Topic: Salt Racer CB 750 OZ style

[Bill/BentON Racing]

It had to be...you tube material for sure!

[johno]

Thought I would have a look at these new pistons on the weekend, just to compare to the standard, Dynoman JE piston and custom JE piston

Rings are the stand out followed by the dome profile, the spark plug relief on Dyno, then the valve cutaway on Dyno man are 34mmm for inlet and 30mm for exhaust  as opposed to old JE both valve cutaway are 34mm, so lose some comp on the JE from too much milling. also takes the cutaway to a knife sharp edge on the exhaust side.

[johno]

[johno]

My plan,
put pistons in,
centre pop the valve centres and spark plug hole centre in case they need to be machined.

Then head off and play doh on reasemble do clearance checks , v to p , head to piston etc
Head off and cc the piston dome to do a comp ratio check.

Make a decision on the piston shape

[johno]

I made up a long centre pop from 5mm stainless rod,   you can see the centre of valve, the spot to dial in the flycutter to

[johno]

This is the tool with point ground on to centre pop the piston to centre the mill on if doing a plug relief hole like the dyno piston.

[johno]

so put the head gasket and head on and cam 125/75, set tappets,  and rotated over a couple of times

[johno]

[johno]

I used a vernier to measure the thickness of play doh to make a rough contour map

[johno]

this is the map.

Non plug side is good at about 7mm
Inlet is good with 3mm  ( 120thou)    but the relief is 34mm diam and needs to be flycut out to say 37mm
The exhaust is good with 3mm and planty of diam room

The piston to head on the plug side is not good, from almost touching to.4mm ( .015 thou) almost from edge to plug.

Needs some work here

[johno]

cut away to double check the thikness

[johno]

So checked the comp ration,
Clearance volume....17.2
swept volume..........190.1
CV +SV divide by CV = 12.05 : 1

The dyno JE had 12.2 :1
The JE valve larger exh cutaway and a less fuller top has dropped the comp slightly.

I will have a think about this as I need to machine to get piston / head clearance, this will less comp as well 

[johno]

If I was a betting man I reckon these pistons were designed for a supercharged engine with a large exhaust valves and a nice hemi chamber 

[Bill/BentON Racing]

Saw some old heads of PO, hemi chamber for sure, but ran in road race bike, so no forced induction. The 836 65 mm kit I got has the plug cut aways! Yeh, that exhaust edge cut away is close. Good luck, no doubt about being ready this year! You go man! K. Bill I think I put a 1080 in this! Haha!

[Old Scrambler]

Thanks..........Professor..........this student is paying close attention

I have the same pistons but will be enlarging both valve-pockets for 35mm intakes and 31mm exhaust.  My F2-head is more of a hemi-design and has less compression with these pistons.............until Dave and I agree on the final plan

[johno]

Hi Den,
35mm in & 32mm  out,   Try it on one cylinder on an old head with cam, they got a habit of hitting, evan with the sunken F3 heads, if you sinkem enough to miss it smashs the flow, the big trade

[Old Scrambler]

The F2 valve stems are about 1mm shorter than K units...............and we added a few degrees to the lobe-centers on a special grind cam. Any day now and we will be testing with 'soft' springs. Everything is on the bench except the cam.

[johno]

As jweeks said johno , 1.6 hp chrysler v8 fizzed up on  24 volts ,will pretty much start anything especially with locked up ign , easier to buy starter nuts from A.P.E  ( should be hardened rattle gun socket this one isn't ,have seen em split ) think same taper as early z900? lota guys cut down Honda alternator hub , mill into nut 11/8,

Hi pete,
yeh you were spot on , I contacted Ape and they said technically they have not made  one for cb 750 but the SNK 1000 had the same taper and would work...............they cost $30 us dollars plus shipping   ciao johno

[johno]

starter nut Like this !

Also Den why dont you try this , lower top side rail , no top fuel tank,  run a fuel tank alongside oil tank with bambino fuel pump,

[Old Scrambler]

Mark..........some thoughts...............our tank is only 1-inch above the top-tube at the front where my helmet sits ...........so not much gain and fuel pumps tend to put pressure on the needle & seat in the carbs.

[johno]

Den I was not so much thinking helmet height but the angle of attack over the back ( also thought it might make some room for my big fat guts. )
johno

[MRieck]

Mark..........some thoughts...............our tank is only 1-inch above the top-tube at the front where my helmet sits ...........so not much gain and fuel pumps tend to put pressure on the needle & seat in the carbs.

Even diaphragm pumps can be to much BUT are generally pretty good with those stock seats. I've had enough problems with gravity feed and aftermarket fuel valves. That lead to drilling  a vent hole in the gas tank cap....that worked.

[Old Scrambler]

The distance from the back of the seat to the stem-nut on the triple-tree will be the same as on my Triumph Tiger Cub...........the tank is about 6-inches shorter than the standard CB750 unit. I will be sitting about 4-inches lower than a standard bike..........so the only thing preventing me from getting lower is my head (with helmet) where it touches the tank.  My eyes are very close to the stem-net...........I have actually touched the nut with my helmet visor while making a run.  To get that low, I lose sight of the horizon but can see the flags along the edge of the course.

Mike.......Yes, to the added vent

Regarding a starter............if you get the nut on the end of the crank, along with a cover and plug to keep the salt away, you will have a conflict with fitting a fairing someday.  We plan to use an on-board CB900 starter with a remote battery and cables. If that won't work, a gear-driven roller-type unit with two Ford starter motors will allow the rider to have sole control to start the bike. I will be at the AMA Super-
Bike races this weekend and hope to take a few pics in the pits.  ....................New pic in my thread  

[johno]

Hi Mike,
Ol tintop posted a pic of you wearing a jewelers rig a couple of weeks ago and I thought what a great idea so I ordered one and it arrived today.

I have been struggling with my eyes big time last year or so with both retinas starting to break away and it makes things difficult engine building, especially my favourite measuring tools and I have been using a big magnifying glass and a portable LED BUT guess what takes two hands and was a pain , these new babies are awesome , two hands to play !  I now reccomend them for old farts,
Thanks for the idea Mike and Tintop 

[MRieck]

My pleasure johno. Those are very nice I might add and they give you that cool mad scientist look. I haven't gotten so used to wearing them that I have left the house and done an errand with them still on my head in the upright position. Needless to say I have gotten some very strange looks.