what does case machining in order to fit a big bore kit imply with an atv?

Question

i have a 300ex that needs case machining to fit a big bore cylinder i bought, what all does this case machining entitle? i know the goal is to accomodate a sleeve with a larger O.D. but does this have to be done professionally or can it be done with a dremel or such as long as one is careful and doesnt get any metal shavings into the bottom end of the motor?

Answer 1

Your question about case clearancing to accomodate the larger cylinder sleeve diameter of a Big Bore kit seems to have mistaken as regarding some other operation.

Not only CAN it be done by hand,but on engines where it's Practical to do so it's the method of choice.

A trx 300 is definitely in the "practical" category.

As far as any matter of "Precision".......
It's a Big,Gaping SQUARE Maw of a hole,,,lol

How Precise is "Putting a round Peg into a square hole" EVER going to be?

They only have radial clearance arcs cut into each side of the square to accept the round cylinder liner.

They're only a few degrees of arc,,,,just a small "piece" of a circle.

What's even easier,,is that they're SHALLOW,,,crancase deck is fairly thin in those areas.
So no need to cut very DEEP into case.

The One tight spot is on the REAR of the case,,,because it's clearance cut runs full depth and blends into what becomes Crankshaft Baffle.

As Daunting as that appears,,,it does NOT require a Full Depth cut.
Only deep enough so that Cyl Sleeve doesnt shoulder/bottom out on Crankcase.

Most all Big Bore Kits are made with SHORTER sleeves,,,so that they can be used with Stroker Kits.
The Shorter Skirt accomodates the Rod Swing of the longer stroke.

One thing,,,You CANT use a Dremel.
Too Small,note nough power,,,
It will most likely be destroyed before job is completed.

Any decent 1/4" 5~7A++ Hand Grinder will do it easily

..................................................
You NEED the power and RPM of a REAL grinder.

Air powered die grinders are CHEAP,,,if you have access to an air compressor with the capacity to run it.

Electric Die Grinders are Big,Heavy,Expensive and Ferocious Eaters,,,, which is generally Just the Ticket!

New,Quality ones are waaay too pricey,,,$150~200 +++>>>>

There's a OLD Sears,a Dumore,a couple of Milwaukees,etc on Ebay....they'll all go off over $50 Im sure,,probly More.

Here's some Chinese Crap,,,,"2 for 1",,,for REALLY Stoopid Cheap.
You would likely NEED Both to finish the job,,,lol
What caught my interest is that they are claimed to be 5 Amp tools.
Most similar junk is only around 2A or so.
(Dremel>>less than 1 Amp)

The "Pro Stuff" is 7~10~12 +++amp range.
Just to put various available Power Levels into some sort of perspective.

If you WANNA Risk the $20~30 for a couple of Alledgedly Suitable Die Grinders,,,,,,Having a Pair makes it a worthwile gamble in my opinion.
I 'bleive you'd have decent odds of at least getting the job done.
NO RECCO,,,I'm just passing along what I stumbled upon
while "shopping" to be able to at least give you an idea.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=300146985989&ssPageName=STRK:MEWA:IT&ih=020


Heres other examples of the Type/Class of tool you really need:
"megadremel",,Foot Long,,4~5lb stuff

http://cgi.ebay.com/Milwaukee-5196-Heavy-Duty-11-Amp-2-Die-Grinder_W0QQitemZ140151130348QQcmdZViewItem?hash=item140151130348

http://www.makita.com/menu.php?pg=product_det&tag=906H

http://www.dumorecorp.com/grinder.htm#hg
(#10 type)

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Cutters

Here's some examples from Long Co.
http://www.helongco.com/

My Choices would be from the NF Series:
http://www.helongco.com/nfburs/nfall.html

*Cylindrical NF in SA3 Size for Guided Router or FreeHand work
and
*Taper Radius End NF in SL3 Size>>IF I was gonna FreeHand Grind it,,,,,and IF Rear Cut Access looked to be a Potential Problem at it's extreme end depth.

Depending upon the Actual Situation with the potentially "Tight" REAR CUT,,,,
I Might chose a
Cylindrical Radius End NF .
It will serve same as a Flat end on the Front and Sides,,,
But Leave a Radiused Step on less-than Full Depth cuts,,,rather than a square shoulder.

The extra working clearnce of it's radiused Nose MIGHT be enough to Clear the CRANKSHAFT at extreme depth,,,enough to allow an adequately Deep Cut----if necessary.

Using "cheap" HighSpeedSteel ones from hardware store are a false economy,,,ESPECIALLY with Aluminum.
They WILL work though---even if not very well

.........................................
It's a waste of time to make a router base and guide,,,especially for a 300ex type crankcase.

Easiest,fastest most practical method remains a hand grinder.

..................
.001 to .002 Clearance is PISTON SKIRT -to-CYLINDER WALL range.

You cannot use anything even near that tight for crankcase releif.
Expansion and distortion would "pinch" the liner and cause really odd reliability problems

You need about 10 or 15 TIMES that much.

.020~.030
20 or 30 Thousandths,,,NOT merely 1 or 2.
1/2 to 3/4 MM,,,,Minimum.

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As you stated,,,SHIELDING the bottom end is critical.

Cramming Shop Towels into engine Does NOT constitute effective shielding.

Easy to keep shavings from getting into motor while cutting.
TUFFER to avoid SPILLING them when you go to Remove the packing.

Time/Effort spent doing a neat,clean shielding and some THOUGHT before Removing it is all cheap insurance.

After packing /taping ,etc,,,,Add a couple Layers of single thickness material which can be removes AS a layer.
1st layer gets majority Out,,any spillage goes to Next.
And so on....
Pays to be ANAL
....................................
Real quick and easy to do ,,IF you have a decent grinder.

Nothing "Precision" about clearancing a case,,,nothing whatsoever.

It's merely adding SPACE,,extra room.

The area and surfaces involved are Non Contact,,Non-Functional.

And in any event,,,a 300 ex is a Square Hole.
It only needs the existing clearnace cuts re-radiused a bit.

Try to be workmanlike,of course

But as long as the minimum clearance is achieved,,,Engine dont care if was Cut with a Hammer and Chisel.

Unless it is I who misunderstand what your project is,,,
and You're asking about something OTHER THAN clearancing a crankcase to accept a larger diameter Cylinder Sleeve of a Big Bore Kit.

Answer 2

Atv Big Bore Kits

Answer 3

the cylinder fits down into the cases, they have to be bored out about.001 or .002 larger than the cylinder . you cant do this at home unless you have a Bridgeport type milling machine & know how to make the fixtures & set up the cases with a dial indicator in the cutting head so they are square with the crank pin. you usually have to split the cases & remove the crank or flywheels to get machining clearence.
check with dragonmans.com in colorado or a local automotive machine shop for prices.
it might be possible to make an adjustable cutter that fits over a mandrel bolted to the crank throw in place of the rod but it would be expensive to make & not very precise.

Answer 4

The machining involves cutting ( Boring) the collar of the crank case to allow a larger diameter cylinder to fit down into the crank case.
If the kit has a stroked crank, some require the inside of the case to be ground to make room for the rod(s) to clear.
This is ** Precision** machining and cannot be done "free hand". It requires jigs and specific cutting tools.

Answer 5

It's not the big bore kit that does the damage but the rider In principal the lower end of the engine is designed to cope with the standard cc barrel and adding a bigger barrel kit only enduces the rider to give it a bit more to get the better speed/acceleration out of it and as the lower end is not designed to this higher specification then BANG and that's that Stick to the standard set up and change the bike as money and your test allows

Answer 6

1

Answer 7

your messing with the structure part of the engine when you start shaving metal off the cases - you better leave this one to the pro's - that way if it ends up being trashed - they buy you a new one.

It is not as easy as polishing a swingarm.

Answer 8

it has to be done on a cnc milling machine. tolerances are very very tight and its impossible to do it free-hand. this is a professional area unless u want to wreck an expensive big bore kit. ur money not mine.

Answer 9

The piston is larger then the old one. The head needs to be made bigger (bored out) so the piston can fit. The head needs to be bored as close to round and size as possible.