Montreal Manchild with an '81 Honda CB750K

Ok, I'll try and get my own compression tester and will run it again. Novice question - the engine doesn't need to be firing, just cranking with the starter motor, and then open the throttle?
 
Well yes. Remove all the plugs so that it turns over easier and doesn't start. The key will have to be on so that you can crank the starter motor over. You will want to hold the throttle wide open while cranking so that there is max airflow into the combustion chamber for proper compression reading.
 
Excellent, thanks a million. I'll probably pick one up from Canadian Tire but have heard the cheaper tools can be a bit squiffy. The brand they sell is called Equus, which if nothing else is one cool sounding word
 
I too have the crappy tire compression gauge with the motorcycle adapters it has served me well and is accurate
 
And you want all plugs out and gas off, throttle wide open or if you are pulling carbs, take them off. Cold comp should be in the 130-150 on that bike but more importantly it should be within 10 psi up or down across the 4. The #4 number hopefully is just the fact the carb was closed and not letting air build. When you add oil make sure it is only a tsp or less too much will muck up the numbers.
 
Got the tool, ran the test again with the throttle wide open (thanks for the info on that) and got much better results -

150, 145, 150, 125 - cylinder 4's the party pooper

I'll add some oil tomorrow and see what gives =)
 
The Jimbonaut said:
Got the tool, ran the test again with the throttle wide open (thanks for the info on that) and got much better results -

150, 145, 150, 125 - cylinder 4's the party pooper

I'll add some oil tomorrow and see what gives =)


Have you checked the valves yet? 125 isn't the floor but it's noteably lower than the other three.
 
canyoncarver said:
Have you checked the valves yet? 125 isn't the floor but it's noteably lower than the other three.

+ 1 on valve check. a tight valve will cause this as it stays open a little to long to build pressure well. That was what was wrong with my CX500 I had 90 PSI. checked and set valves and went up to 150 in each cylinder. If Valves are ok, oil in barrel and re-check if up then you are pretty sure it is rings or bore.
 
Checking the valves is next on the list. Do you have any suggestions on where to buy replacement shims as and when I need them? I'm in Canada, but of course am happy to buy from anywhere as long as I can get them quick!
 
I have a local dealer I go to for those things and funny enough they have the stuff shipped in from MTL so there is a Honda Distributor there. Not sure what your local dealers are like there but they should be able to get you the parts next day.
 
I spoke with my local shop and he can get pretty much what I need and pretty quick too. He's a cool guy too, and has been over to my garage to check the bike over and run a compression test (all for a few beers). I've ordered the shim tool online which should be here next week - after running the valve clearance test it looks like I'll need to switch out some shims too. No idea (yet) what to do if some of the valves are shot, but that's for another day.

Thanks for your advice in the other thread - I'll try the some oil in the cylinder and see what gives. This is by some margin the deepest I've got into an engine, so your help is very gratefully received, thanks man =)

By the way, when I took off the valve cover, there was so much oil in the cylinder head that it overflowed when I turned the crankshaft. How much oil in there is too much? I had to wick some out in order to be able to see where to put the feeler gauges!
 
Amen to that - I've got a Yamaha V Star 1100 Custom - the forums I joined to help me out with some issues I've had with that bike have helped me out no end. It's like having a small team of experts sitting in your toolbox =)

Here's a photo showing (hopefully) the amount of oil in the cylinder head -



It looks like some kind of oil spa for cams - they're lording it up in there like overweight and ageing 80's pornstars, kicking back and soaking it up. All they need is a couple of cigars and they're set. Is that too much oil? It literally overflowed when I turned the crank. Might the oil not be draining - or moving around the engine - the way it should? Could it be a sign of a blockage somewhere, or is it perfectly normal? The photo shows the exhaust cam by the way.
 
lots of oil is good as long as it isn't gummy or jelly like. or milky which would mean moisture getting in.
 
Yeah, most people worry about not enough oil in the heads haha
It should drain down the center with the cam chain.
You want the lobes to be well lubed up.
 
Got the shims measured and found an old school Honda mechanic here who was happy to swap out some the ones out I needed, all is good. Gonna get them in place and then run another compression test.

I also got hold of a can of Honda Carburetor/Combustion Chamber Cleaner which is supposed to help clear out carbon deposits from inside the cylinders. I'll let you know how I get on, and hoping to sort out the compression issue in cylinder 1...
 
That's what I figured Maritime, worth a shot. My man Gabriel told me to empty a good 5 seconds worth of the can into each carb, engine running at about 5000 rpms, and to expect a drop in rpm once I start the spray. One thing I didn't ask him is how to clean out any carbon that's dislodged? The can says to "blow out deposits" but I don't have an air compressor (if that's what the instructions meant), and don't know where to blow anyway.

Any ideas?
 
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