PlanetMinis Forums banner

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

17K views 39 replies 9 participants last post by  sgtbilco 
#1 ·
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




 
See less See more
4
#2 ·


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 ;-)
 
#3 ·
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
 
#4 ·
A.D.H.D Attention Dedication Head Disorder
 
#5 ·
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
 
#7 ·
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.
 
#8 ·
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.....
 
#9 ·
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.
 
#10 ·
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


Hand Finger


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

Auto part Machine Metal Rotor
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

Auto part Gear Engine Vehicle Hardware accessory




Auto part Engine




Auto part Automotive engine part Engine Machine Carburetor


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
 
#14 ·
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 ;-)
 
#12 ·
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
 
#13 ·
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.
 
#20 ·
Storminnorman07, I know this is an old thread, but see you are still active on this site so thought I would ask a few questions. How did this motor turn out? Was it worth the effort? We chatted a bit via email about these things, but it was prior to getting it running. Did you attempt to open up the ports proportionately to the valve size increase? Did you have to sink the valves into the head as much as you cut off the head? I guess you shorted the valves from stock to compensate. Give us an update!
 
#21 ·
I personally feel the engine was a success. It made more power than a takegawa stage 3 kitted xr100 and a little less than the R kitted xr 100. The day I had dyno time the reground cam showed up in don't know why but I brought it with me even though I knew piston to valve clearance wasn't going to fly with the regrind. After getting some pulls with the stock cam I got froggy threw the regrind cam in it and.....well.... blew it to shit. I think with the regrind cam and some tuning into would make the same if not more than the Takegawa +R kit.

Well depends on your perspective of your perspective is the actual diameter of valve head the answer is no. Now if perspective is the percent difference left for valve seat then yes.

Don't remember how much I sunk the valves. It just worked out on this build that with the stroker and os valves that decking 5mm workEd out well. And yes the overall length of valves are shorter then stock valves

Unfortunately no updates I recent got a new house so all my extra time has been working on that. I can say that I started rebuilding it from the chaos and plan know doing a 60mm bore and even larger valves
 
#25 ·
Unfortunately I won't be playing with that engine for a very long time. But if I ever get around to playing with it again I'll do some updates.

If memory serves its was mid 12's and climbing and the Takegawa +R made 13.5. Unfortunately went it popped it was like riding a bucking bronc and the pull sampled the whole hell that was going on while I was trying to get it to a stop. Needless to say the graph wasn't worth anything it looked as if a kindergartener high on acid went drew the lines on it.

Sent from my SM-N920V using Tapatalk
 
#29 ·
Lots of good stuff Chad. And that answered the question on the process to open up the seat guides. You know its important keep the same datum when creating all the features, and once installed, the valve stem guide is the best datum.
I was scanning pit bike parts and saw that Yx-160 slingless crank, and saw it was already 57mm stroke and used the same ID/OD bearings as the first gen engine, except Yx bearing is 1mm narrower (22/56/16 on XR, 22/56/15 on the Yx-160). The 2nd gen XR engines use the smaller mains 20/52/15 like on the Yx-140 it seems. No more questions for now, thanks
 
#30 ·
Hey Storminnorman
Love your work i to have the bug here's a pick of my 73 with a take r head fitted
i went about it by re-aligning the stud holes seems to fit up ok have had it running
and will race it this season in a mini series over here in OZ
it was my original race bike i had in the 70s


Land vehicle Vehicle Motorcycle Motor vehicle Car
 
#31 ·
Hey Storminnorman
Love your work i to have the bug here's a pick of my 73 with a take r head fitted
i went about it by re-aligning the stud holes seems to fit up ok have had it running
and will race it this season in a mini series over here in OZ
it was my original race bike i had in the 70s


View attachment 203889
I like it! I intially thought about doing something like that but figured the purist would burn me on a cross. Interestingly enough in the mist of deciding how to build mine I found that if one machined a custom cam tower you could take the Takegawa roller cam and rockers and mate it with the 73-76' head. What bore and stroke did you go with yours?

Sent from my SM-N920V using Tapatalk
 
#33 ·
Haha heck no. I can get a cam reground way faster and cheaper than retro fitting a take cam on there.

I may selling the difficulty short on this. It's not as simple as make a cam block and your good. There will be clearance issues every where...guides....over lap...etc..

The reason why it's tempting are for the following reasons.
1.) It's a bearing cam vs the non bearing xr cam. Granted with the 73-76' xr 75s that's not a huge gain cause you can do this


2.) The big reason is cam profiles. A roller cam lends itself to being able to have more aggressive profiles. Then you factor that the stock xr cam tower parameters really limits how big you can get with the cam profiles makes the Takegawa cam even more pleasing. I could on with why it would be better but it's much easier just showing results.
we are looking at the red and green lines on this pull. Both engines are same everything except for heads. The red line is a takegawa +R the green line is a takegawa stage 3. Between the stage 3 and R head they are basically the same casting other than the R head has roller rockers and roller cam where as the stage 3 is like the stock xr 100 head. The roller cam setup yielded over 2 hp more which is pretty substantial for a mini engine.

Sent from my SM-N920V using Tapatalk
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top