if only takegawa made a head for the 73-76' xr 75s.....

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if only takegawa made a head for the 73-76' xr 75s.....

This is a discussion on if only takegawa made a head for the 73-76' xr 75s..... within the Vintage Honda XR75 and JDM Vertical Motors forums, part of the General Talk category; yea i know i have a touch of A.D.H.D. going on. i got the valve train components sat so inbetween other projects i decided to ...

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Thread: if only takegawa made a head for the 73-76' xr 75s.....

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    if only takegawa made a head for the 73-76' xr 75s.....

    yea i know i have a touch of A.D.H.D. going on. i got the valve train components sat so inbetween other projects i decided to start on a xr 75 head. valve sizing will end up 28.5mm on intake and 23.5mm on exhaust. stems will be slimmed down from 5.5mm to 5mm. i started roughing in the ports. but just my luck the cable for my porting tool sheered. so needless to say i wont be doing any porting for a few days here is the progress as of now





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    the more imma doing the betta she-a look'n! seats n guides are in, valves are both turned down. as it sits now it clears on overlap but they darn near hit. so i need to sink a little more for clerance. which isn't all that bad, cause... i haven't checked seat and nose pressures yet. but the ole' thumb-o-meter is saying its way to high to. its to the point that i'm debating on how to approach the issue. once i get overlap clearance if its still to high which i have a feeling its going to be. my only options are. knock guides back out and spot face spring seat faces to allow for more clearance or source different spring. both options i would like to avoid. don't wanna spot face the spring seat faces cause i wanna be able to raise the port roof and not blow through spring jacket. which eye guess where i'm at now will already be pretty close on guide boss area of intake port. exhaust shouldn't be to bad due to i'm not going to raise it as high. sourceing another spring to work is easy enough to do. i wanna avoid that cause i wanna keep cost of valve train down to a min. ultimately shooting to be able to dublicate this setup porting and combustion work for around 500 smackers

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    almost done! i'm not thrilled w/ exhaust port but hey what can i do.... small lil bastid couldn't even get my micro welder in there to build it up so i had to leave it alone. cut seats for overlap clearance and finished the combustion chamber. worked both ports a fair amount, still some work to be done yet. checked spring pressures and as i expected WAY to high. so i got my best ppl's one the job looking for a cheap alternative *cough cough* terry..lol heres what i'm working w/ now.
    how intake came from factory
    not finished but its pretty close
    how exhaust came from factory
    not finished and not sure what to do w/ it cause short turn looks like hell in a handbasket
    side view of finsihed combustion chamber
    another view of combustion
    comparison to xr 80 head
    comparison to another xr 75 head

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    A.D.H.D Attention Dedication Head Disorder

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    Quote Originally Posted by 50race View Post
    A.D.H.D Attention Dedication Head Disorder
    lmfao ill have to remember that. fits better than A.D.D. i have so many big valve projects going on. BV V2, klx +r, kitaco SE, xr 75, xr 80, crf 50, xr 100 +R, crf150f. head work wise most are done. rest of the engine well....thats another story. bet you cant tell what i like working better head or rest of engine..hahaha

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    Just noticed, you don't put a beveled squish band around your combustion chambers? I know on two strokes the angle and width of that band is critical, dunno how much of an impact they have on the four strokers though.

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    Quote Originally Posted by Kurlon View Post
    Just noticed, you don't put a beveled squish band around your combustion chambers? I know on two strokes the angle and width of that band is critical, dunno how much of an impact they have on the four strokers though.

    lol thats a question i dont have a good answer for or proof one way or the other. back in the hay day of jordan posting and discussing head work he once made note something along the lines of wanna get different ideas start looking at car ports and combustion chambers, the car industry dumps way more $ into R and D to make engines more efficient better performing yata yata. after hearing that i have paid more attention to the car stuff and have developed alot of different ideas of how i go about porting or doing chamber work. on the car stuff i you don't see alot of the squish band rings like you see in the motorcycle stuff. reason why i couldn't tell you for sure one way or the other. i too have put some thoughts wondering if it has to impact on a 4stroke like it does on a 2 stroke. but have not done anything to try and prove one way or the other if it does or not. i have been getting good gains w/ how i have been doing it. so it hasn't given me much urge to wanna experiment w/ changing what i do.
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    Hmmm, so your good with the big valves not hitting at overlap? nice port work by the way.I tried something similar with my xl75 but in reverse by using a ct70 piston in a decked xr80 cylinder with the xr/xl 75 head.I wanted the pop up piston and higher compression with the tighter xr chamber.I ran into a snafu with both valves touching the piston at overlap.I tried cutting the valve pockets deeper for clearance but I didn't want to go too deep or I would break through or make the piston too thin.The only other thing I could think of to make that combo work would have been to take some valve timing by having the cam reground.I ultimately abandoned the project.....

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    Quote Originally Posted by hobbeekid View Post
    Hmmm, so your good with the big valves not hitting at overlap? nice port work by the way.I tried something similar with my xl75 but in reverse by using a ct70 piston in a decked xr80 cylinder with the xr/xl 75 head.I wanted the pop up piston and higher compression with the tighter xr chamber.I ran into a snafu with both valves touching the piston at overlap.I tried cutting the valve pockets deeper for clearance but I didn't want to go too deep or I would break through or make the piston too thin.The only other thing I could think of to make that combo work would have been to take some valve timing by having the cam reground.I ultimately abandoned the project.....
    yes sir put overlap back to factory overlap clearance which if i recall right is like 0.060 or 0.070". many moons ago when i first started building i did something similar with a xr 80. i decked the snot out of the head and i dont remember now what piston i used but had the same issue. i ended up cutting a lil deeper on notches and sinking valves a lil more and shiming valve springs to maintain seat and nose pressures. after a bunch of fighting w/ it i managed to get it to work. looking back on it now it was alot of work for the gains yielded. much easier just knock sleeve out, oversize and drop a 54 to 58mm piston by doing so not only do you get more cubes but you rasie CR w/o the use of a huge dome.

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    Guess its about time I raise this thread from the depths. I started working on the ole' gal again last week.

    So here's where I'm at...

    I spent a couple days just deciding what I should with the crank. I was jumping back and forth between taking the stock crank and adding 12 more mm's of stroke putting total stroke around 53.4mm. Or taking a 57mm Cdi crank and machining it to work within the xr75 cases. Well...lol if a lil bit more stroke is good a lot bit more stroke is better right? Ha ha so I went with the 57mm stroked crank. So with the 57mm bore with the 57mm stroke she's now sporting a cool 146cc's


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    After getting the crank done I started think eh the stock clutch probably won't hold up to the additional power. So lets see if the vintage guros can call out what's so off/different about this xr75 clutch set up

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ID:	121326 ha ha yes it's all stock xr parts with a lil Norman twist

    I them tossed the weak stocker oil pump in exchange for a takegawa HV pump. With the mix matching of parts she now sports a drive ratio of 3.833 like the big money takegawa clutch

    Tonight I just about got stroker plate finished. Still needs a lil fine tuning

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    Tomorrow cam gets sent out for a regrind to take advantage of the bigger valves, porting, and additional displacement. More than likely ill take the lazy route and have Cometic make me a head gasket since I gotta wait on cam to be reground. Upon getting cam and head gasket she can be assembled and shoe horned in the frame. Then I gotta make a mani to holster a 28mm carb and make a exhaust. After that engine work is done! then the daunting task of figuring out suspension :-0

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    Looking Good! Lets hear about that clutch setup.

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    So you stuffed 5 fiber plates into that basket.....nice

    What change to cam chain length was needed?

    I have a cool vintage "Hypercycle" aftermarket intake that fits a 28mm Keihin up to my big bore (only 50mm) 4-spd XR75.........that head work is killer....nice work man

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    Quote Originally Posted by AHRMA361 View Post
    So you stuffed 5 fiber plates into that basket.....nice

    What change to cam chain length was needed?

    I have a cool vintage "Hypercycle" aftermarket intake that fits a 28mm Keihin up to my big bore (only 50mm) 4-spd XR75.........that head work is killer....nice work man
    Winner winner chicken dinner lol. Stock chain length. If you scratching your head asking how/why here's how when I originally picked up this ole 75 I was going to restore it but I'm a engine guy so I couldn't leave the engine stock. I know most vintage resto guys are very VERY particular on the engine looking factory. So my plan was to take 2 75 cylinders separate a section of one and add that section into the other so it would look like factory cylinder to most. I long since gave up that dream. But the calcs I had done for deck height etc all worked in my favor for me to hack off 0.197" off head, use a shorter rod then add a stroker plate to restore deck height all while keeping stock length chain.

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    Quote Originally Posted by slide1in View Post
    Looking Good! Lets hear about that clutch setup.
    The 73-76 clutch and crank gear are same ratio as the takegawa xr100 unit. So I maintained use of the 75 gears. I then separated a xr 100 basket did some mill work and fitted it to the 75 clutch gear. After getting basket fitted to gear I could of called it good with the xr100's 4 fiber 3 steel setup. I decided to go the extra step and machine the xr100's inner hub and pressure plate to accept 1 more fiber and steel. And wa-la poor mans takegawa clutch

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    She's almost ready to fire up.



    Exhaust fab welded and sexed up. Still have to make a silencer but that can wait for now
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    Pieces machined to alter manifold to accept bigger carbs.

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    Mock up of pieces


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    Final product

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    No more points


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    Last edited by storminnorman07; 08-15-2013 at 11:09 AM.
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