Topic: A Bike Is Born....750/1000cc

[Tintop]

No problem Sammybill, or is that Billysam??

Did a little research with the displacement calculator.  The DOHC 750 crank has a stroke of 62.0, so the ideal bore would be 69.5 which would yield a displacement of 941cc.  Just under my max of 900 + 5% = 945.  It would also be a slightly over square engine which should work well.

970cc uses 70mm pistons, with the stock SOHC stroke of 63.  With a DOHC 62 stroke that would give 954, , so they won't work.  That said, unless someone protests the engine, the extra cc's are unlikely to ever come to light.

[scottly]

Question Bear....will a DOHC CB750 crank fit the SOHC cases??

I have a Cycle World magazine from 11-'79 with an article about a Yoshima-built 1002 CC DOHC 750 using a 900 crank; if a 900 crank can be used in an SOHC case, the DOHC 750 crank should work.?

[Sam Green Racing]

it has to go in back to front. hahaha

[scottly]

DOHC 750 is the same as a DOHC 900, except for stroke and primary gear ratio, correct?

[Tintop]

DOHC 750 is the same as a DOHC 900, except for stroke and primary gear ratio, correct?

Stroke is different - 750 > 62 / 900 > 69, not sure about the primary ratio, but you have to use a GL trans shaft anyway for the HyVo primary chain.  I could use a 900 crank, but would need to use 66mm pistons.  That would give 944cc, which would fit the rules perfectly (900+5%=945).  So the question then becomes are there / is there such a thing as a 66mm piston that would work?  Back to some more research.

[Sam Green Racing]

No, it has to go in the other way about, other than that it fits.
I think the primary and cam drives are reversed, I'm sure the guys that have done it will confirm, I'm not 100% sure.

Sam.

[Tintop]

Did a quick check and CycleX has 65.5 pistons for their 850 kit.  With the 900 crank that would give 930cc, and a long stroke motor.  Would be nice to use one of Mike's billet barrels for the extra cooling of the big fins, but think he said they can only go down to a 70mm piston.

[scottly]

900 crank has 28 teeth on the primary, while DOHC 750 crank has 24 teeth. The DOHC 750 has 28 teeth on the jack-shaft, according to the article.

[Tintop]

How many teeth on a GL jack shaft??

[Bill/BentON Racing]

Yep...we ain't done yet, Bill, you's got to have a bigger rear wheel! Right, so Santa was late, but he brought me a one off 5.5 inch PM rear!

Will this work? lol!

We are moving forward, all be it slow! Bill     Thanks, you know who you are!!!!!

[jweeks]

Nice toy rotor there Bill.   

[Jerry Rxman Griffin aka MuthaF'er]

Nice toy rotor there Bill.   

LMAO, here we go again.... 

Bill that tire is too rounded. But maybe it will hold better with that brake. Let some air out and get the rubber on the road.

Keep up the good work! You tinkering with all the bikes or is anything ready to go? What's the stable's update?

[EnginebyAdam]

How many teeth on a GL jack shaft??

Mine counts 41 teeth.

[EnginebyAdam]

Did a quick check and CycleX has 65.5 pistons for their 850 kit.  With the 900 crank that would give 930cc, and a long stroke motor.  Would be nice to use one of Mike's billet barrels for the extra cooling of the big fins, but think he said they can only go down to a 70mm piston.

I plan on going slightly bigger with 67mm pistons but same idea. Should make for a solid runner.

[dragracer]

Whats going on with the stroker build Bill? I just bought a Cb900 crank off Ebay. Next step???

[Bill/BentON Racing]

Take your case half upper, turn upside down, reverse crank left becomes right, and drop it in..it will fit, but not turn, cause it needs some clearance here and there, not much! That's the start!
Mine on back burner right now. Gotta fix Purple Rain Turbo next. Then Samauto! And my ride, Calendar Girl, plate is full! Haha, Bill....Then check top case half.

[dragracer]

Take your case half upper, turn upside down, reverse crank left becomes right, and drop it in..it will fit, but not turn, cause it needs some clearance here and there, not much! That's the start!
Mine on back burner right now. Gotta fix Purple Rain Turbo next. Then Samauto! And my ride, Calendar Girl, plate is full! Haha, Bill....Then check top case half.

Alright Bill, I looked at your pictures where you started clearancing your cases so that's a good baseline for me. I'm still on the look out for the 1100F rods. I know they come up on Ebay from time to time so i'll just be patient. I do have one question on the pistons you selected. What is the size (mm) of those pistons??? I'd like to have 72-73mm pistons to put in this engine if possible. I think the ones you are going to use had 17mm wrist pins to match the 1100 rods, is that correct? And if I remember right it was posted that the 900 rods were 15mm as well as our SOHC piston pin size. I've got 73mm SOHC pistons  but if I use those, I would have to use the 900 rods and then I'd loose the advantage of longer, stronger 1100 rods.

Lots to consider but its the off season now. Time to do some maintenance work on what i've got now and get some R&D done on the long term crank swap project.

[Bill/BentON Racing]

Mine are 73mm.Pics and info tonight, Bill

[dragracer]

Bill what year XR250 did the pistons come from??

[jweeks]

     Let's not forget that the snout on the 900f crank must be machined off. That's where the advancer/points plate is going. Take a stock SOHC 750 crank and the 900f crank to your local machine shop. Have him/her machine the end of the 900f crank to match the slight recess of the 750 timing end. The 900f crank end is fairly soft and easy to machine. The plate "pin" hole can be located from the casting centerline. The machinist will understand. A fairly easy turning job.
     Remember that the crank determines the seals. Use the 900f seals with the 900f crank. Otherwise you'll leak around the machined end of the 900f crank.
     Clearancing is fairly easy as only a little material is removed from the case to clear the throws. The 900f crank is fairly heavy and can be lightened. The lightening can replace the case clearancing in some areas.
     The 1100F crowd has their own internet forums. Sometimes the rods/cranks can come up there in the classified.

     Somebody should make up an adapter to the splined end of the 900f crank which will allow kick/electric starting in our cases. I haven't the time yet to design that one up, but it can be fairly easily done. Otherwise use a splined sleeve around the crank with a 1 1/8" nut welded to the end of it with a bolt going through the center of it to hold it on. Your normal external starter will start it just fine.

     Yes, after doing all that work, everything will spin just fine in the cases. Depending on the rods used, you'll have 2 to 3 mm clearance with the bottom of the case. Yes, it can be stroked more. Previously done by Superbike Mike Keyte as stated on the Honda Dragbikes section of facebook. "We had a similar project in the late 80's. 40mm intake valves with 8mm stroker and 78mm pistons 1357cc. Made 156hp." There's your biggest CB750 based motor... I'm thinking that something a little smaller would last a lot longer...

[dragracer]

     Let's not forget that the snout on the 900f crank must be machined off. That's where the advancer/points plate is going. Take a stock SOHC 750 crank and the 900f crank to your local machine shop. Have him/her machine the end of the 900f crank to match the slight recess of the 750 timing end. The 900f crank end is fairly soft and easy to machine. The plate "pin" hole can be located from the casting centerline. The machinist will understand. A fairly easy turning job.
     Remember that the crank determines the seals. Use the 900f seals with the 900f crank. Otherwise you'll leak around the machined end of the 900f crank.
     Clearancing is fairly easy as only a little material is removed from the case to clear the throws. The 900f crank is fairly heavy and can be lightened. The lightening can replace the case clearancing in some areas.
     The 1100F crowd has their own internet forums. Sometimes the rods/cranks can come up there in the classified.

     Somebody should make up an adapter to the splined end of the 900f crank which will allow kick/electric starting in our cases. I haven't the time yet to design that one up, but it can be fairly easily done. Otherwise use a splined sleeve around the crank with a 1 1/8" nut welded to the end of it with a bolt going through the center of it to hold it on. Your normal external starter will start it just fine.

     Yes, after doing all that work, everything will spin just fine in the cases. Depending on the rods used, you'll have 2 to 3 mm clearance with the bottom of the case. Yes, it can be stroked more. Previously done by Superbike Mike Keyte as stated on the Honda Dragbikes section of facebook. "We had a similar project in the late 80's. 40mm intake valves with 8mm stroker and 78mm pistons 1357cc. Made 156hp." There's your biggest CB750 based motor... I'm thinking that something a little smaller would last a lot longer...

Jon, thanks for reminding me about the DOHC forums. I'll check it out. My plan is to explore the possibility of an electric starter versus the kick starter. I've got an old 750 DOHC under a shed i can at least source the starter clutch from in hopes of modifying something to work. I'm not in a hurry to get this done but at least i've now got a crank coming my way to begin the process.

Like you said before, i'm not trying to break any records and have no set ET goal. I just want to mess with another project to occupy my mind with the side benefits being a drop in ET somewhere along the way. If this starts to get too costly, i'm putting the brakes on it right away. Its just not worth expending a fortune on the old Honda's from my prospective to go quicker. I can go a lot faster on the KZ based bikes i own or spend that money on a pending Busa based dragbike project waiting in the wings.  I'm hoping that what Bill and I learn from this process can be documented to help others who may be way more serious in building a hot rod Honda than i am. If this was about going faster than anyone else, i could easily put together a nitrous kit from various parts for around $500 and spray the house down till it goes or blows.

[POPS 911]

FRANK:  BUSA will make you leave everything else in the past { HONDA or KZ'S }  my son TROY SMOCK has a shop full of all motor BUSA , stroker , spray , turbo, or ALL MOTOR.  He helped build the first RICHARD [ guy from England ] SUPERCHARGER motor to run for MSP.

[dragracer]

     Let's not forget that the snout on the 900f crank must be machined off. That's where the advancer/points plate is going. Take a stock SOHC 750 crank and the 900f crank to your local machine shop. Have him/her machine the end of the 900f crank to match the slight recess of the 750 timing end. The 900f crank end is fairly soft and easy to machine. The plate "pin" hole can be located from the casting centerline. The machinist will understand. A fairly easy turning job.
     Remember that the crank determines the seals. Use the 900f seals with the 900f crank. Otherwise you'll leak around the machined end of the 900f crank.
     Clearancing is fairly easy as only a little material is removed from the case to clear the throws. The 900f crank is fairly heavy and can be lightened. The lightening can replace the case clearancing in some areas.
     The 1100F crowd has their own internet forums. Sometimes the rods/cranks can come up there in the classified.

     Somebody should make up an adapter to the splined end of the 900f crank which will allow kick/electric starting in our cases. I haven't the time yet to design that one up, but it can be fairly easily done. Otherwise use a splined sleeve around the crank with a 1 1/8" nut welded to the end of it with a bolt going through the center of it to hold it on. Your normal external starter will start it just fine.

     Yes, after doing all that work, everything will spin just fine in the cases. Depending on the rods used, you'll have 2 to 3 mm clearance with the bottom of the case. Yes, it can be stroked more. Previously done by Superbike Mike Keyte as stated on the Honda Dragbikes section of facebook. "We had a similar project in the late 80's. 40mm intake valves with 8mm stroker and 78mm pistons 1357cc. Made 156hp." There's your biggest CB750 based motor... I'm thinking that something a little smaller would last a lot longer...

Jon, what exactly did you do about the primary chain mating to the clutch basket?? I think you said something about sourcing a GL basket. Did you cut the rivets out of the basket and use just the GL gears mated onto the SOHC basket?? I need more info on this arrangement please.

Bear, what did you use to convert from the DOHC crank to the SOHC clutch system??

Oh, and sorry Bill for hijacking your thread but it seems what I'm asking will affect both of us equally.

[bear]

     Let's not forget that the snout on the 900f crank must be machined off. That's where the advancer/points plate is going. Take a stock SOHC 750 crank and the 900f crank to your local machine shop. Have him/her machine the end of the 900f crank to match the slight recess of the 750 timing end. The 900f crank end is fairly soft and easy to machine. The plate "pin" hole can be located from the casting centerline. The machinist will understand. A fairly easy turning job.
     Remember that the crank determines the seals. Use the 900f seals with the 900f crank. Otherwise you'll leak around the machined end of the 900f crank.
     Clearancing is fairly easy as only a little material is removed from the case to clear the throws. The 900f crank is fairly heavy and can be lightened. The lightening can replace the case clearancing in some areas.
     The 1100F crowd has their own internet forums. Sometimes the rods/cranks can come up there in the classified.

     Somebody should make up an adapter to the splined end of the 900f crank which will allow kick/electric starting in our cases. I haven't the time yet to design that one up, but it can be fairly easily done. Otherwise use a splined sleeve around the crank with a 1 1/8" nut welded to the end of it with a bolt going through the center of it to hold it on. Your normal external starter will start it just fine.

     Yes, after doing all that work, everything will spin just fine in the cases. Depending on the rods used, you'll have 2 to 3 mm clearance with the bottom of the case. Yes, it can be stroked more. Previously done by Superbike Mike Keyte as stated on the Honda Dragbikes section of facebook. "We had a similar project in the late 80's. 40mm intake valves with 8mm stroker and 78mm pistons 1357cc. Made 156hp." There's your biggest CB750 based motor... I'm thinking that something a little smaller would last a lot longer...

Bear, what did you use to convert from the DOHC crank to the SOHC clutch system??

I used the GL primary.
You can run the GL 6 bolt clutch as well with a little bit of work, both clutches use the same plates from memory.

I'm using the 4 bolt clutches at the moment but we have fiddled with the 6 bolt clutches in the deep dark past.

Cheers,
Brian

[dragracer]

Bear, are you saying that you used the GL clutch basket assemby or the entire GL gear cluster input shaft in place of the stock SOHC input shaft/gears along with the GL basket?? Sorry, just a bit confused on what you mean by the GL primary.

http://www.ebay.com/itm/130510903139?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT