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Discussion Starter · #1 ·
I have a top end rebuild thread on DTT and just posted this but I want to post this question here too. Could use a bit of advice on this:

I have done some breaking in on the rebuilt motor now and put about 20 miles on it. The bike is running but not idling great and now much power or ability to rev under load. A warm check on compression give 135 psi L and 125 R. question I have is: should I continue to try to break it in and seat the rings or should I disassemble the motor again? My shop said it should kick over at least 150 right out of the gate. I verified the valves were not leaking before asssembly. I have double checked valve tappets clearance. Made sure the o on your the cam sprocket was up at 12:00 when tdc on stator when I remade the cam chain. I had the shop hone and bore with the pistons to measure. I put the new rings on staggered 120 deg. These are the cruzin image rings and pistons. Shiny edge ring on top (no marking on it), dark ring 2nd with marking up, 3 piece oil ring on bottom with gaps staggered slightly, no overlap. Lost of oil on the rings, groves, etc. Tried to keep everything real clean during assembly. I'm using the royal purple sae 30 break in oil. Head torqued per correct order. In my haste I did not measure piston clearances or ring gaps before I rebuilt it. I don't mind to tear it down again if something is wrong, just wondering if I need to be patient and try to get those rings to seat!
 

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20 miles ?

Personally, I'd run it in gently for a few hundred miles, then see how it goes.

'Breaking in' an engine just sounds so brutal ...
 

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Discussion Starter · #3 ·
Ha! Its a matter of breaking it in without breaking it up isn't it, Richard! Yes, I'm glad you chimed in because from searching threads for CL175 I have come to know you as an authority of sorts on these bikes. So those compression numbers don't sound too down in the dumps to you considering it has not been run much since the top-end job? I was told to expect 150 psi by now but I don't really know.
 

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I'm no authority, everything I know has been learnt from this site. :D

Compression readings probably vary dependant on the tester used. However, for what its worth, I've rebuilt two 175 engines. Each had a 1mm overbore, machined at same shop in each case, along with valves ground in by me.

Engine 1 has 140 and 132 psi after running for a few miles. This rose to 155/155 after 120 miles, and at 1800 miles was 160/160.

Engine 2 had 130/130 after first run, rising to 140/145 at 150 miles. This engine now has 1600 miles on it. I've not measured the compression lately, but I've just got back in from a ride, and it was running well, red line in the gears and 9k rpm in fifth, speedo indicating 70mph at those revs.
 

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......... Lost of oil on the rings, groves, etc. ...............
Rings should go back in dry, into dry cylinders - using a lot of oil in the cylinders and on the rings can delay or even inhibit the seating-in process.
Some use just a touch of oil on the very bottom of that tapered cylinder area, just to keep the rings from snagging during installation - otherwise dry.
Like your guy, I would have expected 150-160 psi or more (preferably).
 

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The thought of installing pistons and rings dry makes me wince.

Personally, I always use plenty of engine oil when installing the rings. I just like to run things in gently. I accept that things may be different for race engines.

That said, my first (brand new) CB175 required new rings after first 1000 miles, because I had taken the 'running in gently' to extremes, oil smoke from exhaust on closed throttle.

Every other engine I've had from new has been run sympathetically at first, without problems in later life.
 

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Discussion Starter · #7 ·
Yes, I was surprised to hear the rings should go in dry. how does oil on the parts inhibit the rings from seating?

So bottom line is that maybe I should ride it and give it some more time to break in before undertaking another tear down? Its just a pain because I live in a hilly area and the bike seems to be weak to and difficult to get up the hills (stalling and having to walk it). Richard, on your bike with the initially 130 psi did the bike have any trouble dragging you up the hills? I'm 220 lbs but I figured it should do better than this. It had me wondering if there was more going on yet than just the compression issue. I have good spark on both sides. I rebuilt the carbs oem when I had it all torn down. set up the float height to 19.5 mm I believe, synched the throttle pulls and set the mixture screws to 1.5 turns out from seated. I have rebuilt air filters on it. I have not checked for a manifold leak yet but will probably look at that next. Plugs are sooty (but not oily) and the left one seems to be sooting up sooner than the right. Makes me wondering if its running intermittently on one cylinder - I have heard thats a common problem with the CL/CB 175s. Hmmm. Maybe Ill run it with one spark plug lead pulled first left then right and see how it compares?
 

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Dry assembly was a surprise to me as well, when my machinist first chastised me about it decades ago.

The guy is the best I've ever seen, what he says might as well be carved in stone for me........
But that's the way I've done it ever since - never broke a ring doing it.
 

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I've always oiled piston rings on assembly, been doing it for almost 50 years and haven't had set of rings not seat yet. I don't leave a puddle of oil in the cylinder, I turn it over several times while wiping the cylinder dry with a clean cloth. I don't see how two dry pieces of metal can slide against each other without galling and transferring metal. Be a shame to take the temper out of that new set of rings with all that friction.
 

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While your low compression would certainly contribute to loss of power, your sooty plugs indicate other problems. When you start checking for vacuum leaks get real serious about tracking down other possible fuel or ignition problems.
 

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Discussion Starter · #11 ·
Yeah, I figured with the sooty plugs that could be running rich but I did not consider ignition. I have checked timing and just actually checked it again yesterday and it's good. But it's also a cheap tytronic e-ignition unit that the PO put on with and aftermarket Emgo coil. I still have the old points and coil to play with. Could a weak spark lead to incomplete combustion and cause the sooty plugs?
 

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Possibly, hopefully someone here is familiar with that ignition. I would be more likely to expect the sooty plugs to come from a fuel system problem.
 

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Richard, on your bike with the initially 130 psi did the bike have any trouble dragging you up the hills? I'm 220 lbs but I figured it should do better than this.
I suppose I'm around 170 lbs, depending on state of diet, but given that the bike is only a 175 it goes up hills well enough. I probably run in too gently, and lug the engine rather than rev it, but it would happily go up a long steep hill in town ( Ronkswood Hill, Worcester UK, 30 mph speed limit ) at 30 - 40 mph in the low gears. I actually rode the same hill yesterday, was having to throttle back to keep it down to speed limit. Out of town, there is another hill without a speed limit ( Ankerdine ), with advice at bottom for trucks to engage crawler gear, bike screams up there WOT in third.

Bike is a CL, but I'm running CB gearing. I'd say it pulls surprisingly well at low rpms, given its limitations.
 

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Discussion Starter · #14 ·
I suppose I'm around 170 lbs, depending on state of diet, but given that the bike is only a 175 it goes up hills well enough. I probably run in too gently, and lug the engine rather than rev it, but it would happily go up a long steep hill in town ( Ronkswood Hill, Worcester UK, 30 mph speed limit ) at 30 - 40 mph in the low gears. I actually rode the same hill yesterday, was having to throttle back to keep it down to speed limit. Out of town, there is another hill without a speed limit ( Ankerdine ), with advice at bottom for trucks to engage crawler gear, bike screams up there WOT in third.

Bike is a CL, but I'm running CB gearing. I'd say it pulls surprisingly well at low rpms, given its limitations.
Thanks for the reply. Thats exactly the information I was looking for. Seems like there is a likely bit more going on than just a compression issue, which is actually good news in a way. Once I figure out the other stuff I will be on my way to properly seating the rings, with any luck.

Thanks guys!
 

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Discussion Starter · #15 ·
I made some changes and can report good results. Converted back to points from the cheap crappy electronic ignition and put a new coil, condenser and plugs on it. 2nd bad experience with Tytronic. This seemed to strengthen the spark. Started up and immediately revved to 7000 with no throttle. I shut it off and made some adjustments to the throttle cable. Not enough slack and the throttle slides were not dropping far enough at zero throttle. After startup and idle adjustment I finally got to ride. It's screaming up the hills now!

Only findings now are the it was tough to hold a low idle without stalling (had to keep a little gas on it and stay above 2000) and it is slow to respond to letting off the throttle. It stays revved longer than I would like and only slows down as I am coming to a stop. I am guessing this is just carb adjustment stuff and I'm not too worried about it. I'll get her running right.

Thanks very much Richard and other guys who helped me out on this! I am flyin high tonight��
 

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Discussion Starter · #16 ·
I pulled the plugs and they were still sooty. I figured I would try the 21 mm float height rather than 19.5, if still running rich. I pulled the carbs just now and found a problem. R float has a pinhole leak. Gas could be heard sloshing around. I had already repaired one leak on this float with solder but another has sprung up. In trying to burn off the gas with a lighter it popped on me. What a thrill. Well I'm gonna need a new float! So that explains a lot, including the oil smells like gas :(
Looks like time to change it already.
A flooded float won't float so the gas just floods in. But why did I not see it coming out the overflow tubes?
The good news is the compression rose 5 psi on each cylinder after ride today. Perhaps the rings will seat ok after all
 

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Discussion Starter · #17 ·
And a pic of the scramblers
 

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Old sports car racing trick often overlooked: Run the engine in after a rebuild (short ride for a bike) then pull the head(s) and redo the valves and seats to get solid seal. Then have at it!
 

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Discussion Starter · #19 ·
300 miles in to the rebuilt motor and it’s really running well. Tonight I retorqued the head and the screws on the cam side covers. Then did the cam chain, valve tappet and timing adjustments. I changed the oil and cleaned out the slinger as well. I really like riding this bike. It’s easy to ride and goes just as fast as I want to go, which I admit is not very fast. But it’s got a nice growl taking off from a stop light.
 
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