Topic: Rebirth of paulages' cb735

[paulages]

okay....I didn't know you were going to move up to CR Carbs!

My guess is low 70's HP with those carbs, GOOD fuel, and timing full advanced.

Heck, my 550 feels about 50 HP, and lightened up she really screams until I hit the brick wall at 5,000 RPM's, but that will be fixed with the 125 jets I just ordered. 

Anyway, you bike must REALLY scoot!

~Joe

it's already at 70... we'll see what else i can squeeze out of it and still have a rideable bike, but another few seems reasonable.

[bwaller]

Yea Paul you've been saving your pennies. That beast needs those CR's.

Joe is your engine stock? I have a 591 with stock PD's and a single large K&N with 117.5 mains (51 RWHP)....125's sound way big.

Back to you Paul.

[paulages]

Yea Paul you've been saving your pennies. That beast needs those CR's.

Joe is your engine stock? I have a 591 with stock PD's and a single large K&N with 117.5 mains (51 RWHP)....125's sound way big.

Back to you Paul.

you can have the stage anytime, brent.  a friend of mine runs a shop here called Empire Classics (might as well plug him here...http://www.empireclassicscycle.com/), that mostly caters to classic/vintage british bikes, but he offered to sponsor me if i race this and sell me the CR carbs at cost. i definitely think it needs them.

[traveler]

Are the CR's...26's?

[paulages]

Are the CR's...26's?

i'd probably get 29's.

[Soos]

VERY interested in what the CR is going to be




L8r

me too! i hope to have time for this today... i'll post results as soon as i get them. i'll send those pistons out as soon as i get the new ones sorted out, ok? for now it's useful to be able to measure off of the old ones if the valve pockets aren't deep enough on the new ones.

Not a problem.
Those ones I sent you have been on my shelf for about 2 years now.

l8r

[Soos]

Yea Paul you've been saving your pennies. That beast needs those CR's.

Joe is your engine stock? I have a 591 with stock PD's and a single large K&N with 117.5 mains (51 RWHP)....125's sound way big.

Back to you Paul.

you can have the stage anytime, brent.  a friend of mine runs a shop here called Empire Classics (might as well plug him here...http://www.empireclassicscycle.com/), that mostly caters to classic/vintage british bikes, but he offered to sponsor me if i race this and sell me the CR carbs at cost. i definitely think it needs them.

DAMN, you gonna race this thing?
 
Don't forget you ever run outta oomph, you still got the 65mm(740cc) option and 66mm(763cc) for overbores!

l8r

[traveler]

This bike is just too cool.

~Joe

[paulages]

finally found some time to measure my clearances and compression ratio...

the clay i was working with was not as pliable as i'd have liked, and the mold left from turning the engine through was not as clean as i'd have prefered. the squish band was too messy to measure well, but the shoulder of the new piston is lower than the shoulder of the old one, so i feel safe in that regard. as well as i could measure, it appears i have about .050" clearance between the head and piston. the intake valve worries me a little. again, as well as i could measure, i found .030" between the intake valve and piston. unfortunately, i can't time the cam with the clay in the chamber, so i had to use the stock timing mark. i'll remeasure the clearance with a dial indicator on the valve stem at this point.

the compression ratio is a little surprising. measuring until my measuring fluid (dyed ispropyl alcohol) comes just to the top of the spark plug hole, i found 206cc at BDC and 200cc at TDC, which results in 10.3/1 CR. however, if you subtract the volume of the spark plug, the CR goes up quickly. for example, there is only an angled tip of the plug in the chamber (not even accounting for the fluid in the threaded section as i was measuring), but it's rough volume is 2.39cc. if you subtract this volume from both measurements, you get 203.61cc and 17.61cc, or 11.56 CR.

in any case, i measured the CR of the old pistons the exact same way, so for all accounts these pistons actually seem to have a little less compression. still, it's a good range for a bike that sees pump gas.

[Ecosse]

good to know! as usual paul you are a wellspring of info for we of the 550 (and 500/650 septs) clan.

[paulages]

good to know! as usual paul you are a wellspring of info for we of the 550 (and 500/650 septs) clan.

or guinea pig, maybe?  

on that note, i may have wrongly posted that the A.P.E. HD stud kit for the 500/550 will work with the 550 cylinder... not true. sorry for the disinformation.

[RAFster122s]

So you have 7xx cc out of a 550 cylinder...wow!
I was figuring you had 650 cylinders overbored...

Those compression numbers are intense. Do you have to use premium fuel to prevent detonation?
In an auto you would definitely be using premium and possibly octane boosters.

David

[Ecosse]

In an auto you would definitely be using premium and possibly octane boosters.
David

not necessarily. a lot of that depends on combustion chamber design, as well as timing, spark, et al.

still, with something essentially old tech it is remarkable. who knows where honda's sohc could have gone if not killed by the dohc.

there are good sohc designs out there w/o the power losses of extra valve gear.

[fastbroshi]

  Just for reference, the new BMW M5's CR is at 12.0:1.  But that's with all kinds of electronic wizardry going on.  I think you'll be fine on premium Paul.

[paulages]

  Just for reference, the new BMW M5's CR is at 12.0:1.  But that's with all kinds of electronic wizardry going on.  I think you'll be fine on premium Paul.

i ran this bike at 10.6/1 CR on pump gas no problem. i'm not concerned about it.

[Pinhead]

10.6:1 on pump gas with no problem makes me very happy.

[paulages]

10.6:1 on pump gas with no problem makes me very happy.

"no problem" is relative to having a dyna 2000 and oil cooler. had light pinging before finding the right advance curve and running the cooler.

[paulages]

Bwaller and I had a PM exchange about measuring the compression ratio, and I ended up trying another method to measure.. thought i'd share the results here, in case i'm doing something stupid and one of you smarties can catch an error. 

i took a piece of plexiglass and drilled a couple small holes in it, one for filling with my measuring fluid, and the other for allowing air to escape. i laid the head upside-down on my bench, and greased a ring around the combustion chamber to seal the plexiglass against it. i filled it with fluid, and it measured 25cc. this is my combustion chamber volume.

then, i installed a piston on a rod, and installed the cylinder block, using a stack of washers and a bolt to lightly compress the cylinders against the base gasket. i lowered the piston until the top of the crown was exactly level with the top of the bore, and measured the lowest point in the valve cutout from the deck to be 11mm. greasing the top ring, i filled the bore with fluid until the fluid was exactly level with the top of the cylinder crown of the piston. this measurement was 22.5cc. calculating a volume of this section without the crown discplacement to be 36.02cc (11mm depth X 64.59mm bore), i subtracted the liquid volume (22.5cc), and found that the dome volume is 13.52cc.

the head gasket (measuring an old gasket that was already compressed) is 1mm thick and 65.5mm in diameter, which gives a volume of 3.37cc for the head gasket section. by the way, at TDC the piston sits level with the deck.

so...when you add the head gasket volume (3.37cc)to the chamber volume (25cc), and subtract the dome volume (13.52cc), you get 14.85cc for the volume ATDC.

if the bore is 64.59mm, and the stroke is 55.5mm, the displacement for one cylinder is 181.76cc. add in the volume ATDC (14.85), and you get 196.61cc BTDC.

divide BTDC by ATDC and you get 13.24/1 CR.  


anyone care to check my math?    sounds like i have some work to do... the volume in the plug hole likely accounts for the 6cc difference in the measuring methods (and i used the same method for the last pistons), but i'd like to be dead sure before i go cutting the pistons...

[traveler]

OUTSTANDING!

Thanks, Paul.  It is this attention to detail, and taking the time chronicle it, that is keeping this forum ALIVE!

I, for one, appreciate it!

91 octane fuel, lead substitute, and Octane boost!


Let's hope for 90 H.P.!!!!!!!!

~Joe

[Pinhead]

Do the magic that I'm doing to my CB650 motor!

http://forums.sohc4.net/index.php?topic=64820.msg757873#msg757873

[traveler]

Paul is really pushing the envelope on CB550/650 design.

Wet sump CB's really do have potential, huh?

~Joe

[paulages]

OUTSTANDING!

Thanks, Paul.  It is this attention to detail, and taking the time chronicle it, that is keeping this forum ALIVE!

I, for one, appreciate it!

91 octane fuel, lead substitute, and Octane boost!


Let's hope for 90 H.P.!!!!!!!!

~Joe

i'm hoping for 75!! 

[bwaller]

Paul, I wonder if you should take your depth measurement to the piston shoulder instead of inside the relief to make your calculation for cylinder volume. The negative valve relief volume should be part of the dome calculation.

I'm sure you're accurate, the only thing I did differently was insert the piston at 25mm in the hole, with plexiglass bolted to the deck too to bleed the air out. Results should be same same.

That's a big difference in ratio between the two tests, sorry to throw a fly in the ointment. I'm curious what feedback you get from the builder crowd.

[paulages]

Paul, I wonder if you should take your depth measurement to the piston shoulder instead of inside the relief to make your calculation for cylinder volume. The negative valve relief volume should be part of the dome calculation.

I'm sure you're accurate, the only thing I did differently was insert the piston at 25mm in the hole, with plexiglass bolted to the deck too to bleed the air out. Results should be same same.

That's a big difference in ratio between the two tests, sorry to throw a fly in the ointment. I'm curious what feedback you get from the builder crowd.

i see what you're saying. i thought and thought about which point to measure from, and i believed measuring from the lowest point of the valve relief was correct. thinking about it now, i see that the area i'm subtracting from isn't necessarily what's above deck. the red area below is what it in the chamber though, when at TDC. hmm... i 'm gonna have to think about this one.

here is a crude drawing to explain:



i found the area of the rectangle made by the area of 64.59mm X 11mm, the low point being drawn beneath the lowest point in the crown at the valve pocket. i subtracted the volume of the red area, as found with the fluid.

[paulages]

looking at this drawing, i see that my calculation would put the entire piston shoulder and all of the mass in the center beside the bottom of the valve relief above the deck, which is of course not true. hmmm.. how to i compensate for the negative valve relief?

EDIT: simple... i fill the pockets with fluid until it reaches the shoulder, then add this measurement to the volume measured from the shoulder.... thanks for the wrench in the works, brent! sometimes i just need to think aloud.