Nighthawk Problems Engine Noise

[rekievit]

I wonder if anyone can help me out (again).
So my riding buddy has an 83 Honda nighthawk cb550sc with 24k and a little upper engine noise recently. He went for a ride this morning and we ended up pushing the bike home. He described an extremely loud rattle / ratcheting / banging / metal on metal noise in the engine. He immediately shut off the engine thinking the cam chain broke. We took off the cover and everything looked fine. Nothing out of place or obviously broken. We rotated the engine to check the whole length of chain and it all looked good.
On every turn there was a time where there was a rattle and a time when it was very hard to crank followed by a suction / vacuum sound. The plugs were out for all of this.
We are both mechanically inclined but have never taken apart an engine before.
Any ideas on what it could be and why / how to check?
Thanks much,
Rob

[firstxs1100]

first thing to do

i would suggest the first thing to do is to get you a compression tester and check compression on each cylinder. if you find one that has an extremely noticible difference then you either got a busted piston or a bad set of broke rings. could be a dropped valve to. if you still got the top off then you can check the valve if its an overhead setup. if not the compression test is the only way to tell which cylinder it was.

[rekievit]

I will definitely be asking around for a compression tester. Forgive my inexperience, but how would I check to see if a valve was dropped from the top? I can't imagine seeing anything without removing the cams.
Also is what I described above normal for rotating this engine or should it be smooth throughout?
Thanks for your help,
Rob

[prometheus578]

Interesting... Hydraulic valves.

Sadly, it seems that HONDA doesn't have a page of engine parts to look at.
Here's a link to some parts joint, but at least they have honda micro fiche so you can see what everything looks like.
http://www.cyclepartsnation.com/page...d/7/Honda.aspx
Anyway...
let's see.
With the plugs out, the engine should rotate smoothly all the way around.
Sure, there will be a little odd feeling to it when it hits top dead or bottom dead center, but the engine should rotate nice and smooth-like.
There should be no rattle.
Suction sound...?
Well, with the plugs out you may hear a suction sound through the plughole on the intake stroke.
Now then... going by what you wrote....
Bike recently had an upper engine noise.. then....
Oft times people don't check their cam chain tension. The chain stretches, gets slack, etc. This will cause an upper end rattling noise.
Sadly, what also can happen.. as the chain's slack... it can jump a tooth or two.
When this happens, oh, you'll get all sorts of noises, none of them good.
The cam chain, as you know, keeps the valves timed with the pistons. If the chain jumps, then the rising piston can strike and bend an open valve. Yeah, the bike usually stops running at that point.(after making a lot of noise)
So.. you've inspected the chain... and it wasn't broken.
What you need to inspect next is if the engine is still in time.
Not being familiar with NightHawks, nor do I have the manual for them downstairs, I can't tell you how to proceed.
Usually, behind an engine cover, there is a dial/wheel on the end of the crankshaft with marks, telling you where top dead center is. With the engine crank on TDC, there should also be marks on the camshafts that line up with some indicator somewhere to tell you if everything is in time.
I suggest getting your hands on a manual.
A quick test you could do is, place a finger over a spark plug hole and crank the engine. If the valves are ok, the pressure should push your finger offa the hole pretty much. If you have a bent or open valve, the pressure will really not be there.
So, first step would be to find out what sort of timing marks you have and if the crankshaft is still in time with the valves. Second thing would be a compression check, to see if you have any bent/open valves.

[rekievit]

Thanks again for the help, we will be getting at it soon and testing what you mentioned. Then I will post again, but feel free to keep the suggestions coming. He has a manual so we shouldn't have any trouble testing the timing.
Also one of his friends suggested it might be the stater clutch? I would think if this was the (only) problem then the engine would turn freely, unless it didn't disengage?

[prometheus578]

Not having the bike in front of me, (and the exploded parts diagram isn't too much help, either) it'd be hard to say if the starter clutch was involved.
I can imagine that the starter clutch assembly can be accessed by removing a side engine cover, so you might want to check it anyway.
Rattle... ratcheting... banging.. metal on metal.... I can imagine that if there's damage, it would be readily noticeable.

[randy]

The nighthawks have hydraulic tappets, much like a car and the cam chain tensioner is a similar setup, no adjustments are needed on either. Those motors typically run very quiet. My Brothers ran scary quiet, almost like a sewing machine!

Rod bearings will make that clanking sound when they're gone. The motor will still run and the compression will be fine. Hope that's not it.

[prometheus578]

Hmmm, you're right, Randy.
Bike has an automatic cam chain tensioner.
I didn't notice that when looking at the parts diagram yesterday.

[rekievit]

It does, but i guess that doesn't mean its not broken, about how much "give" should the chain have? We were able to flex it a little.
I will still have him check the timing but if it is a rod bearing is that something i can check without a tear down of the whole engine?