Topic: Engine Turns by Hand Without Head Cover; Won't Turn With Head Cover

[emschmittgen]

So I'm just finishing up doing an engine rebuild on my '72 CB500 Four.  This has been the single biggest mechanical endeavor of my life, so I'm pretty proud of myself right now.  Even though the end of is sight, though, I'm definitely not out of the woods yet.  I just finished putting the camshaft back on, but now I'm having trouble getting the cylinder head cover back on.
Basically (as the subject of this topic states), when the head cover isn't on I'm able to turn the engine by hand/wrench; when I put the head cover on (and tighten it down all the way), the engine will turn to a certain point, then there's so much resistance that you can hardly turn it with a wrench.  If it's of any consequence, I'm pretty sure the point where it's the most resistant is when the third cylinder (third from the left if you're facing the intake side) is on its exhaust stroke.

I guess my question would be, should I be getting this much resistance when I put the cover back on?  The engine is of course still dry from when I took it off the bike; is it possible it's so difficult to turn as a result of inadequate lubrication, and the problem will go away once I add oil?

Any advice and help is welcome!  Thanks in advance.

[754]

There is a procedure to follow re installing that, if not followed , you can bend a valve..

[emschmittgen]

Would a bent valve be causing the problem of all this resistance?  Or likewise, would all this resistance cause a bent valve?
I'm fairly certain I followed the procedure laid out in the service manual, but it's entirely possible I messed up on something.

[mickwinf]

go back and check the valve timing it is very easy to bend a valve even turning it by hand, don't ask how I know! when you turn engine over without the top cover the valves do not move as the rockers are in the top cover. Check the notch at the end of the cam is in correct position when crank it at the "t" mark.

[jamesb]

Yep you can be d a valve. I did it and it sucks. I have a very nice engine in the corner of the shop to prove it.

[Kenzo1979]

Do the rubberband trick on the rocker cover to help avoid problems.  If you look at my Pic gallery, there's a pic of it somewhere in the 80 photos.

[emschmittgen]

Well, sure enough, the idiot that I am bent the two middle exhaust valves...
I forgot about last night when I was playing around with getting this back together.  I didn't fully understand how to set the timing, and I guess I must have messed it up then.   At least I'll know what to do and not do next time.
Thanks for all the advice everyone!

[Xnavylfr]

Please some INFO for my own knowledge!!
What would cause you to bend a valve by installing  the valve cover??
Unless he was talking about the HEAD!!


Xnavylfr(CHUCK)

[mickwinf]

if the valve timing is wrong, before you install the rocker cover, the valves will not open at all because the actual operating rockers are located in the cover, so when the engine is turned before the rocker cover is replaced it seems to be fine as nothing touches. as you fit and tighten the cover at least one valve will be open and if the timing is off you could tighten down so the valve touches the piston resulting in a bent valve!

[Xnavylfr]

SO you're trying to tell me , the clearances are so close between the valve cover and rockers with an engine OUT OF TIME, by installing the VALVE cover you can bend a valve???   I think there is more to this!!   If the cam was timed wrong, YES you can bend a valve real easy! But what does the valve cover have to do with it? The cam and rockers will rotate in the SAME positions, timed or not,covered or not??
WHAT makes a CB500 so distinctly different than other SOHC hondas???


Xnavylfr(CHUCK)

[754]

Now I am not sure what the manual say about this procedure.. But it probably outlines it well .
 Not trying to make the OP feel worse, but the cost of a manual, is probably less than fixing the valves..
 Just bringing it up  because, since. Internet became common, many people work on things till they get stuck, then go online, for help. Before that, a lot of people relied on a manual. Read the procedure you are going to do several times, read it several times, then it should go smoother. Just a tip..

[Don R]

SO you're trying to tell me , the clearances are so close between the valve cover and rockers with an engine OUT OF TIME, by installing the VALVE cover you can bend a valve???   I think there is more to this!!   If the cam was timed wrong, YES you can bend a valve real easy! But what does the valve cover have to do with it? The cam and rockers will rotate in the SAME positions, timed or not,covered or not??
WHAT makes a CB500 so distinctly different than other SOHC hondas???


Xnavylfr(CHUCK)

[/quote

On this engine the rocker stands are part of the rocker cover, it all goes on at once. You can't install part of the rockers then rotate and install the others like a 750.

[Xnavylfr]

http://www.hondahobby.no/website.aspx?displayid=1754

No where in this procedures does it say ANYTHING about the tappet covers or Valve cover will cause interference enough to BEND A VALVE???

OK , then the rockers are attached to the valve cover and not on cam saddles like the 750!!

I got you now!!!  THIS clears everything up!!


Xnavylfr(CHUCK)

[bryanj]

BUT it Does say in the 500/550 Manual that  If you DO NOT follow the correct procedure when fitting the cam cover YOU WILL BEND VALVES---and frequently break valve guides,  Even has a picture to show you what not to do

[Fritz]

Many who are new to the cb500/550 have bent their valves by installing the cam cover without knowing that the tappet screws can get stuck on the sides of the valves stems. If this happens and the valve cover screws are tightened, the stuck rocker arm will push sideways on the valve stem and bend it. It's very likely that the corresponding valve guide cracks too.
So in this case, not reading the manual can cost you one ore more valves, their guides and the machine shop's fee for their servicing the head. You  might think that buying a good used head could be cheaper, but I suppose that many of them suffer the same problem. And even without being abused by someone not knowing about this problem, they most likely have worn exhaust valve guides.

So since you are rebuilding the engine, it's a great time to get out all the valves, inspect the guides for damage and wear and have them changed at a machine shop.

[DH]

Many who are new to the cb500/550 have bent their valves by installing the cam cover without knowing that the tappet screws can get stuck on the sides of the valves stems. If this happens and the valve cover screws are tightened, the stuck rocker arm will push sideways on the valve stem and bend it. It's very likely that the corresponding valve guide cracks too.
So in this case, not reading the manual can cost you one ore more valves, their guides and the machine shop's fee for their servicing the head. You  might think that buying a good used head could be cheaper, but I suppose that many of them suffer the same problem. And even without being abused by someone not knowing about this problem, they most likely have worn exhaust valve guides.

So since you are rebuilding the engine, it's a great time to get out all the valves, inspect the guides for damage and wear and have them changed at a machine shop.



+1, and well said sir..You gotta watch the rockers when you install the cover.

[phil71]

a little clarification.. it't not merely getting  the head cover on cockeyed that bends the valves, it's the combination of where the piston is in its stroke.
WHen you put the cover on, the cam is positioned so that there's going to be a valve in the open position. When it goes on wrong, the tappet gets caught in a place that increases the lift. When you crank down the cover bolts you're just pushing a valve down, into a piston, probably more than one. The stems of the valves are not terribly robust, and CAN bend even without power tools.
   To add to that, the OP said he'd turned the motor with a wrench.. chances are that was where the real damage was done.
  Even if the cam timing was dead on, this is totally possible.
Don't ask me how I know.

[Fritz]

a little clarification.. it't not merely getting  the head cover on cockeyed that bends the valves, it's the combination of where the piston is in its stroke.
WHen you put the cover on, the cam is positioned so that there's going to be a valve in the open position. When it goes on wrong, the tappet gets caught in a place that increases the lift. When you crank down the cover bolts you're just pushing a valve down, into a piston, probably more than one. The stems of the valves are not terribly robust, and CAN bend even without power tools.

Well, there is a warning and a picture in the Honda CB500/550 Workshop Manual. It clearly shows how the tappet adjuster screw can push sideways on the valve stem. And the damage - bent valve stem on the upper side of the guide, as well as cracks in the upper lip of the guide - tells the same story. I don't think that the piston is involved here.

The problem is that even if the guide is not affected, you'll need to bend the valve stem back in order to get the damaged valve out of the head. I am convinced that it is nearly impossible to do this without adding damage to the valve guide.
But since the valve guides are known to wear fast in these motors, it's a good idea to have them changed anyways.
Unfortunately, the valve seats might need to be reground because the new guide's center might be different from the old ones. So it's best to have a machine shop doing the job.

The best way to avoid this problem is to take the adjuster screws out completely and hold up the rocker arms with rubber bands while installing the valve cover.

Cheers
Carsten

[phil71]

The valve doesn't bend unless it meets a piston. That's why he only bent "some" valves. THe bend is always going to be below the guide . Basically, the thing to do would be not to try and push the bent valves back to their closed position, and if the spring isn't too sprung to be compressed, release the valve keepers, and let the valve fall out the bottom. The guides are probably going to be alright. Remember he did this by hand, not by running it, or using the kick start. (at least according to the information here)

[bryanj]

The stem bends if the cover isn't fitted right and the 500/550 does not wear guides excessively Only the 750 F2 does that

[Fritz]

The valve doesn't bend unless it meets a piston. That's why he only bent "some" valves. THe bend is always going to be below the guide . Basically, the thing to do would be not to try and push the bent valves back to their closed position, and if the spring isn't too sprung to be compressed, release the valve keepers, and let the valve fall out the bottom. The guides are probably going to be alright. Remember he did this by hand, not by running it, or using the kick start. (at least according to the information here)

I apologize for my repeating this: On the 500/550 you can bend the valve stems without turning the engine at all. Just install the valve cover without taking care about rocker arm - valve stem interference. When you tighten the valve cover screws, a stuck rocker arm will bend the valve stem above the guide. No piston involved here.
There's no chance of getting the valve out without either bending back the valve stem to its exact straight position or destroying the guide.

I have three cb500/550 cylinder heads in my garage: One had a bend valve caused by my being the unexperienced novice who did not know about the problem, the other two are used heads that I found on eBay.
One of them had two bend valve stems with cracked guides - caused by the same wrong installation procedure. All of them had exhaust valve guides that were worn beyond the specs. So I bought parts and brought the original head to a machine shop. In the end, my error cost me about $80 in parts and $100 for having the new guides installed.

[Bailgang]

The valve doesn't bend unless it meets a piston.

I apologize for my repeating this: On the 500/550 you can bend the valve stems without turning the engine at all. Just install the valve cover without taking care about rocker arm - valve stem interference. When you tighten the valve cover screws, a stuck rocker arm will bend the valve stem above the guide. No piston involved here.
There's no chance of getting the valve out without either bending back the valve stem to its exact straight position or destroying the guide.

+1 to what Fritz said. I too found out the hard way on my 550 before I found out about the rubber band trick.

[Black 750K8]

I have never had a 500 or 550 but have read about this so many times I don't see how people are still doing it. I guess it is like 750 said people don't read manuals like they used to.

[phil71]

Could you not just cut the valve stem above the guide and let it out the bottom?

[bryanj]

Thays the way I've done it since thin cutting discs arrived for small angle grinders (do't have a dremel)