Don Terrill’s Speed-Talk

David Redszus wrote: There is a little trick that might be useful to the amateur engine builder to help visualize and inspect the honed surface.

First hone the cylinder using what ever techniques or process you like. Wash the honed surface throughly to remove all oil and loose metal particles from the surface and grooves. Obtain a 2 to 3 in square of acetate film and a small can of acetone from the hardware store. Paint the honed surface with a liberal amount of the acetone and while still wet, apply the acetate film and hold firmly in place against the cylinder wall for about 2 minutes.

The acetone will dissolve the acetate and will form a casting of the honed surface which can be viewed under a microscope using a side light. The shapes of the plateaued islands, the grooves and the micro grooves on top of the islands will be clearly visible. I call it the poor man's (that includes virtually all racers) profilometer and its a great way to visually compare various honed surfaces.

Fax film as it was called is far from a poor mans profilometer. It is a way to get a three dimensional representation of the cylinder surface. Profilometer reading are two dimensional, being pulled from a straight line contact and making inferences from there. If you are really serious about cylinder bore surface work you would do both because each shows a different range of characteristics.

Fortunately, as in many things, the laws of "good enough" apply to this stuff. If you stay within the range of accepted industry practice you do not often get into too much trouble. When you decide to stray far afield in search of opportunity you may sometimes discover that going out of the proverbial box only demonstrates the reason that the "box" came to exist in the first place. Risk and reward stuff...

David Redszus wrote:The acetone will dissolve the acetate and will form a casting of the honed surface which can be viewed under a microscope using a side light.

Very good tip. What level of magnification is needed to make this useful?

4sfed wrote:

David Redszus wrote:The acetone will dissolve the acetate and will form a casting of the honed surface which can be viewed under a microscope using a side light.

Very good tip. What level of magnification is needed to make this useful?

Ive heard a 500x is what you need. Im gonna look into this. Id really like to try it.

statsystems wrote:

stvermeer wrote:After honing to .0005 from finish size, I let the block sit usually overnight and finish the next morning. Things move around a lot.

I did the same thing.

I even untorqued the torque plate while it sat over night. Even untorquing the torque plate for an hour made a difference in the shape of the bore.

It's the same with the main line.

What does the car itself do to these bores ,etc.etc.? Solid motor mounts on the stock block, with chains or mounts tied to the heads or water pump and hard leaving big tire car. Has to move things around too I would think.

n5ifi wrote:

statsystems wrote:

stvermeer wrote:After honing to .0005 from finish size, I let the block sit usually overnight and finish the next morning. Things move around a lot.

I did the same thing.

I even untorqued the torque plate while it sat over night. Even untorquing the torque plate for an hour made a difference in the shape of the bore.

It's the same with the main line.

What does the car itself do to these bores ,etc.etc.? Solid motor mounts on the stock block, with chains or mounts tied to the heads or water pump and hard leaving big tire car. Has to move things around too I would think.

Everything you do will make some sort of change. What we as builders strive to do is to eliminate all the variables under our control, and to quantify, understand and compensate for the variables we can not control.

n5ifi wrote:

statsystems wrote:

stvermeer wrote:After honing to .0005 from finish size, I let the block sit usually overnight and finish the next morning. Things move around a lot.

I did the same thing.

I even untorqued the torque plate while it sat over night. Even untorquing the torque plate for an hour made a difference in the shape of the bore.

It's the same with the main line.

What does the car itself do to these bores ,etc.etc.? Solid motor mounts on the stock block, with chains or mounts tied to the heads or water pump and hard leaving big tire car. Has to move things around too I would think.

Back in 1978, during a tour of the Mahle piston factory, I was told by their chief engineer,
"An engine is made of rubber, the only question is what is the durometer of each part."

I did not fully understand what he meant. Years later I came to understand that the term "stiffness", is quite relative. As each component (main caps, transmission, motor mounts, head, timing cover, etc), is bolted to the block, the shape of the cylinder bores will be affected. Imagine the bore distortion in Formula cars where the engine block is a stressed member of the chassis. But the largest distortion comes from combustion pressure as it tries to lift the head off the block, tensions the head bolts, and changes the bore shapes momentarily.

Pressure distortion has been studied carefully by gasket, ring and piston mfgs in the hopes of finding a solution to this complex problem. It is not unusual to hone to a specific surface finish, run the engine under load, then disassemble and measure the surface finish at multiple locations to determine the micro wear caused by the rings.
Changes in surface profilometer readings are much more accurate indicators of wear than are bore diameter measurements.

In this discussion, what amount of out of round is assumed for given finish reccomendations?

I've read that perfect circle only reccomends a plateau finish if out of round and taper is less than .0004. That makes sense to me in that a less than perfect bore with a rougher finish will wear in and self correct to a degree.

In a perfect world we would achieve numbers much lower than that out of round and taper but in practice I've never recieved a block from machinists that is honed to that tight of a tolerance across all the bores.

Would it then be advisable to skip the plateau finish to compensate for this with a higher Rpk and and lower plateau %?

Would the only downsides be increased break in time, reduced ring life (how much?), and more debris in the oil during break in?

n5ifi wrote:

statsystems wrote:

stvermeer wrote:After honing to .0005 from finish size, I let the block sit usually overnight and finish the next morning. Things move around a lot.

I did the same thing.

I even untorqued the torque plate while it sat over night. Even untorquing the torque plate for an hour made a difference in the shape of the bore.

It's the same with the main line.

What does the car itself do to these bores ,etc.etc.? Solid motor mounts on the stock block, with chains or mounts tied to the heads or water pump and hard leaving big tire car. Has to move things around too I would think.

I agree with what Barry said. I actually made up a couple of plates to bolt on to the bell housing, mounted motor mounts etc but I found it's difficult to duplicate the loads the block sees while the car is moving.

I have found that people who use chains and torque straps can, sometimes pull that bore out of round. Engine plates cleaned it up. The harder the car left, the more the torque strap pull the cylinder out.

pamotorman wrote:OEM rings are broken in in a cylinder at the ring manufactures before being shipped to the engine assy factory.

No - not correct . . . . . . At the manufacturing plant (or most of them anyway) the rings are placed on a mandrel and then they are lapped to final dimension. This process is done to quality rings, whether the are being manufactured for OEM or aftermarket sales. Note, that there are some piston ring manufacturers who skip this step in order to save money.

Honing/finishing cylinder walls is the same process whether the engine will be used on the street or race track and it is very simple but needs to be done correctly. There must be enough crosshatch pattern (peaks and valleys) to ensure that sufficient oil is retained on the cylinder walls as the pistons travel up and down. The peaks must be cut back somewhat with a plateau hone so that the rings will travel smoothly over the surface.

Cylinder crosshatch included angle will depend to a great extent upon the length of the cylinder (i.e. short stroke vs. long stroke architecture). A short stroke engine will benefit from a "flatter" crosshatch angle and a long stroke engine will prefer a greater angle to insure that sufficient oil travels to the upper limits of the top (compression) ring travel.

There is no magic involved, no smoke and mirrors, just good processes, common sense and acquired skill.

Cylinder crosshatch included angle will depend to a great extent upon the length of the cylinder (i.e. short stroke vs. long stroke architecture). A short stroke engine will benefit from a "flatter" crosshatch angle and a long stroke engine will prefer a greater angle to insure that sufficient oil travels to the upper limits of the top (compression) ring travel.

I find myself in disagreement with this statement. All the technical source materials that I have, suggest that the correct cross hatch angle is 45 deg from horizontal. That means a 45 deg included angle or 22.5 deg half angle centered on the horizontal axis.

Rating points are subtracted for each degree either steeper or shallower than 45. However, a slightly steeper angle is preferred over a shallower angle. A very steep angle (+55 deg) will produce more oil migration up and down the cylinder walls. Most non-OEM engines wall surfaces have shallower cross hatch angles than desired which does not permit adequate oil movement. The correct honing angle is a function of rotational surface speed and stroke velocity. Sunnen, among others, have equations available to determine the proper speed and stroke.

The fax film method outlined above can be used to accurately determine the cross hatch honing angle.

engineguyBill wrote: No - not correct . . . . . . At the manufacturing plant (or most of them anyway) the rings are placed on a mandrel and then they are lapped to final dimension. This process is done to quality rings, whether the are being manufactured for OEM or aftermarket sales. Note, that there are some piston ring manufacturers who skip this step in order to save money.

Honing/finishing cylinder walls is the same process whether the engine will be used on the street or race track and it is very simple but needs to be done correctly. There must be enough crosshatch pattern (peaks and valleys) to ensure that sufficient oil is retained on the cylinder walls as the pistons travel up and down. The peaks must be cut back somewhat with a plateau hone so that the rings will travel smoothly over the surface.

Cylinder crosshatch included angle will depend to a great extent upon the length of the cylinder (i.e. short stroke vs. long stroke architecture). A short stroke engine will benefit from a "flatter" crosshatch angle and a long stroke engine will prefer a greater angle to insure that sufficient oil travels to the upper limits of the top (compression) ring travel.

There is no magic involved, no smoke and mirrors, just good processes, common sense and acquired skill.

Bill, do you finish your cylinders with a brush or with vitrified stones?

Can anyone provide information as to what Ra finish a brush produces on cast iron?

Fine brush, with diameter very close to the finished cylinder bore size, minimal number of strokes, good clean honing oil.

It seems that the brush hone does not remove metal peaks to create a plateau finish. Instead, it merely cleans debris from the grooves, which is useful but not its intended purpose.

Does anyone have a brush hone, polished mirror finish metal surface and a profilometer?
It would be a simple matter to prove or disprove the function of a brush hone.

David Redszus wrote:It seems that the brush hone does not remove metal peaks to create a plateau finish. Instead, it merely cleans debris from the grooves, which is useful but not its intended purpose.

Does anyone have a brush hone, polished mirror finish metal surface and a profilometer?
It would be a simple matter to prove or disprove the function of a brush hone.

I will get profilometer readings for you David. I just honed a LS block at school, 70 grit, 120 grit, and fixed plateau brushes in our sunnen. BTW, this is the way our teacher teaches us. Not trying to imply its correct, just putting the info out there. anyway, check back with values later..