Cylinder Finish

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Mosey
Posts: 66
Joined: Sat Jan 04, 2003 4:27 pm
Location: Western New Jersey

Cylinder Finish

Post by Mosey »

I'm at it again.
How does one check the smoothness of a cylinder wall? These are cast iron cylinders running cast iron rings, and are 3/4" diameter.
Are there standards to compare with?
These cylinders are honed with a brake hone, and I'v heard that you should have a crosshatch pattern, but how deep are the scratches supposed to be?
Bob_W
Posts: 108
Joined: Sat Jan 04, 2003 11:28 am
Location: Central PA

Re: Cylinder Finish

Post by Bob_W »

Search for the Web Site of Flexhone and they will have information describing their products and cylinder finish. I just used one on a 1 7/8" cylinder and it worked fine. However on two of my engines with 3/4 and 7/8" bores I do not use rings. Tried them after the engines had been completed by making new piston / cylinder set and was not satisfied with the performance. Went back to the ringless parts.

Bob W
Mosey
Posts: 66
Joined: Sat Jan 04, 2003 4:27 pm
Location: Western New Jersey

Re:Flex Hone

Post by Mosey »

They are at www.brushresearch.com, and offer numerous engineering booklets free.
Doug_C
Posts: 1254
Joined: Sat Jan 04, 2003 6:48 pm

Re:Flex Hone pre-cautions?

Post by Doug_C »

My understanding is that these are glaze breakers and deburring tools, not for dimensional or improved surface integrity.

My experience with this style of hone is that it will follow whatever shape is in the original as bored. Even exagerating egg shapes as it goes from tight to loose each revolution. I would suspect any good seal difficult to achieve between the cylinder wall and piston or ring to stay in contact over the entire stroke if rippling is present too. Ringed should be less critical than not ringed, but if the ring floats on the high points, it may as well be ringless.

I prefer to keep the sleeve free or pressed in place rather than take the chance of distortion from gripping while honing then relieved out of round at the finish size when ungripped. Some purists may even add heat to hone at running temperatures.

The finish I see most often is from 120grit or finer by lapping or honing with a solid mandrel to keep the bore straight and round as possible.

Any other thoughts out there?

Live Steam group ought to be able to expound on this. [img]/ubb/images/graemlins/laugh.gif"%20alt="[/img]

DC
Dave_S
Posts: 22
Joined: Mon Jan 06, 2003 3:44 pm
Location: Orange, CA

Re:Flex Hone pre-cautions?

Post by Dave_S »

For my 1/2" bore by 1/2" IC horizontal, I lapped both piston (ductile iron) and liner (grey iron) to size. The fellow I bought the plans from states that cross-hatch pattern is fine for full-size engines, but not for models. He says to make the surfaces 'smooth as glass', which I did. Friction is a big problem with engines of this size, and this smooth finish got me going with virtually no break-in period. I'm not using piston rings, but this lapped fit holds compression for > 10 seconds without loss.

Dave
Doug_C
Posts: 1254
Joined: Sat Jan 04, 2003 6:48 pm

Re:Flex Hone pre-cautions?

Post by Doug_C »

Hi Dave,

What grit and technique did you finish off with?

The resources I have come across do suggest a finer finish for non-ringed engines.

It was my understanding that the crosshatch with a steel cylinder liner would help retain oil as cast iron does from open pores. This was to also help in getting the ring to seat.

Nice little engine you have there. I would like to see a bigger version of that for sure. Maybe a lttle run down detail if you could.

DC
Dave_S
Posts: 22
Joined: Mon Jan 06, 2003 3:44 pm
Location: Orange, CA

Re:Flex Hone pre-cautions?

Post by Dave_S »

Hi DC,

I lapped the piston with Cloverleaf 'fine' grit, and then sanded lightly with 600 WOD before finally using a Scotch-Brite pad. Shines like chrome. I mostly did the same with the cyl liner.

The engine is Bob Shores' design. See Floride Modelers for more info on many small engines. Bob's is called the Little Angel, 1/2" bore x 1/2" stroke, but could easily be doubled in size.

Stay in touch.

Dave
_pete913

Re:Flex Hone pre-cautions?

Post by _pete913 »

I see a lot of discussion about cylinder finish, cross hatch marks etc, but the main thing is to get the cylinder round and straight. Back when I was rebuilding full scale engines, we used to routinely finish cylinders with a sunnen hone and 600 grit stones. If the rings fit right and are round, and the cylinders round as well, there is no break in, its broken in the first 10 revolutions. If it isn't so, all the rough honing marks in the world will still only result in a short lived oil pumper.
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