Honing cylinder

[Speedy Builder5Participant @speedybuilder5]

I am making a FarmBoy hit and miss engine and looking at the making of the combustion cylinder.  This is about 3.5″ long and 1″ internal diameter (1.25″ OD)  I intend to bore slightly undersized and then hone to size (leave piston manufacture until cylinder is honed).

Do I machine the cylinder and leave on the bar stock and hold the hone on the saddle tool post, or part off the cylinder and hold the hone in the chuck?

Questions:-

Should the hone be allowed to float if the cylinder is held by its bar stock ?

If cylinder parted off, could I hold the cylinder by hand or must it be fixed to the saddle cross slide?

Should the hone be held by the tail stock?

I intend making the hone to Ramon Wilson’s design.

What do you think ?

Bob

 

[JasonBModerator @jasonb]

If it is the copper headed one to Ramon’s design then that is a lap and not a hone.

Have the lap being driven by the lathe or pillar drill and hold the (parted off) liner in your hand moving it up and down the lap as it turns.

https://www.modelenginemaker.com/index.php?topic=1908.0

[Speedy Builder5Participant @speedybuilder5]

Thanks Jason, I found this link interesting:-

https://www.homemodelenginemachinist.com/threads/little-demon-v8-helpful-hints-hopefully.33799/page-4#post-435345

Bob

[noel shelleyParticipant @noelshelley55608]

Hi Bob, If the cylinder is of the type where the head is separate then once bored to almost size I would hone using one of the commercially available 2 or 3 stone hones. Drive the hone with the lathe at slow speed (300 rpm) and hold the cylinder block in your hand. Lubricate with paraffin and try to protect the bed and lathe from the run off.

Once you are happy with the job then lap the piston to the bore, but remember that the piston depending on material may expands as it warms up and needs to be allowed for if it is to be a real “running engine “. Good luck. Noel.

[DiogenesParticipant @diogenes]

Not sure how critical the Farmboy is in this department but perhaps worth noting the difference between honing and lapping cylinders here;

Commercial sprung cylinder hones will even out minor imperfections and provide a good finish to a bore, but aren’t usually capable of correcting any out-of-round or lack of parallelism.

If you need to true the bore or correct any (obvious or suspected) deficiencies, then it’s best to use a solid lap.

[JasonBModerator @jasonb]

You also need to give some thought as to the type of rings you are going to use, A hone which leave sa cross hatch is best for iron rings but if you are going for O rings oreven ringless then a lap is the better bet.

When Honing with the brake cylinder type hones I tend to use the drill press

[Speedy Builder5Participant @speedybuilder5]

The piston will use a 1″ diameter  “O” ring or if I could find a supplier (at a reasonable cost), an “X” ring (Joint Quadrilobe). Apparently X rings seal with less friction.

Thanks all for the tips.

Bob

[JasonBModerator @jasonb]

A Viton (FKM) O ring should be fine, I have used them on my last six or so IC engines. Just don’t squeeze them too hard, about 5% compression of the ring is more than enough.

[Roderick JenkinsParticipant @roderickjenkins93242]

You certainly do not want to lap the piston to the bore.  The aluminium piston needs a couple of thou clearance.

I have tried an X ring in my Farm Boy and did not get on with it.  I think these X rings are probably better suited to making rotary seals rather than reciprocating.  An ordinary Viton O ring from Blackgates worked for me but if you do want to experiment then Simply Bearings are a good source at reasonable cost and postage.

Rod

[Author]

Posts