Topic: Rebirth of paulages' cb735

[bwaller]

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.

I know exactly what you mean!

[paulages]

ok, i'll leave the above explanation because despite the calculation error i made regarding the volume of the dome, the rest makes sense. i've recalculated, and found the following:

the volume of the valve pockets below the piston shoulder is .15cc (the red areas in the diagram below). not much. the volume of the bore with the piston crown level with the top of the deck is 30.62 (64.59mm X 9.35mm). we'll call this "Z." subtracting the valve pocket volume from the measured negative space volume (X below), i got 22.35cc. subtracting this from "Z" and we find the dome volume ATDC, or "Y" below, to be 8.27cc.



subtracting the bore volume from the chamber volume, gasket section volume, and the valve pocket volume (the red areas below) I got 20.25cc ATDC. now that looks more like my real world measurement.  

add this volume to the displacement volume at BDC, and we get 201.5cc. again, close to my real measurements. divide the two, and you get 9.95/1 CR.

now that's more like it. i'd like to see it just a little higher, but that will require a different head gasket at this point, and i worry about the intake valve clearance.

[Raef]

I have been fading in and out catching up on this,

If you have a cylinder and a piston available, why couldn't you just check it the same way you did the head, with Plexiglas and fluid?

Maybe I missed the reason you couldn't do it that way?

[paulages]

I have been fading in and out catching up on this,

If you have a cylinder and a piston available, why couldn't you just check it the same way you did the head, with Plexiglas and fluid?

Maybe I missed the reason you couldn't do it that way?

i'm not sure if i understand the benefit of what your'e suggesting, but in any case the discrepancy between my real measurements and the mathematical ones are likely due to the difficulty in measuring a higher volume accurately. i'm using a 10cc syringe... half a cc here and there while measuring the large volume, and you get the 5cc difference easily. the BDC measurement is the easy one, assuming that the ATDC math is right, as it's simply BORE X STROKE, plus the volume above TDC.

or maybe i'm misunderstanding... you do realize that i did measure the "X" area with fluid, right? if you have another idea, please share.

[Raef]

I was thinking that you were trying to get the exact volume of Y.

since we know that the height of the dome is 9.35 mm, if you took the area of 9.35mm's of the bore subtracted the volume of X (gotten by using the fluid and Plexiglas method) you should get a very accurate area of Y.

I'm sure some would argue some hybrid calc/trig equation, but this would be easier me

Or another why to check your math would be to press the piston in clay or plaster to get to get a exact impression of the dome, then measure the impression with the Plexiglas method..

just some ideas from someone who is mathematicly challenged

[paulages]

I was thinking that you were trying to get the exact volume of Y.

since we know that the height of the dome is 9.35 mm, if you took the area of 9.35mm's of the bore subtracted the volume of X (gotten by using the fluid and Plexiglas method) you should get a very accurate area of Y.

uhhhhhhhhh... that's exactly what i described doing above. 

[Raef]

HA HA HA I said I was fading in and out, I must have read that part when I was out. thats a good idea you had

[Pinhead]

Why not get a mold of the chamber and the head gasket together, pull it off the head and drop it into a half-full graduated cylinder so you can see how much volume it takes up? Seems much easier than all of the calculations you're trying to make...

[paulages]

Why not get a mold of the chamber and the head gasket together, pull it off the head and drop it into a half-full graduated cylinder so you can see how much volume it takes up? Seems much easier than all of the calculations you're trying to make...

i've made an accurate measurement of the combustion chamber, and the gasket math is basic and easy (pi X r2...). it's finding the dome volume that is a little more difficult, but it wasn't really that hard. if you have an easier way please share.

[paulages]

i moved a lot of this conversation to a thread in the hi-performance section hoping i'd get a little more input, but anyway...

i rechecked my valve clearances with the cam timed right, and have plenty of room. removing about 1cc from the gasket area volume will put my compression ratio at 10.5/1. the current gasket bore is 65.5mm and the crushed thickness is 1.09mm, which results in a volume of 3.37cc (pi x R2 x depth).

if the new gasket is .027" thick (.69mm), then the volume of the gasket area will be 2.36cc (pi x R2 x .69 /1000). if the head volume is 25cc, then the volume above the deck will be 27.36cc. subtract the dome volume (8.27cc) and you get 19.09cc ATDC. add the bore displacement at BDC (bore X stroke), and you get 200.84. divide 200.84 by 19.09 and i have 10.52/1 CR.

hope i haven't bored you all with the math. 

[MasterChief750]

i personally love your mathmatical approach. very interesting to me

[Soos]

Nice work Paul!
Glad to hear these are working out for you so far, have you found out if you need to adjust the depth of the valve pockets yet?



l8r

[traveler]

will be the same bike with more mid range and low end punch.....

~Joe

[paulages]

Nice work Paul!
Glad to hear these are working out for you so far, have you found out if you need to adjust the depth of the valve pockets yet?



l8r

when i clayed a piston it appeared i had really tight clearances on the intake side, but with the cam timed right .094" was the tightest i could find.

[paulages]

ok, on to rings. i was so caught up in making sure the piston clearances and CR were good, i forgot to check ring gap, in case i need new rings.  

since i don't know exactly what the pistons are, it's going to be harder to find replacements, but hastings should have what i need based on the measurements.

anyway, a picture tells a thousand words...



...and stock cb350 (64mm) gap specs:



anyway, the gaps are all less than .032", but that seems huge to me. i've always gone by the .004" per inch rule, which would have me wanting .010"ish gaps.

[Raef]

.010 would sure put you way down on the short end of what Honda wanted.

I think I would rather be closer to the center of the remediations on the ring gaps, I'sure hate to see it get hot and tighten up

[paulages]

Hastings had compression rings, but no oil rings in my dimensions. Luckily, the oil rings were tightest at .016", which should still be fine. I had to order rings for a 65mm bore and will have to file the ends down, but at least I can get the gap right where i want it. I'll have to file about 1 mm off the ends.

just need the rings and the head gasket and I'm back in business! both should arrive by the end of the week or monday....

[paulages]

Ok, I have a deadline! Race school is july 7th to get my novice vest... gotta get it together!

[Kemp]

Paul, you might have a problem with sealing using rings for 65mm bore in a 64mm cylinder. I did that with an H2 Kaw back in the day. Filed the rings down to get correct end gap but they wouldn't seal properly

[paulages]

Paul, you might have a problem with sealing using rings for 65mm bore in a 64mm cylinder. I did that with an H2 Kaw back in the day. Filed the rings down to get correct end gap but they wouldn't seal properly

do you know why? my bore is actually 64.75mm now, so it's not quite that dramatic. hastings didn't seem to think it would be a problem.

[paulages]

my rings and head gasket finally came today. now if i can get some time to button it up i can finally get back on it!

[RAFster122s]

Yaaaahhh!

[paulages]

aaaaaaaaaaaaaaaaaaaaaaaaaaaargggggggggggghhhhhhhhhhhhh!!!!!!!!!!!!!!!!!!!!


#$%*ing cometic sent me a gasket for a stock bore, even though I talked to the tech guy on the phone for 15 minutes about the size of the bore and whether 66mm would compress inwards at all with a copper gasket, etc.  

jesus christ, i wanted to be riding this thing this weekend. i'll call tomorrow and give them hell, but even if they rush order it i won't get it until next week at least. #$%*!

[scunny]

can you cut it yourself ?, do copper gaskets still have a fire ring ?

[paulages]

can you cut it yourself ?, do copper gaskets still have a fire ring ?

no fire ring, and it's only .027" thick, but i want the goddamn thing to be right, you know? i'm actually pretty good with the tin snips, as i used to do install metal roofing and gutters, but i'll still undoubtedly bend it up in the process.

i'll call them first.