Boring Motorcycle Cylinder on a Lathe - How do I do it?

denisj · Dec 8, 2017

HI ALL!!

I am currently setting up my boring bar, but it is much too large for working on small 50-550 cc 2-4 cylinder import stuff like Honda, Marusho, Kawsaki etc.

I have an image in my head of a cylinder block from a BSA or a Honda CB160 mounted on a plate that is attached to the carriage on my lathe.

I would assume from there I would mount the boring bar in the chuck and have it against the tail stock. I think this is the classic method in teh Southbend instruction manual from the turn of the century.

Anyone doing this? I am looking for Ideas and what I can make to adapt this to my lathe.
- My lathe does not have a sufficient swing to spin 2-4 cylinders at a time.

Thank you so much!!

Denis J

AlexO · Dec 8, 2017

denisj said:
HI ALL!!

I am currently setting up my boring bar, but it is much too large for working on small 50-550 cc 2-4 cylinder import stuff like Honda, Marusho, Kawsaki etc.

I have an image in my head of a cylinder block from a BSA or a Honda CB160 mounted on a plate that is attached to the carriage on my lathe.

I would assume from there I would mount the boring bar in the chuck and have it against the tail stock. I think this is the classic method in teh Southbend instruction manual from the turn of the century.

Anyone doing this? I am looking for Ideas and what I can make to adapt this to my lathe.
- My lathe does not have a sufficient swing to spin 2-4 cylinders at a time.

Thank you so much!!

Denis J

If this is a "project" then it's going to be a really tough one. Too many things you need to get dead right and too many places where it can go wrong. They've got specialized machines for that.

muckalee · Dec 8, 2017

You tube video is your friend.

Hodge · Dec 8, 2017

I'm with Alex, not trying to discourage, but real easy to make desk weights or at best cylinders that perform poorly. Sounds like you might be working with hard to come by vintage stuff as well. Aside from getting the bore correct, you have to leave enough for the correct hone job, which is a whole new can of worms. If you Are determined to give it a try I would start with motors that you would not be worried about scrapping. Not just getting it back together and running, but getting higher performance through compression and better ring seal. (I.e. leak down test).

What I've mentioned doesn't even scratch the surface, lots of materiel to read on the subject. This is one Area that a competent shop will put you ahead of the game rebuilding motors.

Good luck, Hodge

Hodge · Dec 8, 2017

Here is a thread from the past with good info.

http://www.practicalmachinist.com/vb/general/who-here-boring-motorcycle-cylinders-139180/

Greg White · Dec 8, 2017

I wouldnt doit, been a cheenist 40 some years, farm it to the pro.
Gw

steve-l · Dec 8, 2017

I have wanted to do this for many years, but after much studying and research decided that it is not viable on conventional lathes and mills. Could it be done?......maybe, but the result would be questionable at best, nor would it be even close to economical in time spent.

Limy Sami · Dec 8, 2017

From hard won experience - singles and some twins can be done by fixing to a face plate - but a boring machine is 100 times easier.

Your lathe hasn't the tee slotted saddle wings etc etc which used to be furnished of lathes of yore for such purposes.

steve45 · Dec 8, 2017

I'm an amateur machinist, for sure. However, I've done a couple of JetSki cylinders on my MILL. I wouldn't think of trying to do it on a lathe, too much mass spinning around. Far too easy for something to come loose and ruin your day.

Doing them on the mill was hard enough for me, and it wasn't without problems. The quill travel was about 1/2" less than the length of they cylinders, so I had to hand crank the table up at the bottom when I reached the end of the travel. Broke a cutting tip halfway through the final cut on the last cylinder.

Send them out!

Joe Miranda · Dec 8, 2017

To answer your question, we bore motorcycle cylinders and I hate to give away a secret - but it is a fairly easy and straightforward procedure. As has been noted, there are things to take into consideration - but it is NOT a difficult procedure.

First off, we make up "torque plates" for whatever cylinder we are going to bore. These are plates that the cylinder bolts to. It takes the place of the c'case and it is an attempt to get the cylinder to "tweak" the same way when you machine it as it does when it is bolted to the c'case.

Hold the torque plate in your 4 jaw and proceed to indicate the cylinder to get it running as true as you can. We like to shoot for no more than .002" TIR. This will take some time. This is one place that the machine shop is typically more accurate than the engine rebuilding shop because the engine rebuilding shop just bolt the stuff down and machine away.

Then you bore to whatever size you are shooting for minus .002-.003". The last .002-.003" is removed with progressively finer hones to arrive at the final size and cross-hatching that is desired.

Measuring the cylinder is the most critical aspect. We like to measure in 4 "clockings" at 4 or more different depths. This way we can verify roundness and cylindricity.

And there you have it. My suggestion is to get yourself a couple of practice cylinders before you have a go at it just to make sure you develop a good and reliable technique before you hang a tile out front that says you're open for business.

john.k · Dec 8, 2017

South Bend used to make a fixture for a 16" lathe that was big enough to bore a T Ford block.The block is mounted on a fixture at the end of the bed,and the boring bar run through via the saddle feed.

sticks · Dec 8, 2017

A few things, right away. Be sure your spindle rpm and 'Z' feed are ideal for the size you bore. Unbolt as much as you can from the saddle to make room for your fixture. Use existing holes vs drilling-tapping any more than you have to. Can you make a fixture so that you can easily bolt different torque plates to a common base?

Your lathe appears to have enough swing for most bike jugs, and the torque plate is a must! I second that you practice on expendable or 'pre-scrapped' parts. IMO, anchoring the workpiece parallel to spindle and picking up center will be enough 'fun' that doing this once should tell you if it was a good idea. Good luck.

eKretz · Dec 8, 2017

Just wanted to add: if attempting this you should have two fixturing plates, not just one. One at the base of the cylinder and one where the head would normally go. This does the best job of replicating the "pinch" condition that the cylinder is in when it's actually installed on the engine. Make them out of fairly thick plate and with holes through slightly larger than the finished bore.

Erich · Dec 8, 2017

People are missing an important piece of info in the post one.
He wants to bore 4 cylinder barrels that are to large to SWING in the lathe.
He has to mount the barrel on the carriage and mount the boring bar between centers.
The challenges are getting each hole centered to the axis of the lathe and micro adjusting the cutter diameter.

There are a multitude of better ways to earn your crust of bread than this job.

Joe Miranda · Dec 8, 2017

eKretz said:
Just wanted to add: if attempting this you should have two fixturing plates, not just one. One at the base of the cylinder and one where the head would normally go. This does the best job of replicating the "pinch" condition that the cylinder is in when it's actually installed on the engine. Make them out of fairly thick plate and with holes through slightly larger than the finished bore.

Using two is preferable in reproducing the "pinch" as closely as possible. We never do. I think the added length of everything offsets the value. Most places don't use two.

As far as 2/4 cylinders, sure - you need to make up a fixture to mount on your carriage. Make sure you get the center height correct because there is no correcting for that. I would "snug" my bolts up and then use the clearance of the bolts to the holes to tap it around to indicate it in.

Jim Williams · Dec 8, 2017

I have an engine shop owner friend who does a lot of motorcycle engine work. He has a boring bar with attachments that permits him to do very small engine bores. He does most of the mc engine work within a fifty mile radius of his shop. Find a specialist like him and you would have no concerns.

AlfaGTA · Dec 8, 2017

Berco AC650-M with the appropriate boring spindle...Bores of 55 mm and up easily done( i regularly do 60mm bores with mine). Better finish and setup in 1/10th the time.
Auto stops so you can be running another job while the bore is being finished.....Its like getting 2 for one.....Flat bed design is easily use able on MC work...

Doing what you propose on that machine is perhaps the hardest least efficient route to go.....Loose single barrels, maybe, but twins and 4's its going to be a dead looser.
Unless this is a hobby or your have no work and this is your only potential revenue stream, go another route....
Cheers Ross

L Vanice · Dec 8, 2017

"Anyone doing this? I am looking for Ideas and what I can make to adapt this to my lathe.
- My lathe does not have a sufficient swing to spin 2-4 cylinders at a time."

Getting back to the question, I did this kind of job three times on a 12 x 36 lathe back in the 1970's. I made two devices. The first was a large used T-slotted faceplate that I modified to replace the compound slide. It attached to the original cross slide using the same mounting method as the compound. I had a locking screw to bear on the cross slide gib so there was no motion there. It worked OK, but I was not happy with the rigidity of the face plate mounting. Next, I bought a new long cross slide top for a Myford Super 7 lathe. It had several T-slots, because line boring on lathe carriages is a common job on the Myford and other lathes. As it happened, the Myford dovetail was a near fit on the carriage of my bigger lathe, just requiring a new gib. I attached a new feed nut to the bottom of the Myford slide and then had a proper horizontal boring machine with power feed, but no vertical feed. Vertical position was adjusted with shims. I made boring bars from long 3MT drill extensions, providing screw adjusters behind the cutters to control the bore diameter. The results were excellent. I have not had to do another job of that sort since 1979, and that lathe is long gone, but I still have the boring bars..

Larry

steve45 · Dec 8, 2017

Erich said:
People are missing an important piece of info in the post one.
He wants to bore 4 cylinder barrels that are to large to SWING in the lathe.
He has to mount the barrel on the carriage and mount the boring bar between centers.
The challenges are getting each hole centered to the axis of the lathe and micro adjusting the cutter diameter.

There are a multitude of better ways to earn your crust of bread than this job.

Silly me! Someday I'll slow down and read more carefully. You're right.

I spent half a day making a 1/2" thick base plate to bolt my cylinders to, but lost my desire to ever bore engine cylinders again!

John Garner · Dec 8, 2017

Don't know enough about multi-cylinder motorcycle engines to comment, but forty-some years ago I bored a whole bunch of air-cooled automotive cylinders on a lathe. Didn't matter that the engine was most often a four-banger, and every once in a while, a six-banger, as all of the cylinders were in their own castings.

The key to the job was in 1) dedicated fixturing to hold the cylinder, and 2) using the biggest boring bar that would fit into the cylinder, held just long enough to get the toolbit all the way through the casting.

The usual setup was to mount the cylinder to the lathe spindle, with the boring bar on the carriage cross-slide (NOT on the compound), but the boss had the snout-nose boring bar and carriage-mounted block-holding fixture to handle multi-cylinder castings.

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