Topic: Too Tight Valves??

[Dr. Frankenstein]

Would too tight valves keep an engine from turning over? I've finally started to take apart the engine on a '72 JDM CB500 I acquired about a year ago, and even when I got it, it wouldn't turn over with the kick starter, so I assumed the engine was stuck...well, this afternoon I got the cylinder head and alternator cover off, and was contemplating the cam shaft sprocket and how to rotate the engine so I could get to those little 10mm bolts on the sprocket and just for the helluva it rotated the alternator and it spun right over! I then used the kick starter lever and it spun right over again, smooth as silk! Why would I be unable to use the kick starter when the engine was in the frame but be able to (easily!) spin the engine over by hand after I took off the cover? Too tight valves? It was very strange!

[jonda500]

You mean you took off the cylinder head cover but not the head? - this normally makes the engine harder to turn because all of the valves will be closed and stay closed so you'll be compressing twice as much as normal.

Did you loosen the tappet adjusters first? - and find that they were all too tight (seems unlikely)?

No, even if so, I don't think it would stop the engine from turning rather it would turn easier with the valves all held open!
John

[Dr. Frankenstein]

Yes, I took off the Cylinder Head Cover after I loosened all the rockers by unscrewing the little nuts on the rocker arms themselves to free them; they were pretty tight on the rocker screws. The Cylinder Head Cover is item #1 in the picture here. This piece normally has all the valve rockers in it, held in place by the rocker arms, and indeed it came off as one piece. When you remove the Cylinder Head Cover you expose the cylinder head and camshaft - the rockers stay IN the Cylinder Head Cover. It was after this removal of the Cylinder Head Cover that I discovered the engine would rotate freely, with the cam and valves still in place, which is why I asked if the rocker arms may have been too tight on the valve heads, preventing the engine from kicking over while it was still in the frame. I have never encountered this problem before of the rocker arms being 'too tight' to allow the engine to turn, but I thought I would ask if this was possible.   

[newday777]

The valves could have been contacting the pistons stopping the motor from turning, once you remove the tension so the valves were closed it was free to turn again.
Did you have the spark plugs out so there wasn't compression building up?
Maybe it has a high lift cam that wasn't degreed in, thus the valves contacting the pistons??

[Dr. Frankenstein]

Yes, spark plugs were out; I took them out weeks ago to spray in some PB Blaster and let it soak b/c I thought the engine was frozen.

High-lift cam...? I don't know...

"The valves could have been contacting the pistons stopping the motor from turning, once you remove the tension so the valves were closed it was free to turn again." Could be - I haven't seen the pistons or valves yet - God I hope not; the CB500 is an interference engine, yes? I don't think it's that, though.  It's just weird.     

Why do I always get the weird problems??                                                                                                                   

[Bodi]

When you remove the cover, the upper cam "bearings" are part of the cover. I don't understand why pulling the cover off would free up the engine. The "bearings" are not very tight normally, it's a steel cam spinning in a plain aluminum alloy bore (no actual bearings are present), this is not an excellent bearing combination so it is fairly loose to allow a generous oil film, and the load is pretty light.
If you loosened the tappets a lot, valves frozen (rusted?) in their guides could have been jamming the engine. If the cam is way out of time, yes valves can hit the pistons and again by loosening the tappets you could have eliminated that.
Cam timing is pretty simple, I'm not sure of the 500 engine though. There will be some marking on the end of the cam, possibly a line. That line may want to be aligned with the cylinder block top with the crank at 1-4 T mark. The cam mark and alignment used may be different on a 500, check a service manual. (note that if you're told to have the #1 intake valve open or whatever... nope - it doesn't matter what cam rotation you're on: a full crank rotation will turn the cam exactly half a turn and have the mark in the same orientation again)

[denward17]

Any indication of oil starvation in the top end?

If the cam was run dry then that could lock it up, maybe?

[bryanj]

If it was stood in one position for a long time some valves may have been siezed in the guides, when you remove the cam cover you are no longer trying to open valves that wont

[Dr. Frankenstein]

I got curious after Denward17's oil remark and ran out to snap a few pics with my phone, and there's no oil in the top end, in those little reservoirs under the cam shaft...I did drain the oil out of the engine before I pulled it out of the frame, but didn't do anything to the top end after I got the cylinder head cover off...the oil in the bottom did look kind of weird though, it was a deep green, almost black color...I don't know, maybe it was just stuck enough to NOT turn over, like a skim of surface rust somewhere...? Rust can do tricky things...I'm going to open her up anyway and see what's what inside - vapor blast the cases, check the specs, etc...but it's just weird that I couldn't get it to turn while it was in the bike, and turned effortlessly (with no weird noises, I might add) once I got the top off. Here's some pics - I haven't touched anything since I took the top off...

Had a thought: could the STARTER be frozen up...? The starter gear, where it goes into the engine...? I have removed the starter, but don't remember if I tried to spin the engine before or after I took it out...

[Rayzerman]

Well, I think I'd put a little 2 stroke oil (diluted say 50% with something like naptha or Seafoam) down each spark plug hole and spin it over..... let sit for a few days.  When you reassemble the rockers, use some moly paste diluted with oil as an assembly lube.  I'd put oil on the cam lobes as well.

[denward17]

Cam and cover look good to me.

I do see something going on with the tach gear, looks worn?
Look carefully at the tach gear where it meshes with the cam, better picture (close up of gear) would help.

[seanbarney41]

Yes, have a good look at what is under your stator cover.  Very common for broken parts to jam starter gears or even for the crank snout to be bent so that rotor does not clear field coils.

[Dr. Frankenstein]

Here's a pic of the gear, and the stator and cover - I don't see any damage on any of them...the worm gear turns over smoothly with no problems; I even looked at the gear in the case where the starter gear goes and the starter gear, and they turn just fine as well...it's just weird. The stator rotor looks a bit off because of the camera angle. It'll be a while, it's cold and snowing like mad here in Virginia and a chilly 31 degrees in the garage, but I'll report back if I find anything out of the ordinary as I go farther - every motorcycle tells a story.