Topic: '77 Cb550 early ring wear

[kerryb]

My friend rebuilt the top end on his engine.  He used a kit from 4 into 1.  After a short season of riding, there were issues with how well it ran, so he he took it to a local shop for diagnosis.  They said his compression numbers were way off and uneven.  Suspicion  is cast at ring wear, my friend says he thought the rings in the kit were pre-sized so he didn't check and file the end gap on the piston rings.  This may or may not be the case, so the bike is coming to my garage so we can diagnose and repair this engine.
What steps would you take now to prove or disprove this theory, and based on the future results, what level of repair would be the best case scenario?
I plan start with a compression and leakdown tests but don't have enough experience to predict the next possible steps.  Your opinions on what to do next are appreciated.

[bryanj]

Leakdown test will tell you where the compression is going by where you can hear the air i.e. exhaust, carbs, oil filler.

In all the time i been working on hondas(since 73) i have never filed ring gaps if the rings were the correct size

[seanbarney41]

Too small ring gap would cause at least a soft seizure and more likely total failure of compression in that cylinder. 
Much more likely that the hone job was bad and/or proper breakin did not occur...if its a problem with rings/pistons.  What about the valves?

[kerryb]

Wow, that's very interesting from both of you.
I spoke to the mechanic that did the testing and discussed the nature of the chronology of the failure.
The mechanic said the compression numbers ranged from high (135) to low (90).  He said the leakdown revealed the valves were leaking too.  He quoted numbers but I can't be sure now. 
The owner, my friend, said the the loss of power was a steady decline over a matter of a few weeks.  Most noticeably was when climbing a long steep hill, there wasn't enough power to increase speed halfway up.
  So the engine is out on the table now, I'll start disassembly tomorrow.  My hope is that we can get away with rings, clean up the valves, and hone the cylinders.  What telltale evidence should I look for during disassembly?  I was told that if we avoided scoring the cylinder walls, the hone and rings might suffice.

[70CB750]

Following

[seanbarney41]

Kerry, be sure and check the valve clearance before you tear the thing apart

[bryanj]

If its been honed once doing it again may well make the piston to bore clearance too big, which may be the problem anyway

[kerryb]

Kerry, be sure and check the valve clearance before you tear the thing apart

I should have thought of that, but didn't...yet?  Thanks for bringing it up.

[kerryb]

If its been honed once doing it again may well make the piston to bore clearance too big, which may be the problem anyway

That's kind of scary moneywise.  What happens if you put new rings into a cylinder that hasen't been honed to recieve them?  Do they need the fresh surface to seat properly?

I guess it's time to get the good camera out to be ready.

[bryanj]

Contrary to what everybody seems to think you DO NOT need to hone to fit rings, you only need to remove the glaze which you can do with wet and dry or a flap wheel.
Honing removes metal and as piston clearance is only 1 thou thats a bad idea

[kerryb]

Checked the valve adjustments last night and here's what I found:
cyl 1, intake, almost .002"  ,  exhaust, tight, no clearance
cyl 2, intake ,almost .002"  ,  exhaust,  .003"
cyl 3, intake, almost .002"  ,  exhaust,  almost .002"
cyl 4, intake, almost .002"  ,  exhaust,  almost .002"

that explains the leak in #4 quite easily,  on the others I listed "almost" because I don't have a .001" feeler gauge in the neat little bent-tip style to get into the cramped spaces.

haven't disassembled it yet because I don't want anything getting mixed up with the other motor just like it going back together first.
Motor is out on the table for easy access.
Here are some pics for illustrative purposes, please don't complain about the brat-bike style...it is his bike, his choice!

[kerryb]

With valves that far out of whack, would I be advised to readjust valves and do another compression check?

[seanbarney41]

I am not sure why the motor is out of the frame yet?

[maxheadflow]

Contrary to what everybody seems to think you DO NOT need to hone to fit rings, you only need to remove the glaze which you can do with wet and dry or a flap wheel.
Honing removes metal and as piston clearance is only 1 thou thats a bad idea

If you run a flap wheel at high speed, how do you get a good cross hatch.  A good cross hatch is important to ensure that the rings continue to rotate on the pistons.

Some think that home a cylinder will make  it to big. Not necessarily an issue. Cylinder leak test will increase but as long as the cylinder is round and the rings properly floating things can still be good.  IMO the big issue ends up being the cylinders become out of round and the rings fail to seat or they settle in location where the gaps line up.  Cylinders to need to be honed with new rings on this stuff.  You can run up to the spec for cylinder wear. The main issue is that you'll get a little piston rattle, mainly when cold and leak down goes up.  Remember cylinder leak test is static, not dynamic.  Personally I only use it whne the compression is good and I want an excuse to tear the motor down..


Not sure how too tight of a ring cap cause a soft seizure.  I'll agree with the fact that genuine Honda rings typically are right on. In fact if you find that they are too tight, chances are that pistons in the cylinders were too tight causing the "soft seizure"   If the ring gap is too tight, the ends butt and they typically break.

[kerryb]

I am not sure why the motor is out of the frame yet?

I'm old,  and the arthritis in my neck can be troubling to work withall the other parts of the bike in the way.  Since I have a J-hook and a hoist in the rafters, taking the engine out seems easier since it was expected to come apart anyway.  I admit, it may have been premature because I'm doing some crude leakdown testing now and figure I should put oil back in to do another compression test.  Cylinder 4 has no leaking noises since the valves were readjusted, but cylinder 1 has leaky noises under the valve cover but not in the intake or exhaust ports. 
Cylinder 4 will achieve only 70 psi compression with me pushing the kicker with my hand (I'm not climbing on the bench to use my foot!).
p.s.  Max commented while I was typing, but that seems to be between he and bryanj...I'll just watch and learn.

We learn by making mistakes, I'm trying real hard not to make any that cost me money...time however is in the column labeled "tuition expenses".

[kerryb]

Engine is now disassembled, I took lots of pictures hoping you see what I can't.  Measured cylinder bores and they are between 2.303 and 2.304, except number 1 which I need to triple check as it is 2.305"  Here are pictures of some cylinder walls and piston rings I need help with.  Do these look OK?  compressed air in the cylinder can be heard escaping past the rings with only 300 miles on a hone and new rings.  Cylinder walls have faint vertical scratches in them.  Do these rings appear to be installed correctly.
First engine internals project, no good field experience yet.  curious if cylinder one was firing properly because there is no carbon build-up.

[kerryb]

Wondering if this picture is good enough to tell if the rings are installed right side up?  The wear appears to have happened at the bottom of the ring.
Ring gap of top ring is now .014"

[dave500]

when you installed the rings did you install with any markings facing upwards?

[bryanj]

1st pic of piston looks like top and middle ringsin wrong grooves

[PeWe]

Photo show wrong rotated oil rails. Both gaps on top of eachother will not seal well. Oil rails gaps must be separated by 180 degrees when assemble.

[bryanj]

Your bore sizes if accurate show excess clearance on anything over 2.303 meaning lack of compression.
They have been honed too much so you need oversize piston kits and a machine shop that will bore to a 1 thou piston clearance, if they say thats too small and will sieze take it elsewhere

[kerryb]

1st pic of piston looks like top and middle ringsin wrong grooves

Confirmed...I took the cylinders and pistons to a reputable machine shop today (the same one my bmw restoration freind uses) and an early observation was that two pistons had the top and second rings reversed.  Another ring was in upside down.  I took one ring off to measure ring gap and it matched the factory specs. 
I measured all the cylinders many times and came up with 2.304" across the board with two spots at 2.305".  Factory spec was 2.303 to 2.304" in the manual downloaded here.  I took more/better pictues of the pistons and rings to put up soon.
I'm hoping the rings are the culprit, but we'll wait for the machine shop's findings and recommendations.  This saga aint over yet.

[maxheadflow]

1st pic of piston looks like top and middle rings in wrong grooves

I see the same thing..

[kerryb]

Finally getting those pics of the rings posted.  Would you agree with these observations?
cyl.  1.  compression and oil reversed, both rings right side up.

cyl. 2.  Rings in right grooves, top/ compression ring upside down.

cyl. 3.  both rings in correct position

cyl. 4.  top two rings reversed, compression ring upside down.

Could this alone account for a major loss of compression?

[bryanj]

Cant tell if they are upside down or not, any markings on the rings face upwards.
Wrong possition or orientation would wear ringsquickly and loose compression