915cc cb750 engine installed

tweakin

tweakin

Beer and Grease
Rather than build another bike I decided to build an engine for my current cb750. I got a 1977 750K and 1973 750 K engine, both complete for $200.


Here is my list:


* Cycle X (Wiseco) 915 pistons and sleeves
* undercut transmission
* lighten/balanced race crank with Super rods (14K redline)
* complete head work
-stage 4 head port and polish
-CB750 5mm valve conversion kit (34mm intake/28mm exhaust valves, guides, seals, springs, and Ti retainers)
* all new bearings and chains
* M3 racing cam chain tensioner
* Heavy duty cam chain with adjustable cam sprocket
* Heavy Duty primary chains
*Heavy duty crank and cylinder studs
* lightened rockers
* Megacycle 125-75 cam
* All the machine work will be done by APE
* The head work will be done by JMR


I already have so much invested in the cb I figured I would just build a second engine with a bit more kick. I want it to be a bit of a sleeper and get close to 100hp.


This will be done as funds become available so I can stay married. ;D I got the K engine tore down last night and all looks good inside.
Thanks for any replies and opinions!


1977K
IMG_8339.jpg



IMG_8345.jpg



1973
IMG_8343.jpg
 
Re: 915cc cb750 sleeper


Christmas in August.... ;D Thanks to the great guys at APE and BigJay. This is supposed to be my winter project but I may have to at least start building up the engine. I can always swap them out when the weather turns.




APE.jpg



APE2.jpg



APE3.jpg



APE4.jpg



APE5.jpg



APE6.jpg
 
Re: 915cc cb750 sleeper

100 hp? whats your plan for the clutch? I'm secretly planning a similar project around my wife...
 
Re: 915cc cb750 sleeper

Realistically I would like to be anywhere between 90 and 100hp. I am already using the A.P.E. 9 plate clutch kit in my 836 build and am more than happy with it.
http://www.cbrzone.com/sohc.html

It is said to be able to hold 9 second power.

ktree said:
100 hp? whats your plan for the clutch? I'm secretly planning a similar project around my wife...
Click to expand...
 
Re: 915cc cb750 sleeper "heads here"

My head came in yesterday from Mike Rieck (JMR Porting) and it is art.... Stage 3 port with 5mm valve stem conversion, HD springs and Ti retainers. This should really wake up my 915 ;D Also had the ports matched to the intake boots and picked up a Megacycle 125-75 cam and ordered a set od Mukuni RS34's. This should be everything I need to complete the build. Thanks Mike!


head1.jpg



head4.jpg



head3-1.jpg



head-1.jpg



head2-1.jpg
 
Re: 915cc cb750 sleeper "heads here"

Very nice. Not wild about those fat valve guides and lumpy ports but should work. Did you get hardened valve caps for those new valves? Crank and rods are sweet too.

That's a big cam, but should be OK with the big motor - will be a bit of a top end monster
 
Re: 915cc cb750 sleeper "heads here"

teazer said:
Very nice. Not wild about those fat valve guides and lumpy ports but should work. Did you get hardened valve caps for those new valves? Crank and rods are sweet too.

That's a big cam, but should be OK with the big motor - will be a bit of a top end monster
Click to expand...
Yes, I have hardend valve caps. The ports are as smooth as can be. The "fat valve guides" just look that way but they are stock sized outside diameter. It is a 5mm valve stem conversion... The head was built by "the man" when it comes to cb750 heads.
 
Re: 915cc cb750 sleeper "heads here"

Just out of interest, did he put that head on a flow bench and give you before and after flow numbers? It would be interesting to see how well they match the new cam.
 
Re: 915cc cb750 sleeper "heads here"

Yes he does have a flow bench but I will take all his experience over that any day, I know this builder knows exactly what he is doing.
teazer said:
Just out of interest, did he put that head on a flow bench and give you before and after flow numbers? It would be interesting to see how well they match the new cam.
Click to expand...
 
Re: 915cc cb750 sleeper "heads here"

To me, flow numbers are essential, and are really useful for matching a cam. Flow numbers are also a predictor of the power that an engine could theoretically produce.

We always get flow numbers for the records unless we wrecked a motor one weekend and need a quick clean up on a spare head for the following weekend and then time is of the essence. They reveal a lot about a motor and where it's restricted. On many older Hondas for example the restriction was the exhaust port and all the intake flow in the world didn't help power until that was fixed and it wasn't always obvious where that restriction lay without extensive flow testing.

We are usually working with much smaller engines where everything has to be right to make them work.
 
Re: 915cc cb750 sleeper "heads here"

Mike knows what he is doing and has been doing this for years.
every racer in the vintage circles that I know sends him their heads.

Im sure if you really asked mike he would give any numbers anyone wanted. but most dont understand them....so its just a number that gets used for internet bench racing.
Most people that use him tell him what the motor is and how it will be used, he has a few different "stages", and thats the end of it.
 
Re: 915cc cb750 sleeper "heads here"

I totally get that. I've seen references to his work all over SOHC forums. He seems to have a good reputation on that forum.

I have experience with a few different porters over the years. Some look great and flow OK, some look OK and flow great and some are excellent.

On one CB77 motor I had three different guys port heads and they looked different and flowed different. One was all top end and lost a lot low down. One gave great mid range and the third had great mid and top end. In all cases they were full race port jobs and all looked immaculate with tapered guides and guide bosses etc.

If I had a SOHC 750 I'd probably send it to Berreth heads. There is someone who is painstaking in his attention to detail and really understands heads in general and those motor in particular. He did/does the M3 head work and they get 90+hp out of a 750. But that's not really relevant to this build, so it's a bit off topic.

It's always interesting to see the work that people do and to see how it works.
 
Re: 915cc cb750 sleeper "heads here"

A lot of options for head work and I am happy you have a guy you would use. I have built many engines and for cb's I would use Mike. For all my Harley builds I use John Hildreth "Hildreth Heads" because thats what he knows.

I would love to see the Dyno sheet of the 750 at 100+hp if has not been bored out those numbers are pretty un believable, but anything is possible. Mark from M3 racing does some pretty nice stuff. Post it up. I would also like to see the different dyno's from the cb77 engines you had done also. I am always into learning and seeing different things. Thanks for your opinions.
tweak
teazer said:
I totally get that. I've seen references to his work all over SOHC forums. He seems to have a good reputation on that forum.

I have experience with a few different porters over the years. Some look great and flow OK, some look OK and flow great and some are excellent.

On one CB77 motor I had three different guys port heads and they looked different and flowed different. One was all top end and lost a lot low down. One gave great mid range and the third had great mid and top end. In all cases they were full race port jobs and all looked immaculate with tapered guides and guide bosses etc.

If I had a SOHC 750 I'd probably send it to Berreth heads. There is someone who is painstaking in his attention to detail and really understands heads in general and those motor in particular. He did/does the M3 head work and they get 90+hp out of a 750. But that's not really relevant to this build, so it's a bit off topic.

It's always interesting to see the work that people do and to see how it works.
Click to expand...
 
Re: 915cc cb750 sleeper "heads here"

Good point tweakin, I'd like to see that M3 chart as well. IIRC Big Benly charts were published a few years ago but what's left of my mind may be playing tricks on me.

We did our CB77 development on an old Brake Dyno - pen and paper reporting back then - no dynojets or computers around. Early eighties. Dyno and flow charts for bikes we race currently are tucked away nice and safe for the moment as you can imagine - there are lots of wild claims about power and some are overstated and some are understated (usually because they are cheating)...
 
You must log in or register to reply here.

DTT Light or Dark

  • DTT Light
    • www.jadusmotorcycleparts.com
    www.lostapostle.ca/
    www.sparckmoto.com

    Spread the Love

    Back
    Top Bottom