Topic: Does your SOHC 750 loose its MOJO with one of these?

[Tom]

Hi guys Here is a blast from the past, my mate Baz emailed this bit of HiPo gear from the MTC 1973 Cattledog it was made in England by Piper Eng talk about a sign of things to come.. DOHC 4V for your CB750. I Bet it cost a bomb too....TC

[Retro Rocket]

MMMMMMMMMMM   i likey....

I wonder if anyone here has actually seen one...

Mick

[MRieck]

 Can you imagine how nice that would be CNC'd with modern valve angles and 5mm valves. 100HP at 8,000....I just about have that with 915cc. It could be the porting...maybe. 

[HondaMan]

Can you imagine how nice that would be CNC'd with modern valve angles and 5mm valves. 100HP at 8,000....I just about have that with 915cc. It could be the porting...maybe. 

Mike:
Have you ever seen the long-ago 1000cc kits from R/C (or maybe it was Action Fours?) where the cylinders were bored so far, and sleeves fitted that could be seen? They came with a much-modified head (bigger in & out valves), big studs, oil cooler and the reinforced cam cover (I seem to remember it was R/C).

The cost of those parts made a brand-new CB750 bike into an accessory in 1973! 

I saw several on AMEN hardtail frames (a pair of them came to me for fine tuning after a whole winter of chop-and-paint, circa 1973) in 'the day'. The one I test-rode after tuning would break the 5.00-16 rear tire loose in 3rd gear by just rolling on the throttle at 4000 RPM. 

[754]

Breaking the tire loose at 4K in 3rd is what I am looking for..

 What did they have for carbs on them..?

[cavebear]

Carbs? We don't need no steeking carbs!

[cavebear]

[cavebear]

[cavebear]

[754]

 Now we are talking...

[MRieck]

 Did those monsters fit on the stock airbox? God that adapter plate weighed 3 lbs.

[MRieck]

Can you imagine how nice that would be CNC'd with modern valve angles and 5mm valves. 100HP at 8,000....I just about have that with 915cc. It could be the porting...maybe. 

Mike:
Have you ever seen the long-ago 1000cc kits from R/C (or maybe it was Action Fours?) where the cylinders were bored so far, and sleeves fitted that could be seen? They came with a much-modified head (bigger in & out valves), big studs, oil cooler and the reinforced cam cover (I seem to remember it was R/C).

The cost of those parts made a brand-new CB750 bike into an accessory in 1973! 

I saw several on AMEN hardtail frames (a pair of them came to me for fine tuning after a whole winter of chop-and-paint, circa 1973) in 'the day'. The one I test-rode after tuning would break the 5.00-16 rear tire loose in 3rd gear by just rolling on the throttle at 4000 RPM. 

Mark...I do remember those "big" kits. It was RC. I never had enough dough for that plus I rode my bike everywhere back then. Those kits kinda limited what you could do.

[cavebear]

Original owner on the RC set spent 6 months talking to them and bought the Weber factory tuning book to get them set up  I have the tuning guide and the carbs are currently set up for a hot 836cc application.

[BLUE71TURBO]

 CARBS ?  Who need's carbs !   

                   

                   

[Tom]

Mike:
Have you ever seen the long-ago 1000cc kits from R/C (or maybe it was Action Fours?) where the cylinders were bored so far, and sleeves fitted that could be seen? They came with a much-modified head (bigger in & out valves), big studs, oil cooler and the reinforced cam cover (I seem to remember it was R/C).

The cost of those parts made a brand-new CB750 bike into an accessory in 1973! 

I saw several on AMEN hardtail frames (a pair of them came to me for fine tuning after a whole winter of chop-and-paint, circa 1973) in 'the day'. The one I test-rode after tuning would break the 5.00-16 rear tire loose in 3rd gear by just rolling on the throttle at 4000 RPM. 

I Bought the bits and built a RC Cobra engine in 1975, I Gotta say RC, Terry Vance and Byron Hines were all very helpfull to this then newby from Oz and they were happy to spend plenty of time showing me the ropes, Had some trouble keeping the head gasket sealed and ended up with the head grooved and some paino wire orings squished into the alloy headgasket, the barrels were a problem with oil leaks, and yes you could see the sleeves thru the gap1-2 and 3-4 it was 70mm 970cc venolia pistons Carrilo Golden rods, RC lightened and fully polished crank, 327 cam with adjustable cam sprocket, manley ss oversize valves heavy springs and alloy retainers, RC Ported and polished head,  lightened and polished rockers Barnett clutch and an ARD Mag, It was hard to start but a real beast when it was running and it had plenty of power and would light up the tyre with a twist of the throttle. i hope to build another shortly not as big, and hopefully oil tight this time, to go in my Rickman, it had had a 1000cc MTC kitted engine but leaked oil everywhere too.. so it got sold..im over the oil leaking barrels. TC

[Retro Rocket]

Hi Tom, you need one of Mike Rieck's billet blocks mate, they are the ducks guts ...

Mick

[Howell]

Piper 4 valve sohc:

http://www.curtisracingframes.com/articles/cycle-canada.html

[turboguzzi]

nice CB porn guys,

which begs to ask, cant you fit a 16 valve CB750F head on a sohc?

never gotten into those motors so pardon my ignorance....

[kos]

You probably could. Bore enters are close and you would have to change cam sprockets to work with standard SOHC chains as DOHC had Hy-vo cam chain. No, wait...you could use DOHC crank and then do the Hy-Vo primary drive conversion. Oh, that sounds like a winner!


Two reasons not to:

1) Those heads had the deep pentroof combustion chambers Honda used in 60"s...and they did not make much power, unless reved to the moon! Even 2 valve Kaws and Suzukis of the period. worked better than this Honda DOHC. In fact Honda never won an AMA Superbike Championship until they went to V4, VF750F's and Kaw beat them the first year they tried.

2) You can bolt in a DOHC engine in a CB750 SOHC frame without much trouble.

And thirdly....You would have to leave this forum, as you would have one too many cams...and we don't want that to happen.

KOS

[BLUE71TURBO]

Hey KOS, TURBOGUZZI was asking if you could bolt a dohc HEAD on a early sohc engine not swaping engines in frames.  

[bear]

You probably could. Bore enters are close and you would have to change cam sprockets to work with standard SOHC chains as DOHC had Hy-vo cam chain. No, wait...you could use DOHC crank and then do the Hy-Vo primary drive conversion. Oh, that sounds like a winner!

We run a couple of hy-vo motors and their the ducks guts. But I'd have to agree I can't see a lot of benefit fitting an 16v head to these motors.
I don't believe these motors produce anything worthwhile re; power over about 8'000rpm.
We've played around with big cams with a lot of overlap and all we where getting was a lot of noise at the expense of throttle responce, reliability and good usable power.
It may be a different story for the Drag blokes and I'm happy to stand corrected, there are certainly greater minds than mine contributing to this forum.
Oh, and now that I've worked out how to post reasonable quality pics, if anybody would like a particular pic of the internals of our motors, one's partially stripped on the bench and our regular race motor will  hopfully be the recipient of a new camshaft courtesy of MRieck tomorrow or the day after depending on the USPS.

Cheers,
Brian

[bwaller]

Oh bear when it comes to pics on here, you don't need to ask, just go ahead & post them. 

[Sam Green Racing]

MMMMMMMMMMM   i likey....

I wonder if anyone here has actually seen one...

Mick

The answer is yes and they made the same for the CB350 twin and the Austin Mini Cooper.
The stumbling block here though is the power (or lack of it) for all that effort. (1,000cc 100bhp)
Honda with their Daytona CRs could only just get close with their wild cam timing and extra revs and we know how long they lasted.
In todays world, a set of 836 pistons, a decent set of valves in a well ported head, throw in a set of carbs and a pipe and you have close to this power and it's reliable.
Perhaps the thing that allows us to to keep our motors together where Honda failed at Daytona is in the cam chain tensioner, over to you Kos.

Sam.

[kos]

Hey KOS, TURBOGUZZI was asking if you could bolt a dohc HEAD on a early sohc engine not swaping engines in frames.


Yes, He did, and I told him how in my first paragraph! Did you read it?

KOS

[kos]

MMMMMMMMMMM   i likey....



Mick

Honda with their Daytona CRs could only just get close with their wild cam timing and extra revs and we know how long they lasted. :'


Sam.

Yes to the wild cam timing, but what really hurt the reliability in those factory RC750's that took on AMA Class C racing at Daytona... was the tall, stiff valve springs. Take a look at the difference in the stock spring and the CR kit spring (970) part number. Another reason to have that hold down cover with bolts to put tenion on the camshaft holders. BTW factory bikes did not use that hold down cam cover!

Now with today's better metallurgy and manufacturing process, springs work much better at much lower spring rates and that is why when members come upon old parts like alloy retainers, high perf springs new in package from 40 years ago...you should keep them in the package not in your motor.

KOS

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