Topic: Cb650 won't start after top end rebuild

[Bodi]

Since it didn't fire with ether, I wouldn't spend too much time on the carbs right away. Getting 12V at both coil wires is not good, usually one points set should be closed with the engine stopped so you have 0V on either the blue or yellow wire. Maybe you just have dirty points - or severely misadjusted - that don't close?

Take the plug out of #1 or #4 (just one!), put it in the spark wire cap and set the threaded end so it touches the engine or frame. Don't hold it, you can get a wicked shock that way! When kicked or cranked (key and kill switch ON) you must see a fairly bright blue spark across the tip electrodes. If you don't, there's your problem - no spark.

[1SpeedD]

Since it didn't fire with ether, I wouldn't spend too much time on the carbs right away. Getting 12V at both coil wires is not good, usually one points set should be closed with the engine stopped so you have 0V on either the blue or yellow wire. Maybe you just have dirty points - or severely misadjusted - that don't close?

Take the plug out of #1 or #4 (just one!), put it in the spark wire cap and set the threaded end so it touches the engine or frame. Don't hold it, you can get a wicked shock that way! When kicked or cranked (key and kill switch ON) you must see a fairly bright blue spark across the tip electrodes. If you don't, there's your problem - no spark.

I tried that with the old plugs as well as new plugs and I'm getting sparks.  They're not the biggest sparks so maybe that's an issue?  I'll try posting a video maybe.

[Bodi]

If there's compression and an OK spark, starting fluid ether will fire, even with the coils reversed (although possibly start a bike fire that way). With full choke I would expect to see/smell fuel on the plugs after a decent cranking period. There may be several things wrong?

- Does fuel come out all 4 drains if each is opened to check?
- Are the carb slides in the right way around?
- Is the cam timed correctly?
- Are the valves seating OK? tappets adjusted close to correct?
- Is the CDI box good? A CDI spark should be strong.

[1SpeedD]

So I took another look at the valves to check their adjustment and they're way off.  I spent a lot of time making sure the camshaft/cam chain was in the correct position during the rebuild so I'll take a shot at resetting the valve clearances. 

The carbs are coming off and getting another run-through in this as well.

[harisuluv]

What was your method of testing with starter fluid?

[1SpeedD]

What was your method of testing with starter fluid?

I pulled the air filter, sprayed into the carb intakes, put the filter back in then gave it a go.

[harisuluv]

I think you should just spray directly into the cylinder to eliminate variables.  I mean, this is kind of the running theme here, you do X but it's not really conclusive so we can't eliminate or affirm any problem in a particular area.

So you pull all the plugs, squirt some starter fluid into each cylinder (don't go crazy).  Then try and start.  I think you will see signs of life.  (put the plugs back in..)

[RAFster122s]

I would worry about the valves if they were way off, you possibly could have bent a valve if it kissed the piston.
The only way to check this (without disassembly) is to see if you are getting equal retraction in the cover when you have the top cover off and the adjusters backed all the way off on the rocker arms. If they are not equal height (seating against the valve seats) then you are going to have to pull the rocker cover and head to address the issue.
A bent valve also won't give you compression when that cylinder is at TDC, another way to test it. Either way, you need to start from a baseline and reset your valve adjustment to ensure you have it right and that the cylinder is at TDC.

Do you have the procedure for setting the valves after replacing the cam?

Not having the valves set properly is a sure fire way to not have a running motor after a top end rebuild.

Looks like you have a bit of rust on the coil's bolt down connection, along with some surface rust from some where on the frame's paint near the coils. I would pull the coils and clean up the connections and clean the paint that's affected, then a coat of wax on the paint will help it be easier to clean up in the future as well as protect the frame from corrosion.  If you have any rust, then I would want to address that after you get her running again...Or, before you put it away next winter (if you don't ride in the winter).

Tell us more about what you did when you installed the cam.
Run through the steps. Copying them from a manual you followed (scan or photo the page) would be a good idea...or link to the procedure if it is in a PDF online and reference the page and section.

OK?

We can help you get it going...just let us know where you don't understand or need clarification.  We can help you become a motorbike mechanic yet...if you have the desire.  Just don't sell yourself short with negative self-defeating thoughts/attitude. It is something you can learn. You learned bike/bicycle mechanics...this is just a little more involved.  Electrics scare most people on bikes. It is complex but just like eating an elephant, the only way to do it is one bite at a time.
Bikes referring to motorbikes on this forum.

David

[1SpeedD]

Ok, so I did a lot of thinking and troubleshooting and came up with the main cause of my issues.  The cam chain wasn't fully engaged on the cog down at the crankshaft.  I set that all right again. 

Now the pertinent issue is valve adjustment.  I adjusted them as per the Clymer manual.  Basically it involves 1-4 TDC, adjust cylinder 1 valves, and then one valve on cylinder 2 and 3.  Then rotate 360deg, adjust cylinder 4 valves, then the other 2/3 valves.  Mostly what I don't understand is how i can tell when cylinder 1 or cylinder 4 is at TDC for the adjustment.  I put a small dowel down the spark plug holes to see where the pistons are at.  It seems cylinders 1 and 4 are relatively the same height when I'm at the TDC 1-4 mark.  Thus some considerable confusion about which valves I should adjust first. 

So assuming all valves are entirely out of adjustment, how should  I go about determining the valve clearances and which cylinder is where? 

[Scott S]

 When #1 is at TDC and you can feel a little play in both rockers, that's when you adjust it the way you described. #4 should have no play at that time.
 Did you line up the mark on the end of the cam with the edge of the head when you installed it? Was the engine at TDC when you did?

[1SpeedD]

I read the bit about the TDC valves having play, but mine seem to be a bit inconsistent.  Mostly it seemed like 1 and 4 had play at TDC.  Thus my confusion about which cylinder I'm actually basing my adjustments off of. 

I did spend some quality time lining up the notch on the edge of the cam.  As far as i could decipher from the manual, the notch faced (riders') forward at 1-4 TDC.  It's easy to get it one tooth off so it took a few tries.  Hopefully that's correct alignment?

[Scott S]

Both valves on #1 should be loose when adjusting them using the procedure you mentioned above.

[1SpeedD]

Well I went to set one of the valves and the fixing nut was seized and the arm was cracked.  I ordered some replacement rocker arms, but for now I'm just waiting by the mailbox.  Just wanted to keep ya'll up to date.

[1SpeedD]

Alright, so I replaced the broken rocker arm, reset all the valve clearances, then tweaked them again after it seemed like things settled a bit.

The manual says .002 for the intake valve clearance and .003 for the exhaust, but I hear a lot of people going to .004 for the exhaust.  Any thoughts?

I replaced all the spark plugs just for the sake of continuity.

The bike fires up on cylinder 1 right away, but the other cylinders won't fire.  It backfires if I keep trying to start it up.  The plugs appear wet when I pull them. 

[1SpeedD]

I went out and double-checked, ignition coil wiring is as per your description.  I checked the spark by pulling a plug and the spark is pretty strong.

[harisuluv]

To start you need:

1) Compression
2) Fuel/Air
3) Spark

You seem to be hell bent on making things hard for yourself.

[Scott S]

For some reason I'm not convinced that you have the cam installed and timed correctly. Just a feeling.

[1SpeedD]

For some reason I'm not convinced that you have the cam installed and timed correctly. Just a feeling.

That's also what I'm trending towards after thinking about it today.  The pictures in my Clymer/Haynes manuals are conveniently not all that helpful.  I seem to have fuel (wet plugs), I seem to have spark (new, tested plugs and properly routed coils), I seem to have compression (passed thumb-over-hole test).  Under the 3 step process harisuluv mentioned, air fuel/spark/compression, things are in order.  Obviously, in reality they're not for some reason and I need a little more help than one word answers (harisuluv)

If you all don't mind, can we break this camshaft position/timing down a bit?

--I interpreted the camshaft installation as aligning the notch towards the #4 cylinder.  (rider's right) 
--timing notch at ignition advance mechanism is aligned to T mark on 1-4 (TDC, right?)
--The notch is pointing towards the font of the bike.
--Viewed from the rider's right, straight on/down the barrel, the notch is parallel to the engine's top surface.
--Cam chain and cog are lined up so that when tightened, the above criteria still remain true

I'll be more than happy if someone explains I'm wrong or 180deg off in any of those steps.  If these steps are indeed correct, I'm open to (wordy) suggestions as to what my next steps should be. 

[harisuluv]

Obviously, in reality they're not for some reason and I need a little more help than one word answers (harisuluv)

With all due respect I have pointed you in the right direction.  You want me to tell you how to do step 15 when you're still on step 1.  I've asked you for pictures and you did provide some however they are so poorly framed that you have managed to tell us very little.  Your pictures of the carbs in a super closeup of two different intakes doesn't help us.  We can't even get a picture of your overall bike!

My last response in your thread was as follows:

I think you should just spray directly into the cylinder to eliminate variables.  I mean, this is kind of the running theme here, you do X but it's not really conclusive so we can't eliminate or affirm any problem in a particular area.

So you pull all the plugs, squirt some starter fluid into each cylinder (don't go crazy).  Then try and start.  I think you will see signs of life.  (put the plugs back in..)

I gave you an extremely clear, concise procedure to help eliminate one of your problems.  Instead what do you have now?  You have not eliminated anything, and the variables that you seem so above troubleshooting are ALL still on the table.

1.  " I SEEM to have fuel (wet plugs)"
2.  "I SEEM to have spark"
3.  "I SEEM to have compression (passed thumb-over-hole test)."

Seem is not any kind of troubleshooting that leads anywhere unless you get lucky.  VERIFY the fuel variable as I did above.  VERIFY that you have spark by checking each one and grounding it to the cylinder head.  If you need more details on that procedure please use the search function.  VERIFY that you have compression with something other than your thumb.

[1SpeedD]

Obviously a lot is getting lost in translation here.  I don't have the energy to argue, and I apologize if I was short.  I'm tired of going back and forth, as i am sure you all are.  I'll figure something out with this bike.  In the end I always do. 

After thinking about it for a while I am ending this thread. 

Thank you all for all the help, I mean it.  Hopefully I'll see you out on the roads soon enough.

[blackbike]

I can't help but wonder about this cracked rocker arm....sounds like incorrect cam timing and consequently bent valve stems and god knows what other damage....

Verstuurd vanaf mijn GT-I9195 met Tapatalk

[harisuluv]

Yeah seems like something that happened immediately post rebuild.  Assuming that if it were cracked before he would have spotted it.