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View Full Version : Is there a way I can Bore my Skidoo/Rotax Cylinder with my Lathe/Mill?



Armilite
03-08-2015, 01:18 AM
I have a Grizzly 12" x 37" lathe, and their G1006 Large Bench Mill.

I have a Skidoo/Rotax 277(72mm x 66mm) 268.8cc, 26hp at 6250rpms, 28hp at 6400rpms, Single with a 11.8cr. I want to Big Bore it to (84mm x 66mm) 365.9cc. Skidoo built a Single for Racing with those 84mm Spec's. The biggest production Skidoo Single made was (78mm x 70mm) 334.6cc, called a 335/340.

My goal is to make 50-55hp at 6400rpms max. Using a retrofitted Dual Plug MotorCycle Head, with CDI, stock 11.8cr, with mild porting, and a Tuned Pipe for the CC used. Using all the different Engine Coatings to fight Heat, Corrosin, Friction.

I need the PTO Taper of the 277/277UL Crank for a Rotax Gear Drive. Older Singles used a straight PTO shaft, and don't work in a 277 Case. A Belt Drive could be used with them others as an option. A (84mm x 70mm) 388.0cc.

All Skidoo/Rotax Singles, used a (4) Bolt Head/Cylinder Bolt Pattern based on a 100mm Bolt Circle(BC) as does the 503F(72mm x 61mm) 496.9cc twin, and the 550F(76mm x 61mm) 553.6cc twin, also use the same Head/Cylinder Bolt Pattern. I know of a 550F being Big bored to a (81mm x 61mm) 628.9cc.

My question is: Is there and attachment/fixture to Bore a 2 Stroke Cylinder on my lathe/Mill, with a HD Boring Bar? The Mill does not have a Power downfeed, the table does have a power cross feed.

How Heavy of Boring Bar would be needed? I don't have one now. I have maybe 10+ Cylinders to Bore right now. Some just need a standard bore job .020", 040", some I want to Big Bore with a Custom Sleeve, and need to Bore the Aluminium Housing for the Bigger OD Sleeve first. All the Strokes are between 61mm and 70mm.

Some Sleeve Info http:

//www.advancedsleeve.com/Documents/Snow%20Catalog.pdf

from Advance Sleeve, some Sleeve OD Spec's.
72mm OD 3.077"
76mm OD 3.275"
78mm OD 3.350"
81mm OD 3.391"
82mm OD 3.430"
83mm OD 3.530"
84mm OD 3.530"
85mm OD 3.605"
86mm OD 3.585"

(84mm)3.530 - (72mm)3.077 = .453" difference, the Aluminium Shell needs Bored for the bigger 84mm Sleeve.

All standard Sleeves can be Bored 2mm over size. You need a minium 2mm wall thickness.

Rich

Armilite
03-08-2015, 01:29 AM
If you don't care about an overbore option, you could use the 82mm Sleeve, and bore it to 84mm.

Armilite
03-08-2015, 01:43 AM
Dual Plug Head will look like this. This is a 14.5cr Race head, I want to use stock 11.8cr.

http://i1234.photobucket.com/albums/ff405/Armilite/Aermacchi%20Dual%20Plug%20motorcycle%20head%20-%201.jpg (http://s1234.photobucket.com/user/Armilite/media/Aermacchi%20Dual%20Plug%20motorcycle%20head%20-%201.jpg.html)

Armilite
03-08-2015, 01:47 AM
Head before conversion.
http://i1234.photobucket.com/albums/ff405/Armilite/MY%20AERMACCCHI%20-%202.jpg (http://s1234.photobucket.com/user/Armilite/media/MY%20AERMACCCHI%20-%202.jpg.html)

http://i1234.photobucket.com/albums/ff405/Armilite/MY%20AERMACCCHI%20-%203.jpg (http://s1234.photobucket.com/user/Armilite/media/MY%20AERMACCCHI%20-%203.jpg.html)

Yow Ling
03-08-2015, 03:45 AM
http://i975.photobucket.com/albums/ae234/YowLingRacing/P1000865.jpg (http://s975.photobucket.com/user/YowLingRacing/media/P1000865.jpg.html)

yes you can bore the cylinders on a lathe.
all you need is a bit of aluminium with a hole in it thats deeper than the spigot of the cylinder, chuck it up in a 4 jaw, use biggest boring tool you have and make sure you leave enough material to hone to final size.

its just a hole

Armilite
03-08-2015, 05:16 AM
http://i975.photobucket.com/albums/ae234/YowLingRacing/P1000865.jpg (http://s975.photobucket.com/user/YowLingRacing/media/P1000865.jpg.html)

yes you can bore the cylinders on a lathe.
all you need is a bit of aluminium with a hole in it thats deeper than the spigot of the cylinder, chuck it up in a 4 jaw, use biggest boring tool you have and make sure you leave enough material to hone to final size.

its just a hole
================================================
Thanks Yow! I have thought of using a Car disc brake rotor. Just bore center hole bigger, and add bolt pattern. Is there a certain size boring bar that you reccomend. I don't have any boring bars yet.

http://i1234.photobucket.com/albums/ff405/Armilite/DISC%20BRAKE%20ROTOR%202.jpg (http://s1234.photobucket.com/user/Armilite/media/DISC%20BRAKE%20ROTOR%202.jpg.html)

http://i1234.photobucket.com/albums/ff405/Armilite/DISC%20BRAKE%20ROTOR%201.jpg (http://s1234.photobucket.com/user/Armilite/media/DISC%20BRAKE%20ROTOR%201.jpg.html)

Yow Ling
03-08-2015, 05:43 AM
That would work, you could bolt it to the faceplate.
I dont have any flash boring bars just secondhand ones I pick up, mine have HSS cutters and work fine, I have one which is about 3/4"
the skinnier they are the less the cut you an take, you arent taking much material out.
practice on an old barrel that you are going to resleeve. A bore gauge is pretty handy to have for doing this stuff

CCWKen
03-08-2015, 11:04 AM
Yeah, use the largest boring bar you can fit to your lathe. Or, use a boring head in the tail stock. One thing for sure though; make sure the piece is dialed in and your lathe is cutting true--Make a test bar. You don't want the bore going off at an angle or funnel shaped.

Ditto on the bore gauge.

You won't have 11.8 CR with a bored cylinder and stock head. The CR will go up unless the chamber is modified or you use a different piston with less pop-up. But that's why people usually bore engines. It's about the cheapest way to gain HP by a higher compression ratio with all other things being equal.

Rich Carlstedt
03-08-2015, 11:30 AM
Rich
I am not knowledgeable about your engine, but if it is small enough in OD, you may want to consider mounting it on the Lathe cross-slide
and mounting a heavy boring bar between the headstock spindle and the tailstock . This boring bar could be 2 inches in diameter and 24 inches long with a adjustable toolbit in the middle. Consider removing the cross-slide and tool-slide and mounting a angleplate to the carriage. Use the wings of the carriage as well for stability . Clamp the angle plate so it cannot move ..except with carriage feed right/left
Mount a boring bar in your 4 jaw, and precisely bore the angle plate to accept the cylinder pilot diameter. Hand drill the 4 mounting holes.
Not you can mount the ten cylinders, one at a time , and then bore them with the heavy bar. All will be the same size, and the only movement is the carriage feed right to left.
What you have done is made your lathe into a horizontal boring mill of sorts.

Rich

PS
This method eliminates the variability you get with boring tools mounted in a moving cross-slide ..that can change the bore size in each setup.
It also eliminates repeated adjusting of the 4 jaw holding each cylinder in sequence . The first ,or final setting in the bar is maintained throughout the operation.
The big question is if the cylinder is small enough in OD to fit on the cross-slide ways (slides removed)

Ironwoodsmith
03-08-2015, 12:08 PM
How do you know you can bore that cylinder 12 mm? The factory big bore may be a different casting. Seems like a lot to remove.

justanengineer
03-08-2015, 03:13 PM
Boring the cylinder is the cheap and easy part here. Youre still going to need to inspect for ovality and cylindricity afterward, maybe hone, and rebalance the rotating assembly. JMO but DIY'ing the bottom end of any engine that youre going to be racing or pushing hard regularly is quite literally burning dollars to save pennies. Good honing and balancing machines along with experienced operators are worth their weight in gold bc they'll get you more power and longevity than otherwise possible for the ~$200 locally I'd guess it'd cost.

shawnspeed
03-08-2015, 04:10 PM
yes you can...a boring head in your mill will work , as will the lathe . Both need proper set ups to to do them well.you can also go this route...http://www.cylinderheadsupply.com/kl4950.html Portable AN style hone from sunnen...you are going to need one to finish hone with any how...and with the coarse stones they will rough out a cylinder in a hurry...they wont fix a crooked bore, or open up a cylinder for a liner, but for going .010 over they are way faster than the bore hone method.I can put the coarse stones in and do 10 to 20 strokes, and then go to my finish stones and bring it home...Just been my experience..Shawn

A.K. Boomer
03-08-2015, 07:15 PM
Your speeds are your biggest concerns as you can do set-ups for either ---

if it's a toss up with the tooling you have then choose the machine with the lowest of speed, you may be very thankful you did esp. on a two stroke bore with interrupted cuts, you just might have to dial it way down just to avoid bore destroying chatter....

thaiguzzi
03-09-2015, 12:37 AM
When i had my shop, one of the common jobs we had was boring out the jugs on 883 HD Sportsters to 1200. That's a half inch of difference! Obviously an iron bore in an alloy cylinder. We had the genuine torque plates, cylinder torqued correctly, dialed in to within a thou, and bored on a fixture on a 12" swing 60's Colchester Student. Left 0.003-4" for the engine recon shop to hone out and put the correct cross hatch on. Simples.

Black_Moons
03-09-2015, 04:38 AM
Some places will bore cylinders for as cheap as $60 to amazing tolerances as they have dedicated boring bars and all the mounting plates ready. Do you really wanna mess with it for so little money saved?

iMisspell
03-09-2015, 07:31 PM
Your adjustable wrench hanging on the shadow board is in the wrong place :p
Thanks for the pic, hope to remember this set up down the line.


http://i975.photobucket.com/albums/ae234/YowLingRacing/P1000865.jpg

flylo
03-09-2015, 10:06 PM
What's this going in a Citation or a TNT? I've owned/raced/flew Rotaxes for 40 years from racing CanAms to sleds to ultralights. IMHO if you want to keep doing these , great get set up right. If only one pay the $50 or so & get it done by a boring shop. Last one I had done was $40 but it's been 5 years & that's all this shop did. BTW don't toss any 277s, 377s or 447s as the ultralight market still needs them. IMHO the 503 is the best air cooled Rotax made. Geardrives on Rotaxes A,B,C or E boxes. We also used a lot of 44o Kawasakis with the diaganal fins on the heads using belt drives, very reliable many flew 1000+ hours, where Rotax recomended 300 hour TBO.

Armilite
05-25-2015, 05:16 AM
How do you know you can bore that cylinder 12 mm? The factory big bore may be a different casting. Seems like a lot to remove.
================================================== =====
Yes, I assume they used the stock cylinder. Most Racing back then you had to use stock parts. The 550F has the same Head/Cylinder Bolt Pattern, hence same material, and I know it has been Big Bored to 81mm. Finding a Piston is more of a problem. The guy who did that Big bore used a Arctic Cat piston.

Armilite
05-25-2015, 05:22 AM
What's this going in a Citation or a TNT? I've owned/raced/flew Rotaxes for 40 years from racing CanAms to sleds to ultralights. IMHO if you want to keep doing these , great get set up right. If only one pay the $50 or so & get it done by a boring shop. Last one I had done was $40 but it's been 5 years & that's all this shop did. BTW don't toss any 277s, 377s or 447s as the ultralight market still needs them. IMHO the 503 is the best air cooled Rotax made. Geardrives on Rotaxes A,B,C or E boxes. We also used a lot of 44o Kawasakis with the diaganal fins on the heads using belt drives, very reliable many flew 1000+ hours, where Rotax recomended 300 hour TBO.
================================================== =========
Actually I want to put it on a T-Bird I Airplane. There all good if built, and maintained right. That's some of the stuff I'm working on. Making them make more HP, and be more durable, using all the different engine coatings, Viton High temp Seals, Ceramic Bearings, Synthetic Oils, etc.

EddyCurr
05-25-2015, 10:05 AM
Finding a Piston is more of a problem. The guy who did that Big bore used a Arctic Cat piston.A piston might be LESS of a problem now than back in the day.

In the unlikely event you are not already familiar with
Wiseco, here is a link to their 2015 catalog (http://www.wiseco.com/Catalogs/Powersports/CompleteCatalog.pdf). 148 pgs, and
that is just one aftermarketer's off-the-shelf offerings.

Should it happen that Wiseco, or one of the other AM
vendors does not happen to have a suitable part listed,
a next step is to contact one or more of the firms about
prospects for making a piston to your specs. They'll have
the blanks and the equipment - it will cost less and be
completed sooner than you might imagine. Try THAT
approach way back when.

If one had time, access to catalogs and a warehouse
of pistons to inspect first hand in the old days, more often
than not, it was possible to find a part from another, very
different source that was ideal 'as is' or with mild adaptation.
Might still be feasible today.

Of course, you can also channel Burt Munro, Mickey Thompson
and all the other greats who cast their own pistons ...

smalltime
05-25-2015, 10:20 AM
A mill won't work for this jug, not enough travel.

Use the lathe, if you must do it yourself. 1" dia boring bar minimum, H.S. tool bit. A carbide bit won't handle the interrupted cut. Don't do the boring head in the tailstock thing.

Do the aluminum block thingy as posted above, but have a VERY rigid settup.

Find a Sunnen honing machine, you'll need it.