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

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.
 
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.
 
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?
 
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.
 
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.
 
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 ;D. 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!
 
Polishing ports is largely a waste of time. Smoothing them is definitely advantageous, but polishing is a bunch of effort with zero reward.
 
Jets

I am about to put in an order for a set of jets. Not completely sure of a range to start with so any input would help from those of you who've gone down this road.


quick reference list of engine mods and info that matter for this:

I am at sea level in a cold area. Anchorage, Alaska.

Bored to 69.5mm pistions.
K&N Filters
1mm Oversized Intake/Exhaust Valves
Ported Exhaust channels
(net yet completed) custom headers and straight through pipes - will just be running open headers initially until I build my pipes and mufflers.



So I was thinking of buying a set of 120, 122, 125s. Does this seem like a good place to start or far off? Pretty sure I have 110's in there now.

I also have PJ's modified air corrector.
 
On the 360 engines, the exhaust will be one of the most important determining factors in jetting.

For short exhausts, that end around the foot pegs, you'll want to go +10 over stock (Strangely enough, you lose power, but still require more fuel. This exhaust length is not recommended).

If you're going two-into-one, +5 on the secondary main is a good place to start.

Longer exhausts will make the engine come alive right around the 7,000 RPM mark. I recommend a total exhaust length of between five and six feet, assuming you keep the stock diameters.

My 360 is bored out to 378cc, I'm running +1mm on the intake and exhaust valves, I've shaved the head for extra compression, I'm running a hot cam, AND I have open intakes with velocity stacks. Even with all that, I'm on +5 on the jetting (Running 115 secondary mains) and the bike is running well (at 200ft above sea level).

Short version: Keep your stock jetting, save your money, only buy jets once you've figured out if you need them.
 
If you run too big a head pipe you also need a lot richer secondary jetting.
Brendon is running 125 secondary mains and plugs are just about perfect
Seems stock INNER pipe diameter is correct (about 1-1/8"ID, 1-1/4" OD)
If you use 1-1/2" pipe and it's too short overall, your going to go crazy trying to jet

Did I do the complete carbs or was it just new air correctors?
I stopped making them as carbs need some extra mods to various circuits, air correctors help mid range a lot but things can be 'better' I was still experimenting when I first made them (about 3+ yrs ago)
 
Thanks to both of you for the input. I will wait on the jets.

PJ- Just the air correcctors. I got them from you probably about 1-1/2 years ago or more. If you are interested, once I get the bike running I would like to send you my carbs.

My plan for the exhaust is new headers and making my own straight through mufflers. They will extend a tad passed the rear axle (which is 1.5" further back than stock). Should be within and inch or so of the stock overall length.

Will 1.5" diameter pipe work if the overall length is close to stock or will it will be too big? I guess the problem there would be the gases slowing down too much?

I am wondering about issues with mounting new headers to the head with a 1/4" smaller outer diameter pipe with the original mounts.
 
You should be fine with the longer exhaust.
You've probably seen the pictures of the one I made, it's about 4"~6" longer than stock
No problem about carbs when your ready
 
Long exhausts, baby:
521467_10151001039145159_1346676056_n.jpg


Plus... they sound good:
http://www.youtube.com/watch?v=FmYW7GBX4y8
 
Sonreir, I like the sound of your exhaust. Is that the MAC 2 into 2, or a stock head pipes and aftermarket mufflers?

I've been thinking of going to the MAC 2 into 2, but would like to hear it first, and if it sounds close to what you have, it is exactly what I want.
 
Looks like stock head pipes with a 'kick up' extension then aftermarket silencers (although muffler is probably a better description ;) )
 
Yeah. I haven't found any reasonably priced head pipes in reasonable condition. The MAC 2 into 2 look snice, but I suspect it will sound similar to my 2 into 1 MAC system....A little too loud...Sonreir system is a little loud, but it has a nice throaty rumble to it...

I am not is a rush, so I will keep looking. The aftermarket universal silencer choice is much larger then the CB360 specific set.
 
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