Topic: Ultimate motor

[mdl91881]

So the 78F is almost a "frame roller" just waiting on few parts. I'll get some pics up under my build when I get it together.

Now that that is done time to look to the motor.

So my question to everyone is....

I want this old 500 lber to have some go to her.  So lets hear some motor input... I still want it to be reliable because it is a street bike.

My only "grey" area is that it is a F model and I know some things are differnt in the heads.

So far my list includes....

1. 836 kit
2. cam, not sure on what kind
3. heavy duty studs
4. heavier valve springs
5. ti retainers
6. Dyna ignition and coils, maybe dyna 2000 havent decided yet
7. lighten and balance crank
8. HD cam chain
9. adjustable cam sprocket
10. kerker exhaust

so what works good together, what brand is best,  and the number one question, is this old moter worth that kind of money when you can get new HP so cheap on some newer bikes.




 

[MRieck]

 I'd use a K or early F head. You can get Ti retainers from R/D but you have to use their springs. And the kit is very expensive. Dynoman makes new valves for that head and 836 pistons for the larger chamber. Stuff costs more for the F2 head. I'd add porting to that list too.

[Sam Green Racing]

Better ask him how experienced a rider he is before porting the head for him Michael.

Sam.

[mdl91881]

other than cost is there any reason to go with a K head vs keeping the F

[Sam Green Racing]

Stuff costs more for the F2 head. I'd add porting to that list too.

valve/guide wear is heavy on the later Fs

 

[HondaMan]

Better ask him how experienced a rider he is before porting the head for him Michael.

Sam.

+1...the 750 can already do 130 MPH....

[754]

This thread ids useless without mentioning carbs!!

And I would go a lot bigger for an Ultimate motor, but if you want long life..go 836..

[Sam Green Racing]

Better ask him how experienced a rider he is before porting the head for him Michael.

Sam.

+1...the 750 can already do 130 MPH....

We've just picked up a full streamlining for the CR Mark, we'll be needing some very small back sprockets

Sam.

[333]

"Back in the day" the saying was "the more radical the engine, the less reliable it will be".  This was said for all engines, not just motorcycles.  And I'm guessing it is still true today, especially if we are talking about older engines.

Now I'm not trying to talk you out of building your engine the way you want.  And I say these things having rebuilt an engine or 3, but have never "built" one.  Every engine I have done starts on the first pull, first kick, or within 5 seconds of hitting the starter button.  Every 836 I've seen doesn't start anywhere near as easily.  I worked for a guy who sold a K5 to his brother who did the 836 kit.  A couple years later, he bought it back and went to the trouble of putting it back to stock because it ran so unreliably.  It still runs today.  He is trying for a record- most miles on a single set of points.  The last time I asked, he was around 60K.

No question.  An 836 can run like a raped ape(when warm).  But reliable?

[754]

An 836cc should not be hard to live with, nor be hard starting..

add a good 3 anle or more valve job to the list in the OP

[KB02]

...and the number one question, is this old motor worth that kind of money when you can get new HP so cheap on some newer bikes.

There in lies the Million dollar question. And the truth of the matter is, only you can answer it for yourself. There is currently a Honda CBR1000 with a buy it now price of $1600 on ebay right now. Lots more power and better handling then you'd be able to get out of one of these old girls that we tinker on. I am planning on spending between $1500 and $2000 on just my engine for my K8 build. To me is it worth it? You bettcha!! To one of my buddies at work, is it worth it? Not really. He'd rather have the CBR on ebay.

It's a love and a passion that drives me on my project. Plus you get the bragging rights when you tell people about all the work that went into your engine. 

I say build it. (and send the head to Mike)   

[sparty]

and the number one question, is this old moter worth that kind of money when you can get new HP so cheap on some newer bikes.

For me, the money I spent to a high horsepower CB750 was worth it.  Few people will have an engine like mine and that appeals to me.  I have said this before, anyone can buy a out of the box superbike, but not everyone can have a Hot Rod CB750.

If you are going to build it, be sure to do it right.  It will cost you, there are no shortcuts and it can't be done for $2000.  Rods alone are a grand.  Add on CR carbs and you are near $2000.  Cam, bore, headwork, Dyna 2000, studs, APE crank, pistons, retainers, valves, etc ...... ya see where I am going?  You have to be serious about your engine.

Sparty

[lordmoonpie]

more tuning = less reliability for sure but also you need deeper pockets. I guess you have to optimise all of the factors of use, cost, reliability and how long you want to spend rebuilding her each week   

$2000 for an engine build sounds good to me but then I wanted to build an engine for a challenge as much as anything - to get power equal to or btter than M3 and get (hopefully) around the eternal achilles heel of the 750 by using a DOHC crank in an SOHC motor. As a result almost everything inside my cases bar the clutch basket has been thrown away and replaced.

One day I'll add up the cost and probably fall off my perch with shock but just the big ticket items include pistons at $850, rods (one off) at $2000, close ratio gearbox $3000 and that's ignoring the odd bits like mirror pattern one off shift drums and so on....

I may be a bit mad spending this on a nearly 40 year old motor but the challenge was there to be aimed at....all I need to do now is finish it off and see if it starts     

[Sweep]

For what it's worth my 836 starts within 5 seconds with the starter and on the first kick when warm and idles reliably.  I've not tried kicking it cold but I have enough kick start only bikes so I think I'll skip it.

[Jerry Rxman Griffin aka MuthaF'er]

and the number one question, is this old moter worth that kind of money when you can get new HP so cheap on some newer bikes.

For me, the money I spent to a high horsepower CB750 was worth it.  Few people will have an engine like mine and that appeals to me.  I have said this before, anyone can buy a out of the box superbike, but not everyone can have a Hot Rod CB750.

If you are going to build it, be sure to do it right.  It will cost you, there are no shortcuts and it can't be done for $2000.  Rods alone are a grand.  Add on CR carbs and you are near $2000.  Cam, bore, headwork, Dyna 2000, studs, APE crank, pistons, retainers, valves, etc ...... ya see where I am going?  You have to be serious about your engine.

Sparty

Where Sparty is going is the bank to the tune of about $5000. Not for the faint of heart or billfold. I'm with you Bud! If you're going this far you'd better go all the way or you're wasting your first $3000 on a blown engine!

[Terry in Australia]

Well as much as I'd like to bore the pants off everyone here with tales of my "ultimate" 836 engine, I think we've all been "trumped" by Lord Moonpie!

I better get going with my RC Suzuki GS1000S rebuild, I think the good Lord might be able to kick my Honda's arse, ha ha!

[lordmoonpie]

Well I'm not so sure Terry - the lump has not yet been started after all. It could be the biggest, most expensive smoke display ever seen when it all comes down to it 

It did get me thinking though - I'd better get the spreadsheet cranked up and see how much it is costing me. Maybe I could have just bought something instead? Mind you, where's the fun it that 

[lordmoonpie]

Hmmm, now I sat down and added it all up.....I could have bought a 999R Ducati instead!

Just got the megaphones and paint to go - engine build including all sundries, blasting, polishing, parts, etc is currently standing at $17,400 USD and I still don't know if it'll run!!

Well at least it kept me off the streets for the past 5 years...

[Terry in Australia]

Oh my Gawd! Either you're dedicated to the SOHC 750, or you've got waaaay too much disposable income! Post some pics mate, I'm drooling all over this keyboard!

[754]

WHY.. do you prefer the DOHC crank???

[MRieck]

Hmmm, now I sat down and added it all up.....I could have bought a 999R Ducati instead!

Just got the megaphones and paint to go - engine build including all sundries, blasting, polishing, parts, etc is currently standing at $17,400 USD and I still don't know if it'll run!!

Well at least it kept me off the streets for the past 5 years...

Not to hammer home 754's point BUT the Chain primary?

[Terry in Australia]

Mmmnnn, Hi-Vo primary and cam chains, lovely!

[lordmoonpie]

That's exactly it Terry - I could have gone the CB750A route to get hy-vo primary but thought I'd go the whole way and get a hy-vo camchain as well so I can use all that horsepower and not worry about the chain breaking.

Of course this is where the can of worms gets opened....clearances, chain guides, cam sprocket...

It's gone together at least 

[MRieck]

That's interesting about the HyVo cam chain....most folks go the with the roller chain ie. Hayabusa chain conversions, late KZ/GPZ engine dragracers using early chain setups etc

[moham]

Hi-Vo primary and cam chains

for those of us un-enlightened (myself), what is the Hy-Vo?