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Tech help - KDX 200 cylinder Boring

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Posted by: omrik88---------------------

Hi,
*
I have a Cylinder of a KDX 200 1986, 66mm(standard?) which is worn and damaged and i have to over bore it.
The question is - what Diameter can it be bored to and still NOT having to put a sleeve in ? (if its safe for the engine).
*
From what is written in this forum, when you bore a cylinder, you have to do some porting work afterwards,
correct?
But will this be so important even in a case you are boring over just 1-2 mm for example?

About replating : will this add some thickness to the cylinder walls?

Thanks for your help!


Posted by: omrik88---------------------

Any help please?
Do someone know what kind of Alloy was this KDX 200 cylinder cast from exactly? (1986)
If Re-plating it after Boring , should it be the same as the original? (Chrome-Moly).

*Does someone have an idea how much an over-bore+replate & hone should cost?
Thanks!
I would appreciate your help!


Posted by: motopsycho87---------------------

I would get it nicasil plated. Chrome tends to be reserved for sports bike engines now.

I had mine (1989 kdx200sr) replated recently and it cost me £220 including Mitaka piston kit (which was £80).

http://www.wiseco.com/ProductDetail...986&AppID=27254 tends to be the largest oversize I can find. If you hunt well you will probably find a piston with the same measurements from another bike but with a larger bore.

Standard - pi x 33² x 58 = 198.429
1mm ovrsze - pi x 33.5² x 58 = 204.488

6.059cc increase... wow!

Remember mate, your bike is a 2-stroke. For less money, send the barrel off to be ported and have the head machined to get the right squish clearance. Ir if you are pretty handy with tools, do it yourself, a lot can be gained by just cleaning up the ports with a dremel! Download A.Graham Bell's book on 2 stroke tuning if you want to know more.


*edit just reread, you have to get it done anyway, sorry! invest in a dremel and do some port cleaning before you send it away, or ask them to do it while it is away!


Posted by: EYY---------------------

Sleeving costs the same as plating, and when done properly there is no loss in power or reliability whatsoever. Plus, if you get it sleeved you can hone the cylinder and have it bored oversize and it won't cost much. The only thing that may be seen as a problem by some people is the altered transfer of heat...


Posted by: julien_d---------------------

Quote:
Originally Posted by EYY
Sleeving costs the same as plating, and when done properly there is no loss in power or reliability whatsoever. Plus, if you get it sleeved you can hone the cylinder and have it bored oversize and it won't cost much. The only thing that may be seen as a problem by some people is the altered transfer of heat...


I disagree. Installing a sleeve WILL affect the factory porting. There is no way to perfectly match the sleeve ports to the cylinder ports. How much affect this has will vary depending on who does the work, how well it is done. Also, a sleeve will last nowhere near as long as aftermarket plating. Sure, you get a couple cheap overbores out of it, then the sleeve has to be removed and replaced. Aftermarket replate will have superior heat dissipation, and last longer, without affecting the factory porting. Barring some catastrophic failure which damages the plating, a good after market replate should last for many top ends.


Posted by: omrik88---------------------

Thanks for the help guys!

* Julien_d , i have an experience with another cylinder which was sleeved and had a bad porting job done to it. It has alot of power, but it never works clean, and is very hard to idle/tune/jet.

I prefer going with boring and plating, and no sleeving. But i still don't know how much "material" i can remove in diameter from the bore?
Does anyone know what is the Tolerance for this? before having to use a sleeve!

*About pistons-in Wiseco website for example,for year 86-88, they make them in sizes up to 68mm. But they say that any oversize piston requires sleeving.
Is this a Must? or just they're opinion?

Thanks


Posted by: motopsycho87---------------------

1stly with JulienD's post, though what he says is true, it is virtually impossible to match the stock porting, you can still improve on stock porting, once again, seek A Graham Bell's book for advice on that! A lot can be done with a £15 rotary tool set .

2ndly, take the barrell off and look at it, that is your best option, normally it is down to clearence to oilways (transfers on 2t) and coolant ways to determine overbore. I would say it is just wiseco's opinion, if they can supply something and get people to buy it they will. I doubt anyone on this forum is going to go into the proper engineering aspects of an overbore, where you need to find the forces being applied to the aluminium cylinder, the amount of heat, the aluminium's heat dissipation properties blah blah blah blah. Basically, if it looks safe, go ahead, trial and error is the way forward :D!

If you overbore 2mm you will need to tickle your ports up a little, as all ports should have a gentle radius flaring into the cylinder, but once again, a cheap rotary tool and you can work wonders, once you start cleaning up ports and flowing things a bit you'll be amazed how much material you want to remove!

It's a 2 stroke, have some fun with it! No matter what you do you are going to make it less reliable, just make sure it is jetted to suit and that you are running a decent ratio of oil (so many tests indicate roughly 16:1 has performed best in race situations!).


Posted by: julien_d---------------------

Why are you determined to bore it over? Even a 2mm overbore is not going to add to performance. Any reputable shop that does re-plating can strip, weld any damage, and re-plate back to factory specs, all for a reasonable cost.


Posted by: motopsycho87---------------------

Standard - pi x 33² x 58 = 198.429
1mm ovrsze - pi x 33.5² x 58 = 204.488
2mm ovrsze - pi x 34² x 58 = 210.638

2mm = 12.209cc extra

Now add head being skimmed to the correct clearance, plus porting, plus better jetting, plus new exhaust, plus timing changes

it all adds up. I know we will return to the argument of "but its a woods bike, if you want a crosser, buy a crosser" but some of us just love modifying things :D! Let him do it and see where he gets.


Posted by: julien_d---------------------

Boring a cylinder out and re-plating I would not consider a mod. More of a waste of money. If it has to be plated, just get it re-plated. There's no reason to bore it.


Posted by: motopsycho87---------------------

How is it a waste of money? The boring is normally charged about £15 for any barrel? The piston usually costs the same standard or oversize. I think someone's a little jealous :P.


Posted by: julien_d---------------------

Sure. And I think someone is a little dense, but I don't go around saying it.


Posted by: motopsycho87---------------------

Love you! x


Posted by: K D---------------------

omrik88

Check out Pinsonnault Racings website they offer some over bore choices up to 70mm (223cc)


Posted by: motopsycho87---------------------

http://pinsonnaultracing.com/KDX175200BigBoreKit.aspx

wish i had $595 laying about now

so basically, the answer is yes you can, if you can get a 70mm piston, you can quite happily overbore the bike, but you will need to modify the head and porting to suit to get it to run its best

Works out as £381, which is pretty good, I had mine re-plated with a new piston kit a few months ago and it cost me about £220, so you are talking an extra £161 for porting and head machining work, not bad if you don't have the equipment etc to it yourself!!!


Posted by: K D---------------------

Getting the piston is the easy part if you google the part number in the parts kit 750M07000 it is available from a lot of sources. It is an overbore piston for the 220.


Posted by: omrik88---------------------

Thanks again for the help guys!
I'm not looking for Performance at all... i just want to fix the cylinder and keep it as close to Original as possible!
Julien d - you said that a good shop can fix that groove in the bore, strip the plating & replate back to standard bore. I didn't know this can be done, great
Any ideas how much this process could cost?

Motopsycho87 thanks for that book - alot of info!

I appreciate your help!



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