Topic: High Performance Bore Kit Questions.....

[Retro Rocket]

anybody fancy trying it.

I know there's a "N" missing but Sam, get your mind out of the gutter.....

[jweeks]

77 mm bore by 71 mm stroke is 1323 cc. That's as close as I can figure it. Don't assume the spacer is just due to the stroke increase. There may be some sleeve milling that's being offset by the spacer. 9mm over stock is all that you usually can fit. Yes, the article showed a 9.5 mm stroke increase for that 1380 motor. I'd guess that anything over a 5 mm spacer would also require some case relief and welding in some lumps if it's possible. The horsepower per cubic inch would be down due to the lack of air to pump through it. Your midrange torque would be nice, but the top end wouldn't be the rush that you'd expect. A 4 valve head would help that kind of displacement. A 900F head on top of that displacement would be far more interesting to me.... (Yes, in theory it can be done having the same bore spacing)

                                           Jon Weeks

[Sam Green Racing]

anybody fancy trying it.

I know there's a "N" missing but Sam, get your mind out of the gutter.....

Not sure what you're on about Mick but it means something totally different in the States anyway. 

Back to guessing whats in there and my final guess as I've got better things to do

836cc pistons with an 18.406mm spacer (including gaskets) = 1324.999cc. 

It would be much easier to lock the thread and wait for Daddy to come up with the real figures.

Sam.

[Bill/BentON Racing]

Just looking at the bikes,no doubt they have turned some healthy numbers! Sammy,don't you be locking no threads!!!! ;)We're racing @ Commerce this coming Sat. the 13th.Paul C. putting on motorcycle class ET,along with the BIG Nostalgia car race/show!!! Going to run Calendar Girl,will be working on race prep for Samauto.Bill

[Big Jay]

anybody fancy trying it.

I know there's a "N" missing but Sam, get your mind out of the gutter.....

Not sure what you're on about Mick but it means something totally different in the States anyway. 

Back to guessing whats in there and my final guess as I've got better things to do

836cc pistons with an 18.406mm spacer (including gaskets) = 1324.999cc. 

It would be much easier to lock the thread and wait for Daddy to come up with the real figures.

Sam.

Sam;
You can't increase the displacement with a spacer plate.   

[Big Jay]

Here is some food for thought guys. When we stroke these cranks, we can not relocate the oil holes through the crank. So on a 8mm stroker, we offset the journal 4mm. This makes the oil holes in the rod journals 4mm off of center.

We have done this on Hayabusa cranks, and it is kind of edgy.

Next, the main thing to consider when putting a big stroker in these inline fours is that the clutch basket will interfere with #4 con rod at some point.

As for the photo of the motor with the thick plate under the cylinder block, you really can't figure how much stroke it has based on that. You realize that you drastically shorten the rod ratio when you do big strokers. I would assume that motor has rods longer that stock to get the ratio back to a reasonable number, hence the need for the thick plate.

We have a project like that going thru the shop right now.


Skiparachi;  Put one of our clutches with two extra plates in it and it will hold anything that motor can put out.

[jweeks]

Jay,
     We're talking about the 900F cranks in the 750 cases, not the CB750 stockers. You start with a 6mm longer stroke. The welding and offset grinding is in the 2-3 mm more range, which doesn't move the oil holes as much as a big stroker CB750 one. Some of us manage to avoid the limits of the clutch basket with the automatic powertrain. 

                                                    Jon Weeks

[Sam Green Racing]

anybody fancy trying it.

I know there's a "N" missing but Sam, get your mind out of the gutter.....

Not sure what you're on about Mick but it means something totally different in the States anyway. 

Back to guessing whats in there and my final guess as I've got better things to do

836cc pistons with an 18.406mm spacer (including gaskets) = 1324.999cc. 

It would be much easier to lock the thread and wait for Daddy to come up with the real figures.

Sam.

Sam;
You can't increase the displacement with a spacer plate.   

Damn Jay, you've just wrecked all my plans for my new stroker business, what am I going to do with 3 tons of alloy plate?
 

[Big Jay]

Jay,
     We're talking about the 900F cranks in the 750 cases, not the CB750 stockers. You start with a 6mm longer stroke. The welding and offset grinding is in the 2-3 mm more range, which doesn't move the oil holes as much as a big stroker CB750 one. Some of us manage to avoid the limits of the clutch basket with the automatic powertrain. 


                                                    Jon Weeks

What do you do about the hy-vo chain sprocket on the 900 crank. Do you convert the motor to hy-vo?

[Retro Rocket]

Aussie racer and hipo Honda engine builder Rex Wolfenden uses boldor cranks and as far as i know he uses the hyvo chains, so he must do some sort of conversion...  By the way, the engines Rex builds are very quick and very successfully raced, Many Australian historic championships ...

[Red Good]

Does the early wing main shaft sprocket not have a hy vo chain and compatible with the 750 transmission shaft?

[jweeks]

"What do you do about the hy-vo chain sprocket on the 900 crank. Do you convert the motor to hy-vo?"

Hondamatic 750's come with the hy-vo. It drops in with minimal clearancing using the 900F hy-vo chain.

"Does the early wing main shaft sprocket not have a hy vo chain and compatible with the 750 transmission shaft? "

Yes Gold Wing parts can be adapted for a hy-vo clutch. It's the easier way to a big stroker crank.

                                                                Jon Weeks

[Sam Green Racing]

The CB900 crank has been used successfully in the sohc motor but the 69mm stroke that it offers won't give anywhere near the capacity that this guy is claiming (1325cc) with what looks like a stock block.
Jays 71mm 1000cc conversion only comes out at 1092cc with the 900 crank.
Even Mike's billet block with 77mm pistons would only come out at 1285cc with the same crank.
I'm not 100% sure if Jays 71mm conversion is the maximum for the stock block but if it is, the crank would have to throw an  83.6mm stroke to achieve 1324.12cc.
The strange thing is, our new member has been seen on line several times and has not posted any further information to explain how his father achieved this big motor, perhaps daddy don't want us to know.....or it isn't as big as he thinks it is.
 

Sam.
 

[jweeks]

Sam,
     I've discussed this with Bear before. 69 mm is the 900F stock stroke. There is room for more stroke in Sohc 750 cases, at least in my "big" motor. (69 mm stroke by 74 mm bore) Bear said that there was another 2-3 mm clearance depending on the cases used. I asked Jay at Valdosta last year if he could stroke a 900F crank. The answer was yes. So, my best guess is that 72 mm is the limit for most cases. If I can ever afford it, my ultimate motor would be 72 mm stroke by 77 mm bore with a different head for the airflow that the displacement needs. Building them this big is great for midrange, but top end horsepower won't be increasing anywhere near the % increase in displacement. You can build them relatively big, but making big horsepower is all tied in with air flow through the top of the motor.

                                                          Jon Weeks

[Sam Green Racing]

I agree 100% Jon but looking at what looks like a stock block, I doubt he has 77mm pistons in there

Sam.

[mick7504]

The crank looks to be a stock CB750 or an auto crank.
The bottom photo is of an auto crank which is basically a copy of the CB750 except for the HyVo gear cut.
Have a Captain Cook (look) at the rotor drive. 

[jweeks]

I brought my stock automatic crank and a 900F crank to my local machinist when I built my stroker motor. He turned the end off of the right side in the above picture middle crank to match the bottom crank (in the picture) dimensions. The material cut easily; it's not super hardened steel. You use the the stocker for dimensions to locate the points plate pin hole and drill and tap for the small stud that goes into the end of the right side of the crank. The end result is exactly the same as the stock automatic crank end. (bottom right side in photo)

The left side of the crank you don't machine to match. It's shorter and splined. It takes more engineering and custom part machining to adapt it to electric start one way clutch gear + charging generator. It can be done, but best not done with the stock automatic parts. It's far easier to machine a starter nut to fit over the spline and retain it with a bolt going into the existing threaded hole on that end of the 900F crank. You use an external starter to turn over the crank for drag racing applications. My starter nut on my 900F crank sticks out less than the one I had used on the stock automatic crank version that I had run previously. You could machine a longer nut to cover the splines and retain it with the end allen bolt (like in the picture) so that it would look like the stock crank appearance. I don't know why you would want to, but it could be done.

What I'm saying is that you probably can't tell which crank is being used by the supplied pictures. I can take pictures of my drag Hondamatic motor using the 900F crank, but without motor disassembly, it won't solve any debate.

Sam is correct. A stock block can't fit 77 mm bore pistons. Don't know with resleeving what the limit is ....(72 mm ??) You can build a very big bore without enough support between bores to brag about the size, but the ring seal won't work with flexing sleeves. I've tried that with my 450A Hondamatic drag bike (85 mm or 11 mm oversize was one mm too far.... ) I ended up relocating cylinder studs to allow a bigger od sleeve to solve my problem there. The point is to never assume we aren't crazy enough to try something that others say won't work... 

                                                                     Jon Weeks

[Bill/BentON Racing]

So,what we're saying is .........we want ANSWERS!!!!!!!!!!! or time sheets,dyno runs,time to back up Z claims!!!! Bill

[Big Jay]

Sam is correct. A stock block can't fit 77 mm bore pistons. Don't know with resleeving what the limit is ....(72 mm ??) You can build a very big bore without enough support between bores to brag about the size, but the ring seal won't work with flexing sleeves. I've tried that with my 450A Hondamatic drag bike (85 mm or 11 mm oversize was one mm too far.... ) I ended up relocating cylinder studs to allow a bigger od sleeve to solve my problem there. The point is to never assume we aren't crazy enough to try something that others say won't work... 

                                                                     Jon Weeks

Our 71mms used sleeves that would not break thru into the air passages on most blocks.

[bear]

As you can see looking at the pic below. We had barrels cast but once we ventured past about 74mm with the compression we needed to run using methanol it was impossible to  keep head gaskets sealed because it would strip the barrel studs out of the cases. Boring the top cases to fit the larger sleeves took to much material away around the threads for the studs.

Cheers,
Brian

[sohc boy]

So,what we're saying is .........we want ANSWERS!!!!!!!!!!! or time sheets,dyno runs,time to back up Z claims!!!! Bill

[sohc boy]

as you know the sohc taper is quite  large , 900 dohc spline is rather small ,was all planned to use this in a drag motor ,with a sleeve an nut , after talking to a few guys about using a remote starter on a 12 -13:1 methanol ,locked up ignition motor , i'm a bit hesitant to try it , for fear of spapping it off , any one done this ?   

[jweeks]

11.5 compression on gas with a 74mm bore with steel rods, I had no problems.  A gear reduction starter should turn it over just fine in my opinion.  Use the existing mate to the spline to make your collar. Weld the nut, use a good strong retaining bolt and you should be fine.  Just remember to use the 900 F crank seals  not the  750 ones.

                                                                     Jon Weeks

[bear]

as you know the sohc taper is quite  large , 900 dohc spline is rather small ,was all planned to use this in a drag motor ,with a sleeve an nut , after talking to a few guys about using a remote starter on a 12 -13:1 methanol ,locked up ignition motor , i'm a bit hesitant to try it , for fear of spapping it off , any one done this ?   

Our motors run a CR of 13 Pete and starting isn't an issue with ours.
We have a roller starter but usually use the std kick starter no worries.
The locked advance could be an issue I suppose

Cheers,
Brian

[sohc boy]

thanks Jon an BEAR , for that info,i'll give it a go , have gear reduced starter , may main concern is locked advance ign , has a real kick to it ,used to kick start 836 motor 12:1 38deg ,snaped kick shaft , smashed my knee an ankle few times ,so not real keen on kicking it , plus  drag rules here, they must be self starting ,