Topic: Bigger Problems Than the Clutch

[Dr. Frankenstein]

Trying to rebuild this '72 JDM CB500, and I think I have bigger problems than the clutch post I posted earlier. I believe I got the clutch cable set correctly, so turned my attention to the valves.

I set numbers 1 and 4 at the "T" mark, did the valves for them, and then tried to set 2 and 3 - I rotated the engine by hand and rotated it through 1 and 4, then rotated it through to 2 and 3 to bring it around again, and as it got up to 1 and 4 again it got really tight! Like something was interfering with the rotation of the engine.

So Imagine this - I rotate the engine by hand up to valves 1 and 4, and set the valve clearances, .002 Intake and .003 Exhaust. No problem.

I rotate the engine up to #2 and 3, rotate past that to bring it around again, just to rotate it around to 2 and 3, and as I get up to 1 and 4 again, it's like it 'hits' something, or something is interfering with 1 and 4, causing a lot of drag on it. I am able to rotate the engine past that point with some effort and everything rotates smoothly; but it rotates by 2 and 3, goes by 1 and 4 no problem, goes past 2 and 3 again, but as it comes back up to 1 and 4 a second time, I get that 'interference' or 'drag' feeling...I use some effort to rotate past the 'drag' or whatever it is, rotate it past 2 and 3, it goes fine past 1 and 4 again, but as it comes around to 1 and 4 again, it's like something is interfering with it.     

Pistons 1 and 4 move up and down together as do 2 and 3 - so why can I rotate past 1 and 4 at first with no problem, go past 2 and 3 and as it heads up to 1 and 4 again it gets tight...?
I've been thinking about what could be dragging in there that would make it so hard to rotate on the second go-around...I made sure that no rings were sticking out when I put the cylinder head on, I put a little oil on the cylinders to lube things up a bit...but it does have new rings...could those cause something like that?

I'm on the home stretch with this bike and really would prefer that it not 'grenade' when I try to start it. Any ideas??

[seanbarney41]

do you know what compression feels like?  Are you doing this with the spark plugs in or out?

[scottly]

Are you trying to set all 4 valves with the crank at the 1-4 T mark at the same time? You need to set both valves on each cylinder separately, then rotate the crank a full 360 degrees to set the other cylinder in the pair.

[Dr. Frankenstein]

Sean - yes, I do; and the spark plugs are out.

Scott - No, as per the manual, I set #1, then rotate it 360 degrees, and then set #4; it's during this second rotation that it starts to feel weird. Like I said, I set #1 no problem; I rotated it through 2/3, and as I was coming up on the second rotation to set #4, it seems to 'bind up' as I get to the T mark; I've never felt anything like it before...my first thought was that I'd screwed up and somehow let a ring hang (which HAS happened in the past!) , but because of that previous experience I made damn sure to get all the rings in the cylinders when I put the cylinder head on the engine - and besides, even if I had screwed one up, #1 and 4 move up and down in unison - and if it was something 'hanging', why am I not feeling that 'stiffness' throughout the whole rotational cycle? Therefore, why is it so hard to rotate it only through the second revolution and not the whole thing?? 

I'm thinking/hoping it's just the new rings wearing in... I've had this engine (across several different builds) open at least six times and I am very familiar with its innards -

...but I just had a thought: could the rocker arm shaft be binding on #4...? I did have the whole cylinder head cover apart to clean it; could I have re-installed it incorrectly...? (Although I can't imagine How...the rocker arm shafts pretty much just lay there...)

I've successfully rebuilt a previous '72 CB500K, and my '74 CB550K - torn the engines down to their cases and rebuilt them successfully - well, with the exception of stupid stuff like not ensuring the cam chain adjuster was in its little slot in the bottom of the engine, a bad starter clutch spring, a kick starter that wouldn't disengage b/c the guide plate was bent ...all stuff you can't really 'see' until you rebuild the engine...but each time something weird reared its head after I had completed the build, I had to do it all over again, probably six times now across two different CB's...so, Yah, I'm familiar with these engines. And that's why it bugs me so much - I've never come across this weird 'rotating' problem before and have no idea what's causing it. And of course, the only way to 'find out' is to open it up...Again!   Which I am trying not to do...

I was able to set the valves on all four cylinders...I don't know - maybe it's nothing. When I rebuilt this motor, I honed the cylinders, vapor blasted the pistons, put in new rings and piston clips, and Yes, rebuilt the cylinder head cover...but I want to make sure it's nothing serious before I try to start this engine. I keep coming back to 'new rings'...can/does anybody concur? I used plenty of assembly lube when I put it back together - I just Don't Know....

[newday777]

If you are worried about a ring(s) put a bore scope in the cylinders and check for scoring on the walls. If you don't own one, go to an autoparts store that offers loaner tools.

[Dr. Frankenstein]

Hey, there's an idea...I do have one...

...although I did find this tidbit on the internet:

"Tight Piston Rings/Sleeve: If the cylinder was bored and honed too tight, the piston can bind at the highest point of compression, particularly before the new rings have seated and during the initial heat cycles."  This sounds almost exactly like what I'm experiencing.

As per Newday's suggestion I ran my borescope into the cylinders, and only #4 showed some vertical scoring; it wasn't bad, but it was there, just a few light lines (2 or 3) on each side of the cylinder, so I believe that's my culprit.

I have honed cylinders before with no problem; I usually use a bar hone to hone the cylinders, but in this case I used a 56mm flex hone, and only lightly honed the cylinders, probably no more than 10-15 seconds apiece; when inserting the rings, I checked the ring gap for the proper clearance in the cylinders on the top and middle rings, and they were in spec...but my question is, how do you hone a cylinder 'too tight'??  And how/why does the piston 'bind' at the highest point of compression??  Has anybody heard of this before? And what's the fix??

[HondaMan]

Hey, there's an idea...I do have one...

...although I did find this tidbit on the internet:

"Tight Piston Rings/Sleeve: If the cylinder was bored and honed too tight, the piston can bind at the highest point of compression, particularly before the new rings have seated and during the initial heat cycles."  This sounds almost exactly like what I'm experiencing.

As per Newday's suggestion I ran my borescope into the cylinders, and only #4 showed some vertical scoring; it wasn't bad, but it was there, just a few light lines (2 or 3) on each side of the cylinder, so I believe that's my culprit.

I have honed cylinders before with no problem; I usually use a bar hone to hone the cylinders, but in this case I used a 56mm flex hone, and only lightly honed the cylinders, probably no more than 10-15 seconds apiece; when inserting the rings, I checked the ring gap for the proper clearance in the cylinders on the top and middle rings, and they were in spec...but my question is, how do you hone a cylinder 'too tight'??  And how/why does the piston 'bind' at the highest point of compression??  Has anybody heard of this before? And what's the fix??

You can't get less piston clearance using a hone.
I have felt this in a 550 before. In that one it turned out to be the worn primary chain, which would seemingly bind a little bit when I would turn teh engine. It happened when I was setting points: in the non-CB750 engines you can turn the crankshaft both CW and CCW at the big nut with no problems (on the CB750, turning the engine CCW with the big nut will almost always bend the 6mm shaft holding the points cam, then causing 'timing jitter' under a strobe - not a good thing) unless the primary chain is much worn: then the chain seems to unevenly 'stack' the many little plates and then it gets 'sticky' when that spot again rolls over the crankshaft's pulley. In that one, if I kept turning it the right direction for 2 or 3 more full revs it would straighten up, but I could almost always repeat that 'binding' feeling by turning it forward about 1/4 turn, backing it up and forward again a few times while watching the multimeter and timing marks for the 'points opening' event.

[Dr. Frankenstein]

"You can't get less piston clearance using a hone. " I know, Right..??   But that sounds like what I'm experiencing...("Hey, it's on the Internet, it must be true!"  )

I'll go out and play with it, see if I can get it to do it backwards as well as forwards before I roll it out into the driveway and pour gasoline all over it.... Just Kidding! (Or AM I?? )

(10 minutes later...) Yeahh, it does it going the other way too - but there's only 11K miles on it - ! It's a '72 - I never noticed this problem w/ the other CB's you guys have helped me rebuild...I would think the primary chain would last a bit longer than that...unless of course it was a Friday in the factory and the guy was hungover or something...   More likely though I think the PO just severely neglected it, trashed it, put it up and forgot about it. So what's the remedy? New Primary chain? (Ouch...!)

I'm assuming trying to start this thing before I fix that would be a Bad Idea.

[bryanj]

I have seen 500 primaries shot at 10,000, depends greatly on servicing correctly and with correct oil along with how much right wrist and how violently

[HondaMan]

I have seen 500 primaries shot at 10,000, depends greatly on servicing correctly and with correct oil along with how much right wrist and how violently

Yeah, what He said ^^^^ .

[Dr. Frankenstein]

Yup. Well - seeing as how it was probably a US serviceman's bike - so God Knows how many hands it went through before I found it, and what I have found and corrected so far - I have a feeling this bike was righteously abused before being abandoned. So, I guess another tear-down and primary chain is (somehow) in my future...would that likely fix it?

 

[scottly]

I set #1 no problem; I rotated it through 2/3, and as I was coming up on the second rotation to set #4, it seems to 'bind up' as I get to the T mark;

Try backing off the #1 adjusters and see if it still binds.

[Dr. Frankenstein]

Number ONE or number Four...? I think the problem is with #4 - but what would backing off the adjuster tell me?

[scottly]

Number 1. Try it and report back..

[Dr. Frankenstein]

WHOA! It moves A LOT easier, through 360 degrees! I backed the screws way out and No More Binding!  What did that do? Did I just have the valves set way too tight?  What's going on??  Dude, let me touch the hem of your robe! 

[scottly]

When you set the #1 valves with the crank at TDC on the compression stroke, the valves were fully closed. When the crank is turned 360 degrees, the #1 valves are open during the overlap between the top of the exhaust stroke and the start of the intake stroke. Double check the cam timing.

[Dr. Frankenstein]

Hi Scott - the WiFi went out here RIGHT after I got your response so I haven't been able to log back in until now - but I wanted to say that given the possibility that I had made a mistake, I went back in to re-check and re-do the valves, and thought I had gotten it right - but when I redid everything once again I was immediately unable to rotate the engine again; I couldn't rotate it at all, and did not want to push my luck by pushing harder and breaking off the spark advance tabs. With all the valves loosened up, it rotates fine! I took off the cover and checked the cam timing, and that seems to be okay - the little notch at the end of the cam shaft is aligned with the surface of the cylinder head, and with all the valves loosened up the engine rotates easily.

I loosened up the valves again and will try again today, but I wanted to ask if perhaps the CB500 manual is wrong?? When I re-did the valves, I followed the CB500 manual instructions for adjusting the tappets to the letter, but as I mentioned everything was super-tight again - I've attached the pics of the manual and the manual's instructions. Mystified as to why I can't seem to set the valve lash (I have adjusted valves before), I went back and scrutinized the CB500 manual's instructions and notice that it makes no reference to setting the valves on #2 and 3, besides for the little "X" and "O" diagram, which only tells you to check the valve clearance - but there is no instruction for rotating the engine to adjust 2 and 3.

Usually, I set 1 and 4, rotating the engine 360 degrees after each one to get the appropriate piston at TDC and set the valve lash; then I set it at "T" on 2 and 3 and repeat the process, which is what I tried to do the first time, leading to that 'binding' feel  - but the CB500 manual doesn't say to do that, only to check the clearances on 1 and 4 and then check the clearances on 2 and 3 without rotating the engine according to that little diagram...which I thought was strange, but 'okay'...

I checked the Clymers manual that I have for the CB500/550, and that says to rotate the engine after each adjustment, so that's what I'm going to do today and see if that makes a difference - but are the instructions in the CB500 manual wrong, or am I just an idiot??  I have another '73 CB500 that I think I used the Clymers manual for and had no problem. What am I doing wrong??

[bryanj]

That is the very first itteration of the manual and does have some odd translation but i think it is correct, if you go th sohc.co.uk in alladins cave you can download the later version along with all the 550 supplements.
Personaly i always do 1&4 at T and adjust whichever isnot on the rock(exhaust closing inlet opening) rotate 360 and do the other 1 or 4 then set to 2&3 and do the pair not rocking rotate 360 and do other pair.

This way put each individual cylinder on tdc compression to adjust, the table in manual should work, i just am old school

[Dr. Frankenstein]

Yeah, right! And that's the way I do it to, but I think this 'early' CB500 manual leaves something to be desired, in some areas - wouldn't be the first time... I'll try it your (our!) way and see what happens.

[scottly]

If you leave the #1 valves loose and set the other 3 cylinder's valves, does the motor still rotate?

[bryanj]

Is it possible you have a bent valve sticking in thecguide?

[Dr. Frankenstein]

Scott - Yup! Sure does...

Bryan, I do believe that's the culprit - when I did the engine, I had some trouble pulling out the #1 Intake valve. The #1 Exhaust valve seems to be fine. I replaced the valve, but not the guide. It's a new valve, it dropped right in - I hope I didn't screw it up.  I didn't have any lateral play in the valve though, so I figured it was okay - I guess not.

This time around, with all the valves loose and the engine spinning freely, I set the spark advance to "T" on 1 and 4 and set the valve lash on the #1 cylinder, then tried to rotate the engine. Same problem - it bound up. I set the lash on all the valves except #1 and it spun right through, although the tappet screw on the #2 Intake was 'scratchy', it took some effort to screw it in to where I could set the lash on that one - So I'm assuming I need to replace the #1 Intake valve guide, and hopefully not the new valve I put in. 

I do have a press to get the old one out, and the operation doesn't look too difficult; what valve guide tool does the 1972 CB500 take, do you know? 5/5.5mm?