Topic: How to get a bit more out of a CB750

[Tom]

I was told years ago that there is no substitute for cubic inches, and that’s hard to argue with, I remember years ago looking at a ski boat it had a blown Bbchevy, man it went, written on the Stern “powered by cubic dollars” and I think that’s about right too. OK I bought a 1976 Rickman CR750 duel seat with mags and Triple discs in 2005 and have been collecting bits ever since, I now have quiet a collection of old school hipo bits and pieces mainly R C stuff with some other bits, that I will build two engines with, One for the Rickman and another for a Amen Savior Chopper but what size? In the past I have had a few, a new K1 std, then kited it with an 836, then built a RC 970, and the Rickman came with a 1000 but it had serious oil leaks between the sleeves and I sold that engine, I have the following sets of pistons with barrels ready to go what do ya all think?
Std 736 cc 61mm, Ape 836cc 65mm, Venolia 850cc 66.5mm, Henry Abe 895cc 67mm, or MTC 1055cc 73mm. I have a range of cams like Norris RX2, Norris RX3, RC315, RC327, along with RC ported heads with big valves etc RC adjustable cam sprockets, messnermoto cam chain adjuster, RC golden rods and Yoshi Superrods lightened balanced cranks RC lightened flywheels, RC welded clutch hub Barnett clutches and under cut gearboxes, with a couple F1 solid output shafts. For carbs I have a set of Delorto DHLA40 carbs with 30 mm choke tubes and a set of 29 mm smoothbores. Thanks for your thoughts both engines may see the drag strip very occasionally but mainly street and I have a few bikes so they are not going to wear out!

[Don R]

 It appears you are poised to have some fun. You might check into some good rods if the Yoshi's are modified stockers. Watching with interest.

[corky]

Sounds like a cool collection of parts! For a street motor, would you be able to use the 67mm kit and sleeves without windowing the cylinders? This would prevent the oil seeping/leaking headache. Do you have specs on those norris cams?

Good luck with the build!
Daniel

[PeWe]

Norris RX2 has been up before.
Below from an old Swedish reseller.
I know a guy that got his vintage racing CB750  (62mm JE pistons) to give +86whp on dyno with a Norris RX2 cam. Plus ported head, carillo rods, V&H 4-1, CR31 carbs.

Cam: H750RX2   
Hot Street/ Roadrace. Ideal for 836cc
Lift
IN: 0.381"  (9,68mm)
EX: 0.357"  (9,07mm)

Duration:
IN: 290 degrees
EX: 280 degrees

********************************
Cam: H750RR   
Cafe/ Roadrace. Ideal for 900c or high-revving 836cc
Lift
IN: 0.380"  (9,65mm)
EX: 0.357"  (9,07mm)

Duration:
IN: 290 degrees
EX: 280 degrees

[Tom]

[/quote]

Sounds like a cool collection of parts! For a street motor, would you be able to use the 67mm kit and sleeves without windowing the cylinders? This would prevent the oil seeping/leaking headache. Do you have specs on those norris cams?

Good luck with the build!
Daniel

Thanks Daniel, I am fortunate to have two sandcast barrels which have much more meat and the Henry Abe 67 sleeves don’t go anywhere near coming thru, so all good they are also turned down where they enter the case and the case does not need boring which is convenient, the MTC 73 mm sleeves are also fitted to a sandcast barrel and to my utter surprise I can’t see any breakthru and the engine is dry there too, this was the reason I sold the 1000cc engine that came with the Rickman I didn’t want to go there again but now I think I may? The RX2 was fitted to one of my sandcast with 850 kit, but I have put it back to standard, here is the info on the RX3 I have

[Tom]

Norris RX2 has been up before.
Below from an old Swedish reseller.
I know a guy that got his vintage racing CB750  (62mm JE pistons) to give +86whp on dyno with a Norris RX2 cam. Plus ported head, carillo rods, V&H 4-1, CR31 carbs.

Cam: H750RX2   
Hot Street/ Roadrace. Ideal for 836cc
Lift
IN: 0.381"  (9,68mm)
EX: 0.357"  (9,07mm)

Duration:
IN: 290 degrees
EX: 280 degrees

********************************
Cam: H750RR   
Cafe/ Roadrace. Ideal for 900c or high-revving 836cc
Lift
IN: 0.380"  (9,65mm)
EX: 0.357"  (9,07mm)

Duration:
IN: 290 degrees
EX: 280 degrees

Thanks for the info on the RX2 PeWe I got this in a Sandcast and it’s in good shape so may find it’s way into the chopper with 67mm 86whp ain’t too shabby, the Yoshi Super rods I have are Alloy ones I will get some pics cheers

[PeWe]

Cam open/close numbers are tricky to compare with other cams if not specified at a certain lift like 0.004"(1mm) or 0.005" (1.25mm).

[Tom]

It appears you are poised to have some fun. You might check into some good rods if the Yoshi's are modified stockers. Watching with interest.

Don the Yoshi Superrods I have are alloy ones, are you the Don with the ‘69 Firebird?

[Tom]

Cam open/close numbers are tricky to compare with other cams if not specified at a certain lift like 0.004"(1mm) or 0.005" (1.25mm).

PeWe this is the other Norris cam spec I have it may be of help to someone

[RAZZ]

If you want to go 73 mm you Can take a look on Mikes billet block I dont know if hi still has any in stock..

Billet blocks....who will pay...pics added 9/7/09...10/24....2/10
 https://r.tapatalk.com/shareLink/topic?share_fid=13548&share_tid=49438&url=http%3A%2F%2Fforums%2Esohc4%2Enet%2Findex%2Ephp%3Ftopic%3D49438&share_type=t&link_source=app


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[PeWe]

Cam specs are always interesting!
Norris cams have been asked about earlier.
It seems that an extra cam is always welcome!

[Tom]

If you want to go 73 mm you Can take a look on Mikes billet block I dont know if hi still has any in stock..

Billet blocks....who will pay...pics added 9/7/09...10/24....2/10
 https://r.tapatalk.com/shareLink/topic?share_fid=13548&share_tid=49438&url=http%3A%2F%2Fforums%2Esohc4%2Enet%2Findex%2Ephp%3Ftopic%3D49438&share_type=t&link_source=app


Sent from my iPhone using Tapatalk

Hay Razz what a read wow, I am planning on using the 73mm Early Sandcast barrel that came off the old drag bike, it’s not showing any break thru between 1/2 and 3/4 and is oringed with piano wire squish ring for the copper head gasket. So will give it a try and I already own it Hi. But those CNC barrels are beautiful but I will need to win lotto first.

[Tom]

Cam specs are always interesting!
Norris cams have been asked about earlier.
It seems that an extra cam is always welcome!

PeWe I read your CNC 1000 build thread Awesome did you ever get it on the Dyno it would be interested to know the numbers but even with out them it sounds great and I bet it brings you joy

[PeWe]

Yes, last dyno in October last year.
Max 101whp. Next under the min limit, 99whp. Worse weather and chain really bad, could snap so I told the dyno guy to not make too hard WOT and throttle offs.
(Chain wax killed that tough chain really quick not lubing the rubber x-rings.)
Verify jetting updates most important.
Bike had got another head now so the numbers are very interesting.
101whp head is a ported K2 head with F2 inlet valves (34mm), Ex Kpmi 28mm.

Latest head for this season a 392 head with later design matching the K6 and Billet block better.
Valves are Kpmi 33.5/28.5mm, shortened and sunk stock guides and probably better ported. It should give a little bit higher static compression numbers with thinner base gasket 0.01", before 0.02" RCS. Chambers 23.6cc, before 23.7/23.8cc.

Cam retarded 1.5 degrees compared with before to hopefully get more at 9000rpm

It would be fun to enter the 106whp area as the father of the Billet block (Mike Rieck) has reproduced so far on his bike into the hunt for 110.

Photos in the K6 build thread.
There is another link to a thread when fixing the K2 head.

http://forums.sohc4.net/index.php?topic=180468.msg2158919.msg#2158919

Comparing dynos charts. My chart has torque in Nm.
91.99 Nm  = 67.85 ft-lb
91.35 Nm  = 67.38 ft- lb

[Tom]

Thanks for posting that up PeWe that’s awesome you cracked the ton, I suspected it would be up there, and Mikes 106 Wow. Funny how we are always looking for a little bit more, I spent my working life in Satellite communications and we were always looking for another Db, which was also very elusive, but I say a drip here and a drop there and before long you will have a puddle, keep up the great work and thanks. For posting up cheers Tom

[PeWe]

Lots of inspiration on this forum!
Others experiences and knowledge makes rebuilds easier and very fun.

[PeWe]

Tom, do you plan an engine build?
That would be fun to follow.

[Don R]

It appears you are poised to have some fun. You might check into some good rods if the Yoshi's are modified stockers. Watching with interest.

Don the Yoshi Superrods I have are alloy ones, are you the Don with the ‘69 Firebird?

 Yes that's me, I'm waiting on a purge regulator to weld the SS exhaust.
  I have a set of mtc rods in my drag bike motor, 2 sets sold at the PO's auction but I was holding my money for a sandcast bike. I got it and went back later for the drag bike. A lot of the drag bike's parts were gone by then, I did get the header though. 

[Tom]

It appears you are poised to have some fun. You might check into some good rods if the Yoshi's are modified stockers. Watching with interest.

Don the Yoshi Superrods I have are alloy ones, are you the Don with the ‘69 Firebird?

 Yes that's me, I'm waiting on a purge regulator to weld the SS exhaust.
  I have a set of mtc rods in my drag bike motor, 2 sets sold at the PO's auction but I was holding my money for a sandcast bike. I got it and went back later for the drag bike. A lot of the drag bike's parts were gone by then, I did get the header though. 

Cool,love my ‘68 Firebird had it 43 years this year, it got a ss exhaust 1987 or 88 and it’s still good. I lucked out with this drag bike had some nice parts and I will rebuild the engine much as it was but with a Messnermoto cam chain adjuster, and an ARD so it should go ok it will be going into my Rickman that’s been languishing for the last few years waiting, I got my two Sandy’s finished two years back for the 50th and last year built a Z1 and rode it down to the Stone movie Anniversary ride just before lockdown And have been doing a bit on a K1 resto but having trouble with too many Que jumpers that are pushing in and pushing the projects back. But it’s all good

[PeWe]

Z1 900 has so beautiful tank, side covers, seat and rear design. Plus a fantastic engine!!

[Tom]

Ok what is it? I have a 73 mm barrel and MTC 73 mm pistons and have read lotsa different cc’S so in the MTC cattledog it says it’s 73mm=1055cc others refer to these as 1060cc in the RC Eng cattledog 73mm =1080cc what do you guys think? any Math experts out there?

[PeWe]

Hi Tom,
73mm pistons, stock 63mm stroke: 1054.69cc
66mm stroke: 1104.91cc
69mm stroke: 1155.13cc

I guess 69mm stroke was the common when stroked (+6mm)?

[Tom]

Thanks PeWe, 1055 it is, I have got another RC Cobra to put together, this all started in 1975 my first trip to the USA and to RC and bought a Cobra what I needed. This pic is outside RC with my girlfriend loading the goodies in the Nova. To bring back to Oz.

[Tom]

All the bits laid out pre assembly 1976. And here I am at it again 45 years later.

[scunny]

Been there, done that, got the t shirt.
enjoy it