# boring a cylinder



## shuswapkev (Nov 12, 2014)

I have some motorcycle cylinders I need to put some sleeves in...  this is a 26 douglas....  the head is cast with the cylinder  the valves come out thru some pipe plugs in the  head
I am boring them in a mill drill with a boring head...I need to bore 5 inches...so my boring bar is about 6 inches...
I have made a boring bar and jig to hold the cylinder

my problem is I am getting a very rough surface just cutting maybe 2 thou at a time...some of the problem is the rust pitsand chattering after them

any tips??


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## SG51Buss (Nov 12, 2014)

I've bored many motorcycle cylinders in the '70s, on dedicated boring bars made by Van Norman and Kwik-Way.  These machines were quite rigid and had large diameter quills, with very slow speed and feed rates.  The bits were carbide, and were sharpened on fine diamond wheels with special jigs.  I always kept my bits sharp, anything less invites problems.  0.002" depth-of-cut is about what I'd use for initial rough cuts, less for final cuts,  and that involves only the very tip of the cutter.

A friend of mine was experiencing a similar problem, on a large, multi-bit resurfacing machine.  He claimed his bits were sharp, and they did indeed feel sharp, but when examining them with a 10x loupe, you could see that the critical edge of the bits were rounded.  Resharpened them properly, and his surfacer produced clean cuts...


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## 12bolts (Nov 12, 2014)

Not knocking your equipment, but I believe your problem lies here.


shuswapkev said:


> ...mill drill with a boring head...


5" deep is a long way in, bearings, quill extension, tool run out. Any other accessible equipment? The more info you can supply, the more help this group can provide. And believe me, collectively its *A LOT*.

Cheers Phil


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## Vladymere (Nov 12, 2014)

I have no experience at this but wonder if you might be better served mounting the cylinders in a lathe and boring them.

Vlad


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## davidh (Nov 12, 2014)

Vladymere said:


> I have no experience at this but wonder if you might be better served mounting the cylinders in a lathe and boring them.
> 
> Vlad[/QUOTE
> 
> ...


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## Fabrickator (Nov 12, 2014)

When I used to bore Harley cylinders we had a Van Norman on a 2" thick, steel surface ground table and they were mounted from the bottom. HSS tool, we took 2 X .004" pass and then a .002" pass for a .010" over piston.  We honed the remainder to .0005 - .001" loose fit/dry.

I was taught by an old Tennessee guy that had been working on Harley's all his life.  He would hone it until you could slide the piston in the bore WITH a .002" X 12" long feeler gauge on one side/dry and pull the feeler gauge out with a slight bit of drag.

An old timer instructor chuckled, agreed it works, and told me to measure them when I went for Harley Factory Training in 1979 in Milwaukee.  :lmao:

That said, if I was restoring an old '26 Douglas, I wouldn't use my home shop equipment (or a mill/drill) and have them done professionally.  Too valuable to screw it up and I have over 35 years of motorcycle, racing engine and machining under my belt.

Rick


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## f350ca (Nov 12, 2014)

I had good results boring a Wisconsin cylinder on the lathe, forget the depth of the bore, 6 or 7 inches, more than I had stroke on the quill of the mill and didn't want to crank the table up and down. Ended up with a good finish and couldn't measure any taper with a dial bore gauge.




Greg


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## shuswapkev (Nov 16, 2014)

thanks heaps for all the advice...
 sounds like my machines and cutters are not up to the task....always wanted to buy  BIGGER
looking back most of the trouble was when my cutter hit the rust pits and that started the chatter which just got bigger
obviously a wiggle boring bar

I have done single cylinders in my lathe with good results...made a 2 inch dia boring bar..but these cylinders were open at both ends...the dougy head is cast with the cylinder
need a monster of a lathe to fix it in

the engine rebuilder wasn't real keen on boring these for me...may have to go back and try again...

what I may try is bracing my boring bar...a collar about 3/4 around the business end of the bar and another plate against the lower face of the boring bar with braces reaching up to the flat lower face of my boring head...which is about a 4 inch dia...with maybe some screws to push against the bottom of the boring head provide a bit of pressure...??  if that doesn't give me a good result straight away...in the truck they go...

and again...I certainly appreciated the advice


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## Wreck™Wreck (Nov 16, 2014)

Rigid hone after boring in mill or lathe.


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## crazypj (Oct 1, 2017)

Douglas cylinders will need a special fixture no matter how you bore them.
I would probably use lathe and fabricate an oversize boring bar just slightly longer than you need then bore in lathe. Are there screw in plugs to access valves? (I'm assuming it's a side valve engine)
 A good rigid hone will fix pretty much all problems with surface finish but a good one isn't cheap plus you need a high torque drill to turn it (I've been using a 400 rpm Harbor Freight 1/2" for a few years now, not used more than a few times a year though)
Using drill to turn hone gives way more control to correct any out of round or taper as you can feel tight spots.


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## TORQUIN (Oct 9, 2017)

Did you clean the bore with acid first? I have been told that if not, when your tool hits aluminum embedded in the cylinder walls it will damage the tool and mess up the rest of the bore being cut.

Chris


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## crazypj (Oct 9, 2017)

I've heard of muriatic acid being used to clean aluminium off cylinders but never met anyone who has actually done it if re-boring. If build up is thick enough it's quicker and easier to scrape or chisel it off. Basically, get rid of the worst ten set up and bore. 
I've also heard a lot of theories about setting up for boring, majority are wrong for various reasons even though they work.


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## rgray (Oct 9, 2017)

shuswapkev said:


> the engine rebuilder wasn't real keen on boring these for me...may have to go back and try again...



I'm not familiar with a douglas cylinder but one thing to consider is that the boring won't have to go all the way to the head surface. It will require an offset tool. I thought I had a larger offset tool but the only one I can find gets the cutting edge about .115 from the bottom of my boring bar. 
Measurements of how high the piston travels in the cylinder and the height of the top ring will give an idea if that would do the job or not.
Ideally a cutter that protrudes below the boring bar would make the machinist feel safer doing this job. Cuttings piling up in the bottom can be a concern also if there is nowhere for them to go.
My pictured boring bar is an S model that has suction for chip evac but the shroud for the cutter to make this work well would not fit the extended offset cutter. The suction would still exac a percentage of chips but not as many.


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## crazypj (Oct 15, 2017)

Doh, only just checked original post date - 2014 
t would probably have mounted cylinders on a 'custom' angle plate bolted to cross slide.  You can flycut with tool in chuck (or on faceplate) to make sure it's 'square' then mount cylinder to it with large diameter boring bar in chuck One thing I found when boring motorcycle cylinders, sometimes you have to 'spin' much slower witha feed around 0.004"/rev. Lot of toolbits required extra clearancing as well.


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