Depth Mic out to .001 or .0001 ? Great thread, thank you for sharing.

 

[Jim Allen]

Brian,

The depth micrometer has a resolution of .001" & there is no .0001" scale on the barrel. The same micrometer is used to set the engine's timing & deck clearance. We use sleeve & head shims to set the engine's timing & deck clearance to exact numbers. I'll show a simple trick that enables the engine's timing to be set accurately.

Jim Allen

 

[Brian Spitzer]

Jim,

What type of thimble do you prefer on your Mic, ratchet of friction? Have you found any difference in the repeatability and or accuracy of the Mic?

 

[Jim Allen]

Jim,

Regarding cleaning parts goes, we use an ultrasonic wash system with deionized reverse osmosis water for our final cleaning. Maybe overkill, but we are making dental instruments. We have to conform to certain regulatory requirements. Really works well on things like carbs and other things that have small hard to access orifaces.

Bob

Bob,

I received the following information from a fellow engineer.

"Hi Jim,

I saw on another site someone suggest to you ultrasonic cleaning to prepare your pistons for fitting. I would advise against this for pistons made from aluminum. I use Ikohe E60H and E 300 H Elmasonic ultrasonic cleaners at work to clean the paint bell cups that spin at 60K on the Sames electrostatic paint applicator bells fitted to the 7 axis fanuc machines I service at Daimler. At 37Khz these machines can peak nearly 2 hp of energy and erode certain materials due to cavitation. This cavitation was enough to pit an aluminum bell cup we tested. The titanium ones one the other hand held up. This is enough to lead me to believe that the results on an aluminum piston and other types of metals and materials would be less than satisfactory! This may explain why their cleaning tanks are made from cavitation resistant stainless steel and why Bob has no problem cleaning dental tools with them.

Take Care...."

I think cleaning with a soft brush & a 50% solution of Ultra Dawn with Super Strength Greased Lightening does the job. A hot water rinse makes the aluminum parts squeaky clean.

JA

Jim,

What type of thimble do you prefer on your Mic, ratchet of friction? Have you found any difference in the repeatability and or accuracy of the Mic?

Brian,

I have no preference. What matters is to use a quality micrometer, not one of the cheap imports, & keep the ratchet or friction device in good working order. Also the adjustment of the spindle's vernier scale to zero & the spindle's thread lock to remove play should be done.

JA

 

[BobHorowitz]

Jim,

Very interesting. I wasn't suggesting that you use ultrasonics, just sharing info and techniques. In fact, I am aware of the possible erosion. Even though our ultrasonics tanks are SS, they have to be replaced after being in service for about 10 years or so. They get eroded to the point of perforating. You can actually see a pattern in the erosion that shows the position and shape of the transducers.

Bob

 

[Jim Allen]

Thanks for sharing all this Jim, this stuff is lost forever unless it's passed on!

Do you just push the piston in as hard as you can until it stops? Or there a certain amount of "feel" involved?

Obviously you look for a certain distance BTD for the piston to stop, how is this distance arrived at?

How much further up the sleeve does a piston travel that's say 0.0001" (one tenth) smaller?

Thanks again!

Terry,

I push the bottom of the piston with "considerable" but not "excessive" force. One way to tell if you have used enough or to much force is when you turn the cylinder with piston right side up to remove the piston. Use the same tool placed on the piston's crown & strike the piston's crown with the palm of your hand. If the piston comes out easily the fit is to lose, if you need to strike the piston several times it is to tight.

We're considering building a tool to measure how much force is being applied. The reason this has not been done is because no two parts are exactly the same dimension. For instance, the .0015" to .0017" total cylinder taper is measured over a distance of .500" from the top of the cylinder to the top of the exhaust window. We use a piston stop distance, measured from the top of the flange to the piston crown of .265" to .275". These numbers apply to only this engine with its particular bore & stroke. In depth bench testing tells us which cylinder taper & which piston top taper works the best. As I stated previously, these numbers cannot be applied to an engine with a different bore & stroke.

I can answer your last question only as it pertains to the parts & finishes described. Using a piston that is .0001" bigger or smaller will change the micrometer reading .005" to .008". This would apply to onlly this engine!!

Jim Allen

 

[Jim Allen]

Building quality high performance engines involves the detailed preparation of many parts. The photos show what is done to a typical piston. Notice that there is no sharp inside radius or sharp edge left on bottom of the piston's skirt. Even the wrist pin hole in the piston is chamfered before final honing to size. A small hand press is used to insert the wrist pin. The wrist pin is a slip fit on the front side & pressed into the back side.

Jim Allen

 

[Jim Allen]

After the pisons are fitted to their cylinders, they are de-burred & the wrist pin hole is honed to size. They are throughly washed again & assembled with a connecting rod, wrist pin & "C" clips. Crankcases that have been de-burred, throughly washed & carefully heated for bearing insertion will be used to set the engine's timing & deck clearance. THIS IS DONE WITH A DEPTH MICROMETER! NO DEGREE WHEEL OF ANY KIND SHOULD EVER BE USED IN THE BUILDING OF A SMALL ENGINE! Since the piston would push the cylinder up out of the crankcase, a very simple tool must be used to accurately set the engines timing & deck clearance.

Jim Allen

 

[Terry Keeley]

Thanks for sharing all this Jim, this stuff is lost forever unless it's passed on!

Do you just push the piston in as hard as you can until it stops? Or there a certain amount of "feel" involved?

Obviously you look for a certain distance BTD for the piston to stop, how is this distance arrived at?

How much further up the sleeve does a piston travel that's say 0.0001" (one tenth) smaller?

Thanks again!

Terry,

I push the bottom of the piston with "considerable" but not "excessive" force. One way to tell if you have used enough or to much force is when you turn the cylinder with piston right side up to remove the piston. Use the same tool placed on the piston's crown & strike the piston's crown with the palm of your hand. If the piston comes out easily the fit is to lose, if you need to strike the piston several times it is to tight.

We're considering building a tool to measure how much force is being applied. The reason this has not been done is because no two parts are exactly the same dimension. For instance, the .0015" to .0017" total cylinder taper is measured over a distance of .500" from the top of the cylinder to the top of the exhaust window. We use a piston stop distance, measured from the top of the flang to the piston crown of .265" to .275". These numbers apply to only this engine with its particular bore & stroke. In depth bench testing tells us which cylinder taper & which piston top taper works the best. As I stated previously, these numbers cannot be applied to an engine with a diferent bore & stroke.

I can answer your last question only as it pertains to the parts & finishes described. Using a piston that is .0001" bigger or smaller will change the micrometer reading .005" to .008". This would apply to onlly this engine!!

Jim Allen

Thanks again for all the info!

So there is much testing and a certain amount of "feel" still involved, you don't just make the parts to a certain size, with a certain tolerance and put them together!

ps: I'm sure Henry is very proud his engines are still being made with care and precision...

 

[Jim Allen]

Terry,

There is a great amount of testing necessary. This testing only becomes valid when the parts involved are made "correctly" to whatever number is being used. If the number being used does not work, you try another number. However, you must be able to make & know you have made the number in question! The feel part becomes easy to do when you have cylinders that are honed round within .00005" & pistons machined round within a .0001". As I said before, the pistons are machined in .0001" steps. Also the machining of pistons must be done so that the piston is round during it's final machining operation before being parted off.

Jim Allen

 

[Jim Allen]

Setting the engines timing & deck clearance is done with a depth micrometer. First the timing is set. Notice the .200" thick gage block under the lip of the cylinder. Without this piece the piston would lock up in the top of the cylinder making an accurate measurement impossible. .001", .003", .005" & .008" sleeve shims take care of any machining differences & allow the timing to be set accurately at .190". The micrometer will read .390" with the piston rotated to TDC & the .200" gage block in place. Substracting the .200" from .390" gives .190".The same depth micrometer measures the depth of the machined head button. It should be machined at a .185"depth. Substracting .185" from .190" gives .005". The deck clearance is set at .018", therefore .013" of head shims will be added. If the head measures more or less than .185", .001", .003", .005" & .008" head shims take care of any machining differences.

Jim Allen

 

[Jack ODonnell]

Jim; Have a question, on the sleeves you are working on. They all appear to have a single D shape exhaust port. Do you feel the single D shape is better than the three exhaust system. Also if you would what exhaust timing do these engines use. Do you use time area for the exhaust or is the timing only figured at the high point of the exhaust port. J.

 

[Jim Allen]

Yes Jack, the single "D" shaped exhaust, which is wider in the top, proved to be the best thus far. The entire top edge of the window is angled downnward 15*. Exhaust windows that have pickets always have the problem with the pickets becoming heat sinks the effect the returning charge from the tuned pipe. We increased the stroke of the engine to the maximum. This gives a greater increase in the time area numbers compared to making the bore larger. The exhaust timing is calculated from from 1/2 the engine's stroke, the center distance between the connecting rod holes & the distance from the wrist pin's center to the top outer edge of the piston's crown. At the peak of the exhaust arch, the calculated timing is 198*. However the arch itself makes the engine act as though the exhaust timing is 190*. We also believe that there is a softening of the shock wave that is created when an exhaust window that is straight across the top opens suddenly.

JA

 

[Jack ODonnell]

Jim I agree with you 100% The fastest tether car engines I have run have been with the D shaped exhaust !! Thanks Jim. J.

 

[Jim Allen]

The wide top D shape also helps to keep the piston from hitting the top edge of the exhaust window, which is common in some straight top exhaust windows. There is one straight top exhaust window that equals the performance of a D shape top. It's very wide, radiused top corners, can give an exhaust window width that is approaching 85% of the bores ID. There is also a second top angle of 33*49' cut in the middle of the exhaust window to give a timing of 194*. The remainder of the exhaust windows top edge is cut at 190* with a 15* angle.

Jim Allen

 

[LohringMiller]

I believe the only reason to use a divided exhaust is to keep the ring from breaking with a ringed piston.

Lohring Miller

 

[Jim Allen]

The construction of consistently high performing racing engines requires a very clean work enviroment. At Aero Precision Machine a seperate climate controlled building, separated from the machine shop, provides this area.

Jim Allen

 

[Bradley Ward]

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

Do you know Arnold Jewell?

 

[John Beardslee]

Arnold Jewel? Doesn't ring a bell with me, sorry it was while I taught at Lake Shore, 1968 to 1990, did he work or own Modern?

Thanks John

 

[Bradley Ward]

Arnold Jewell is one of the greatest trigger maker's in the world in my opinion! Up there with Walter&Lynnwood Harrell's powder throwers and John Kriegers barrels! 3 names that are American Icons in the advancement of modern benchrest shooting!