Topic: Re: Bigsam302's 76 CB750F (915cc): Project Helen – Running Report!

[Bigsam302]

Mike recommends the CX-7 camshaft for the 750 higher compression big bore (836-915) kits.

That port job should really wake up the motor, Sam.

I have some of the same spec goodies going into my 750 motor.  I cannot wait to see what a little beastie she becomes.

Cycle X HD primary chains and tensioner
Cycle X race transmission
Slightly Lightened and Balanced crankshaft
Balance rotor
Cycle X Super Rods
Wiseco 836cc big bore kit
Cycle X Super Gasket set
Mike Rieck Stage IV port job, Kibblewhite 5mm valve conversion kit (34mm intake/28mm exhaust valves, guides, seals, springs, Ti retainers,
spring bases and lash caps), Serdi valve job, head milling
HD Cam Chain
APE adjustable cam sproket
APE HD studs
Cycle X CX-7 cam
Cycle X racing cam tensioner
Cycle X Cam Tower Stabilized Valve Cover
Cycle X Spin-Off Oil Filter Mount
Setrab Oil Cooler

We are on the same page!  I have all that stuff as well.

[SOHC4 Cafe Racer Fan]

Mike recommends the CX-7 camshaft for the 750 higher compression big bore (836-915) kits.

That port job should really wake up the motor, Sam.

I have some of the same spec goodies going into my 750 motor.  I cannot wait to see what a little beastie she becomes.

Cycle X HD primary chains and tensioner
Cycle X race transmission
Slightly Lightened and Balanced crankshaft
Balance rotor
Cycle X Super Rods
Wiseco 836cc big bore kit
Cycle X Super Gasket set
Mike Rieck Stage IV port job, Kibblewhite 5mm valve conversion kit (34mm intake/28mm exhaust valves, guides, seals, springs, Ti retainers,
spring bases and lash caps), Serdi valve job, head milling
HD Cam Chain
APE adjustable cam sproket
APE HD studs
Cycle X CX-7 cam
Cycle X racing cam tensioner
Cycle X Cam Tower Stabilized Valve Cover
Cycle X Spin-Off Oil Filter Mount
Setrab Oil Cooler

We are on the same page!  I have all that stuff as well.

Sam,

I thought so, too. The motor is very similar in spec to Doctor D's 750SS. Twinline was able to get 80s rwhp.

[Bigsam302]

Sam,

I thought so, too. The motor is very similar in spec to Doctor D's 750SS. Twinline was able to get 80s rwhp.
[/quote]

Yeah, I based my motor off of Tweakin and DoctorD's builds.  My only regret is that I have never rode a stock CB750 before.  It would be nice to have something to compare my build too.

[SOHC4 Cafe Racer Fan]

Well, in comparison to the bike you are building, the front end is spindly, the brakes are MUCH less powerful, the front handles a fraction as well, and the motor is anemic compared to one with a big bore, port and cam.  It will be like night and day.

[CBertels]

This build looks amazing, great job!

[Bigsam302]

Today I made some pretty good progress.  Yesterday there was a huge heat wave in SOCAL and I didn’t spend much time outside working on my bike.  I did end up baking my heads and they came out nicely.  One thing that I wish that I would have done was file down some of the imperfections in the casting and smoothed the fines out.  It looks great, but I think it would have looked even better.



I installed the base gasket, Cycle X Cam Chain Tensioner, and the cam chain slider.  Even though you can’t see it in the picture, I did install the dowels and the rubber gaskets at the base of the head studs.




I took out my 915cc Pistons and they look gorgeous.  It’s a shame that they are going to be hidden in my engine.  I also had the pistons coated.  That’s why the skirts are black.

[Bigsam302]

After a lot of careful reading (and re-reading), I checked all of my piston ring gaps and everything looked fine.  I installed the piston rings and got started assembling the rest of my engine.





I managed to get the cylinder block on.  This was a pain in the butt!  Pistons 2 & 3 went in very easily, but 1 & 4 worked every bit of my patience.  I had to step away for a few minutes and try again.  Finally, I got the block installed.




Next the cylinder head went on without a problem.  I had to remove my steering damper to get it on, but I was able to put it back in its original location without an issue.  I really like the way the mount turned out.





I did run into one very big snag.  One of my cam shaft tower bolts was bent and stripped.  Luckily, it wasn’t in my cylinder head at the time.  I was trying to put a double nut on it so I could screw it into the head.  That’s when I noticed that it was in really bad shape.  So I had to stop there for the day.  I was able to find another one on ebay and I should have it by the end of next week. 



Stay tuned for more updates!

[calj737]

It's good that you hit a else. Now, you can re-torque the head bolts after an overnight sit. Release them in reverse order, then step them into their final torque in three phases. Once that's done, you can safely button up the top end!

[Bigsam302]

Thanks for the advice Cal! I'll give it a shot. I was just going to check it again by trying to torque it again tomorrow.

Sent from my GT-I9505G using Tapatalk

[SOHC4 Cafe Racer Fan]

Sexy-looking motor.  +1 on the re-torquing.

[Jerry Rxman Griffin aka MuthaF'er]

Now for the fun part - dialing in the cam. ;-)

[Bigsam302]

Yeah, I'm not looking forward to that part!

Sent from my GT-I9505G using Tapatalk

[Konradwax]

I want to see this bike run:)

[SOHC4 Cafe Racer Fan]

Me too!
Sam: when you get close, let me know.  I'd love to see it run.

[Bigsam302]

Me too!
Sam: when you get close, let me know.  I'd love to see it run.

Don, no problem.  I'll let you know when I'm about a week out.

Sam

[brandEn]

That engine looks great!

[Bigsam302]

That engine looks great!

Thanks, I appreciate it.  You should see it with the carbs on it.  I put them on last night just to get an idea on how they would look, and they look awesome!  I hope to have the engine finished off this weekend.  It all depends on how frustrated I get dialing in my cam.

[SOHC4 Cafe Racer Fan]

Sam,

Mikuni RS34s?  If so, did they go on without a fight?

Don

[Bigsam302]

Sam,

Mikuni RS34s?  If so, did they go on without a fight?

Don

Don,

Yes, I have the RS34s.  They went on a lot easier than I thought.  I did have to put a little pressure on them, but they slipped on just fine.  I didn't have to soak or heat up the boots at all.  I did add some WD-40 as it says in the manual and it worked.  When I spoke with Ken at Cycle X, he told me that the trick is to get a set of new boots from a 78 CB750K.  They are really hard to find, but there is a company in Canada called Vintage750 that reproduce the boots.  They worked perfectly! 

Sam

[SOHC4 Cafe Racer Fan]

Interesting about the K8 boots.  I wonder if that trick will also work with a K2 head??

[Bigsam302]

That's a good question.  I don't see why they wouldn't.  I thought that the heads (K0-K6, and F) were the same size, just different internals, gaskets, cam towers, etc.  Plus, they have to be spaced properly to fit on a CB750.  So the boots should still line up just fine.  Give Ken a call.  He will know better than I do.

Sam

[Jerry Rxman Griffin aka MuthaF'er]

The K8 boots are larger at the carb than all the predecessors but same at the head. The F2/F3 are larger at both. Both these use the newer carbs.

[SOHC4 Cafe Racer Fan]

Thanks, Sam. I will keep this in mind for my 750K2, as I am leaning heavily in favor of the RS34s.

[mkoski]

Hey Sam, I have been trying to track down an F tank, just like the one you have! And it looks like you aren't using it! 

Any way we can cut a deal?

Thanks,

Matt

[Bigsam302]

Thanks, Sam. I will keep this in mind for my 750K2, as I am leaning heavily in favor of the RS34s.

From everything that I have heard about them, I think that you will be happy with them.  Of course I'll give you a review of them as soon as I test them out.