'74 CB383 (CB360) - a Mighty Mouse adventure bike

[Treesus]

Any input on checking piston to valve clearance with the OS valves? Eh?

[Sonreir]

Do it.
Use plastigauge or plasticine clay.  Torque everything to spec and rotate the crank (slowly!) two full rotations.  Take everything back apart and measure the clearance.  You'll want at least .020" between intake valve and piston and .040" between exhaust valve and piston.

[Treesus]

Thanks Sonreir. I'm going to head off and get some plasticine.

[Treesus]

Ok. I did two clay tests. I figured the first one was unreliable because I forgot to set valve clearances after bolting the head and valve cover up.

So I re-did the test. I guess I should have put the clay on thicker because only the exhaust valves touched. So I measured everything anyhow.



Left Exhaust Impression was about .058" with a possible minimum of .056" (may have just forces the caliper on that one).

Right Exhaust Impression hovered around .059" with a possible .055" minimum.

Left Intake valve didn't make an impression, nor did the Right Intake. So I just measured the clay I had laid down to see how thick it was.

Left side varied between .1" and .059", the Right side between .1" and .053".



Am I ok in thinking that since the Intake Valves didn't make an impression and the clay was 3 times thicker than .020" I am good to go or should I check with thicker clay to make sure they are not too far away (as in not opening all the way)?

I watching the valves through the spark plug hole and everything seemed to open as it should. Also watching the rockers. Probably turned the engine through 4 or 5 rotations while watching everything.

[Sonreir]

Sounds like a successful check to me.  I'd run with it.

[Treesus]

Ok. I did an acentone test before the clay test and all valves sealed nicely.

So, I've got the engine loosely mounted in the frame and did a compression test.

Does anyone have an idea of what a cold, unseated compression ballpark figure should be? The book says to tests while the engine is at operating temps. And though not stated this is, obviously, with seated rings.

My right cylinder is easily pushing 151 psi, however the left is barely hitting 95-100psi after 3 checks. Any ideas? Or should I completely ignore this because the engine has not been run?

[Sonreir]

Assuming the valve clearances have been set, the two cylinders should both be fairly equal.  Cold compression test on my rebuilt 378 engine yielded 151 and 153, if I remember correctly.

[Treesus]

Disregard. I checked the valve clearances and did it again. Vastly different. Got 179 PSI Left and 172 PSI right.

Whew. I had myself scared.

[Sonreir]

Close enough.

[canuk, eh]

awesome build here treesus, really inspiring. almost makes me want to crack open my 200t and get real down and dirty with it.

the only point i might make is that when i did a mechanics course(heavy duty  mind you), i had an engines instructor who was really into performance this kind of stuff. he always said if your going to polish, do it until you can see your own reflection in the metal. his suggestion was to get some kind of buffing tool that would fit on the end of your drill and fit snug into your ports, then buff until your wife divorces you  . i have never tried it myself, so i cant say how much it will do, but it always seemed like it couldn't hurt as long as you dont touch your valve guides/mating surface too much.

again, amazing stuff here, your a real inspiration for the gear-heads!