Topic: Salt Racer CB 750 OZ style

[johno]

754......BMW its changed since the last time I was there in the mid 70's, simliar format spiralling down, more interesting displays now.
Yes I went to the museum , they have split it into two sites now and segregated it into science at one site and engineering at the other.

Dennis, am using home made 32m flat slide Mikunis set up.   after talking to a couple of old blokes who done the bonny thing on cb 750 in mid 70''s who run webbers with 31mm, 32mm, 33mm chokes I am now thinking should have kept the webbers or played safe and run 31mmm carbs......they had lots of reasons but I am taking the gamble as I believe Mikes head flow and or port diam will work best with 32mm carbs,   be interesting exercise.

I dropped off the pistons and new barrels today with strict instructions.
JE pistons recommend 2.5 thou, I have asked for 2.3 thou, on all four pots, bores parrallel, last thou honed in 500 - 600 grit
based on the rings are honda and I believe thats the standard honda finish.
The pistons will stay ah la natural , no baked on moly skirts, no ceramic top coating, reasons errrrrrrrr didnt help last time !
I was  going to have a go at the holy grail of engine building,  that being zero leakdown but I couldnt get the gapless rings in size I required so hoping with a bit of attention to detail like torque plate on barrels when honing , minimal spec end gap, dry assembly and start under load on rollers I might get 2 or 3 %  I'd be happy with that 

[cbornotcb]

Johno, Iv'e just made a cutaway trimming jig for 32mm flatslides if you need to clean up any just off idle probs you may, or may not have ? I'll send it to you if you need one, just let me know mate.
Tiny

[johno]

Got the barrels back today , measured them up, the man was good , exactly where I asked at 2.3 though, hatch finish was spot on at 600 grit as expected with the sunnen computer u beaut machine, makes life easy with the right gear.

light face on the barrel / head surface ready as I am going to try one of those new fangled MLS gaskets,
whats the go with these babies I am thinking of just a smidgin of permatex only on the oil galleries circle protrusion just in case they weep is that the go ??

So wrist pins , the original dynoman JE pistons had short 50mm long wrist pins 3mm thick wall,  where as these older JE pistons
 ( not as old as Billy bling) have normal std length of 53mm with std honda 2.5mm thick wall about 3 grams lighter than the shorter thickwalled JE pins.   SO I was going to use the standard Honda pins as they fit and are lighter than JE , how ever when I looked through my 3 sets of good used std pistons and miked up the pins they were all worn about a third of a thou to half a thou.
In my old junk pistons I found a new set of pins from RC Eng Venolia pistons just shining like new, BUT they are 56mm long with 2.5mm wall thickness so I will have a go at machining the hardened steel one end to see if I can get 3mm off them and save me buying a new set of standard honda pins off ebay.
ciao

[bwaller]

I searched for lightweight tapered pins and along the way kept some notes. These pins are not tapered and if you need 53mm then only the 900 pins would fit the bill.

CB750 DOHC  OD 15mm  ID 9.10mm  Length 50.38  44grams

CB900 DOHC        15mm      9.10mm             52.95  46grams

CBX1000             15mm    10.10mm              50.37  38grams 

[Old Scrambler]

B........Your teaching me something new..................thanks.

[bwaller]

The Yosh 810 kit piston pins were 56mm long & tapered @ 36 grams if you're lucky enough to find any.

XL175 & the CB350 twins used 15mm pins 56mm long and both @42grams.

[scottly]

G'day, johno. I believe I read something here a while ago about pins made from tool steel, possibly by APE? You might try sending a line to Big Jay or Pat?

[johno]

Hi Scottly,   no worries re the wrist pins,   they were pretty hard near the surface but like all case hardened steel was soft as butter once into the meat.   I burnt up two new tips but the job turned  ( no pun intended) out well.

On the pics the stock on the left , then two of the pins , one with the original end , the r/h/s pin shows the macjined edge and bevel etc.

so stock pin was 18mm x 53mm weighed 41 gms
Venolia pins modified fro 56mm long to 18mm x 53mm weighed 40gms

So once again after all these years ol Russ is still supplying parts to the world of hi perf or record attempting sohc Hondas.  They are from a set of his Venolia big bore kits. 

[johno]

So all the piston replacement and machining is now completed.

Man it is so nice with good ol fashioned rings, they look so bullet proof, feel so strong ,  ahhhhhhh just like the old days boys 

I set  them up end gaps  .011 thou top, .014 second .023 thou oil ,   
On a postive note for the new age dudes if I had to fit them again I would machine the bottom of the sleeves to minimise the entry bevel as I feel no bevel would be better ,   I felt the problem was as the ring entered the bevel,  control was lost and the rails have room to roll as the barrels are tapped down, thin enough to fit between the piston and bore,  so my advice is minimal bevel 

[johno]

OOPS 
I was talking about the new age , skinny arsed 1.5mm rings on JE pistons, NOT these nice stock Honda rings

[Bill/BentON Racing]

johno, looking good, thanks for the info and update, Bill

[Old Scrambler]

Nice Work, Mr. Johno

Those pistons look REAL smooth

[johno]

wasnt going to but I decided to give the bottom end a good clean after the melted piston give the lower end a spray.

Things looked good, the bearings are all clean etc

[johno]

I have to change over to the M3 damper hub I have ready to go and check the number two rod small end etc

[johno]

[johno]

all done, changed over the damper hub, cleaned out both cases, conrod cleaned up OK 

so good to go for the reassembly

[Old Scrambler]

Merry Christmas

I see the COOLING fan is working in your shop

[johno]

On Wednesday I reassembled the bottom end, had problems in the gearbox, made a rumbling noise , loud , dont know what is causing it ?

Had a nice family xmas day, ate too much, drank too much , chilled out ready for a bash at the engine today.

[johno]

found the loud rumble noise problem 

Bummer I know how Frank dragracer feels now , putting gearbox in , pulling gearbox out , putting geabox in etc 

I put in the modified primary drive ( you can see the allen head screws replacing the rivets if you look close) and I checked the roller bearings by hand etc and they felt and looked OK !   BUT they werent , I'm gutted one set of rollers had the smallest nick ,that made a loud rumbling noise like it was a gear problem.   I dismantled the cases again , got the #$%*s so I put in the standard drive hub in that I pulled out and noo more noise      Learn by my slackness, be anal when checking the roller bearings, cant believe it made such a racket.

[johno]

So all cleaned up again and put back together , third time lucky
Going  to have a week holiday  , then reassemble the top end and see how it all  goes

[Bill/BentON Racing]

Nice, this year's visit will be different! K. Bill

[dragracer]

Glad you had success with the transmission. Its okay to walk away for a minute to regroup but the key is to never give up. Its not like we'll be able to get our money back once its spent.

[johno]

Your right Billy, we got good pistons and rings in this year 

[johno]

Back into it today !
cleaning up the new barrels

[johno]

out with the old barrels in with the new, will use the old barrels for a 836 bore