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Discussion Starter #1 (Edited)
I got my 1980 CX500 Custom running after I got it from a friend who had it sitting outside for an unknown (but lengthy) period of time (27k miles). I got into the bike (and home-mechanic) hobby about 3 months ago and I have fallen in love. This is my first bike :D I have been learning so much and I have my friend and his pops to help me when I get stuck or need to learn difficult new things (his father owned a dealership for 30 years and is very familiar with servicing almost every bike up until the early or mid 90's). Schedules however conflict often and this is a large job that I would definitely like some help from any knowledgeable people I can find.

So far this is my progress on the bike:
  • Rebuilt carbs with new jets, gaskets, o-rings, everything except the pilot jet and the press-fit slow-jet
  • Ultrasonically cleaned the carbs (I picked up an ultrasonic cleaner on amazon for just over $100)
  • Adjusted valves
  • Replaced tires
  • Cleaned rust out of the inside of the tank
  • New battery
  • Rebuilt front calipers
  • Replaced master cylinder
  • Bled brakes
  • flushed radiator with coolant flush fluid
  • Changed oil (never touched the filter but it's empty now and I have a new one for when I finish working on the engine)
  • Synced carbs
  • Set fuel air screw
Note: after adjusting the valves twice in a row, 24 hours in between on an engine that was left to cool over night, each time making sure the pistons were at TDC and the second time getting my friend to help to make sure I didn't do anything blatantly wrong the first time, the piston covers had a clicking sound that increased or decreased frequency with the RPM of the engine.

Compression is low at 100psi in the left cylinder and about 110-115 in the right.

MPG is only around 20-23 no matter if I drive a whole tank very aggressively and keep the engine above 5k RPM or very passively and keep the engine mostly under 4k RPM.

It burns oil slowly (I noticed after a couple months or about 1k-1.5k miles that the oil was about half way in between the end of the dipstick and the beginning of the hatched, good, section), noticed I was low on oil and it definitely burns oil shortly after starting it cold if you really pay attention to the exhaust, I believe it burns some when it's warm as well but I am not certain.

Here's how I fucked up:

I accidentally set my torque wrench to 17 ftlb instead of 7 ftlb and stripped the threads on the cam chain tensioner bolt.​

I now have to take apart the engine to fix that with some helicoils. While I am in the engine I want to do a triple bypass and I already have all the parts in my cart from DSS for that. I am going to buy a rae-san ignition module as well.

What I need help with:

I need help determining what the cause of low compression is and how to fix it. I assume it has something to do with worn rings, marred cylinders, worn valves, worn valve guides, bad valve guide seals, or any combination therein. I am still very new to all of this so I appreciate any and all help, suggestions, advice, tips, tricks, and general assistance on any of the above or anything else :)

Edit: added bike mileage of 27k to the post
 

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Next step would be compression test, compression test with oil squirted in the cylinders and leak down test. Though it sounds like you may have a rebuild in your future.
The extended park may just have the rings gummed up. If the 'wet' compression test is good, I'd try seafoam first.
The oil consumption doesn't seem terrible for an elderly bike

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Discussion Starter #3
Next step would be compression test, compression test with oil squirted in the cylinders and leak down test. Though it sounds like you may have a rebuild in your future.
The extended park may just have the rings gummed up. If the 'wet' compression test is good, I'd try seafoam first.
The oil consumption doesn't seem terrible for an elderly bike

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I already have done a compression test and gotten 100 psi in the left and 115 in the right, much less than the 170 that it should be at stock. I have squirted some marvel mystery oil in the cylinders but neglected to to the compression test again afterward, and at the moment the engine is completely out of the bike on the garage floor. I am definitely rebuilding the engine lol, I have a stripped cam chain tensioning bolt.

What is a leak down test?
 

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Leak down is when you pump air into the cylinders with the compression tester attached. Time the compression drop and look for bubbles in the cooling system. It's a moot point though since the engine is out and the heads are coming off anyway.

The FSM will give you specs for cylinder out of round tolerance. Are you planning on rebuilding the head while you're at it?

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Discussion Starter #5
My only plans are to fix the tensioner bolt, do the triple bypass, and fix compression issues. The last item on the list I have no idea what is required or recommended or even how to disgnose what im holding in my hand by visual inspection. Should I rebuild the head? I have never done engine work before save for I just got done replacing the starter clutch gear in my 89 Ninja ZX600R which required removing the clutch, secondary shaft, oil pump, oil pan, water pump, and radiator. So I'm a total newb even though I learn quickly :)
 

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Compression leaks out the head gasket, rings or valves.
If it was the gaskets, you would have been blowing steam out the pipes.
Pistons and rings need to come out. Hopefully, a cylinder hone and new rings will be all it needs.
It's unclear to me if the valves need attention. Common wisdom is if compression comes up with oil in the cylinders, the valves are okay. If you're doing all that work, I'd look into what it takes to do the head too

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Discussion Starter #7
I read somewhere that if it burns oil when it's cold and either reduces or completely stops it's burning when warm then it's likely valve guide seals that are worn and need replacing. How do I confirm that with visual inspection?

I haven't seen anything leaking out of the pipes but I also haven't looked closely if it's something I could easily miss.

I don't know if compression went up when oil went into the cylinders because I did not do a compression test after putting in oil :(

Only reason I am concerned about the valves is because the adjustments I made didn't fully stick (or rather the tolerances were off the next day so maybe they stuck but something else is at fault since the tappets certainly had not moved, and they were way different from where they were originally, to where I adjusted them the first time, to where I found them before adjustment the second time, to where I adjusted them the second time) and there was that clicking sound, very audible. I don't know what could cause that or if it even is cause for worry.
 

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Discussion Starter #8
I should add (I'll edit the original) that the bike has 27k miles on it.
 

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I read somewhere that if it burns oil when it's cold and either reduces or completely stops it's burning when warm then it's likely valve guide seals that are worn and need replacing. How do I confirm that with visual inspection?

I haven't seen anything leaking out of the pipes but I also haven't looked closely if it's something I could easily miss.

I don't know if compression went up when oil went into the cylinders because I did not do a compression test after putting in oil :(

Only reason I am concerned about the valves is because the adjustments I made didn't fully stick (or rather the tolerances were off the next day so maybe they stuck but something else is at fault since the tappets certainly had not moved, and they were way different from where they were originally, to where I adjusted them the first time, to where I found them before adjustment the second time, to where I adjusted them the second time) and there was that clicking sound, very audible. I don't know what could cause that or if it even is cause for worry.
Are you sure that each time you adjusted the valves you had the engine at top dead centre on the compression stroke? Adjusting the valves on the wrong stroke will give noisy valves due to wrong clearance.
 

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Discussion Starter #10
I opened the inspection port, turned the engine until the flywheel mark labeled TR lined up with the arrow when adjusting the right cylinder. I repeated that process but with the mark TL for the left cylinder. I took out the plugs as I didn't trust that I read things right and wanted to confirm that the pistons were extended and I had it in the right place since it was my first time ever adjusting valves. I assume it is my error of some sort that is responsible for the noise as it didn't exist before I went in there, I just don't know what I did wrong, or maybe I am wrong and something really is wonky with the bike and not my wrongdoing.
 

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Discussion Starter #12
Is that possible if I was on TR when I was adjusting the right cylinder and TL when adjusting the left? does it matter if I rotated the engine CCW or CW when turning the flywheel to the proper position?
 

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Discussion Starter #13
to add onto that as well, I don't believe the markings on the flywheel were incorrect nor do i think I read them wrong as when I first adjusted valves, the right cylinder was WAAAAAYYY off, but when i went to the left cylinder it was almost perfectly in spec, and I "set it up" the same way I did with the right. The exhaust valves on the left the first time were perfect and I had to adjust both intake valves since one of them was out of spec, the other was fine.
 

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You need to rotate clockwise looking from the front. left is left as you sit on the bike.

On a 4 stroke there are 4 parts of the cycle - suck, squash, bang, blow.

You were meant to make the adjustment at the top of squash - all valves closed.

You did it at the top of blow - exhaust valves still open and inlets beginning to open due to valve overlap.

In short TDC comes around TWICE in a 4 stroke cycle. You've picked the wrong one.

Go back, find the TDCs with the great flapping valve clearances {not the 3 and 4 thou you set} and readjust them here.
 

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Discussion Starter #15
There are a few groupings of lines on the flywheel, I got the "right and left" orientation right, the lines are FR, TR, TL, FL, and a few more unlabeled lines. I had the flywheel at TL and TR unless you are telling me there are 2 TR and 2 TL on the flywheel, in which case then I did not know that. If that is what you are telling me, am I correct in my understanding that you are telling me that the correct one will have a lot of clearances in the valves when I get there? or rather more than the other one?

Did I screw anything up by rotating it CCW at all? Luckily I rotated the engine CW just by sheer chance and orientation of the wrench most of the time unless I slightly passed a mark then I would turn it back CCW.

Does anyone know how to diagnose compression issues with the engine apart? what I should "break open" and inspect and what I'm looking for? Also how to diagnose slow burning of oil if it isn't fixed by the same fix for fixing the compression like worn rings?
 

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The marks TL etc. will line up on both the compression stroke ( all valves closed) and the exhaust stroke ( exhaust valves open ). If the valves are adjusted on the exhaust stroke they will be very loose on the compression stroke and therefore quite noisy.
 

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Does anyone know how to diagnose compression issues with the engine apart? what I should "break open" and inspect and what I'm looking for? Also how to diagnose slow burning of oil if it isn't fixed by the same fix for fixing the compression like worn rings?
The time for diagnosis is before taking the engine apart. If you have already removed the cylinder heads you can get an idea of how well the valves are sealing by filling the combustion space with gasoline and seeing if it flows past any of the valves.
Your oil usage may be due to bad valve stem seals.
If you do remove the cylinder heads be sure to order your head gaskets from Murray's Carbs.
 

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Check this out. With or without the tool.
 

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Discussion Starter #19
The time for diagnosis is before taking the engine apart. If you have already removed the cylinder heads you can get an idea of how well the valves are sealing by filling the combustion space with gasoline and seeing if it flows past any of the valves.
Your oil usage may be due to bad valve stem seals.
If you do remove the cylinder heads be sure to order your head gaskets from Murray's Carbs.
I haven't done anything yet other than remove the engine from the frame. The engine is currently sitting, still assembled, on my garage floor. I don't know what the best step forward from here is.
 

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Check this out. With or without the tool.
OOOOH, thank you for the video :D I have been relying on the manuals which are nice, but it's definitely really useful to see and hear someone demonstrate and explain it, thank you so much, ill watch it fully in a bit and keep it for reference when I go to do the adjustment again :)
 
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