Straight 8

[stevehuckss396]

honing is done to purposefully roughen the surface slightly to hold oil while the rings bed in And finally to allow the bores to be finished to an exact size

Hi Artie!

The trend today is to finish the cylinders to an almost mirror finish. Bob Shores recommended the cross hatch be polished out. As for size, I bored in the mill and double stroked each hole meaning I took a cut then a spring cut in each bore. Top to bottom on the bores and difference between bores is well in spec now.

As bad as my rings are, they will never bed in anyway Hahahha!!


Thanks Artie!!

 

[cfellows]

More nice work, Steve. By the way, what kind of cutter do you use in that boring head?

Chuck

 

[stevehuckss396]

More nice work, Steve. By the way, what kind of cutter do you use in that boring head?

Chuck

Boring bar with a 3/4 shank. It has a carbide tip with a nice big radius on the end. Not sure but looks like .0625 radius. I did it free hand so I really dont know.

 

[deere_x475guy]

Damn fine work Steve.!!!!!!

 

[stevehuckss396]

"Lap to a mirror finish. Do not leave herringbone scratches to retain oil for the piston. Rarely does a piston lack oil, the PROBLEM is to prevent oil migration from the oil pan, around the piston and into the combustion chamber."

Bob Shores

 

[NickG]

That's quite interesting, sort of makes sense. You'd think the piston would also bed in faster without oil being retained in those surfaces too. On full size engines when you're running them in they used to suggest using crappy oil. But with todays cars, there don't tend to be any major running in instructions, well you don't have to change the oil after 500 miles, then after 1000 miles etc, so that suggests the bores are a good finish to start with. I guess with any kind of running the bores get polished to a mirror finish anyway.

Seems like this could be one of those subjective topics, i've never needed to hone or lap a bore on any of my engines yet, always had better results without but I haven't made an i.c. engine yet.

Nick

 

[stevehuckss396]

Seems like this could be one of those subjective topics, i've never needed to hone or lap a bore on any of my engines yet, always had better results without but I haven't made an i.c. engine yet.

Nick

When i made the sleeves for the Peewee, i did the whole job on the lathe. I even bored to finish size -.002. Then when I pressed them in, The bores were finished with a lapping tool. In that case the bores were out more than .0005 from top to bottom and the finish was not so good. In this case, the finish is smooth as a babys but and very little taper if any. Why fix it if it aint broke.

 

[Artie]

Ive ben thinking about the honing thing and now have 'a theory'. In the full sized item the rings are forced quite hard against the cylinder walls and when being bedded in even harder by slow revs and high load (high cylinder gas pressures pushing the rings outwards). The hone marks are there to hold oil to protect the surfaces during this period.

Little engines are never going to be loaded to that level and also never run for any appreciable length of time. Give these to points. I wouldnt hone either. As you say get a good smooth finish and go.

Keep it up mate.

Artie

 

[stevehuckss396]

As you say get a good smooth finish and go.

Also need to make sure there is no taper from top to bottom. I have measured mine a few times and the difference is only a tenth or two. If there is more than a few tenths, personally I like the lapping tool to remove the taper.

Have to be round, straight, and shiny!

 

[joeby]

I'm not entirely convinced that the honing is done to hold oil.

When engines are mass produced, from castings that are probably still "green" how much out
of round are they. How about rings, one size doesn't easily fit all.

A lot of years ago I worked on small engines for extra money, many of them were the aluminum bore B&S. If you didn't hone them, the rings would have a really hard time seating.

Could it be possible that the honing created a little "traction" to get wear started?

Would it also be possible for the newer engines to not need honed because of better control in manufacturing creating better fitting parts?

Kevin

 

[stevehuckss396]

Started on a set of pistons today. I make the pieces long and turn a diameter on the end so there will be something to hang on to.

The piece is chucked and the OD is turned and the ring grooves are cut. My target was .8495 - .850. I managed to hit the target 8 times in a row. 2 of them were so close i rubbed them with some paper rather than take a chance of cutting under size.

The pieces were flipped upside down and I sat and watched the mill clean out the bottoms.

Tomorrow I hope to get them cross drilled and installed on the rods.

 

[gbritnell]

Hi Steve, first off, you're making great progress on this mini monster. Second, do you have any problems with all the chips getting on the Z axis leadscrew?
George

 

[stevehuckss396]

do you have any problems with all the chips getting on the Z axis leadscrew?
George

Not at all G. I was only stroking Z .650 down. The ball nut was about 5 inches above the "dirty part of the screw. The screw will be cleaned and blown down before i bring the head back down. Normally the screw is hidden but Z is almost all the way up exposing the lower few inches.

 

[deere_x475guy]

Gang, he did all this today while giving me cam and Mach3 support....Nice job Steve it's looking great!

Here's a couple of Karma points for you!

 

[rake60]

Beautiful build Steve! :bow:

This thread is at the top of my "check it first" list.

Rick

 

[Rustkolector]

Steve,
I am really enjoying your build. A little rambling about cylinder bores. In my opinion the cylinder finish is not as important (provided it is reasonably smooth) as the straightness of the bore, and the piston rings. I have gotten good straight bores with lapping. The last engine I built, I had the cylinder finished on a Sunnen pin hone. This cylinder was absolutely straight (by my measuements). This engine has great compression, and has never burned oil with 20+ hours of use. I have always had trouble measuring 10ths accurately with telescoping bore gauges, so I have resorted to using gauge blocks for more accurate cylinder bore measurement. With a good bore measurement, I have been making better rings. I follow the Trimble method (ring radial thickness, etc.) with only a few shortcuts. You should find that these rings will seal very well initially,and quickly improve. I use straight mineral oil for ring break-in. Friction modifiers in motor oils do a wonderful job of reducing friction in an engine, but they also slow ring seating of low tech CI rings. Ask any small aircraft mechanic.

You can also consider plateau hone with one of those dingleberry hones. It doesn't open the bore measurably. They are used by speed shops after cylinder boring. http://www.goodson.com/technical_support/tech_library/PlateauHoning.php

Jeff

 

[m_kilde]

Hi Steve

I too must say it is a very interesting build to follow - thank you for sharing.

Kind of mass production and still you will end up with only one engine ;D

 

[stevehuckss396]

thank you for sharing.

Kind of mass production and still you will end up with only one engine

Your welcome.

That is the bad part of a multi-cylinder engine. You have to make alot of everything. Any body that has built a motor with 8 or more cylinders, My hat is off to them. This is why I built the CNC milling machine.

 

[stevehuckss396]

Well today was another awesome day in the garage. We have pistons!!

I hate drilling into anything round because, well, it sucks. I never seem to hit center or my drill seems to drift so i came up with this solution so i could "measure once, cut 8 times". I grabbed the smallest piece of square stock i could find. I turned 2 diameters on it, one being the diameter of the skirt ID - .002 and the same length as its depth. I also turned the smaller diameter .002 smaller than the second step way down in the deepest part of the piston recess.

Then i put it in the mill and milled off enough material so the center was left and was .248 wide. That makes the width .002 less than the slot in the piston.

The piston went on about 3/4 of the way and with a few light taps, it slid right on. I didn't even need to hold it on there but i still used my thumb just in case. Knowing it would work and knowing the large square surface is the bottom of the piston, I found center and that edge and laid out the hole and drilled it .010 larger than the wrist pin.

Then one after another I slid them on and spot drilled, drilled and reamed all eight pistons.

After that step was done I rechucked them in the lathe and parted them off.

I dont have a collet to fit the pistons so i wrapped them in a piece of paper to keep from scuffing them up. If you were wondering what the 3rd ring groove is for. That groove is the top of the piston +.005. I faced the top of the piston until the groove was gone and then took .005 more. The top edge was broken with a piece of 320 grit paper.

All that was left was to debur the wrist pin holes and FINISHED!! Wooohooo!

 

[chuck foster]

looking good steve :bow: :bow:

i have always had trouble drilling wrist pin hole's, but after seeing the way you did it ........... i think my problems are over ;D

thanks for letting us look over your shoulder and watch a master at work Thm:

chuck