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Motorcycle cylinder boring: Bridgeport vs Lathe?

Maschine

Aluminum
Joined
Dec 16, 2011
Location
Maryland
I've spent the last few years outfitting my home shop with first a nice Bridgeport and then a nice Acer 1440G lathe. I'm a real amateur though, not very proficient at using either one (yet). In fact, I don't even have the lathe powered yet (working on an RPC for it, while the Bridgeport is powered by a VFD).

Anway, I'm into rebuilding old motorcycles and soon will have a need to rebore a coupla jugs for an old 2 stroke (about 2.5" bore). I've done some reading on it and I was surprised to hear quite a few people downing on the Bridgeport's ability to do this job with reliable accuracy and without chatter. I would think it would be the cat's meow for a job like that? And then it seemed several people sang the praises of using a lathe and how it's much more accurate and rigid for that sort of job. So now that I have a nice size lathe that weighs over a ton, I'm thinking maybe I can build a simple fixture to bolt the cylinder (using its own mounting holes) to an adapter mounted to my lathe's face plate. Then get a rigid boring bar setup and bore the cylinders that way.

I'm not doing this to make a living, nor do I mind a lengthy setup time. Just would seem a shame to have bought all these fancy machines and not actually use them for something useful like this. I know I can outsource the job as I have in the past. But if I could develop a sense of confidence I could do this job, I might go for it. Especially if I find some old junk cylinders to practice on first.

Also, I have an old AMMCO hone, which I believe is similar to the Sunnen.

Any and all comments welcome.
 
yes pratice , the cost of messing up not worth it , you can do them with the hone alone roughing then finishing . 2 strokes can pose problems with hone alone do to missing material on the sides were transfer port and the tails are not , they do not support the hone and the lack of material will cause hone to cut over size below the ports on the sides this does not seem to afect thing much as it is not thrust face . A Ammco is no the quality of a Sunnen , for the sunnen often key way stones are availible having twice as many supports and stones so the do no mind the ports .
 
I've spent the last few years outfitting my home shop with first a nice Bridgeport and then a nice Acer 1440G lathe. I'm a real amateur though, not very proficient at using either one (yet). In fact, I don't even have the lathe powered yet (working on an RPC for it, while the Bridgeport is powered by a VFD).

Anway, I'm into rebuilding old motorcycles and soon will have a need to rebore a coupla jugs for an old 2 stroke (about 2.5" bore). I've done some reading on it and I was surprised to hear quite a few people downing on the Bridgeport's ability to do this job with reliable accuracy and without chatter. I would think it would be the cat's meow for a job like that? And then it seemed several people sang the praises of using a lathe and how it's much more accurate and rigid for that sort of job. So now that I have a nice size lathe that weighs over a ton, I'm thinking maybe I can build a simple fixture to bolt the cylinder (using its own mounting holes) to an adapter mounted to my lathe's face plate. Then get a rigid boring bar setup and bore the cylinders that way.

I'm not doing this to make a living, nor do I mind a lengthy setup time. Just would seem a shame to have bought all these fancy machines and not actually use them for something useful like this. I know I can outsource the job as I have in the past. But if I could develop a sense of confidence I could do this job, I might go for it. Especially if I find some old junk cylinders to practice on first.

Also, I have an old AMMCO hone, which I believe is similar to the Sunnen.

Any and all comments welcome.

Issue is that the way you are planning it, either one is holding the boring tooling from only one end. A horizontal mill could support it at the off end as well as at the spindle, but you don't have one.

I can put a 2" bar I have into that 2.5" bore with a 10EE or Cazeneuve lathe with far better rigidity than I can put ANYTHING onto an R8 collet or R8 milling-cutter holder.

There's your first limitation on the BirdPort.

Then cometh lack of significant rigidity back of that R8 - notoriously challenged, especially if the head can tilt as well as swivel.

That doesn't rule-out using the mill. Your faceplate fixturing has to be damned good, too lest it bring more problem than solution.
 
Lathe every time, ......and it's no where near as complicated as the mountains of bullshit posted all over the web, including this site will have you believe.
 
Thanks. It sounds like supporting the other side of the boring bar is the key for max rigidity. My lathe has a 1-9/16" hole through the spindle. Would it be possible (or advisable) to fabricate a holder for a bronze bushing that can set within a custom built taper that sits in the spindle's flared opening where the chuck (or faceplate) is? Since the spindle bore is 1-9/16" I could probably pretty easily fit a bushing in the tapered spindle insert with a 1" bore through it. Then I would have a rigid and precise support for the boring bar that actually would allow the boring bar to penetrate fully supported into the spindle as it moved through the bore.

Does that make any kind of sense or sound like a reasonable idea?
 
I have used a lathe a number of times for Vincent HRD 500cc made a jig out of aluminum turn a good size chunk turn a shoulder to go in chuck then face turn a counterbore same as cylinder bore then transfer bolt pattern you can do on mill


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Thanks. It sounds like supporting the other side of the boring bar is the key for max rigidity. My lathe has a 1-9/16" hole through the spindle. Would it be possible (or advisable) to fabricate a holder for a bronze bushing that can set within a custom built taper that sits in the spindle's flared opening where the chuck (or faceplate) is? Since the spindle bore is 1-9/16" I could probably pretty easily fit a bushing in the tapered spindle insert with a 1" bore through it. Then I would have a rigid and precise support for the boring bar that actually would allow the boring bar to penetrate fully supported into the spindle as it moved through the bore.

Does that make any kind of sense or sound like a reasonable idea?

Backwards is all. Look up "lathe as boring mill".

What you fab is a means of mounting the jug to the carriage. Bar is driven at the HS, supported at the TS. Jug is traversed along it.

PITA. You should be able to JF single-side this one.
 
Like the others said, I can't imagine a B'port approaching a lathe for this sort of job...with either tool that's assuming you are using it properly. If nothing else, the mill would be much tougher to set up.
 
Backwards is all. Look up "lathe as boring mill". What you fab is a means of mounting the jug to the carriage. Bar is driven at the HS, supported at the TS. Jug is traversed along it.

I've seen a few videos online where people seems to mount the cylinder on the chuck and bore it that way. But I'm sure it can be done the way you describe too. Question is, which way is best?

 
Keep in mind as well that the BP does not have enough quill travel to do anything but the smallest engines. If you are not going to get a proper cylinder boring bar the next best thing is a horizontal milling machine. Lots of them around for 500-1000.00 Many have power feed on the Y axis.
 
Thanks. It sounds like supporting the other side of the boring bar is the key for max rigidity. My lathe has a 1-9/16" hole through the spindle. Would it be possible (or advisable) to fabricate a holder for a bronze bushing that can set within a custom built taper that sits in the spindle's flared opening where the chuck (or faceplate) is? Since the spindle bore is 1-9/16" I could probably pretty easily fit a bushing in the tapered spindle insert with a 1" bore through it. Then I would have a rigid and precise support for the boring bar that actually would allow the boring bar to penetrate fully supported into the spindle as it moved through the bore.

Does that make any kind of sense or sound like a reasonable idea?

You mean a piloted boring bar, ......I wouldn't bother, they're a pig to set up on engine lathes - turrets can be bad enough - just make up a big ass boring bar say 2'' dia, with a slot in the end for a carbide lathe tool - brazed are more than enough, for maximum rigidity - take off the compound slide and pack up to height n clamp to the cross slide.

TAKE IT VERY EASY.....shut the speed right down on that size lathe under 50's better than over make sure the cutter is not rubbing, say 0.004 / rev minimum feed, ............... cut your way in, then cut your way back out without touching the cross slide, which takes out any spring and reduces taper .....you're probably looking at a max 0.010'' DOC, .and if the cutter is correctly ground you will have no trouble crossing the ports

As you say, a few scrappers to practice on and you'll soon have the job sorted
 
I've seen a few videos online where people seems to mount the cylinder on the chuck and bore it that way. But I'm sure it can be done the way you describe too. Question is, which way is best?

Legacy "best" is to put it on one of my milling machines. Burke Horizontal. USMT Quartet's horizontal spindle.

By preference, I'd put a vanilla, rented, field-portable piloted boring rig into the drillpress. Faster that way. Might not be an option if your drillpress weighs less that 4400 lbs, Avoir, though.

In real life? I'd send it out.

Average 2-stroke motorbike dasn't have as many jugs as a Wasp Major (28) nor a Napier Sabre (24), so who needs to tool-up for a career at it?
 
I didn’t notice what type of cylinders you expect to work on but the two strokes I’ve worked on all have iron liners in aluminum. If that is what you have you heat the aluminum, drop the liner out, bore it in a lathe, do your porting etc. and put the liner back in - then hone to size with a Sunnen Y-72 mandrel (for your 2.5 dia)
What is the purpose of boring in the first place? Most of the time very little needs to be removed to go to the next piston size and that’s a job for a good hone not boring.
 
By the way, what 2 stroke bikes do you have?
I have Bultacos that I’ve registered for the street, women and children run for cover when they hear me coming.
 
As others say above, boring motorcycle cylinders on a lathe can certainly be done. There are some videos on this on You Tube. That said, it's important to have torque plates for the cylinder that are bolted in place to simulate the stresses that are encountered when they are installed. A lathe would be far superior to a BP or similar mill, IMHO.
 
I didn’t notice what type of cylinders you expect to work on but the two strokes I’ve worked on all have iron liners in aluminum. If that is what you have you heat the aluminum, drop the liner out, bore it in a lathe, do your porting etc. and put the liner back in - then hone to size with a Sunnen Y-72 mandrel (for your 2.5 dia)
What is the purpose of boring in the first place? Most of the time very little needs to be removed to go to the next piston size and that’s a job for a good hone not boring.
Modern 2-strokes have plated cylinders, probably from the 80’s.
Not sure why you would take out a liner, work on it and then put it back in again. Most everybody would do the work on the liner and barrel at the same time.

The next oversize piston would typically be .5mm, it would be tedious to try and hone all that material, much faster to bore and then finish hone the bore.
 
Racing Kart engines were .1mm each size and the reason for removing the liner was to do your porting and matching, I did 100’s of them in the 70s but I don’t think it’s allowed in most racing classes now.
 
Full disclosure: I read the first 2 sentences only . Lathe any day of the week. Make a fixture, mount cyl dead-nuts square abd w/near 0 TIR and have at it. Agree w/Limy, voodoo need not apply.
 








 
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