case match vs port match

steve /

stevep1989

Oct 20, 2007 11:11PM

eventually im gonna crack my moby case to change out the bearings. i figure while im there, i want to do a case match. this is for a few reasons:

-I feel like it's easier and more straightforward than porting. case matching means you have two holes. make this hole the same as that hole. done. im decent with a dremel, some files, i think i can make it happen.

-i feel like i can get better performance with the case match.

is there any point on case matching w/o porting? porting still scares me, while the concept of case matching seems much more friendly. will it make a difference w/o the porting? is there anything else i should know before i do it? keep things smooth, round, no filings where they dont belong...

Re: case match vs port match

steve /

stevep1989 OP

Oct 20, 2007 11:11PM

poorly titled post. should read "case match vs. porting"

Re: case match vs port match

WariSesi /

Oct 20, 2007 11:32PM

Porting is easy steve, even a girl could do it.

Seriously tho if you use rifflers which are curvy end files, you can do your port job without mistakes. Takes way longer then a dremel but with a dremel one bad slip and it gets real expensive.

no point really in doing one without the other and if you have considerable down time in the winter you may as well go to town and do it all at once.

Re: case match vs port match

steve /

stevep1989 OP

Oct 21, 2007 12:11AM

even a girl!?! haha i would use a range of tools im sure, but my issue is the insecurity and mystery of porting. with case matching, its "match this to this". with porting, there are a lot of variables. ie if i make it too wide i lose all my lowend or if I i make it too tall my timing goes to hell (these are just out-of-my ass examples, they may or may not be true but you get what im sayin). i guess i'll just ask this: if i port EXACTLY to the specs provided in the Wiki, what am i gonna get? I'll probably get some gains, but are there losses involved as well? i guess the way i see it is if there are some specs im DEFINITELY shooting for, with some idea of the results, then i can do it. if theres any mystery going on about what needs to be done and what the effects will be, i'm a little bit more reluctant. kinda makes me a wimp, but hey, i like my moby.

Re: case match vs port match

lee's anus is leefungchowOG /

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zach

Oct 21, 2007 02:09PM

if you don't take a risk and fuck shit up, you will never learn NIKE!!! just do it

Re: case match vs port match

steve /

stevep1989 OP

Oct 21, 2007 02:53PM

haha a little more reckless than i try to be but yea, im starting to lean that way anyways. Kriedler shop manual "Nothing ventured, nothing gained"

Re: case match vs port match

Shalerrr rrr /

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shaler

Oct 21, 2007 02:55PM

porting isnt really that bad. you just have to be mindful of a couple things, especially concerning the exhaust port.

the exhaust port on motobecanes is that size for one reason -to limit power. raising the exhaust port will increase upper mid range to peak rpm power but will always take a chunk out of the low end, therefore i wouldnt advise rasing the exhasut port more than the 3mm or so that the artcile in the wiki suggests. however, you can also stand to widen the exhaust port a fair amount which will also increase the mid range to upper rpm power without sacrificing too much in the low end. as a general rule its not advised to make the exhaust port wider than 0.65-0.70 of the bore diameter (39mm). any wider and the rings will bulge out into the exhaust port too much and snag. when widening the exhaust port, its good to make the center of the top of the port 4-5 degrees higher than the ends. this will gently close the rings as the piston moves up in the bore and cut down on ring wear.

read 'two stroke performance turning' by A. Graham Bell (found here and that should help you out immensely.

Re: case match vs port match

Shalerrr rrr /

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shaler

Oct 21, 2007 02:56PM

sorry, here

Re: case match vs port match

WariSesi /

Oct 21, 2007 06:56PM

shay is right, also put a bot of a camfer in the edges of the ports which will help ease the ring into position. also a clean passage is way better then a polished one so take any roughness off the port walls but do not polish it. obviously you have read some about the porting because you know what size and width will do to performance. the recipe on wiki is one that works for sure.

Re: case match vs port match

steve /

stevep1989 OP

Oct 21, 2007 07:11PM

i read a bit of that book by Bell. definitely easier reading for me than that other one.. "two stroke tuners handbook" or something. i read up on the porting section a bit too, so i have all those formulas for actually calculating the ideal port size/durations. but i assume somebody already used formulas similar to that to get those measurements in the wiki anyways. im more than happy just to go by their specs, but my biggest concern is how much of a loss i'm going to experience in lowend from widening the 2mm on each side as specified. i can see myself doing about half the widening just cause im not wicked keen on doing a bunch of work, and in the long run actually just making a tradeoff. the 3mm seems a bit robust as well, i could see myself probably doing about 2. i think itd be better to start conservative and then go back for more if i want. and then yes, rounds chamfers smooth i think i can pull that all off. this.. all makes me think.. i need a timing cam puller. anyone know what shops sell em? thanks for the help,

-Steve