Topic: CB750K6 -76 project back to life with more updates

[PeWe]

Hi Johno,
Your experienced comments and thoughts are greatly welcome!

Last dyno (blue) a day with worse weather and a rotten drive chain that looked to snap in any minute, instructed the dyno guy to avoid heavy throttling. It was more to verify last jetting adjustments. Before too rich at idle and around 3500-6000 area.
I have reduced needles 1/2 notch after that last dyno in blue.

Dyno charts do not show idle and steady crusing speed 120-140kmh that were too rich.

I saw what the rich jetting had done during a very short time when lifting the head a month ago. 1585km after last head change when pistons were cleaned to shine.

That helped me to trust the dyno guy's recommendation to reduce needles more than my idea about 1/3 notch to 1/2 notch.
Initially 3:6 notch from top changed to 2nd + washer. Too rich fuel screws a limited time a part of all carbon too, adjusted before last dyno by 1/3 turn less. 1 1/8 to 3/4.
One step richer pilots fixed the balance further to the needle area (32.5-->35)

I wonder if compression will increase which might need  leaner jetting again.

I felt the difference when finally hitting the 100whp area. Probably the increased compression that did it.

Last head for longetivity, stock guides shortened 3mm in port area and sunked deeper to ensure higher lifting cams. 11.5mm lift does not hit guide seals.
Another thing where valves and pistons will set the limit.
33.5/28.5 mm KPMI valves.

The throats might not loose that much compared with 34mm valves. I did not measure, maybe same size as the 99-101whp head.

Lets see if compression will increase with thinner base gasket and a little bit smaller chambers. Now 23.6cc, before 23.7/23.8cc. 197.5-202.5PSI with a cheap tester.
The pistons ring lands might complain if too high.  JE forged pistons must be challenged to do what constructed for!!
Correct compression for power and less need of fuel.

It's OK if it will reach 9000 rpms on 5th gear rather quick. At least  a constant acceleration up to 210kmh, the final step to 220kmh a little bit slower.

Same cam, Megacycle 125/75.
IO opened at 26* at 0 lash as camcard last time.

If I retard it, maybe a little bit extra at and after 9000 rpm. 1 degree later if that will be noticed.
Piston and ex valve should not complain about that small difference, I hope.
Tune with more valve lash might not be possible if compression is at the limit.

Most fun on street should be an advanced cam by a few degrees if clutch will allow it.

Engine is currently waiting for new head gasket. The old did not like to be reduced.

Rigid HD studs and metal gaskets should have less need of high torque.
I have thoughts about head-cylinder package swelling when hot. Studs might not extend in lenght matching that, ending up in nuts to dig deeper into head.
Fiber gaskets can give, but not RCS and MLS.
My old ported head with 5mm stemmed valves had nuts sunken rather deep, especially ex side.

Before always 27-28 Nm (20-20.6 ft lbs), next time 25Nm (18.44 ft-lbs), retighten the day after as usual.

(Later found 25Nm not enough for MLS to seal, 20-22 ft lb needed.)

My wife prefer my brown K2, almost stock with 4-4, 57 whp. Not that sudden throttle response as this bike.

My K6 with Hindle 4-2-1 not that loud as my K2 with 4-4 no numbers at steady cruising 100-120kmh.

The latest head not yet started.
I'm happy to have seen the tight oil holes in time. All holes fine tuned by a 9.0mm drill. Oil feed holes got another round with 9.5mm drill.
I started a thread about it with really good feedback from others.

I like to be the rider on common roads. A road racer!

Feel the improvements not really affecting top speed, more about reaching it quicker before road is out of stock!!

Last dyno with the K2 head with F2 invalves....


Photos of latest head (392) not yet tested. Camera does not show how correct chambers are shaped and aligned vs gasket (72mm MLS).

[SOHC4 Cafe Racer Fan]

Those are some impressive numbers!

[algophobe]

Boy you went all out on grinding those shrouds on the head. You did it yourself?

[grcamna2]

subscribed

[PeWe]

Yes, numbers finally in the  area installed parts should give
Head ported by a shop less than 2km away from my house.

A little bit more compression  did it. The head before made 93whp as most on dyno with DP315 cam and 4-4 (Yamiya no numbers).
That head ported even more. Maybe too much opened ports for street. My other heads probably provide higher flow velocity when not carved that much.

The new head shown here last month not tested yet.
It was built for longetivety.

My first head have 5mm stemmed valves with bronze guides. Nuts sank into head. It needs to be repaired, replace some guides. All if steel guides can be found for 5mm stemmed valves. I have an 890cc CR 12.5-1 kit that should work with that head and maybe an DP315 cam or Megacycle 125-20. Another engine build.

100whp head an old ported head, my nearby shop improved  to use my not much used valves, F2 34mm inlet valves, 28mm ex. F2 valves have soft tips so lash caps needed. But they are not very hard either.
This heads chambers equalized by me last year, measured chambers and left it to my nearby shop to shave off 0.5mm to reach a better volume for the pistons. My ideas were right!!

This thread when I did that and found out how to measure the chambers.
http://forums.sohc4.net/index.php/topic,184356.0.html

The last head to match the look of K6 and hopefully longer lasting.

I'll see how it will perform.
I like the Megacycle 125-75 cam, very streetable as my RC295 also is.
I have a new DP295B that look exact as my old RC295.
Build waits for a new head gasket.

[PeWe]

I got inspiration for port design on this thread.
http://forums.sohc4.net/index.php?topic=175958.0 

I saw another head here at nearby shop where ports were not that much opened, also with that style.
 When I commented the not much opened ports, "only 762cc". 34/28 valves.
That bike produced +86whp on dyno with Norris RX2 cam. Compression must have been good. Bike for vintage racing. Engine for repair after a valve was dropped messing up the head, piston, bore, carillo rod, crank.....

That  together gave me the idea that next head should get similar style.

[PeWe]

New MLS 0.03" head gasket arrived today from Dynoman.
Yes, the old was really flat compared with the new that has pronounced ridges.

I cleaned the oil feed holes with restrictors again after check of chambers with naphta to see if stayed, not leaking via valves. OK.

So head back on, tightened 25Nm.
(Later found 25Nm not enough for MLS to seal, 20-22 ft lb 27.1-29.8Nm needed.)

Retorque again tomorrow and mount the cam. Hopefully time it too.

The constructive post by Johno helped me to decide for retarding cam just a little.
Around 1- degree later than before (In opened 26*---> 25* at 0 lash) if that will add some after 9000rpm.
I do not want to miss power in the important 3500-6000 area.

[SOHC4 Cafe Racer Fan]

That head looks immaculate.

[PeWe]

Thanks!
Fins are OK and match the year 76 too. Many years on that bike so a K2 head looked strange.

[PeWe]

One good step further today. Cam timed, valve lash, plugs and valve cover sit where it belongs.
I found planned timing at first attempt!
I remembered how sprocket sat before, just retard a little bit.
This was meant to happen!!

I'm happy that I compression tested the previous assembly with bad head gasket. MLS not much used but this time not good. I have reused thicker MLS on my 836 without problem when gasket was not much used.

I have timed differently too.
Last time IN open at 27* which was 1 degree advanced compared to 100whp setup.

This time retarded just a little to hopefully get more power from 9000rpm. This head will hopefully flow better too. More squish area.

(Megacycle 125-75 cam)
@ 0 lash
IN: 24.5/56.5*
EX: 54/24*

Previous 100whp setup on dyno:
@ 0 lash
IN: 26/55*
EX: 55.5/23*

[PeWe]

Ready for check of ignition timing before carb synch.

Hindle 4-2-1 reminded me about its really good fit and low weight when I mounted it today.

This time I made sure it has a little bit more clearance under oil pan, not against the rear part of pan and bolt head.

[grcamna2]

That Hindle fits tight.

[PeWe]

An Easter Miracle!
The blue is ready for the road.
- Verified ignition that was good. I have set it as before, marker pen marks. Had to verify 1:4, 2:3.
- Synched the carbs that could improve a little. Other head, different valves, later kam timing.
Engine runs fine with not much rattle.

- Tank on
- Gave the new chain a little lubing by Motorex Spray. Rubber X-rings must be lubed to not wear too quick, goodbye chain.
- Filled tank to full with Shell Very Power.

A ride is waiting. Maybe tomorrow or/and day after.






Oil pressure at idle after around 5 minutes 1000-1200 rpm.


Synching carbs, tank hangs in ceiling. Timing lamp fed by a separate battery on the floor.
A fan gave it a little bit cool wind.

[PeWe]

Finally on the road again.
Nice sound.
Pulls fine too, good throttle response on 5th gear in 180kmh
Tested once after a full warmup during my 160 km ride.

Topped the oil tank when back home to 5mm under max on dipstick. (Added 15mm). I usually fine adjust oil level after an oil change, at least 30 minutes ride with some throttling.


How it idles at a stop beside the road on this very ride.
https://www.#$%*ute.com/video/CVJQEPcqt1Ca

[grcamna2]

The blue-bike looks good on the road now.Does your season start the beginning Spring Time where you live ?

[PeWe]

Weather can differ but the first ride last week of March the last years.
Back in the 80's bike was not ensured for traffic all year. Registration into hibernation wintertime. Ensurance was very expensive. Middle of April was the goal back then if ready for road. Easier today with garage in my house. Warm and dry.
Small jobs can be done while waiting for food.

Last years with cheap ensurance all year around, the few early days can be used.
 
Season usually starts in April. Cold days can occur the first half. Today around 13C and sunny.
Tomorrow and days after only a few degrees, maybe snowflakes.

[PeWe]

Weather right now!
Behind my house.

I made right decision to ride the bike yesterday so I know it works fine.
Yeah, Global Warming as some ?#$@% claim!

I clearly see that springs becomes colder. Not first year here.

[grcamna2]

You certainly would welcome some Global Warming up there Per ! 

[PeWe]

Yes, since we pay for it!

I accept how weather can change on this living planet. Be lucky to get my time in an OK period, not sudden freezing cold or opposite that have happened in the history, thousands and millions of years ago and will continue....

[andy750]

That Hindle pipe looks good Per. Always nice to have a successful first Spring ride. I got the K4 out yesterday for the first time - great to be riding again. Temps started off in low 40s then climbed to mid 50s.

[PeWe]

Hi Andy,

Fantastic feeling with first ride on a bike. Especially if something is changed.
The new head seems to work.
I'll visit a dyno later on. I hope carbs are correct now.

I like the Hindle despite its angle that removes stock passenger footpegs.
Possible to ride without too loud noise but will be loud with a darker tone when twisting. The hole thru the muffler is 50mm without any restrictive junk inside

[Don R]

 I enjoy your component testing stories and keep them in mind as I do work on my bikes.

[PeWe]

I have got inspiration, knowledge and  others experiences on these forums so it is very difficult to not upgrade and build.

Hindle was mentioned in other threads before.
I was recommended to try a 4-2-1 by my local shop av few years ago.

My next project is to find steel guides to my old ported head with 5mm stemmed valves.

Some of the bronze guides need to be replaced. Ampco 45 mentioned to be very durable, but stock steel Honda seems to last longer.

I"ve read that 4 valve/ cyl bikes can have thinner valve stems.
Maybe Honda 1100XX Super Blackbird guides.
http://aperaceparts.com/tech/1999cbr1100xx_1.html

Enough if they are bigger and can be machined to fit.

But, I doubt the outer diameter is enough to sit in a head designed for 6.5mm stemmed valves.

[PeWe]

Another ride today which was a plug ride. 150km.
Yesterday a carb whisper ride of 200km.
A few degrees warmer today, +12 to 9C. No risk for snow

The result of yesterday was changing pilot jets to one size smaller. From 35 to 32.5.

Better today but still too rich on low lifts. Today mostly at small reduction of throttle.

I changed pilots again direct when back home. Now 30 that must be fine.

I'll see if needles needs to be lifted a little.

Another ride needed to verify 1/2 step (washer) or 1 step.

Last year strange need of going richer on pilots verified by dyno A/F and test rides with plug check now going back to more what was working rather OK the years before.

The only change this winter is another head with just a little smaller chambers, 33.5/28.5mm valves, thinner base gasket.

KN filters cleaned and oiled just enough with KN oil should not affect this that much.

This is much better though.

[andy750]

Hey Per,
I fitted the Avon Roadrider tire to my front wheel and last night went to install the wheel - had to air the tire down to get it in without removing the fender. Went in ok with a bit of wiggling. When it was clamped up the tire spun freely but when I added the front brake it was binding (ran fine before the tire swap). I checked the brake pads and they seem all the way in. My next step is to check if the axle is aligned properly - visually it looks ok. Any experience with this?

Thanks
Andy