Topic: CB750 chambers differs in volume - Result in HP & Nm

[PeWe]

This ported earlier head has one chamber that is around 1cc larger than the other.
Cyl 2 has 23 ~24cc , the other about 1cc less.

Valves: IN 34mm (F2), EX stock 28mm

- Should I grind the other chambers as the larger one?
It is more carved on plug side.

- Or better to weld the larger one and grind?

To be used with JE CR 11:1 pistons now having a  24.4cc head in need of higher CR.

Gasket on photo is a 68mm MLS I used when marking.


Easiest is to grind the other to come closer in volume.
But better to check before making an eventual mistake.

Another alternative is to accept the 1/22 difference. 4.5%
If compression will be around 200PSI on the 3 other, 190 PSI on this larger one. No risk making a mistake.

[johno]

Hi Pewe,
Before you make a decision to grind try measuring the valve depths on no. 3 and 4 cylinders  and compare to see if a valve has been ground in for some reason, that could make 1cc difference.

use a set of vernier callipers to measure from valve end to spring base and compare to others.

[PeWe]

Hi Johno,

I had that in my mind when looking at them. If the larger volume has deeper cut valves. I could not see (visually) that from chamber side.


My other head used now with even more volume has more material removed at the plug side so it is possible to grind there.

[PeWe]

Made a test with new fiber gasket.
The chambers can not be wider on plug side. #1 a little.

Will check with the shop nearby how to make 1,3 and 4 as chamber 2, at least much closer.
Chambers already too wide for 836.
I guess the porting was done for +67mm pistons many years ago.

I know we are many that like tech porn pics!

****67mm fiber gasket ****


*** Cyl 4, 3 ***


**** Cyl 2, 1 ***

[PeWe]

Tested a 65.5mm MLS. Maybe not for chamber 2.
My 836 and 849cc cylinders need another head.
Using a 67.5mm MLS/fiber and 65.5 mm bore might work though.



*** Cyl 4, 3 ***


*** Cyl 2, 1 ***

[PeWe]

Fixed the chambers, now same volume. My method to measure OK for relative measurement, absolute not that good. I think the chambers are more like 24cc.

Head is ment to sit on my other engine build with super rods. Will test it before winter on my K6.
These hemi chambers will like 12:1 pistons. CycleX has 890 kit with domes for caves like these. Dynoman has a little bit flatter 12.5:1 67mm pistons. I'll see what will be easiest to use.

My DP315 or Megacycle 125-20 to help the 12:1 pistons to breathe.
(My 125-20 cam has 0.388" In lift, not 0.338" as written everywhere. The cam card followed the cam and timing say the same)
**** 68mm MLS fits OK ****


**** leveled the head before volume test ****


**** Not a Colt or Glock, a Bosch! ****


**** My covered valve cover before paint worked fine as work stand with "leveling screws" (cam holder screws as RC used for the powerful springs used back then) **** 

[johno]

Per ,
When cc 'ing you need a piece of plastic or something with small hole in to cover the chamber or the meniscus will get you every time.

[PeWe]

I tried plexi but it did not work that well. I can test again, just for sure.
It worked well anyway with colored alcohol, flat surface. Not convex as water.

Edit: Tried again. It worked this time.
Same result as before. My "problem" is that I have to reload the syringe that only contain 20cc.
I follow same procedure on all since most important here is same volume on all 4.

[johno]

maybe you drank some of the alcohol Per, that would explain the discrepancy 

[johno]

I use green coolant for filler, perspex with 5mm hole in to fill, position fill hole to one side of the chamber as its easier to chase the air bubble down, and a smear of grease between the head and the perspex to seal as the head will be on a slight angle chasing the bubble.

If that doesn't work PeWe..........more alcohol

[johno]

Probably not a concern Per but have you indexed the spark plugs ? maybe a big washer under plug is where volume is ?

[simon#42]

you will never get an accurate reading with a syringe , get yourself a burette they are only cheap

[PeWe]

No washers under plugs. I test plugs until I find one sit oriented with gap to IN.
I'll see if I measure more. Most important here was to make chambers more equal since I saw that number 2 was larger. First photos show that.

When mention it, easier to find matching plugs when on the bench. This heads plug threads were very equal which made it tricker to find a plug.
Had to go thru 25 plugs...

Heads on bikes were easier, max 10 plugs to check for all 4 on each bike. If not matching one cylinder it matched another.

I'll try to find a better tool to measure the chambers. I'm curious to know the absolute value of volume.

EDIT:
Tricky to find something to measure liquids with here.
I found a tall buret for 50ml with on-off. To be ordered, nothing like that or similar were I live.

I have measured the amount I used earlier today into a 100ml measuring cylinder. It is ~25cc something, as it look like ( not less) and will fit the pistons I have had in my mind for that head.

Found one, I hope they can ship cheaper since shipping is a robbery!
https://www.betterequipped.co.uk/burette-plastic-50ml-prd0168p-123

[PeWe]

Since I cannot wait for an eventual answer from seller in UK of a buret shipped with OK shipping, £10 instead of £35.

I made a similar design with a hose, ID 10mm.

Calculated the lenght that cover 22-27cc. 280-345mm.

(Like calculate displacement using very small piston 10mm, but very long stroke, 320-330 mm)

Hose lenght 400mm.
Put a bolt in one end, bottom, sealed with grease

Hose attached on a folding rule.

I used plexiglass to ensure completely full chamber.
Filled chamber, sucked the alcohol/ water mix back from the just filled chamber with syringe and filled my hose. Lenght noted and later calculated to ml (cc).

I let it hang upside down between measurements to get  all fluid out of the tube before next. Max 1mm staid.

Same procedure on all 4, so comparison of chambers OK, same error on all.

Very little liquid not possible to suck up. I guess max 1-2mm missing into the tube which is max 0.15cc.

Double checked 1 measured volume into a measuring cylinder placed on a scale not that accurate. It verified the procedure, though.

Chamber volumes 25.4-25.6 cc

Mill head 0.5mm, takes off around 1.5cc taking it to 24cc which will work on K6 11:1 pistons and next build using 12:1 pistons with DP315 or 125-20 cam.

This will also fix the chamber 2 extea wide diameter that is shallow, making head to work with 836 too

Next step is shave off 0.5mm from head, asap.

Chart is calculations made in Excel to get a picture of various volumes.
 All measured chambers calculated individually




**** Reset scale with another empty measuring cylinder just before, 25 grams is the liquid ****

[PeWe]

Update:
Chambers are OK now after:
- My massage to make them closer to each other.
- Shaved off 0.5mm as I had calulated should fix it.
The real thing and my theories matched.
No 2 chamber too wide shrunk in too as planned.

Head can now work with 836 and up.

Below test with 65mm MLS, maybe 65.5mm.

I might test the head soon on my K6 with 71.25mm CR 11:1 pistons.

Funny, 71.25 mm is same as the heads new height. It must mean something....

[johno]

Well done PeWe, mission accomplished.
So now you have the chambers cc'd you said it was going to be used on two engines with 11:1 and 12:1 pistons , you stated the advertised piston comp ratios but not the bore sizes so let us know what the true comp ratios will work out to be with each bore size you plan to use.
Also Per did you have this head flowed ?   you have so many combinations I can't remember ? 
cheers Johno

[PeWe]

Hello Johno,
No flow data on the heads. Wind is measured in m/s here... km/h works too!! and Dyno....
The restored head has not as much opened in ports as my old.
The restored has F2 Inlet valves (34mm) std stems, stock KPMI ex valves.  Old head on bike now has also 34mm but 5mm stems.

I'll use it with 71.25mm pistons (1005cc). Gasket is now 0.0400, I'll try 0.0300 that shorten another cc. (Dynoman JE pistons 11:1)
The other engine build might get this head later on.

The 1005cc get another head. I have a head marked 392 upside down, but chambers less than 23cc (22.5-22.9), not 24cc as 392 is said to have.
That head will get 33.5/28.5mm valves. The design of that head fits my K6 with billet block better.

Head shown here an earlier design that will match an earlier cylinder.
I plan to give CycleX 890 12:1 kit to be used on my extra engine build and used on my CB750 K2_2, my 3rd bike. Wife see only 2 today  The 3rd has most of the parts. This time not letting the stock devil interfere the build!!

(Before doing this I have to swap frame on my stock K2 that has cut frame today (great help during its engine's progress). This frame better with next build and does not need to be checked by vehicle inspection. My stock K2 get another not cut frame that has registration need of vehicle inspection. Must be painted first.)

Only one issue making progress really slow.  
My old head has collapsed alu under the nuts on ex side. I saw that before and did not see the alu make holes smaller.
Now impossible to get head off without taking out the studs which goes off  with much effort. I have to push, bend and pull them up all they way after I have moved them out of the case threads.
All long studs on ex side removed, the shorter trickier to get by double nut. I have "lubricated" double M8 nuts on those 4 short studs with Loctite 272 (red hard thread locker). Will cure 24 hours and then hopefully possible to get the studs out.

Studs are HD studs so they sit rather tight in head. I had all off 3 years ago and happily not locked them with Loctite.

If 272 will not hold the nuts, I'll go up with metal glue Loctite 638 or 648. I have both, 648 is thinner. Then I'll have issues to get the nuts off, I guess 1 hour in oven 250-300C will probably remove nuts from studs when off from engine.
These  studs'n nuts drive ME nuts!!

I'm eager to test this head with less cc, higher compression and a hotter cam. Coming weekend. The stud off delays at least 2 days.

[PeWe]

Old K6 head with 5mm stem valves off today after some banging on a stock ex spigot I mounted as leverage and banging point
It will be interesting to investigate if the bronze guides are worn.

Pistons cleaned, almost like new. Bores look fine after almost 20.000 km.

Head got new 0.03" MLS gasket. Perfect to have parts on the shelf.
The old refurbished head with 6.5mm valve stems got on.

I drilled the holes for cylinder studs with 9.0mm drill from inside out. Some holes were already a little tight.

Old style orifice got its hole refreshed with 1.0mm drill. Plus a few in the shower head side.
I did not trust the old corroded metal with eventually smaller holes.

[bear]

I'm like'in your work Per, keep it up.

Cheers,
Brian

[PeWe]

Thanks Brian,
It goes slowly forward. Cam installed and timed after various needs of redo and adjustment of cam holder contact with in lobes1, 4.

I had ideas about advance cam some extra but remembered clutch slip when engine is not really warmed up.
Throttle full from low was ok after 15 minutes.

Clutch has the tougher Barnett springs for CB 550 and other smaller CBs, late clutch from F2.... Billet pressure plate

I'm curious to measure compression with my cheap tester.
If compression follow the chamber volumes or if cam adds some luck making all equal as this thread started with.


Adjust lash tomorrow. Hopefully start it too.

It will get new Honda bagged carb boots, the old had huge cracks on cyl 2,3.
The cracked were bought as OEM, not in Honda bags, but Honda labels that might be own copies by the seller.

Newer Carb boots are softer than the boots bought in the 80's.  Must not be clamped too hard I guess.

Good quality forged thick domed JE 71.25mm CR11:1 pistons from Dynoman survived without any heat marks going inwards.
JMR Billet block Nikasil treated bores look fine despite the heat the last 500km since last plug check not screaming white- gray.

[johno]

You are a machine Per  .  you make me feel lazy , can't wait to see how the beast runs.

[Medyo Bastos]

I’d like to see Per run too!


Sent from my iPhone using Tapatalk

[PeWe]

Read Terry's projects if you want to feel really lazy. He is working really hard

I'm not running, a quick walk is OK except for 5 minutes left of the happy hour in quick need to order in the bar!

I had just entered a domino effect of failed parts and need of more compression. One thing revealed another issue when taking things apart ....
That had to be fixed.

Good to have a spare ported  head and gaskets.

[PeWe]

Started it this evening. Runs fine but might need a carb synk which can wait.
Compression test is next to verify all 4.
Early looking head now.

Hopefully good weather the next days to see how it deliver.

[PeWe]

The result of the initial chamber question!
All 4 rather close

The engine was exersised  yesterday to blow it clean from old bad spirit. +200 km ride, a number of WOT from various rpm's on 5th. 4000-7000 to ca: 8500 rpm.
17:48 gearing.

Really good news to verify no damage on cyl 2, 3 that had much lower compression.

- I wonder how high pressure is possible for a street bike on normal fuel, (Shell V-power)?
Dyna-S ignition.

Now 5- 10 PSI more than the old head with 24.4cc chambers (190-195 PSI) and slightly thicker head gasket 0.004, now 0.003.

Cam similar, now 125-75 with similar data as my marked "RC295" cam.
125-75 has 2 degrees more overlap according to my timing notes at 0 lash. I do not know the  lobes ramps differences for eventual real values with running lash.

RC295 has fatter lobes.
Synchronized carbs today. Engine idles very fine, 1000-1200 rpm no problems!

I prefer 1200-1400 rpm which make it easier at take offs.





125-75   vs  "RC295"  (engraved at the end under washer)



Note!
The real compression is higher since the hose to gauge have a volume adding up.
OK to compare all cylinders and with others using same model.
I guess this is like a cheap Harbor Freight model.