shaving kdx head

agitt73

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#1
how much should i shave off of my cylender head
a buddy of mine shaved 8 thousands off of his
what do you recomend:silly:
 
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#2
I recommend you have a good think about what Octane rating of the fuel you will run EVERY time. Once you decide that then you can decide on the compression ratio to run.

Skimming the head will reduce squish clearance which is generally a good thing as manufacturers play on the safe side. It will also raise the compression, also a good thing for the same reason as they don’t want the bikes to blow up when you run them on what passes for petrol in Elbonia. About 12-13:1 should be the max, but I don’t know how bad your pump gas is. 14:1 for proper race gas. Maybe more if you are keen, but I doubt it.

Then you have to measure the volume of your head & do a little math, but if you'd included your bike & year maybe some kind chap has the info to hand. (I mean like do you have a 1967 KDX 400 or what?) This will be close (for the same squish clearance, math will equalise the clearance, butt from yor spelink this may proove difficolt –kidding dude) but bikes do vary so play it safe.

Oops I see from your profile it is a 2000 200.

I could go on about Maximum squish velocity but assume it will be about right for the intended purpose.

You should also poke some solder through the spark plug hole & measure the squish accurately. Measure in several places as head are not always square. You should take it down to about 1mm to be safe for a 200 trail bike. This may or may-not take the compression unbearably high.
 

agitt73

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#3
many people reconmend it BUT!! why can nobody give me an answer:think
 
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#4
Well gee, that’s because the problem is with the question grasshopper. Sorry probably too young to remember Kung Fu, though last time I past through the states it was re-running.

The answer is totally dependent on the fuel you run & the manufacturing tolerances of your engine. I’ve told you the expected c.r. you should run with the fuel & the squish clearance you should run. (So the piston doesn’t hit the head at peak revs).

I could tell you to shave it down to min squish clearance ie: if it was 1.9mm at lowest point now, take 0.9mm off it. But I won’t as I don’t know how high that will raise your compression ratio, & if it’s too high it will detonation & blow the engine.

This is the part where you have to learn how to measure the cr... Or give your engine to a tuner who should get it right & or know from experience with your model, well enough to guess. He earns a living.

Engine upright (lift front wheel). Piston to top of bore. Syringe full of 2 stroke (will end up being~17cc). Fill up to bottom of spark plug & 2 threads up to account for sparkplug recess.

You now have the head volume. Now take the head off wipe it all out reassemble & measure it again. OK now you have the head volume.

Head volume + bore cc divided by head volume = c.r.

Stay on the conservative side of cr. If you want to read more find a book like Graham Bells 2 stroke tuning or similar.
 

Sage

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#5
Well like the last guy I could say take .040" off the sucker but if the last owner took of .020" then we will have a slight problem. first off here's some Q's that need to be answered:

Is the top end fresh?
Did you check the squish before you took it apart?
What do you have for cylinder pressure with a fresh top end?
What type of gas do you want to use ALL the time?
How good are you at jetting? - The hotter you build it, the more it will be effected by the "cloud over the sun" deal.

after getting the answers to these questions, then we can give you a answer on how much to cut, and that will vary from person to person, it's one of those "What oil is best questions".

When my 220 was stock I took .038" off the head and .015" off the cylinder top and use 2 base gaskets to raise the ports up. when I was done the bike had 203 psi of cylinder pressure and I run it on 92 pump gas with redline at 45:1, it works very well.
 
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Sage

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#6
Also if your not sure what your doing, seek help from a good source other than a forum, not to knock the forum but you can get all the info in the world and really screw up your engine if you don't know what your doing.
 
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#7
I couldn’t agree more. Unless he said Ricky Martin is a crap singer, in which case I’d agree more.
In your quest for the desirable it is easy to seek the magic answer (sorry still on this Kung Fu train of thought).

The money you give to a reasonable tuner may seem a rip off for a simple machining job but you are buying his R&D time as well as a few mistakes he made along the way to becoming proficient.

If you want to have a play yourself --read up. Arm yourself with some knowledge, if you get fanatical this can be almost as enjoyable as riding itself.
Sick huh?
 

agitt73

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#8
my bike is stock besides pipe silencer reeds tires (wise co piston this fall) i bought it new
i think david trustrumass dose not realize my abilty as a mechanic
the only thing i need a manual for is tighting specs but for engine
mods i don't know so much:p
 
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#9
I'm not trying to patronise you, you're right, I have no idea who you are,

Both Sage & I have taken a bit of time to try & give a helpful response that won't get you into trouble & Sage's point asking how proficient you are as a tuner is valid because how would we know?

When I said read up I don't mean about the mechanical disassembly I mean about tuning, Check out the TSR SW site etc. Yeah the measure the volume twice crack isn't a dig - I always do it in case I've had some oil leak away but if I get the same answer twice it should be correct.
 
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agitt73

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#10
fmf says to take of 16 thousands all i wanted to know
is what other members take off i asked eric gore for a
price (email) and he never answerd so i was thinking
of doing it myself with emery cloth on a sheet of glass
if i decide not to do it my self i will have fmf port and do'er
all at once;)
 

Canadian Dave

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#11
You’ll want to remove some material from the base of the head AND alter the squish band so a piece of glass and some emery paper just isn’t going to cut it. Eric has head mod prices on his site, $35 jumps to mind. I wouldn’t be surprised if Sage also does head mods?

You're going to have FMF do your cylinder and head ?????? There's no question they'll be able to port for more power but I’d be looking at someone with a lot more KDX experience than that. I’d be looking for a dedicated porting specialist with the experience and programming to deliver exactly the kind of power you’re looking for ( not one profile fits all ) or someone who specializes in KDXs. JMO

David
 

agitt73

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#12
fmf done a 95 kdx 200 for dirt rider
maid her run snapper like a mx'er
except for the top end it was a little
slower than an mx'er:D
 

Sage

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#13
Originally posted by agitt73
i think david trustrumass dose not realize my abilty as a mechanic, i was thinking of doing it myself with emery cloth on a sheet of glass.:scream: :think
And to think that people spend all that money on a damn lathe & end mill! Happy engine building! let us know how it runs, maybe you'll get some engine work off the forum when word gets around?!:p
 

agitt73

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#14
sorry im a poor white boy that cant aford them
expensive tools or to pay everybody else to
work on my bike:confused: :silly: :p
 

WoodsRider

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#15
?

Originally posted by agitt73
... doing it myself with emery cloth on a sheet of glass...
How do you plan to keep it square with the centerline of the combustion chamber? :think

FWIW - Find a machine shop with a lathe. Set-up and machining .016" off the head shouldn't cost you more than $50. Just don't expect the same results that Dirt Rider published. :scream: