CB550F No Compression

T

tripledose

New Member
Hey all,

I recently decided to replace the head gasket on my CB550F Cafe Racer. Given I was just going to replace the rocker cover gasket due to an oil leak I don't know what possessed me to continue down a bit further and get myself in trouble apparently. Now that everything is back together, following the manual, I have zero compression when I try to start it with the electric start. To my knowledge I've done the cam timing correctly lining the notch with the head surface facing towards the bike, align with the T for 1-4 and also with the cam sprocket notch at about 2 o clock. But I have no compression. I've tried every possible variation that I can think of for the cam timing, sprocket, valves etc and still no compression. This was a perfectly fine running bike until I did this to the poor girl. At this point i'm not sure what the situation is or what steps I should take to proceed so I'm hoping someone has some suggestions.

I don't recall now but if the surface of the head had a scratched up finish would it cause the compression problem? I installed the gasket dry based on a recommendation too so I'm not sure if that's an issue either.

Here is a shot of the bike as it sits now:

IMG_2402.JPG


At this point I'm a bit tired of messing her up so I've debated taking it to a dealer locally that said they'd look at it but since I've done so much to this bike I'd like to be able to bring her back to working order on my own if I can.

Thanks for any suggestions.
 
So you've got no compression as in like zero? If that's the case the can must be off. Low compression and no compression mean different things. Do you have a compression tester?
 
Tim said:
So you've got no compression as in like zero? If that's the case the can must be off. Low compression and no compression mean different things. Do you have a compression tester?
Click to expand...

I do have one yeah. It's what I used previously to test the compression back when I was first building this just to see where things were at. I have all 4 plugs pulled and the throttle wide open and the reading stays at 0 the whole time.
 
What happens when you put the plugs back in? Try that - all of them in and test compression.

Sent from my A0001 using Tapatalk
 
Tim said:
What happens when you put the plugs back in? Try that - all of them in and test compression.

Sent from my A0001 using Tapatalk
Click to expand...

Ok thanks. Just tried. No difference. Still Zero reading and no gas on any of the plugs at all. When I roll on the throttle it sounds like the carbs are closing as it goes from a sucking sound to just quiet. This sounds like the cam timing could be off but, I'm not an engine guy, and I don't know how many ways I've tried the timing already and I always end with the same result.
 
Maybe check the Schrader on the side of the compression tester? Had one stick one time. It was rather obvious though
 
BurdetteDR said:
Maybe check the Schrader on the side of the compression tester? Had one stick one time. It was rather obvious though
Click to expand...

Thanks.. yeah.. I tried that to see if it was stuck or made any difference in the readings if I tried pressing it a few times. It's free moving. Since there's no gas on the plugs I'm concerned I jacked up the valves or the timing somehow and that's the reason I have no compression.. I assume with no compression no gas would be drawn into the cylinders. I just don't see any other way to adjust the cam timing any more than I've tried. So weird.
 
barnett468 said:
.
there is only one way to set the cam timing . . either its right or its not.

.
Click to expand...

Ok well that's good to know because I've been confused about some things I've read. Specifically about the cam sprocket needing to be on a certain way or it could be 180 out. I took pictures before hand so I knew what it should look like after I put it back together. Which is why I'm so confused about the compression.

I set the timing mark on the motor to T 1-4. Then I aligned the cam notch level with the top of the head and facing towards the bike as the manual dictates. Then I installed the cam sprocket on the cam, chain included.

When it came to valve adjustments, I had backed the tappets all the way out when installing the rocker cover so I needed to reset all of them. I noticed that when I was adjusting the valves that with a certain rotation where I was supposed to check 1 inlet and exhaust, 2 exhaust and 3 inlet, that the 2 exhaust wasn't adjustable at all. So I rotated the cam 360 degrees and this time I was able to adjust these properly.
 
Backing up a bit - when you turn the engine over (using the kicker or e-start?) without the compression tester in and all 4 plugs in - do you 'feel' compression? If there is truly zero compression, the engine will just turn over easily with no resistance.

Just want to make sure we're talking about literally zero compression, and not just 'low' compression.

If the cam is 1 tooth off, you could easily have 1 valve open a tiny bit at TDC. It doesn't take much to lose all compression.
 
tripledose said:
So I rotated the cam 360 degrees and this time I was able to adjust these properly.
Click to expand...

360 degrees is a full circle . . if you rotted the cam 360 degrees, it was exactly where it was before . . 180 degrees is a half circle.

do all of this with the spark plugs removed and once finished, turn the engine over slowly by hand 2 full rotations to insure the valves are at least not hitting the heads.

it would have been better to put it at tdc then simply put liquid white out on the front of the cam horizontal to the head, or on the end with a corresponding line on the head etc, but hindsight doesnt really help you much now.
.
 
Tim said:
Backing up a bit - when you turn the engine over (using the kicker or e-start?) without the compression tester in and all 4 plugs in - do you 'feel' compression? If there is truly zero compression, the engine will just turn over easily with no resistance.

Just want to make sure we're talking about literally zero compression, and not just 'low' compression.

If the cam is 1 tooth off, you could easily have 1 valve open a tiny bit at TDC. It doesn't take much to lose all compression.
Click to expand...

When I take a plug out and use the electric start I can feel my the suction on my finger and when I manually turn the motor using a wrench I can hear the intake through the carbs. It's just with either gauge I have from multiple tester sets the needle never goes any higher than zero.
 
Well the problem has been found. A friend came over and showed me the leak down test and it was determined that all 4 intake valves are bent and stuck open. This was confirmed after taking the head off. I believe when I was putting the rocker cover back on, one of the million times, I didn't back the tappet screws all the way out and hosed the valves all up. I just ordered a used head complete with valves etc off ebay so hopefully that'll work out well and the problem will be resolved. I never thought of putting an air hose into a cylinder when its intake was supposed to be closed and see if air came out the carbs.. sure enough that showed the problem.

Thanks everyone for responding previously.
 
You just found out the hard way that correct cam timing is critical - get it wrong and pistons touch valves (and pistons seem to win most of the time).


Hope you get it sorted when the new head comes in. Take your time and make sure it's right before you turn the engine over or else you'll end up with more bent valves.
 
Not so much a problem with cam timing.....the problem is the the end of the rocker touching the side of the valve stem when tightening the cam cover down. The arms have to be lifted during installation. Refer to the factory manual. It is not uncommon.
 
Hard way to learn, but a good lesson. Don't only back off the tappets, but you can use rubber bands across the top between intake and exhaust tappets to hold the rockers up when installing the cover.
 
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