# Cylinder boring



## cdyoung1985 (Sep 8, 2017)

So a buddy just got his late grandfather's mill and lathe given to him, and none of us are machinists by any means. Welders, fabricators, general diy guys, but not machinists. I've got a klr250 dual sport I'm rebuilding, and the cylinder has been left out in the rain a few times. So before I order one, I'd like to try my hand boring. It has a torque plate on the lathe, and power everything. It's old, his grandpa passed in 84, and the stuff is older than that, but in emasculated shape. Looks like it belongs in a showroom floor. 

This would be my first lathe project. Wondering what I need for the tooling? I know I need a boring bar, assuming I need it to be a bit longer than my stroke? What kind of material? If it goes at all well, I'll also be boring my Harley 883 instead of buying a kit. 
Plan on tinkering with the lathe a bit before jumping into the bore, but don't think it'll be that bad.


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## killswitch505 (Sep 8, 2017)

I would attempt to bore a cylinder on the mill before doing it on the lathe using a boring head. I can get a pretty great finish with a boring head but I think you'll have to follow up with a honer.


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## Aukai (Sep 9, 2017)

I have not seen it done on a lathe, but with the right fixtures, I guess it is possible. Now, cylinder wall finish, and ring selection can be very important here. Now days it is common to get a ring selected by the manufacturer for the application, and have a specific cylinder finish for that ring. They use profilometers to see the microscopic finish after honing. Piston to cylinder clearance is important also, I'm sure that it will still run well with the old fashion stone, and cross hatch, but check with the manufacturer you want to use for the right rings. Just my suggestion good luck.....


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## GoceKU (Sep 9, 2017)

I've done couple of 49cc cylinders, i'm using an brazed carbide boring bar 30x30mm shank and i'm power feeding on the slowest feed my lathe has also im power feeding out of the bore, in some 2 stroke cylinders that have large ports in the bore is possible to get chatter in that case the cylinder is scrap, and always hone it to final size, for honing i use diesel fuel as a lubricant, best of luck and a rusty cylinder is a good thing to practice on.


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## MarkM (Sep 9, 2017)

Before you attempt to bore it I would use a proper hone to clean up the rust.  Get a proper measurement and you may find you may not need to bore it out.  Diesel or Kerosene works well with hones.  Make sure it is a spring loaded hone to keep concentricity.


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## f350ca (Sep 9, 2017)

I rebuilt an old Wisconsin twin a while back. Boring it on the mill would have required using the knee as the cylinder was deeper than the quill stroke. Didn't relish all that cranking so set it up on the lathe. Made a heavy boring bar to compensate for the reach and all went well. Machined to a couple of thou oversize and used a Sunnen hone to take it to size.











Greg


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## cdyoung1985 (Sep 9, 2017)

Thank you all for your tips. I'd say one of the biggest reasons I'm planning on using the lathe is it's torque plate, rather than the mills clamps. Plus it's a single cylinder, and my Harley's cylinders are separate, so nothing like f350 posted. 
I plan on using a hone to finish, thought it was required. 
Biggest question right now is the boring bar. I think I want the liquid cooled one, unsure of diameter and length...


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## tq60 (Sep 9, 2017)

Before experimenting with creating scrap check into having it done. 

Places that do this have correct everything to get it done correct and to spec.

Cost of tooling likely more than that of the job.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk


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## MarkM (Sep 9, 2017)

Your biggest enemy with boring the cylinder will be the boring bar flexing on you.  Coolant isn t so critical.  More of a luxury for this application.  Use the biggest diameter bar you can and the least amount of stickout possible to do the job. I would stay away from carbide and use high speed with a very sharp edge.  Carbide needs to get under the matarial and may cause you more grief with it wanting to rub and flex with the little amount of material you want to remove.  Yes the hone is needed to give you the cross hatch pattern to help seat the rings.


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## Groundhog (Sep 9, 2017)

Not sure how much the torque plate will help with a single cylinder bore, I guess that would depend on how badly you clamped it the mill. Torque plates, as I'm sure you know,  are generally used (with questionable need) with multi cylinder heads to limit distortion. Can't hurt though!
I've bored cylinders on both lathes and mills with good results. Only bored cases (for big bore jugs) on a mill though.


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## cdyoung1985 (Sep 9, 2017)

MarkM said:


> Your biggest enemy with boring the cylinder will be the boring bar flexing on you.  Coolant isn t so critical.  More of a luxury for this application.  Use the biggest diameter bar you can and the least amount of stickout possible to do the job. I would stay away from carbide and use high speed with a very sharp edge.  Carbide needs to get under the matarial and may cause you more grief with it wanting to rub and flex with the little amount of material you want to remove.  Yes the hone is needed to give you the cross hatch pattern to help seat the rings.


Thanks, very good information. Figure I'll try the dirt bike first since it isn't such a big deal. Going to be a while, but not that long it that makes sense...


tq60 said:


> Before experimenting with creating scrap check into having it done.
> 
> Places that do this have correct everything to get it done correct and to spec.
> 
> ...


 It would be cheaper than doing one, yes. But I don't just want 1 cylinder bored in my life. We have most of what we need, and I have the capability to learn it. Probably changing my degree from a welding certificate to an associate's degree because it includes courses for machining. I'm a built not bought kinda guy. Wouldn't be surprised if we build the tool to bore my cylinder. Not planning on it, by it isn't beyond the realm of possibilities.


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## MarkM (Sep 9, 2017)

I like your approach.  How will we be craftsman if we take the easy way out.  A challenge today is a skill for life.  No biggie making your boring bar.  Rigity rigity Rigity.  Figure how your going to hold the cylinder and think about clearance on the end close to your chuck.  You may need to shim it againt the chuck to allow the tool to finish the bore.  Not needed but if your looking for a challenge and a great boring bar do it with an eccentric rather than concentric to aid with rigity.  Drill a deep hole from the back end and tap it for a bolt.  Fill it with lead or soder and tighten the bolt to add pressure on the lead once cured.  Great dampening effect and does wonders for vibration.


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## BogusSVO (Sep 9, 2017)

General rule of thumb is bore the bore .003 smaller than the finish bore you want
Your hone that last ~.003 or so out to set the PTW

Most all blocks are bored dry and honed with oil

Bad thing most all parts store hones are just glaze brakers

Look at sunnen AN hone stones, 

BTW my avatar is a Kwik-Way FN boring bar


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## cdyoung1985 (Sep 9, 2017)

MarkM said:


> I like your approach.  How will we be craftsman if we take the easy way out.  A challenge today is a skill for life.  No biggie making your boring bar.  Rigity rigity Rigity.  Figure how your going to hold the cylinder and think about clearance on the end close to your chuck.  You may need to shim it againt the chuck to allow the tool to finish the bore.  Not needed but if your looking for a challenge and a great boring bar do it with an eccentric rather than concentric to aid with rigity.  Drill a deep hole from the back end and tap it for a bolt.  Fill it with lead or soder and tighten the bolt to add pressure on the lead once cured.  Great dampening effect and does wonders for vibration.


I like that, a challenge today is a skill for life.
And you meant rigidity, not rigity right? Want to make it as unbendable as possible?
Thinking I could make a gusset that runs most of the way down the bar? Would think as long as it doesn't contact the cylinder it wouldn't be an issue.
Unsure of what eccentric and concentric are at this point. I'm far from a machinist, but I have a thing for pretending I know what I'm doing, and before long convincing others I really do. I don't, but don't tell them that.


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## Silverbullet (Sep 10, 2017)

You really do need the ring set to Ck your bore. You'll need your oversize set to get them fitted . Bore to your ten over and take the compression ring and place it in the cylinder and Ck the ring gap it must have room. If the ring fits to loose or tight your engine won't perform or last. Your specs, will tell you what's needed. Small engines have been my extra income for. Years


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## Silverbullet (Sep 10, 2017)

cdyoung1985 said:


> Thanks, very good information. Figure I'll try the dirt bike first since it isn't such a big deal. Going to be a while, but not that long it that makes sense...
> 
> It would be cheaper than doing one, yes. But I don't just want 1 cylinder bored in my life. We have most of what we need, and I have the capability to learn it. Probably changing my degree from a welding certificate to an associate's degree because it includes courses for machining. I'm a built not bought kinda guy. Wouldn't be surprised if we build the tool to bore my cylinder. Not planning on it, by it isn't beyond the realm of possibilities.


Very easy to make a boring bar.


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## MarkM (Sep 10, 2017)

Yes I meant rigidity.  Guess I need to go back to school.  As far as the eccentric.  Say a shaft would need to be turned down between centres.  A concentric shaft has the centre holes drilled in the centre and then turned down.  An eccentric  would have the centre holes offset and then turned down between centres.  The portion being clamped and holding your tool would be the concentric portion and in between would be your eccentric portion.  Really not needed.  It adds a bit RIGIDITY and some clearance.
I also meant a challenge can lead to knowledge that will stay with you for life and yes the possibility of a scrapped part may enter the equation but how are we going to learn?
I should do a better job of proof reading before I hit the post button. Way too much on my plate at the moment.


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## TomS (Sep 10, 2017)

For what it's worth many years ago, I'm talking about the 70's, I bored the cylinder on my 125cc Honda two stroke.  I made a mounting plate that replicated the cylinder mounting flange on the case.  Set up the mounting plate in the lathe, dialed in the mounting plate bore, then faced the mounting plate.  Bolted the cylinder to the plate and bored the cylinder to size leaving a few thou for honing.  I had a local auto machine shop do the honing.  Motor ran great.


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## MarkM (Sep 11, 2017)

Hey BogusSVO I wonder if the Kwik-way fn Boring bar could be configured to do mobile line boring.  In the ball park of a decent mag drill as far as price goes.   On it s own without the stand could you replace the spindle shaft with a long shaft to be set up using cones  for alignment between bores say for example a backhoe bucket?  Off on a tangent here but have never worked in an automotive machine shop and it intrigues me.


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## benmychree (Sep 11, 2017)

A cylinder boring bar is made to work vertically or at worst at 45 or 60 deg. they are not made to operate horizontally, the issue is internal lubrication.


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## BogusSVO (Sep 11, 2017)

MarkM, The KW-FN is what they call a "portable" boring bar it is designed to  lock down with an adapter to a head bolt hole.

It also self centers with a 3 point paw

Now to lay it down on its side may have issues

IIRC it has a max depth of 14 inches, but seldom do I go more than 5 to 6 inches


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## cdyoung1985 (Sep 15, 2017)

TomS said:


> For what it's worth many years ago, I'm talking about the 70's, I bored the cylinder on my 125cc Honda two stroke.  I made a mounting plate that replicated the cylinder mounting flange on the case.  Set up the mounting plate in the lathe, dialed in the mounting plate bore, then faced the mounting plate.  Bolted the cylinder to the plate and bored the cylinder to size leaving a few thou for honing.  I had a local auto machine shop do the honing.  Motor ran great.


That might not be a bad idea, do the expensive part, and have a pro finish it...

Sent from my SM-J327P using Tapatalk


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## patmat2350 (Sep 18, 2017)

While on words and spelling, you might want to check the meaning of your first post:

"...the stuff is older than that, but in emasculated shape."


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## BROCKWOOD (Sep 19, 2017)

Immaculate = Like new or exceptional condition.  Yeah, you would not like what emasculated is.

Interesting discussion, boring out cylinders.  I have hopes of graduating to cylinder boring myself!


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## crazypj (Oct 1, 2017)

First cylinder set I bored was a 1966~67 Honda 160 block to take 175 pistons. I think I used a Bridgeport but it was so long ago I forget (around 1974)
Since then, I've done literally thousands of motorcycle cylinders.
I taught cylinder boring as part of 'Clinic 3- Machine Shop' at Motorcycle Mechanics Institute, Orlando for over 3 yrs (so several thousand students) Almost everyone could bore and hone a cylinder to within specification of +/- 0.0002" by the end of 3 week course (at least all my classes) The problem with boring on mill is lack of quill travel which is usually 5" or less. A lathe can sometimes be much more useful if you have a large enough bar. It would be better to make something that will bolt on in place of tool-post and take a 'spring cut' or two before honing, Bar should be 2~3" steel to give greatest accuracy, use croos slide to set cut. The KLR cylinder doesn't need torque plate, do you mean to bolt it to a face plate? If your not familiar with using DTI it can be a pretty frustrating experience to get things centered up properly. As for poster who said torque plates probably aint needed, correct but some engines MUST use torque plates as they 'distort' the cylinder to fitted shape (Harley Davidson 'Evo' cylinders distort around 0.001"~0.002", center gets 'smaller' when fitted if torque plates ain't used) You will need a rigid hone (Sunnen, Ammco, etc) to finish size cylinder accurately, the 3 leg spring hone won't work to remove any out of round or out of parallel. You'll also need a bore gauge, the cheap $50.00 ones are not worth the money, you need 0.0005 " resolution minimum, 0.0001" is way better (and 'only' about $175.00 more expensive)
Initial set up may be substantially more than paying to have bore done but it will repay investment many times over when you start doing modifications  (swapping cylinder liners, 'big bore' kits, etc) I would probably try and find KLR300 piston spec to see if it could be fitted into 250 cylinder. 
As for doing 883 Harley, no idea how many students did their own before HD stopped supplying pistons (hundreds of $125.00 piston kits instead of $800+ piston/cylinder kits) You have to remove 0.495" from bore to go to 1200cc, makes cylinders a LOT lighter. Modified 883 head is actually 'better' than stock 1200 head, there is enough material to make ports a much better shape and size (and way cheaper than buying Buell 'Lightening' parts)


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## crazypj (Oct 1, 2017)

Oh, if your a bunch of fabricator weldors, you will probably have access to all sorts of steel 'offcuts' to convert into useful tools. 'Grinder and paint made me the welder I am today LOL


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## cdyoung1985 (Oct 1, 2017)

crazypj said:


> First cylinder set I bored was a 1966~67 Honda 160 block to take 175 pistons. I think I used a Bridgeport but it was so long ago I forget (around 1974)
> Since then, I've done literally thousands of motorcycle cylinders.
> I taught cylinder boring as part of 'Clinic 3- Machine Shop' at Motorcycle Mechanics Institute, Orlando for over 3 yrs (so several thousand students) Almost everyone could bore and hone a cylinder to within specification of +/- 0.0002" by the end of 3 week course (at least all my classes) The problem with boring on mill is lack of quill travel which is usually 5" or less. A lathe can sometimes be much more useful if you have a large enough bar. It would be better to make something that will bolt on in place of tool-post and take a 'spring cut' or two before honing, Bar should be 2~3" steel to give greatest accuracy, use croos slide to set cut. The KLR cylinder doesn't need torque plate, do you mean to bolt it to a face plate? If your not familiar with using DTI it can be a pretty frustrating experience to get things centered up properly. As for poster who said torque plates probably aint needed, correct but some engines MUST use torque plates as they 'distort' the cylinder to fitted shape (Harley Davidson 'Evo' cylinders distort around 0.001"~0.002", center gets 'smaller' when fitted if torque plates ain't used) You will need a rigid hone (Sunnen, Ammco, etc) to finish size cylinder accurately, the 3 leg spring hone won't work to remove any out of round or out of parallel. You'll also need a bore gauge, the cheap $50.00 ones are not worth the money, you need 0.0005 " resolution minimum, 0.0001" is way better (and 'only' about $175.00 more expensive)
> Initial set up may be substantially more than paying to have bore done but it will repay investment many times over when you start doing modifications  (swapping cylinder liners, 'big bore' kits, etc) I would probably try and find KLR300 piston spec to see if it could be fitted into 250 cylinder.
> As for doing 883 Harley, no idea how many students did their own before HD stopped supplying pistons (hundreds of $125.00 piston kits instead of $800+ piston/cylinder kits) You have to remove 0.495" from bore to go to 1200cc, makes cylinders a LOT lighter. Modified 883 head is actually 'better' than stock 1200 head, there is enough material to make ports a much better shape and size (and way cheaper than buying Buell 'Lightening' parts)


Ton of great knowledge there, thank you!


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