Topic: Operation Streetfighter: Motor Build

[laminaytrap]

I was going to post this in Projects, but i think it has to many questions, so I am posting it here

So I have been running my budget and timeline for my bike and it looks as though i would be smarter to invest my time and money into the motor build first, and work on the frame mods and suspension/Brakes when there is time, maybe during the summer.

So that being said I am working on my motor rebuild plan.

The Bike is a '77 CB750k with ~24000 miles on it. It smokes under heavy throttle, it smokes on downshifts, it rattles a bit, and sometimes drops second gear/ false neutrals. Currently running Kawi Zx6r Mikunis.

I rode the bike all summer and fixed issues as they arose, but i think it's time it saw some love before the next season.

Wish List:
~70rwhp - Currently butt dyno currently says 35
No Leaks
No Smoke
4-2 Exhaust (no rush)
New Carbs (can wait)
New Ignition (can wait)
Charging System Upgrade (currently using component rect/ ford reg i.e. Not super clean) also can wait

So the thing i need help with is how far should i go on a motor of this vintage?

I know it was run without/with suspect filters for a long time, meaning there is a chance the bore/valves need attention.
I am planning for sure to go as far as an 836cc kit, head rebuild, and a cam, but really my main goal is a solid reliable engine that is not the dog that it is today.

So the list:
Parts
836 Kit or 2nd over kit
Gaskets Seals etc
Cam Chain (Rivet) Solid Hd/F Chain
Cam Chain Tensioner (wheel at least)
Valve Seals
Valve Springs
Starter?
Valve Guides?
Valves? unless bent
 
added
Undercut Tranny
Shift Fork
Shift Drum
Primary Chain Tensioner
Cylinder Studs Upgrade (dreading this...)



Labour (Me)
Disassemble From Bike
Remove Valve cover, rockers, cam, head, cylinder, pistons
Disassemble Head (Valves, seals)
Clean everything (parts wash, strip, blast, paint black)

Labour (Shop)
Valve Job
Cylinder Bore/Hone

So the questions.

Is it smart to go 836cc vs 1st or 2nd over if i am going to need to bore it already?

Can a regular starter/alt place rebuild my starter (weak solenoid, otherwise very strong)

Will i need new valves/ guides if i am already doing a valve job? or will the old parts suffice (presuming no bends)

Is there any point in taking the whole engine apart and working on the bottom end?

Should i be addressing the transmission issue now? Is there an easy fix besides undercutting?

And the question that has really been bugging me is do i have to open up the combustion chamber for the 836 pistons?
I have never seen this mentioned, nor have i seen mention of head/block decking operations. Are any of these things needed?

I've rebuilt 5 motors in the past and i've learned over the years to make sure your ducks are in a row before you begin.

Thanks in advance for any info, this forum has lots of info, but i find it hard to find specific info on some subjects, so thanks in advance!!





Possibly these things along the way aswell,

Oil Pressure + Easier Shifting HOW TO / WALKTHROUGH

http://forums.sohc4.net/index.php?topic=78643.msg877816#msg877816

CB750: Drilled cam towers for more RWHP.

http://forums.sohc4.net/index.php?topic=59423.0

[Retro Rocket]

I would go 836 if it needed boring but that just me.. , most of the power in these old girls is locked up in the head, best place to start after piston kit. I would be inclined to use the Mikuni carbs that you have, they should work very well if set up properly. It sounds like you have a good idea of what is involved, how much money do you want to spend.? Porting the head will be the best way to get the HP you are looking for, followed by a decent cam, plus, if you use those Mikuni's then it will save you around $750 dollars on CR's or similar, and the mikuni's have accelerator pumps and , in my opinion, will be better for the street....
When you have made up your mind what you want to do there are some very good engine specialists on the site for referral...

Hope this helps a bit..

[brandEn]

If your transmission is giving you fits then you need to open the cases. You need to do that to replace the cam chain anyway. Once the head and jugs are off it "should" only take you around an hour or so to split the cases. Once in there most people agree that the primary chain tensioner should be replaced just because the rubber is old. To fix the tranny just swap in whatever is worn with a good used one from Ebay or the classifieds here on the site.

The starter solenoid is mounted to the electrical panel under the left side cover so your starter is probably good.

[Jerry Rxman Griffin aka MuthaF'er]

That engine is one of the stronger ones in stock trim. Your butt dyno should be feeling 60+ hp if it were new. Your sprocket gearing may be suspect. I'm with Retro, if you gotta bore, then bore, not refresh with 1 or 2 over. You may be able to get 70hp just with a 836 and cam. Porting would be icing on the cake and make a cam REALLY come alive. I'd do the valve springs especially if you don't get the tranny squared away. When it pops outta gear on full throttle and the springs can't keep it from floating a valve you are hosed. From the sound of it you'll need to open the cases so you may as well replace all internal chains and hardware.

[HondaMan]

Whatever you do, DON'T use a riveted cam chain. Very few riveted ones I have seen on cammed 750 engines survive very long. There are HD chains available, but one of the best is Honda's "F" series chains, from the 1977/78 F2/F3 bikes. Their middle part number is "-410-".

If you bore to 836cc and use high-compression pistons like Wiseco (use .0022" clearance with those), polish the valves, install a cam like the Megacycle 125-00, install bronze valve guides (you will need those, anyway, at 24k miles on a K7), get the jetting right and increase the spark duration, you'll find the bike completely changed next time you ride it out. Don't use a Dyna S ignition: that will SHORTEN the spark duration, instead.

You will also need HD cylinder studs, a new cam chain tensioner kit for the post-1976 engines, a new C5 gear in the tranny and possibly a new L shift fork. Check the shifter drum to see if the tip of the L fork's groove is worn off, causing the loss of 2nd gear engagement, very common on K7/8 bikes. This then causes the rounding of the gear dogs on C5, often damaging C2's slots in the process. You can send the whole gearbox to CycleX or API for back-cutting, which would be highly recommended if you are also increasing HP.

 

[laminaytrap]

Wow,

Thanks for all the replies.

So pretty much I should be taking this motor all the way apart.
Plastigauge mains and possibly replace lower halves? Check out the rod bearings.
Inspect Transmission bits, correct a necessary.

Now I had a friend (old time ex-racer) who says that the output shaft bearings are a weak spot on these bikes. Good info?

So finally what else once i'm in there that's gonna cost me money?

If i'm going to spend money in the motor obviously i want to work from the inside out, so carbs/charging/igntion can all be done after the motor is back in the bike and broken in/riding, and for that matter future head work is just a matter of a new head gasket down the road. Even cam later if need be, just spend all the money fixing the long block.

Monies wise 1500-2000 was my max, lesser the better, the rest of the bike needs work too.

Oh and a note on the Mikunis,
They are pretty cool, and if i didn't have to run a pump for them i'd be even more sold. But they sit at a poor angle due to the extreme angle of the ZX6r head vs honda's goal to keep the carbs level on the 750s. Might sell 'em and find something else about the same size at a better angle.

As for suspect gears, yes they are pretty tall, not too sure but something like 17-40. Neither sprocket is CB750k, chain obv. 530.

So with the stock 17in rear wheel how high rev is acceptable for sustained highway riding? Last summer I rode about 9k miles, the revs were starting to worry me, doing 6000+rpm on the hwy 60-80mph kind of freaks me out. And 80-95mph is pretty much as fast as i could ever get it to go.

So

Race Cutting                $300
Bore Hone                   $200
Head Refresh               $300
Cam                             $199 (cyclex)
Valve Springs               $70 (Cycleone)
V Seals                         $20 (Cycleone)
Primary Tensioner        $80
Cam Tension/slide       $50
Used Shifting Spares   $100
Gasket/Seal Kit            $150-250
Cam Sprocket              $39
Valve Guides               $69
Super Studs                $160 ($75 at cycleone)
Pistons                        $500  (wiseco) ($200 at cycleone)
Cam Chain                  $39
Clutch Stuff                 $50-100

If i calculated right that comes out to 2500 bucks...

Not sure how i feel about that, plus some tax/shipping/and some deals along the way.

And in the interest of saving machine time, super flow valves should go in with the valve job... RIGHT???!!?

So what corners do you cut? Am i over or under on this stuff... I just pulled most of it from CycleX for reference.

I still need tires and sprockets at a minimum to ride. But with this much work it would be pretty kick ass.

This is also without any mention of bottom end work, bearings, rods, crank etc.

So are the bottom ends almost always good?

[HondaMan]

Generally, the bottom ends (cranks & rods) are fine. Your friend's info about the "final drive bearing" is bogus: that's a long story, covered accurately in my book. Yours is more than fine, up to 100 HP.

The most likely things:
1. Valve guides will be worn, causing significant power loss, and oil leaks. You can either install new bronze guides (like API guides) or: I can now offer bronze liners in the guides, for about $100 less than new guides during a valve job.
2. Boring to 836cc with Wiseco or Cycle X piston kits will net about 8-12 extra HP, all else being equal (with stock carbs and cam). It all depends on the rest of the 'stuff' around it: for example, avoid pod air filters, or you will lose a whole bunch of power, period.
3. Adding a cam like the Megacycle 125-00 will help quite a bit with the 836 bores.
4. Porting and adding a quench band to the head will also increase midrange power more than you might expect, and more than most folks understand (until they ride it). Polishing the valves also helps, or use the new Superflo valves (also polished) if you want a teeny bit more flow on top of it all.
5. Your tranny will need to be fixed up by either API or CycleX: they can back-cut those worn gears for you, which should be done with any 836 hi-perf build, anyway.
6. New clutch plates (whole set) from Honda (best bet) will run about $70.

Those will be the high points. Generally, these full rebuilds range in cost between $2000 and $3500, just depending on what you want to get in the end.

These engines are made to rev. At 70 MPH, with normal gearing, they spin about 5500 RPM, depending on tire size. They will run ALL DAY at 6500 RPM without breaking a sweat, provided you are using good oil of 20w50 weight (non-detergent - use Motorcycle oil only!). Castrol 4T is good, Bel-Ray is better. Avoid "V-Twin" type oils, as they are very high detergent and will foam in these bikes, causing many problems.

Example: mine has 140k miles on it, and spent much of its life on hiways as fast as I could go with 2 aboard and all [her] gear. I watched the tach above 7k in top gear for many, many hours on these trips. The bike never cared. 

[laminaytrap]

Well that makes me feel better about the Revving, which means once my motor is built shorter sprockets can go on and it'll rip real good.
Obviously the only place to save money in the early stages is to skip headwork/cams, but that's where all the fun is so... obviously the sol'n is to just make more money...

[MRieck]

 No one mentioned using oversize intake valves. The valve is the largest obstacle involve with getting charge into the cylinder. Use the 33.5 Superflow valve (same price as the standard 32mm) AND HAVE THE INTAKE SEATS BORED TO 90% OF THE OS VALVES OD. Backcutting the intake valves also helps.This will make the biggest difference and will enhance a larger cam. A competent machine shop with a Serdi should be able to do this along with a good valve job. If you cannot find one let me know. It works very well with the 836 kit as the larger bore deshrouds the intake valve. The valve reliefs in the Wiseco's are plenty big enough so clearance is not an issue.

[Greggo]

This sounds like a fun build to watch. 

[laminaytrap]

And in the interest of saving machine time, super flow valves should go in with the valve job... RIGHT???!!?

Haha I did mention that big valves would make sense. How much more machine $$$ are we talking about over a STD Valve Job?

[MRieck]

And in the interest of saving machine time, super flow valves should go in with the valve job... RIGHT???!!?

Haha I did mention that big valves would make sense. How much more machine $$$ are we talking about over a STD Valve Job?

CycleX lists all the valves as Superflow that is why I made that statement. I charge 20.00 per seat as you have to blend the port into the seat following the boring. Working on the seat with a fresh valve job can be a little tense but I have done it hundreds of times at this point and a competent person should be able to do it as well. A good wat to do it is to bore the seats  prior to removing the old guides...don't have to worry about nicking newly cut seats. Sometimes it is not partical secondary to time constraints, condition of the old guides etc

[HondaMan]

And in the interest of saving machine time, super flow valves should go in with the valve job... RIGHT???!!?

Haha I did mention that big valves would make sense. How much more machine $$$ are we talking about over a STD Valve Job?

CycleX lists all the valves as Superflow that is why I made that statement. I charge 20.00 per seat as you have to blend the port into the seat following the boring. Working on the seat with a fresh valve job can be a little tense but I have done it hundreds of times at this point and a competent person should be able to do it as well. A good wat to do it is to bore the seats  prior to removing the old guides...don't have to worry about nicking newly cut seats. Sometimes it is not partical secondary to time constraints, condition of the old guides etc

M:
This also begs the question (to me...): have you found suitable valve seat replacements? I have some K0 heads that need this treatment, thinking about rebuilding them. Water damaged the OEM seats badly.

[Xnavylfr]

If you can find a F model head and cylinders then bore it to 836 and cam it you'll be ahead of the game..
F Model heads already have bigger combustion chamber and larger valves. The F model STOCK piston is domed for HI COMP. where as the K model is flat.

You might check with the guys for engine work also, they do a lot of 750 work for the Honda Chopper group.

http://cycleonemanufacturing.com/      ask for KATE

Xnavylfr(CHUCK)

X

[Jerry Rxman Griffin aka MuthaF'er]

When Chuck refers to F head he is referring to the F2/F3 77/78 head. At least that's what I'm reading into Chuck's thoughts as the original -392 75/76 F head had regular size valves in it. 

[Xnavylfr]

You are correct, 77/78 F model, the change in engine configuration is why it was called the SUPER SPORT!



Xnavylfr(CHUCK)

[burlybear]

that's going to be fun!

[MRieck]

And in the interest of saving machine time, super flow valves should go in with the valve job... RIGHT???!!?

Haha I did mention that big valves would make sense. How much more machine $$$ are we talking about over a STD Valve Job?

CycleX lists all the valves as Superflow that is why I made that statement. I charge 20.00 per seat as you have to blend the port into the seat following the boring. Working on the seat with a fresh valve job can be a little tense but I have done it hundreds of times at this point and a competent person should be able to do it as well. A good wat to do it is to bore the seats  prior to removing the old guides...don't have to worry about nicking newly cut seats. Sometimes it is not partical secondary to time constraints, condition of the old guides etc

M:
This also begs the question (to me...): have you found suitable valve seat replacements? I have some K0 heads that need this treatment, thinking about rebuilding them. Water damaged the OEM seats badly.

Yes mark...I get cast iron seats from Kibblewhite. the head on my current engine has the intake seats replaced. The Kibblewhite seats are harder and cut much, much better.

[laminaytrap]

So much good info! Thanks all!

So currently being evicted so hopefully post move i can setup shop in my new place, classic story of rental fraud. Guy illegally sublet us the apartment, took the money, didn't pay the owner then left the country, all unbeknownst to us.

About my current carb setup.

The float angle is a concern, i have them working ok, but i believe the angle may be affecting my tuning/ may make it impossible to dial in consistently in the future.

You can see that the bowls are at a pretty severe angle relative to the engine/ gravity. Because the m is pressurized the bike runs pretty as the floats close from the pump pressure, but they always leak a bit after I stop.





Ideal angle is more like this...



aside from adjusting port angle, any suggestions? Should i try to get some angled rubbers, or just swap for a carb setup with a flatter bowl angle? I do like the CV/Butterfly setup, makes it very forgiving tuning-wise and easy on cables.

As for Pistons, the CycleOne 836 flat-top kit is $200 and the Wiseco Forged 836 kit is $400-500, any downside to running the cheaper pistons? Will it still clear Big Valves/Cam if i heads that route? Looks like it's got significant cutouts. I am not likely to do much roadracing ... not much

P.S. one of the pictures for both kits are exactly the same... one of the other pictures looks like the skirt if full vs.cut and definitely one is flat and one domed, probably worth at least  .5 on compression... hmmm

[brandEn]

Following along on this one...

Did you mean Cycle X pistons or CycleOne?

[laminaytrap]

The CycleOne FlatTops as listed here:

CycleOne Engine Parts Page

Vs the Wiseco Forged on the same page (assuming same as Wisecos on CycleX)

Ed: link fixed

@branEn: Just looked at your thread, Your bike looks so clean!

[brandEn]

OK I found them. Cool, I never saw those before. I am in the market for pistons too. Curious to see the comments here.

http://www.cycleonemanufacturing.com/id280.html

[HondaMan]

OK I found them. Cool, I never saw those before. I am in the market for pistons too. Curious to see the comments here.

http://www.cycleonemanufacturing.com/id280.html

The flat-dome ones appear to be the same ones I get from Cruzinimage on eBay for $160. They are from Thailand.

[laminaytrap]

Just for reference:

Honda bigbore ebay

Those come out to $135 plus duty... that's a far cry from $500

@HondaMan: How do those stack up as far as compression/ performance? Is it worth the extra $350 to get the Wisecos?

Anyone who's used em feel free to chime in too!

[Retro Rocket]

I think the main differences are that the cheap ones are cast and have a lower compression ratio so you will get a performance gain due to the bigger bore size with the cheap pistons but the Weisco's are forged and a better option if you are chasing high performance....