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Machine Shop and Tool Talk

Re: How it's Done 3-5


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  #101  
Old 05-03-2016, 01:09:13 AM
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John Tice John Tice is offline
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Smile New boring bar stand

Wow; how long did you say that you worked at the factory? You appear to have written the instruction manual! Dont be a stranger; we need more like you.

I leave my table top dry & wipe it clean as much as I can. Ive found when expanding the centering fingers that its very helpful to expand contract & rotate the spindle at least 3 times. This is especially helpful if Im attempting to center in the exhaust port areas on a 2 stroke cylinder. This technique can be used when the pistons are only +.25mm / +.010 oversized when bore clean up is questionable.

Since we now have a vertical power hone, a +.25mm bore increase is better accomplished with our Sunnen hone head instead of boring the cylinder. The hone head seeks the bore average center in the process as it strokes up & down through the cylinder.

If Id known of your air float trick, we probably would have done the same thing on our table; I may still give it a try.

Thank you for the input
JT
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  #102  
Old 05-03-2016, 06:22:53 PM
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Default Re: How it's Done 3-5

Do the air float, you'll love it. It's a bit scary drilling into your machine tool though! Especially when you do the side intersecting hole. *Squirt some oil in the hoses periodically before you connect them for a super good air seal and float.

Your power hone is a lifesaver but I didn't have one in the dealership. As you know a .25 bore often wouldn't take out the wear or damage in a bore. I would regularly put a .002 feeler gage under a pin to offset the bore fore or aft depending on what side the wear was.

As a bit of minutae, back in the early 70's days of Honda 2 stroke dirt bikes a new cylinder was technically worn past the first OS right out of the box. They were so scared of sticking them the ran the clearances exceedingly large. Including relieving the exhaust bridge by about .020. This caused piston breakage. AHM sent the regional tech guys to see what I was doing as my builds ran well. When I told them my clearances they said I was nuts. Next year all their sizings were published close to mine.
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  #103  
Old 05-07-2016, 11:30:59 PM
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John Tice John Tice is offline
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Question More on Skirt Clearances

Lets back up a page or so & talk about skirt clearances. There is a lot to think about in piston fits, Plate or sleeve. First; its commonly thought that a plated cylinder dissipates heat much better; therefore the plated cylinder uses a much tighter cylinder skirt clearance. Its time to back up another page or so & consider how tight the sleeve is fit into your aluminum cylinder? LA sleeve & Advanced Cylinder Sleeve companies both tell how tight the new sleeve needs to fit, true enough but how is the sleeve fit in your aluminum cylinder?
If you take your top end to your favorite Hot Shoe racing cycle shop & have them fit a new ported sleeve; how is your new sleeve fit to your cylinder, knowing how tight is only the start.
At times a cylinder which has been sleeved by others comes to us for repairs. The sleeve was manufactured by one of the previous mentioned companies. The Sleeve was beautifully produced but had a Bum fit. This conversation has nothing to do with the manufacturers mentioned.



This is what our customer got from another Hot Shoe rebuilder & tuner. I suspect that the shop knew that the fit was incorrect but was helpless for a repair solution.

Fitting a sleeve is much like fitting a piston; the final honed fit must be precise.

A CR500 Honda cylinder waiting for the new sleeve.

After the precise honed fit has been produced; the press fit which has been previously determined needs to be reconsidered. The sleeve fit helps determine the final piston skirt clearance.

An accurate dial bore gauge is a must in every engine builders tool box
The key to this precision fitting business is the coefficient of linier expansion of cast iron & aluminum. When heated to higher temperatures, aluminum expands significantly more than does cast iron. We use 500 degrees for our elevated temperature to insert cylinder sleeves. Its highly recommended that the machinist measure both the aluminum cylinder & iron sleeve at room temperature & 500 deg. This is the key to figuring the new sleeves shrink or press fits. In our shop we use a -.002 for 125s & smaller, -.003 for 250s & -.004 for 500cc cylinders. Its highly recommended that temperature & size measurements are periodically taken. In the process of doing cylinder liner installations; Ive found that Honda & Yamaha periodically fit sleeves from -.001 to -.0015 press fits. With these looser fits the stock OEM liners can usually be pressed in & out at room temperatures.
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  #104  
Old 05-07-2016, 11:34:00 PM
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John Tice John Tice is offline
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Question More on Skirt Clearances

How do we fit our sleeve installations? We first ruff bore a plated cylinder +.250 larger than the std. bore diameter. This will net the final sleeve thickness of 1mm after the cylinder has been over bored another 2mm oversize. The final sleeve thickness is rather thin but necessary to ensure proper function of any power valve installations. This is the general oversize of sleeve in a 2 stroke bore; weve got an Excel spread sheet programmed to produce bore consistency.
Next the new cylinder sleeve is ruff turned to +.010 larger than the aluminum cylinder. With the new sleeve +.010 larger than your cylinder bore; the aluminum cylinder is finally precession honed to the new sleeve press fit. I use this system of fitting the new sleeve as it helps greatly if making a mistake fit.
With all of these dimensions flying around in every direction; its necessary for the engine builder to have a thorough knowledge of arithmetic & geometry. Have a few hand calculators in your shop for handy instant access. Remember that 4/ .03937 = 101.6mm, the conversion factor from inches to millimeters.

After the cylinder is heated, the new sleeve is lowered & alined. A light press is applied to the top of the sleeve to make sure its bedded in place.



After the final bore is completed, off to the cylinder hone. We use a Sunnen connecting rod hone as it gives the best control of cylinder sizing. Yes; you need the proper piston skirt clearance, but as of the clearance the cylinder must also be round & straight. Squaring with the bore is best accomplished by mounting a cylinder upside down. (More on this in other sections)
I use a double stone three point connecting rod mandrel for cylinders under 2-1/2 in bore diameter. Above 2-1/2 a double stone AN type of mandrel is used. Both of these mandrels render a smooth round & straight bore when used by a skilled operator.


Large hone type AN head for bores larger tan 2-1/2


Smaller 3 point mandrel used for cylinders less than 2-1/2.
You may notice the cylinder hanging by a couple of Bungee cords. With my bad back as many of us suffer from; the cylinders are hanging from the ceiling which enables the cylinder to be flipped from end to end, taper control & easy measurements.
(Other types of honing equipment are noted in another section.)

Back to the Skirt clearances; I use the resources of Wiesco piston who has a cycle engine mounted on a Dyno for testing skirt clearances. Wiesco claims that their forged pistons are machined in such a manner that they need barely more than a zero skirt clearance to run without seizing. Granted this is only for testing purposes.
Ive found that the recommended skirt clearances which are printed on each Wiesco piston box; works fine for most cast & forged 2 stroke pistons. With the very short skirts on late model 4 stroke engines, its wise to contact the particular piston manufacturer for clearance advice. Now days both types of pistons are machined to run minimal skirt clearances. After the honing is complete the ports are deburred & the cylinder is rinsed in the parts washer. The measuring tools are rechecked for accuracy; the skirt clearance is double checked, the piston is fit, top & bottom of the cylinder. Any discrepancy in accuracy can be corrected before the job is delivered.
Cast or forged pistons; sleeved or plated bores, when we hone the final skirt clearance; I most always add +.0005 to the recommended fits. With this slight addition to the clearance; I maintain that both types of cylinders each have close to the same heat dissipation rate.

Youre comments & criticism is more than welcome; we all learn together.

John Tice
503-593-2908 Alternate 541-508-3944
www.smallenginemachineworks.com & www.nwsleeve.com
Turning Custom Cylinder Sleeves Since 1971
http://forums.everything2stroke.com/...d-the-Shop.com
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  #105  
Old 05-17-2016, 08:07:09 AM
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John Tice John Tice is offline
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“How it’s Done” Can be the start of a new career for those who read the thread. We need new blood in the cylinder & machine shop area. I’ll help you get started at no cost; We spend hours on the evening phone tutoring new & prospective students. Whether setting up new equipment or learning how to operate your cylinder boring machine. Give me a call most any evening until 9pm pacific.


John Tice
503-593-2908 Alternate 541-508-3944
www.smallenginemachineworks.com & www.nwsleeve.com
Turning Custom Cylinder Sleeves Since 1971
http://forums.everything2stroke.com/...d-the-Shop.com

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  #106  
Old 08-04-2016, 11:10:58 PM
Randall Strickland Randall Strickland is offline
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Default Re: How it's Done 3-5

Hey John,] thanks for taking the time to help others, I rebuild model a and t fords as a hobby,wish I had started earlier in life,I've sleeaved a few model a engines,I was wondering if you use the kwik way cutter or the replacable carbide cutter,I am self taught and enjoy these threads.
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