Topic: Salt Racer CB 750 OZ style

[johno]

there you go Bill,I know you like to get to the bottom of things.

[johno]

Another pic,   looks expensive doesnt it 

I showed it to a few of the local hot bike specialists and they were evenly divided over the cause.
half top piston lip , half  the blokes reckon the oil ring.

SO
at this stage I think it started with the top lip breaking away, then the alloy building up on the bore took out the thin oil ring, by this stage the flame front would have been directed to the pressure loss point being the hole behind the oil control ring and would have been like a torch just melting and turning the small hole into a big hole.
Thats my two bob's worth.

SO
what caused the top lip to break away, well its hard to tell and I dont know it it can be attributed to one thing or a combination, ie ceramic coating removed at the point, fell on shop floor, too thin between the ring groove and valve cutaway, detonation from big spark advance , could be any or all,  so I have made the decision it doesnt matter. I have to move forward.
Firstly I will not use those  pistons again, due to the depth they machine the valve cutaway, even on a bigish cam like the 125/75 it had plenty of clearance under the valve .140 thou to be exact , that meant it could have been machine less by almost .100 thou ( 2.5mm) greatly adding to the strength in that stress area.  Even if I got blanks to achieve the less depth  the diam for the 34mm valve makes it high risk option. Also I had a couple of forum people contact me saying they had seen the same problem with those pistons , Also the  two rings are not for me , .020 thin rails just suck, stress me out and waste my time. When a dealer tells you the rings are a good seller .....

SO
what to do. Right now I have to deal with the valve clearance requirements on a 62mm bore, its not piston / valve friendly so I am thinking of Cycle X wiseco 34mm 836 hi comp piston kit  12.5 :1  then I will drop big Jay a line and see if he can shorten the stroke by 4mm for a result displacement of around 760cc the max allowed. the extra 2mm on the inlet side would give some security for the valve cutaway.

I am looking at changing the carbs as I want more space for a big oil tank and may want to lower the top frame rail so I can run the bike in altered class A 750 as well as MG 750
I was thinking make life easy for myself with 31 Keihins but I got back some info from Electron , interestingly he reckons with Mikes work 34mm vlave down to .9 then blended back up to a 32mm port he says the 34mm electrons would be the go........so does that mean the 34mm Mikunis would be OK......would the change of bore stroke make any difference. ?
now you know why I am having trouble sleeping and feeling like I'm running out of time for next year 


Anway thats where I am up to, ciao boys.

[Bill/BentON Racing]

Thanks. Wow, you got a lot to think about! Would have been nice if they had cut the relief about half as much. Small problems........lol! You will be ready for next year! K. I like your theory on failure...something to that effect for sure. Keep us posted, you will succeed!  Bill

[mick7504]

At least you've got a bit of time on you're side now johno.
As you would know mate, time can be you're biggest enemy in these situations.
In fact, a bigger enemy than fcuken valve reliefs in some combinations.

Don't go losing any sleep over those pistons or what happened.
That aint gonna change.

You'll get it right next time mate.
We already know that.

[Old Scrambler]

Johno.........I like the big piston / short stroke idea................Looked into it myself a couple of months ago.  The AMA rules limit me to a .050" overbore from stock to run in CLASSIC.  If I was running in the standard classes............that's the way to go with care to observe the reduced angle affect on rod-stress at the point of highest cylinder pressure.

My pistons are J&E so may be a little different from yours.  Also, our head is from an F2 and has about 1mm more valve depth than the K head.............a little less than that at the outside edge of the valve.

Suggestion............if the cylinder is good, replace the bad piston and run the motor after checking valve to piston clearance on the 'off' stroke.  The bike may have had a weak piston or a degree or two change of the cam will solve the problem.   

[Jerry Rxman Griffin aka MuthaF'er]

That cylinder HAS to be toast now! Mine was bad but not broken and we had to resleeve.

How's the crank look?

[Bill/BentON Racing]

Johno, I may still have some J&E pistons like I sold Dennis! Interested, way high compression! Bill Can post pics.

[johno]

Hi guys,
re the comments;
Mick, yeh I wished I had used your engine now 
Jerry, yeh the bore was toasted just like yours    the crank dont know yet , will be a few weeks before I redo the bottom end just to be sure.
dennis , there was no valve to piston contact ! originally when checking I noticed that when the piston was rocking inlet up it just snicked the edge  so I removed the 1mm head gasket and clearanced the piston until it missed , then when the head gasket went back in the 1mm higher position gave the valve plenty of room, it s just they way I used to do things when I was in a hurry trying to make a dollar, leave off head gasket ,measure , use cutters , when eng turns OK and put in gasket plenty of clearance , nice and fast, no stress.   ....Although this time I did do the play do measurements before and after just cos I wanted it perfect.  fat lot of good that was though . It was an intersting exercise Dennis as I left about 10 eng HP on the table as a trade for reliability, that wont happen again , everything will be the maximum, carbs , comp, camshaft and exhaust with max HP at 10,500 RPM    will use the big RC 315 cam ( big for 750) rather than the 125 / 75.   At least if it blows this time it will go with a bang to calm me down for awhile  OR it will give old waterbottle a shot up the *@#* 

Bill; YES please let me have a look , I'm still open for options in the piston dept. cant wait
cheers johno

[bear]

I am looking at changing the carbs as I want more space for a big oil tank and may want to lower the top frame rail so I can run the bike in altered class A 750 as well as MG 750
I was thinking make life easy for myself with 31 Keihins but I got back some info from Electron , interestingly he reckons with Mikes work 34mm vlave down to .9 then blended back up to a 32mm port he says the 34mm electrons would be the go........so does that mean the 34mm Mikunis would be OK......would the change of bore stroke make any difference. ?

CR or Flat Slide?

Cheers,
Brian

[johno]

Hi Brian,
Nothings easy is it, I cant make my mind up yet, my instincts say make life easy for myself with CR31 but after the Electron man got back to me with 34mm is perfect ( he has them in 2mm increments so could sell me 32 if he wanted ) He has his little check sheet of experience and the engine mods and insists the flat slide is what its all about , for his whole kit ready to bolt on ( throttle, fuel lines etc )  for around $1,200 US:  So that got me thinking if the flat slide makes that much difference on the Electrons and 34mm is the go then do I go the 34mm Flat slide Mikuni ?  and will it be OK .       Anyone had a go with flat slides on smaller 760cc capacity ? , I  was looking at Doc D dyno posts , his was 836cc I think from memory , I must have another look and see what hapened mid range , not that I will be in mid range , I'll just adjust gear sprockets until it runs max RPM in top and see what happens.
As you can see Brian lots of planning.  I reckon it would be easier just to make a big banger  second thoughts reading of your journey that may not be the way to go 

hey evan ol Burt Monroe burnt two sets of pistions before he got it right

[Doctor_D]

Hi Brian,
Nothings easy is it, I cant make my mind up yet, my instincts say make life easy for myself with CR31 but after the Electron man got back to me with 34mm is perfect ( he has them in 2mm increments so could sell me 32 if he wanted ) He has his little check sheet of experience and the engine mods and insists the flat slide is what its all about , for his whole kit ready to bolt on ( throttle, fuel lines etc )  for around $1,200 US:  So that got me thinking if the flat slide makes that much difference on the Electrons and 34mm is the go then do I go the 34mm Flat slide Mikuni ?  and will it be OK .       Anyone had a go with flat slides on smaller 760cc capacity ? , I  was looking at Doc D dyno posts , his was 836cc I think from memory , I must have another look and see what hapened mid range , not that I will be in mid range , I'll just adjust gear sprockets until it runs max RPM in top and see what happens.

Power delivery isn't quite as smooth as the CR's for some reason, but overall the mid range is fine they make and great gobs of torque across the range.  Better top end by a few HP than the 31's as well.  Watch the tips of those damn fuel screws.  Fragile buggers that break off in the idle port, causing all sorts of problems. There's also a good assortment of velocity stack lengths to get them tuned properly.   I think I have the 50mm stacks on there now.

[bear]

Hi Brian,
I reckon it would be easier just to make a big banger  second thoughts reading of your journey that may not be the way to go 

hey evan ol Burt Monroe burnt two sets of pistions before he got it right

I'm happy to prep. one of the Hy-Vo's to throw at that other late model roller if it's still available.
And as for our old mate Burt, I'm more than comfortable with my offerings to the "Gods of Speed," I just hope they are.
Maybe we can come to an arrangement with the Webbers.

Cheers,
Brian

Cheers,

[Tintop]

Maybe we can come to an arrangement with the Webbers.
Cheers,
Brian

Think your about third in line for the Webers Brian.

Cheers - Brian

[scottly]

I am looking at changing the carbs ..

I was thinking make life easy for myself with 31 Keihins but I got back some info from Electron , interestingly he reckons with Mikes work 34mm vlave down to .9 then blended back up to a 32mm port he says the 34mm electrons would be the go........so does that mean the 34mm Mikunis would be OK......would the change of bore stroke make any difference. ?

If you want to make life easy on yourself, keep the Webers. 

[bear]

Maybe we can come to an arrangement with the Webbers.
Cheers,
Brian

Think your about third in line for the Webers Brian.

Cheers - Brian

Oh well, I'll get back in my box then.

Cheers,
Brian

[Tintop]

Oh well, I'll get back in my box then.

Cheers,
Brian

With scottly doing the Weber cheering section, will all be back in our box Brian.

[mick7504]

How 'bout big and nasty johno, and have their balls for bookends. 
Hyvo/Stroked/Billet Block.
Ring the Police. 

[johno]

Tiny,
Whats happening in your shed?

Have you recovered from the trip yet?
johno

[johno]

WEBERS FOR SALE.

Sorry Scott, you inspired me but I need more room in that area of the bike and the top frame rail is coming down a tad.  I shouldnt be the person saying this but fair dinkum while I had the bike out at the lake there was a constant stream of people  lining up to talk about the bikes and the webers.  My son couldnt believe it and commented on it regularly during the day.    Those carbs are synonamous with classic honda sohc hot rods.

So I am not sure the best way to do this but there were several PM,s from intested people and also on our for sale thread , I am figuring the price will change peoples mind so evan though I have noted when they were posted  I feel the best way is I'll post the price , if any of those people are still interested I will revert back the original enquiry list for first refusal offer.    So if the price doesnt scare you off just let me know again if your interested, PM would be the best.

So the value;
New replacement value;  All Aus $
Two 40 DCOE webers ( Italian made)  venturis 31mm all jetted suit Honda sohc @ $517 each so 2 of $1,034.
RC Engineering manifold, refaced and tidied.......say...............................................................................$ 100.
Linkage arms and screws      more but say.............................................................................................$25.
New Honda 450 throttle cable , modified outer  .....................................................................................$30.
New long travel quick action throttle suit cable and linkage    .................................................................$60.
2 Return springs new   ...$7.
4 new foam air cleaners ...$69.
8 stainless mount bolts and rubber dampers ..........................................................................................$16.
2 rubber manifold gaskets in alloy frame  ..............................................................................................$76.
Spare set of 115 main jets                ...$30.
Cobra kit, all new  32mm venturis complete with all jets, tubes, idles, airs etc suit .................................$ 200.
New fuel hose      ...$10.
4 head manifold rubbers  all 2 &3, 2  new 2 resoftened, all new clamps...................................................$80.
                                                                                                                                           total Aus $1,737.
                                                                                                                                                   US $ 1,563.
In my mind they have to be worth at least half new price, so Oz $800. or US $750.

It may sound a lot but thats nearly the cost of what I spent over the last 3 months just giving them a freshen up and the optional 32mm carbs internals.

So if your intersted still PM me ,  I will offer in order of original enquiries.      cheers guys, 

[johno]

[bear]

Johno,

Hung the leathers up tonight. Couldn't work out why they where so heavy so I checked the pockets.
Cheers, mate your a legend.

Cheers,
Brian

By the by PM sent.

[cbornotcb]

Tiny,
Whats happening in your shed?

Have you recovered from the trip yet?
johno

Recovered, yeah, (almost)
Back at work
Test ride tomorrow,,but,,,,,
Private road rental (Mr Plod quote estimation) $1800 + Taxis for 2 yrs ?
Option #2
a REAL private road (desert rats 'rod club), total length, 800 mtrs, no front brake, 1st 3 gears not really useable @ wot, just a few milliseconds spent in each gear, 4th & 5th gather up mtrs rather quickly (800 mtrs ain't much to gather up)
I need a dyno, methinks, or more of that  " private " road luck Iv'e been using, but worry the luck bucket will be empty soon ?
Now, if I were 20, I'd just do it, and spit chips if things didn't go to plan, they usually don't,,,,,
Sensible Tiny ?

[Jerry Rxman Griffin aka MuthaF'er]

   As AOL says, you have mail 

[Bill/BentON Racing]

Johno, here you go!

Oh,you want what's inside!

Pretty,with 3 rings 1.5,1.5,2.8mm

another.Clearance was a problem here also! 15 years ago, some things haven't changed!

again

another

Let me know if interested. Dome height .400 not relieved for spark plug. Bill

[mick7504]

Large Intake + Small Bore = Big Headache?