Boring out a small engine cylinder

[rslaback]

My main hobby is collecting small engine projects and every now and then fixing one. I've always regarded cylinder damage as the line in the sand as to toss or throw but I recently happened upon a snowblower project that was a couple years old and only got half of an oil change before it was fired up to be used again. The piston galled the cylinder so it would need a bore job and an oversized piston.

I have a decent amount of machining experience and access to a Bridgeport and a 90 degree mount plate. I'm thinking of helping myself to a cheap boring head and giving it a go. Worst case I am out $75 and I learned something.

Any tips and tricks to give a first timer?

 

[The Cobbler]

if it is worth your time, and oversized piston is available & cheap enough, sounds like a good learning experience

 

[txvwnut]

The issue you might run into is tool chatter as you’ll need a tool long enough to reach the bottom of the cylinder due to the quill on the Bridgeport being too large to fit the cylinder bore. Light cuts and slow feed might keep chatter to a minimum.

 

[vwpieces]

Can't help ya on the Bridgeport setup, but I have more than once cleaned up a cylinder wall from a piston seizure. With aluminum to cast Iron the Iron usually wins and most of the galling is aluminum embedded in the walls. Careful sanding of just the aluminum might offer up a pleasant surprise. After that a ball hone and slap it back together.

 

[Firebrick43]

Forget the boring head and get a sunnen style 4 stone engine hone and use in a tank of kerosene sitting on a drill press. Use corse stones to rough out and finer ones to finish the last .005 or so.

I picked up an an-112 for 100$ on eBay several years back.

the more important part is the measuring equipment. Dial bore gauge is the best but quality inside micrometers can be used if you know what your doing.

frequent measuring while honing will tell you if your bored are cylindrical, bell shaped, or barrel shaped.

it’s is absolute hell to get a small engine block set up on a bridge port and aligned with the bore. Especially with angled cylinders.

motorcycles with jugs are not to bad but to hell with every thing else.

 

[MBfreak]

+5 on Firebrick 43.
That will work very wll.

Ola

 

[FMB4]

motorcycles with jugs are not to bad ...

I worked with another Yam mech that used a good 4 stone hone about as often as he did the boring bar. Don't remember him having any problems doing so. This included racing machines. He, of course, used a name brand dial bore gauge (might have been Snap On).

 

[rslaback]

My main concern with destructive honing would be that there is additional material from the piston around the crank skirt. Not sure how I remove that well enough to trust the hone to make a cylinder. It's an aluminum block without a sleeve so I can't just muriatic acid it.

Seems like using a 90 degree plate like this wouldn't make the setup that bad. Am I missing something?

 

[Packard V8]

My main concern with destructive honing would be that there is additional material from the piston around the crank skirt. Not sure how I remove that well enough to trust the hone to make a cylinder.

Seems like using a 90 degree plate like this wouldn't make the setup that bad. Am I missing something?

More info on "additional material"?

X2 - the Bridgeport quill diameter is 3.375"; larger than most small engine bore diameters, so what tooling do you own which will reach the bottom of the cylinder?

Also, just know the block will require honing after boring, so one setup or two?

the more important part is the measuring equipment. Dial bore gauge is the best but quality inside micrometers can be used if you know what your doing.

X2 on dial bore gauge measuring being critical. Disagree inside micrometers are a viable option. Most professional machinists can't repeat the same measurement within a thou twice in a row and a hobby guy will be all over the place. In fact, I've got a like-new Starrett inside mic set I'll let go cheap because it's hardly ever been used in thirty years.

jack vines

 

[rslaback]

More info on "additional material"?

X2 - the Bridgeport quill diameter is 3.375"; larger than most small engine bore diameters, so what tooling do you own which will reach the bottom of the cylinder?

Also, just know the block will require honing after boring, so one setup or two?


X2 on dial bore gauge measuring being critical. Disagree inside micrometers are a viable option. Most professional machinists can't repeat the same measurement within a thou twice in a row and a hobby guy will be all over the place. In fact, I've got a like-new Starrett inside mic set I'll let go cheap because it's hardly ever been used in thirty years.

jack vines

The original owners of the engine failed to put oil back in after an oil change. The engine ran hot causing galling between the piston and the cylinder wall as well as the rod and the journal. The galling in the cylinder has caused the cylinder to now have a gouge in it as well as a ridge where additional material was deposited.

I'm confused by all of the concern that I have seen that the quill won't fit down into the bore. Why would it need to? It looks like boring heads are available that with a vertical or angled bar and the head itself should be longer than I would need. I guess I could potentially run out of stroke on the quill but if that were to happen I would imagine I could just use the knee for the last little bit.

 

[PoorUB]

I agree with the Sunnen hone. I have an AN hone with AN100 and AN500 stones. The AN100's I use for rough boring in cast cylinders and the AN500 stones for aluminum and finish bores in cast.
I had a small engine shop for a few years and bored hundreds of small engine blocks with this set up. I will caution you need a healthy drill to run it. I have a slow speed T-handle Milwaukee drill to run it.

 

[ez-duzit]

...I guess I could potentially run out of stroke on the quill but if that were to happen I would imagine I could just use the knee for the last little bit.

If you decide to proceed with this project, which I believe is a waste of time and money, given that you have neither the tools nor experience to do a workmanlike job of it, use the knee travel (not the quill) for the entire boring operation, if the quill travel is insufficient.

 

[rslaback]

If you decide to proceed with this project, which I believe is a waste of time and money, given that you have neither the tools nor experience to do a workmanlike job of it, use the knee travel (not the quill) for the entire boring operation, if the quill travel is insufficient.

You must be a ton of fun at parties. How exactly is it that you learn new skills?

 

[Firebrick43]

A 4 stone sunnen style hone will make a round bore even with the extra material from the piston transfer. Now you have to do your part to make it cylindrical. To much time in one spot can make it bell mouth at the top or bottom. But even then the sunnen style 4 stone hone is not to prone to this like spring loaded 3 stone hones are.

the main issue with Bridgeport’s is aligning the bore. Guess what, hardly any engine have the bore perpendicular to the mounting faces. And it doesn’t matter to the engine but if to mount the block and center the boring bar at the top it will not be centered at the bottom.

To get top and bottom lined up will require considerable time shimming and sweeping with a long fingered coaxial indicator and you would be done honing by that point.

Engine boring bars are all mounted on the head face in someway.

jugs such as on harleys, lycomings, continentals, and air cooled vehicles/porsches can be done on a mill but most of the time the are done on a sunnen hone in a jig. A sunnen hone FYI is different than a sunnen 4 stone portable hone.

 

[rslaback]

A 4 stone sunnen style hone will make a round bore even with the extra material from the piston transfer. Now you have to do your part to make it cylindrical. To much time in one spot can make it bell mouth at the top or bottom. But even then the sunnen style 4 stone hone is not to prone to this like spring loaded 3 stone hones are.

the main issue with Bridgeport’s is aligning the bore. Guess what, hardly any engine have the bore perpendicular to the mounting faces. And it doesn’t matter to the engine but if to mount the block and center the boring bar at the top it will not be centered at the bottom.

To get top and bottom lined up will require considerable time shimming and sweeping with a long fingered coaxial indicator and you would be done honing by that point.

Engine boring bars are all mounted on the head face in someway.

jugs such as on harleys, lycomings, continentals, and air cooled vehicles/porsches can be done on a mill but most of the time the are done on a sunnen hone in a jig. A sunnen hone FYI is different than a sunnen 4 stone portable hone.

Is the head surface not perpendicular to the cylinder bore? Seems like indicating off the head machining in both the x and y should get you pretty close if they are (and I can't see why they wouldn't/shouldn't be).

 

[Firebrick43]

Is the head surface not perpendicular to the cylinder bore? Seems like indicating off the head machining in both the x and y should get you pretty close if they are (and I can't see why they wouldn't/shouldn't be)

Yes they typically are, but your not mounting to the head face. Again shimming and tweaking. Time and aggravation .

Also forgot, you have to drive x back to the same place after measuring. And then you have to deal with quill diameter and if its an M head lack of quill travel ~3”. J heads and series I and II have 5” which should be enough.

Also sunnen 4 stone hone can be used on a lot of other projects in the future. Vee engines would be insane on and Bridgeport but with a large 1/2 corded slow drill no issue with a 4 stone hone.

But even though you asked for advise and nearly everyone is telling you to not use a Bridgeport, you don’t want to hear it apparently. So use a Bridgeport. It’s your money and time.

 

[theoldwizard1]

So after solving this problem, figure out how to cheaply "sleeve" worn rod bearing journals on small engine. Oversized pistons and rings are usually available. Rods with undersized "big ends" are not !

 

[American Locomotive]

Like others have said, the most important thing first is establishing whether or not oversized pistons are even available for this particular engine.

 

[Firebrick43]

So after solving this problem, figure out how to cheaply "sleeve" worn rod bearing journals on small engine. Oversized pistons and rings are usually available. Rods with undersized "big ends" are not !

Kohler K series can be machined to accept inserts from a N62 continental engine. This engine was in the allis chalmers G. Cleevite 77 and federal mogul bearings are available last I knew, been several years. They were availible at .010, .020, and .030". rod was bolted together and bored and then a groove/notch machined in for the locating tab.

If the crank isn't to bad and can just be polished its typical to just face the rod and cap faces where they bolt together off by .0025" (.005" total) and use a sunnen hone back to nominal or a even a little smaller to match the polished crank.

 

[Packard V8]

They were availible at .010, .020, and .030". rod was bolted together and bored and then a groove/notch machined in for the
locating tab.

FWIW, the locating tab is just there so blind guys can assemble engines. If using an off-brand bearing, just grind off he locating tab - straight from a Clevite engineer.

jack vines

 

[ez-duzit]

FWIW, the locating tab is just there so blind guys can assemble engines. If using an off-brand bearing, just grind off he locating tab - straight from a Clevite engineer.

jack vines

If these are the locating tabs I remember they prevent the bearing inserts from spinning.

 

[theoldwizard1]

Kohler K series can be machined to accept inserts ...

You must be as old as I am talking about Kohler K series !

... then a groove/notch machined in for the locating tab.

You must not have been inside of any of the newer ≤10 HP engines. No rod bearings ! Just aluminum rod on cast iron crank.

If the crank isn't to bad and can just be polished its typical to just face the rod and cap faces where they bolt together off by .0025" (.005" total) and use a sunnen hone back to nominal or a even a little smaller to match the polished crank.

If you face the rod a cap, wouldn't you wind up with an egg shaped hole ?

 

[Firebrick43]

You must be as old as I am talking about Kohler K series !


You must not have been inside of any of the newer ≤10 HP engines. No rod bearings ! Just aluminum rod on cast iron crank.


If you face the rod a cap, wouldn't you wind up with an egg shaped hole ?

um, the kohlers never had rod bearings either. I cant think of a small air cooled lawn/garden engine that did in the last 40-50 years. Putting N62 bearings in is to save the rods (or make them turn 5000 rpm for tractor pulling) and requires boring the rod out.

It may not work on other engines due to dimensions. I have found that most industrial grade engines such as the kawasaki, honda, and briggs vanguard are more durable than a kohler, and by the time they need overhaul its generally cheaper just to toss them and buy another. They also start easier, quieter, and much easier on gas. I really don't miss the old kohlers. Kohler parts have gotten pretty stupid priced of late as well.

Yes facing the rod cap seating surface off does make an egg shape hole. That is why you hone it back circular with a sunnen hone. .005" is about the limit however due to the fact that facing it off only takes so much out of the width compared to the height.

 

[Packard V8]

If these are the locating tabs I remember they prevent the bearing inserts from spinning.

You'd think so but you'd think wrong. The bearing is locked in the rod by compression, not by the tab. Many 21st century engines do not have the locating tabs on the bearings or the notch in the rod; robots don't need them.

jack vines

 

[laser3kw]

here is a youtube video showing just what you are doing
I had a similar procedure when I built 5hp Briggs engines for racing karts.
Ours was a little more sophisticated using dedicated fixtures for aligning the crank axis to the cylinder.
To fast of a spindle speed will cause the upper part of the jug to oscillate and cause chatter. You will actually here it "ring"

 

[engineer2]

Fun project that you can learn a lot from. Raising the compression ratio can wake up those small flatheads.
Even if it doesn't work out, a $120 HF Predator is a drop-in replacement for many snow blower engines.

 

[FMB4]

Well, I'll relate when a Yamaha mechanic I know managed bore a 'last shot' (no larger oversize piston available) MX cylinder on a bar by a bit (har-har) more than several thousands of an inch. Said mechanic walked up the service manager with ruined cyl. in hand. Manager said "so, it's finished huh? (or something to that effect). Mechanic dropped the ruined cyl. into the large steel trash can that sat next the manager's desk. I, the mechanic, then told him that ya, it's 'done'...