Topic: Ultimate motor

[lordmoonpie]

ust to keep the debates going - here's today's picture...crank cases with hy-vo primary inside are joined and the pistons on the Arrow rods. The HD studs are in and the rear camchain tensioner installed. This is a custom made piece from KA performance. Essentially it's a copy of the SOHC slipper design used by M3 but modified to have a 16mm wide track for the hy-vo camchain instead of a central 2mm track for the traditional roller chain.

On the right of the picture you can see the CB350 K4 rotor grafted onto the DOHC crank, above that the plug for the starter motor (referring to another thread on the forum!) and above that the final drive sprocket - thinned down to 520....

[MRieck]

 I tell you Lordmoonpie I appluad your efforts. It is easy to extract horsepowerout of modern engines (and so it should be) but where is the fun? Besides....having to install 32 4mm stem valve keepers in a tiny bucket bore blows.  :DThat engine is outstanding in regard to execution. I imagine you spent many hours developing your plan AND many hours getting the one off parts. Thanks for sharing all your hard earned info so freely.
  Mike

[lordmoonpie]

Hey Mike it's a pleasure! Aside from the challenge, one of the things that really got under my skin was the total lack of help and in fact in some cases, misinformation that the CR750 experts around the world were willing to provide. Some of them were slipperier than a politician with their replies, answering the question but without passing on any information. Some just told me half a story so you set off following the path they indicate just to hit a big fat dead end.

So when this baby is finally all put together and running, I'm gonna write the whole thing up in detail and publish it on the Internet so anyone else who wants to build a darn good CR750 replica can do so without the frustrations and that includes a full list and contact details for all of my suppliers.

In the meantime, happy to post pics and progress here as long as you guys find it interesting enough to read and comment on, good or bad 

[bwaller]

I agree it is refreshing to see such a good clean build with all the extra experimentation towards not only power improvement but with reliability as well. Good work, you have my applause also.

Sharing your progress is very decent of you, but I might suggest you contact Mitch Boehm when you're done. Motorcyclist is branching out with a new publication called Motorcyclist Classic with Boehm as editor. I wouldn't pretend to know what they look for in terms of content, but I'll be subcribing and this interests me!!

[MRieck]

I agree it is refreshing to see such a good clean build with all the extra experimentation towards not only power improvement but with reliability as well. Good work, you have my applause also.

Sharing your progress is very decent of you, but I might suggest you contact Mitch Boehm when you're done. Motorcyclist is branching out with a new publication called Motorcyclist Classic with Boehm as editor. I wouldn't pretend to know what they look for in terms of content, but I'll be subcribing and this interests me!!

Great idea about the magazine article.

[Terry in Australia]

The hy-vo camchain I accept I have done simply because Pete Rhodes said it *should* be possible but he didn't know if it had been done. I'm a total sucker for a challenge so I set out to fit the hy-vo camchain too and use the DOHC crank. It creates hellish problems with tensioners and the head clearances and I'm the first to admit that I'm not far enough through the project overall to run the engine and see if it works, BUT, it's different, it's been a challenge, it's been rather exciting (sadly!!) to overcome the obstacles at each turn and it's really good fun to be trying something a bit new.   

G'Day M'Lord, that's great work, I love those pistons, they look like the 12.5:1 CR Arias pistons in my 836CC engine? How difficult was the grafting of the smaller alternator rotor?

I'm surprised that little was known about using the Hi-Vo cam chains on CB750's in Britain though, Axl (Satanic Mechanics) has been talking about them for as long as I remember, and Rex Wolfendon has been running them in his engines forever.

Maybe you should send your experts out to the colonies for some refresher training, ha ha! Well done again, keep the pics and info coming!    

[lordmoonpie]

Thanks Terry - the pistons are wiseco 62mm straight from Mark McGrew. Funny really I've tried to get another set from him and he just never ever replies. Wonder what's going on there, maybe I'd better go to Dynoman! Not sure what compression this will give me but I've got 12.5:1 in the back of my mind for some reason?

Anyway, the crank work was done by Pete Rhodes here in the UK to fit the rotor. Apparently it's an easy enough mod, the hardest part is setting the machines up with a dirty great crank in them to trim down!

Next build pic attached, with the barrels on, the front camchain blade can go in. Can't use the original CB750 blade as it's also got the central ridge for a roller chain so this has to be altered as well. The one I settled on was a CB250N blade with about 1.5" trimmed off the bottom to fit the 750 cases. Of course there was a lesson in this little episode too - I bought the first blade and chopped it and chewed it up and made it fit but it was left in a not too nice state after all the experimenting to fit. No matter I thought, it wasn't expensive so I'll order another one and do the final mods I'd arrived at with the original blade. DOH!!! I had just butchered the last blade stocked by David Silver and he was showing the part as obsolete worldwide!!

Thankfully a very small local Honda dealer had one in old stock...phew! Another close call averted....

[lordmoonpie]

I'm surprised that little was known about using the Hi-Vo cam chains on CB750's in Britain though, Axl (Satanic Mechanics) has been talking about them for as long as I remember, and Rex Wolfendon has been running them in his engines forever.

Forgot to say that I talked this through with Axl a while back and he said that it all seemed possible but again, hadn't had the experience of building a hy-vo camchain SOHC. maybe he's done it in the interim since I first spoke to him. Most of the guys from down under who email me for info get my details from SatanicMechanic and most seem interested in the primary rather than the camchain which is odd given the apparent historic weakness of the camchain and the more reliable primaries?!

[jaguar]

i would be very interested in reading more about your build in an articl form. 
im building my own cafe/CR750.  starting the motor soon and would like something powerful and reliable.

[Terry in Australia]

I'm surprised that little was known about using the Hi-Vo cam chains on CB750's in Britain though, Axl (Satanic Mechanics) has been talking about them for as long as I remember, and Rex Wolfendon has been running them in his engines forever.

Forgot to say that I talked this through with Axl a while back and he said that it all seemed possible but again, hadn't had the experience of building a hy-vo camchain SOHC. maybe he's done it in the interim since I first spoke to him. Most of the guys from down under who email me for info get my details from SatanicMechanic and most seem interested in the primary rather than the camchain which is odd given the apparent historic weakness of the camchain and the more reliable primaries?!

Yeah, well that's got me stumped too mate, I can understand that for absolute "no holds barred racing where every pound matters and the bike gets rebuilt every other race meeting" roller chains would be the preference only due to their lighter weight, but for an engine that you're hoping will last for many years with absolute reliability, the Hi-Vo's have to be the way to go? Am I missing something? (apart from the obvious................) 

[lordmoonpie]

Well here's today's pic and a particular problem with the hy-vo camchain idea. In the SOHC head it's machined nicely to accept a roller chain on a thinner cam sprocket. Add the hy-vo chain in and it fits in the cam chain tunnel OK but you than have to naturally fit a hy-vo cam sprocket. First problem - to get one that will have the same number of teeth equal to twice the crank teeth to get the good old 2:1 ratio crank to cam. Secondly, it has to fit the shoulders of the SOHC cam.

So, I took the original SOHC cam sprocket and found an equivalent hy-vo sprocket that was the right ratio. I suspect there might be a honda sprocket that will be a straight bolt on but couldn't find anything so settled on a CB700 cam sprocket for the hy-vo variant. I then had a custom sprocket made up with the CB700 teeth and thickness for the hy-vo and the internal slots and lobe cutaways to match the SOHC sprocket. It was slotted for 10 degrees of movement as well to dial the thing in.

All bolted up and....disaster! The thickness of the new hy-vo sprocket meant that when the engine turned the cam sprocket bolt heads didn't clear the cylinder head. It would have been a fairly quick stop for the engine if I hadn't noticed that one!

Solution was to trim back the heads on the cam sprocket bolts which seem to have a lip around the outside of half a millimetre or so and then also dish the centre of the custom cam sprocket so that it's the same thickness as the SOHC sprocket right out to 10mm from the teeth. It then all bolts up fine with decent clearances side to side. The picture is a bit blurry unfortunately but should give an idea of the finished item...and that I thought was the final challenge sorted. Oh how wrong I was 

[Terry in Australia]

Oooer, more mechanical porn, beeeootiful M'Lord, just beeeootiful............ 

[sparty]

Thanks Terry - the pistons are wiseco 62mm straight from Mark McGrew. Funny really I've tried to get another set from him and he just never ever replies. Wonder what's going on there, maybe I'd better go to Dynoman! Not sure what compression this will give me but I've got 12.5:1 in the back of my mind for some reason?

Anyway, the crank work was done by Pete Rhodes here in the UK to fit the rotor. Apparently it's an easy enough mod, the hardest part is setting the machines up with a dirty great crank in them to trim down!

Next build pic attached, with the barrels on, the front camchain blade can go in. Can't use the original CB750 blade as it's also got the central ridge for a roller chain so this has to be altered as well. The one I settled on was a CB250N blade with about 1.5" trimmed off the bottom to fit the 750 cases. Of course there was a lesson in this little episode too - I bought the first blade and chopped it and chewed it up and made it fit but it was left in a not too nice state after all the experimenting to fit. No matter I thought, it wasn't expensive so I'll order another one and do the final mods I'd arrived at with the original blade. DOH!!! I had just butchered the last blade stocked by David Silver and he was showing the part as obsolete worldwide!!

Thankfully a very small local Honda dealer had one in old stock...phew! Another close call averted....

Quick question:  What is up with the sleeves in that picture?

Sparty

[Terry in Australia]

Are you talking about the little line of oil around the tops of each bore, or the vertical line in #3 Art? I'm guessing that's just oil too. Cheers, Terry.

[sparty]

Are you talking about the little line of oil around the tops of each bore, or the vertical line in #3 Art? I'm guessing that's just oil too. Cheers, Terry.

Yep, that's it.  I am on a school computer with poor picture quality.

Art

[lordmoonpie]

Phew - you had me worried then 
Yes it's just oil in the bores to help squeezing the pistons in - see how fresh that picture was 

[754]

Could the area under the bolts be spotfaced or counterbored?

Would buttonheads give better clearance?

Could you remove a bit off the cam tunnel?, you did  trial fit the head before final assembly.

[lordmoonpie]

Probably yes to all of those but I figured that if the centre of the sprocket was the same thickness as the SOHC sprocket it had to work. Also it loses a fair bit of mass from the hy-vo sprocket without compromising strength. A good compromise solution I think?

[754]

if it is the same thickness, you would theink they would not hit. The outer part of the sprocket is where I would think thete is a problem. Is it harder to get the cam through?

[lordmoonpie]

No it's OK actually - the outer is fine, well there's enough clearance. It was just the sprocket bolts. As the holes for the cam were modelled on the SOHC sprocket it sits perfectly on the cam shoulders too. Of course I still have to run it up to prove it all, so not 100% certain just yet 

[Terry in Australia]

How far away are you from firing that beast up mate? Have you got a video camera with sound? Ooooer!

[Sam Green Racing]

I think Terry is about to arrive

Sam.

[Terry in Australia]

I think Terry is about to arrive

Sam.

Well it is the nicest thing I've seen on this site in a while Sammy, ha ha!

[Sam Green Racing]

I don't know Terry, the babe thread has a good selection on it today

[Terry in Australia]

Any porn site on the web has pictures of pretty girls Sammy, I look at this site for motorcycle stuff, and that engine is very pretty!