250x head/cylinder decking/milling question

[bumpnzx3]

first off- this site is great- i have been doing all sorts of lerking around here over the past couple weeks- all sorts of good information- finally decided it would be a good idea for me to go ahead and join.

now for a little background on my 250x. i have had several 4-wheelers and dirt bikes over the years- all of which stock besides the usual pipe and filter. i just recently sold my dr350 and had some $$$ burning a hole in my pocket- and eventually got the itch to play on 4 wheels rather than two. a guy i know had a bone stock cherry 250x that he bought new and rarely rode. he let is son in law use it for the weekend- and he managed to run it out of oil- i dont know the entire story as to how this happened- nor do i care. the owner then went and bought all new everything- bearings, clutch plates, had the cylinder bored once over, a new piston,- the whole bit. before he started to re-assemble this thing- he and his wife split up (again- dont know the whole story- nor am i all that concerned:devil: ). he decided to sell it since he never had the time or the desire to ride any more. i asked him how much- he said if i had $300 in my pocket i could have it. well- it was on a friday after i had just cashed my check- so i went home with a 250x. now all i have to do is figure out how to get it back together from scratch. on the plus side he did have a honda factory shop manual. wish me luck boys:D

i bought this with the plan of just putting it back together- and just keeping it stock- besides a pipe and filter. well- much like everything else i own (ford focus, 383 s-10, fzr600- all of which anything but stock and on the bottle)- i have talked myself into thinking a stock 250x just wasnt my thing.

i am going with this route:
sparks pipe, k&n, wb 245 cam, p&p head, etc.- and a little higher compression just not sure how:confused:

i read the entire article on head decking in the FAQ section- but i am a little on the confused side- since that was mainly aimed for the 400ex. i dont want to get a higher compression piston since the one i have is new and the cylinder is fresh, nor do i want to go with a more radical cam (i know this has nothing to do with the compression- i was just making a statement as to why i didnt choose a little more cam) since the valve springs/guides/retainers are also all new- and i dont want to replace them with aftermarket stuff. i also have a complete gasket and seal kit from k&s (they sell all sort of gaskets and such on ebay). ok- no onto my real question- in order to get a little more compression- i plan on taking the base gasket out and just using rtv sealant of some sort (when they say the base gasket i am assuming they are talking about the gasket the goes between the cylinder and the bottom end of the engine?) i have access to a machine shop to have the cylinder or head decked- i know the guy that owns it- and he does simple stuff for free for me. but my question is- do i have some taken off of the top of the cylinder or the bottom of the head? also- how much do i have taken off? how much does the compression go up for every thousandth (*sp?) taken off? i am going to go with the decking/milling route rather than a thinner gasket since i already have the head gasket and the machine work is/will be free.

thanks in advance for anyone that can help-

[wilkin250r]

Well, you have yourself a project and a plan, and that is good. However, you may be jumping in just a little deep.

When decking the cylinder or using thinner gaskets, there are more things to consider other than strictly compression and reliability. You need to carefully measure your clearances and tolerances to make sure everything will fit back together and work properly. Obviously, if you buy an aftermarket piston, this research has been done for you by the manufacturers.

I do not mean to insult you in any way, but if you are not familiar with squish band tolerances, deck height, and how to directly measure compression ratio, as well as measurement techniques to evaluate your final assembly, I would recommend a completely stock rebuild (including OEM gaskets), or sticking to proven aftermarket products.

I use myself as an example. Even though I know many of these issues and techniques, I personally don't dare to make such modifications to my equipment. Instead, I'll use proven aftermarket products.

[bumpnzx3]

no insult taken- i completely understand what you are saying. i know a descent amount- a little more than enough to be dangerous:D i was just hoping that someone else had already done this research/measurements that way i didnt have to. i am not looking for a huge jump in the compression number- just a little- just looking for a little more hp without much of any money spent (the reason i dont want to replace a new piston and valvetrain in place of a larger cam and higher compression piston). he11- even if i can pick up a small jump in compression bu using rtv only on the base gasket- and not worry about valves slapping the piston and such- i will do it. i just thought since i was already buying a cam and i have already started porting the head-i would just try to get a little free compression.

on a side note- the gasket sets from k&s on ebay- i used that brand on my fzr that i have as well as on the quadsport 230 i used to have also. i never had any problems with leaks or fitment of any kind. on the same token- they say all of the gaskets are the same thickness as factory- whether or not that is true- i have no idea:confused:

[bumpnzx3]

bump- anyone done this before with a stock compression pistonon a 250x? can i at least do one or the other- not use the base gasket or take a little off the head or top of the cylinder?:(

[bumpnzx3]

bump one more time-

looks like i am gonna have to do some research on this on my own- although i do find it hard to believe i am the first one to try to do this on a stock compression piston:(

[2004TRX450R]

another thing to consider is cam timeing. When you bring the head closer to the cylender you also bring the cam closer to the crank. This will make your cam chain tensioner have to take up more slack in the chain and will make you cam timeing off. It won't but a lot but will be some. The new cam you bought (or any cam for that matter) has a set timeing that it was designed to run at. By altering it you may loose a little performance from it. It may be noticeable it may not. Also I wouldn't use RTV on the base gasket if you leave the gasket out. I would use something like Hondabond. RTV will react to petrolium based products such as engine oil. Hondabond won't. So if there is any that squishes out it will stay there if you use HOndabond but if you use RTV it could get eaten away and fall into the engine. The only proper way to increase your compression on an overhead cam style engine is to either weld up portions of the combustion chamber or use a hi comp. piston unless you have adjustable cam sprockets so that you can adjust your cam timeing.