KX85 to 100?

beerbudget · 03-04-2008

Can a KX85 cylinder be bored to a 100 or 105? I know a KX100 cylinder will work but considering just boring the 85. Also will the head work or will it have to be reworked also?

griffbones · 03-04-2008

Yes the KX85 cylinder can be bored out to the 52.5mm size and then replated. Basically that is what a KX100 cylinder is anyway. In the past many of the top builders preferred to use the KX85 cylinder when doing big bores due to the better exhaust porting on the 85, but the late model KX100 cylinders now have the same exhaust port dimensions so this isn't such a big deal now.
Now to achieve a 103.5cc you will have to install a Hot Rods 2mm longer stroke crankshaft and the 52.5mm piston.
To achieve the 105cc you will need the 52.5mm piston and you will have to have someone stroke a crankshaft for you, as it requires a 48.5mm stroke, and no one is making a pre-made 48.5mm stroke crank for the little KX's. This 105 set-up will require machining of the crankcases for rod clearance, where as the 103.5cc set-up will not require any crankcase mods as the Hot Rods 2mm over crank is a drop in ordeal.

beerbudget · 03-04-2008

How about the head? Will I need a 100 head?

griffbones · 03-04-2008

Quote:

Originally Posted by beerbudget

How about the head? Will I need a 100 head?

You will have to have the head re-cut or buy a KX100 head in order to run the 52.5mm piston. If you have a stroker crankshaft installed, you will have to have a head re-cut not only for the bore size, but for piston clearance and correct squish band too.
Actually Eric Gorr does a big bore kit using the Wiseco KX100 pro lite replacement piston, which is readily available just about anywhere. Eric is very reasonable on his prices and he can do the cylinder boring, port the cylinder how ever you want it done, machine the head, have US Chrome replate the cylinder and supply the top end kit, all for around $400 - $450!

It would cost that much just to get a new KX100 cylinder form Kawi, and then you would still have their **** plating! I have US Chrome replate all of my little Kawi cylinders at the first piston change, because the stock plating is complete crap!

beerbudget · 03-04-2008

Thanks for the info again Griffbones! Just looked at his site. The KX is on the low end of the price range. Nice!

F_27stryker · 03-05-2008

SO what are you deciding to do?

beerbudget · 03-05-2008

Come up with the $$$ and send it in! Looks like the way to go after reading the info on the site.

stevied645 · 03-06-2008

Anyone know who does this kind of work in the uk. ive been thinking about boring mine out to either a 285 or 310, heard that there is no point in going to 310 is this the case??

Sapper69 · 03-06-2008

Don't mean to hijack, But. hey Griff, anyone making a 125 bb kit for the 100?

KickassKX125 · 03-06-2008

310 in a 250. To my mind that would be in the coolant channels without a bb kit.

griffbones · 03-06-2008

I have only heard of making a KX100 into a 105cc, it is basically the same cylinder casting as the KX85. Keep in mind fellas, that when going big bore by that much percentage larger than stock cc's, it normally requires stroking too. You can't make that much of a cc change with boring alone, the cylinders aren't thick enough, and besides that, having a bore that much larger than the stroke would be a crappy running engine anyway. I think they may make an over bore piston for the KX100, if so you might be able to get a little bigger than 105cc but I am not for sure. Another thing to keep in mind is the fact that there is more to making power than just cc's! And a big bore without supporting port work will normally run strong in the low end but fall flat on it's face in the top end. I guess what I am saying is that it is a package deal to do it right.

F_27stryker · 03-07-2008

5cc is not worth it my friend

stevied645 · 03-07-2008

Quote:

Originally Posted by KickassKX125

310 in a 250. To my mind that would be in the coolant channels without a bb kit.

im talking about a bb kit! cant find anyone that does them in the uk

griffbones · 03-07-2008

Quote:

Originally Posted by F_27stryker

5cc is not worth it my friend

That is not really true! It depends upon the model, on some bikes stroking is an enormous improvement, on others it is not, the KX's gain a lot from this proceedure.

griffbones · 03-07-2008

Quote:

Originally Posted by stevied645

im talking about a bb kit! cant find anyone that does them in the uk

Contact Eric Gorr at Forward Motion, Eric ships to the UK.

stevied645 · 03-07-2008

Quote:

Originally Posted by griffbones

Contact Eric Gorr at Forward Motion, Eric ships to the UK.

lol do you know how much a phone call will cost me lol, Ill try get a email addy for him unless you have one Griff?? is it worth goin to 310 or sticking to 285. Im only thinking about this at the moment but i have the cash to do it just need to find out if its worth it or sell my 250 and get a thumper.

griffbones · 03-07-2008

Quote:

Originally Posted by stevied645

lol do you know how much a phone call will cost me lol, Ill try get a email addy for him unless you have one Griff?? is it worth goin to 310 or sticking to 285. Im only thinking about this at the moment but i have the cash to do it just need to find out if its worth it or sell my 250 and get a thumper.

Just go to Eric's web site.
Eric Gorr's Forward Motion - High Performance Dirt Bikes

03-04-2008	#1 (permalink)
beerbudget Newbie Join Date: Dec 2007 Posts: 19	KX85 to 100? Can a KX85 cylinder be bored to a 100 or 105? I know a KX100 cylinder will work but considering just boring the 85. Also will the head work or will it have to be reworked also?

03-04-2008	#2 (permalink)
griffbones Another old dirt bike guy BTK Expert Join Date: Sep 2006 Posts: 565	Yes the KX85 cylinder can be bored out to the 52.5mm size and then replated. Basically that is what a KX100 cylinder is anyway. In the past many of the top builders preferred to use the KX85 cylinder when doing big bores due to the better exhaust porting on the 85, but the late model KX100 cylinders now have the same exhaust port dimensions so this isn't such a big deal now. Now to achieve a 103.5cc you will have to install a Hot Rods 2mm longer stroke crankshaft and the 52.5mm piston. To achieve the 105cc you will need the 52.5mm piston and you will have to have someone stroke a crankshaft for you, as it requires a 48.5mm stroke, and no one is making a pre-made 48.5mm stroke crank for the little KX's. This 105 set-up will require machining of the crankcases for rod clearance, where as the 103.5cc set-up will not require any crankcase mods as the Hot Rods 2mm over crank is a drop in ordeal. __________________ '05 KX85 w/103cc engine '97 DR407 '83 CR60 '05 TTR230 '07 250XCW

03-06-2008	#8 (permalink)
stevied645 Wants better weather! BTK Expert Join Date: Nov 2007 Location: Scotland Posts: 730	Anyone know who does this kind of work in the uk. ive been thinking about boring mine out to either a 285 or 310, heard that there is no point in going to 310 is this the case?? __________________ *KX250/500 Hybrid LOL Scary Stuff*

03-06-2008	#9 (permalink)
Sapper69 Turtle Wax Taster BTK Intermediate Join Date: Jul 2007 Posts: 161	Don't mean to hijack, But. hey Griff, anyone making a 125 bb kit for the 100? __________________ REAL MEN MEASURE WITH INCHES, not centimeters!

03-06-2008	#10 (permalink)
KickassKX125 Now after another 125!! BTK Expert Join Date: May 2007 Location: Helmsley, North Yorkshire, England, UK Posts: 895	310 in a 250. To my mind that would be in the coolant channels without a bb kit. __________________ Jamie 1996 CR250: IT LIVES!! and bloody goes aswell, lol! After another KX125 to kill the garden!

03-04-2008	#3 (permalink)
beerbudget Newbie Join Date: Dec 2007 Posts: 19	How about the head? Will I need a 100 head?

03-04-2008	#5 (permalink)
beerbudget Newbie Join Date: Dec 2007 Posts: 19	Thanks for the info again Griffbones! Just looked at his site. The KX is on the low end of the price range. Nice!

03-05-2008	#6 (permalink)
F_27stryker MMmmm taste like dirt! BTK Beginner Join Date: Mar 2008 Location: Kentucky Posts: 64	SO what are you deciding to do?

03-05-2008	#7 (permalink)
beerbudget Newbie Join Date: Dec 2007 Posts: 19	Come up with the $$$ and send it in! Looks like the way to go after reading the info on the site.

03-06-2008	#11 (permalink)
griffbones Another old dirt bike guy BTK Expert Join Date: Sep 2006 Posts: 565	I have only heard of making a KX100 into a 105cc, it is basically the same cylinder casting as the KX85. Keep in mind fellas, that when going big bore by that much percentage larger than stock cc's, it normally requires stroking too. You can't make that much of a cc change with boring alone, the cylinders aren't thick enough, and besides that, having a bore that much larger than the stroke would be a crappy running engine anyway. I think they may make an over bore piston for the KX100, if so you might be able to get a little bigger than 105cc but I am not for sure. Another thing to keep in mind is the fact that there is more to making power than just cc's! And a big bore without supporting port work will normally run strong in the low end but fall flat on it's face in the top end. I guess what I am saying is that it is a package deal to do it right. __________________ '05 KX85 w/103cc engine '97 DR407 '83 CR60 '05 TTR230 '07 250XCW

03-07-2008	#12 (permalink)
F_27stryker MMmmm taste like dirt! BTK Beginner Join Date: Mar 2008 Location: Kentucky Posts: 64	5cc is not worth it my friend

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