cb175 piston & cylinder damage and request for oil control ring

petalboat

Member
Joined
Oct 9, 2020
Total Posts
23
Total likes
0
Location
Athens, GA, USA
Hi- My 71 cb175 lost a cam chain going 60 on the highway- it came apart at the master link. I pulled the head off and saw no apparent damage- took to my machine shop to make sure and they concurred. I looked at the pistons and they both have a fair amount of carbon buildup. I pulled the cylinders and found skirt damage on piston 1 (right side) and corresponding scoring on cylinder. This is ~2000 miles after rebuild with new oem pistons and cylinders, and I don't feel I've been particularly hard on it - soft break in, very regular oil changes (after startup, after 100 mi, and every 500 since) with cleaning filter. Anyone have any ideas why I'd be seeing so much carbon? or why scoring is happening? It wasn't burning oil, wasn't smoking, and appeared to be running happily. I was going to clean it up, put it back together, and see if I notice any change in performance, etc.
piston.jpg cylinder.jpg cylinder 2.jpg
I was planning a ~500mi trip in early october - but then during that cleanup/"rebuild", I snapped an oil control ring. Anyone have one they'd be willing to ship my way? I definitely prefer the 1 piece, if possible. DM me! :)

Now that I can't quickly put it back together I'm going to have my machinist take a look at cylinders and tell me if a rebore is required. Anyone care to venture an opinion? Before my ring breakage, my optimistic thinking was that it was running fine before, so it'll probably run fine now.

Thanks!
 
Last edited by a moderator:
You didn't say if you used STD bore pistons on the previous rebuild, or what? It matters for even just an oil ring replacement. Curious what the machinist will advise.
 
standard 52mm- i bought the bike in pieces and it came with a new oem set of cylinders/pistons/rings- i'm curious too! i was able to find a set of rings close by to me so they are ordered. i guess i'm still in the optimist mindset, haha, and i do really want to make it on the planned trip. sad about the masterlink- when i initially put it together I assumed I put the clip on backwards because at my first oil change i found it on the magnetic plug. I counted myself lucky as i reinstalled it, but looking back I should've just bought a new one. I would say lesson learned except I'm probably going to put it back together with my new ring set this time and feel lucky again, haha - perhaps my ufollow up post will be from the side of the road.
 
Your machinist is absolutely certain there are no bent valves? Typically when a cam chain comes apart or breaks there is at least one bent valve on a twin. You should leak test them to be absolutely sure.
 
I was surprised, too, which is why i took the head to him. he pulled it apart and checked everything out and says nothing was wrong. i saw no marks on pistons to indicate impact -i did quick/dirty fill chamber with gas and see if it leaked with valves closed and it didn't.
 
i hope so, i guess i'll know for sure once it's back together! i know the tappets were close to perfect because i had just adjusted them- are these motors actually interference? the other factor is that when i got the bike, the journals were destroyed and it was obvious the pistons had nailed valves. I found a shop that machined in roller bearings for the camshaft rather than sourcing journals.
 
petalboat said:
i hope so, i guess i'll know for sure once it's back together! i know the tappets were close to perfect because i had just adjusted them- are these motors actually interference? the other factor is that when i got the bike, the journals were destroyed and it was obvious the pistons had nailed valves. I found a shop that machined in roller bearings for the camshaft rather than sourcing journals.
Click to expand...

Too bad you didn't do a build thread with all that going on. The roller bearing mod would have been interesting as well as the particulars on the STD pistons and bore prep on a new cylinder. How are your small end rod bores BTW?
 
i found this group a little too late to do build thread.
Actually, I didn't do anything special to prep cylinders- they had a nice looking crosshatch in them and ring gaps were perfectly in spec so i just oiled up and assembled- perhaps that is why they're damaged now?
I didn't take bottom end apart-it was low mileage (6000) and I guess I gambled on it being okay. There is some play in rods when i rock them side to side - is there a relatively easy way to see if those are in spec?
the roller bearing mod was done by andrews motor shop in NC: https://andrewsmotorsports.mybigcom...5-cam-bearing-conversion-cylinder-head-ahrma/.


Edited to add: ooh, you were asking about small end rod bore- i didn't immediately feel any play in piston on rod - i'll definitely check that when I reassemble and at least compare to the other side- thanks.
 
petalboat said:
i found this group a little too late to do build thread.
Actually, I didn't do anything special to prep cylinders- they had a nice looking crosshatch in them and ring gaps were perfectly in spec so i just oiled up and assembled- perhaps that is why they're damaged now?
I didn't take bottom end apart-it was low mileage (6000) and I guess I gambled on it being okay. There is some play in rods when i rock them side to side - is there a relatively easy way to see if those are in spec?
the roller bearing mod was done by andrews motor shop in NC: https://andrewsmotorsports.mybigcom...5-cam-bearing-conversion-cylinder-head-ahrma/.


Edited to add: ooh, you were asking about small end rod bore- i didn't immediately feel any play in piston on rod - i'll definitely check that when I reassemble and at least compare to the other side- thanks.
Click to expand...



It does seem to be fairly serious scuffing damage for the low miles. Did you have piston/ bore clearance checked? IOW, could that be pre-seizure scuffing? I just did a crank swap due to worn rod ends so it was on my mind and can wonder what issues or results could be from that problem.
 
i'm with you on thinking the damage is a lot for such low mileage, and i definitely have had sleep interrupted thinking it could be pre-seizure damage! I didn't have clearance checked but i will ask my machinist to take a look when i see him tuesday as I don't have the tooling to do that.
 
petalboat said:
...are these motors actually interference?
Click to expand...

Yeah, most Honda OHC engines from that era are. Anything that turns 9000 to 10,000 rpm is pretty highly tuned and usually bends valves when the cam stops before the crankshaft does, in my experience it's pretty typical that at least one valve is open when the cam stops turning.
 
ancientdad said:
Yeah, most Honda OHC engines from that era are. Anything that turns 9000 to 10,000 rpm is pretty highly tuned and usually bends valves when the cam stops before the crankshaft does, in my experience it's pretty typical that at least one valve is open when the cam stops turning.
Click to expand...

All the more reason to be really thorough looking for both prior and current issues. Getting one in pieces is a bag of tales for sure.
 
I don't want to be the wet blanket here but the likelihood of just replacing the rings and running it as is with the expectation that all will be good rates a 10% probability.
From what I see the piston to cylinder clearance was on the tight side, likely well below minimum. So it got hot and started to seize with material transfer from the piston to the cylinder wall.
 
Thanks LongDistanceRider - your point is taken and was really where i was when i saw the damage. what i don't understand is why i had no issues with it previously- or perhaps that was putting extra pressure on the timing chain causing it to come apart?? wouldn't there be some bad sounds to tip me off that there is pre-seizure occuring? i'll update once the machinist has a look. if it's too tight, perhaps i can machine/hone it to within spec while keeping std rings.
 
You wouldn't hear anything over the normal engine noises. There's a slim chance of the cam chain during failure of over advancing the timing but then there should be damage on the other cylinder/piston as well plus the damage should appear on the tops of the pistons as well like a mouse was nibbling little pockets out.
You put the engine together from a box of parts of unknown provenance. Assumption being that the new pistons were good and the bore looked good. However if the pistons were stored laying on their sides or even with heavy stuff stacked on top the skirts could have been out of round. The cylinder may have been out of round or tapered. Without the years of experience telling you to check and recheck every piece for measurements and tolerances you put it together assuming everything was good and 90% of the time it would have been. We've all done it at some point in time.
One of the bikes my son is bringing supposedly has a rebuilt engine in it. Guess what? I'll be taking the engine apart to insure that it was done correctly. Trust but verify.
 
And it could even have been that the pistons were put in the opposite cylinders that they were fitted to after boring (if the bore work was fresh). .001" tighter could have been enough to cause a brief seizure.
 
thanks. honestly, i didn't realize the tolerances were "that" tight. live and learn - or, maybe learn? we'll see as i move forward, haha.

ancientdad: that's a sad thought that i could have put them in the "wrong" cylinder- and one that i had after reading longdistancerider's post as well.
 
Well, it would only have been wrong if the PO or his machinist had actually marked the pistons and cylinders, otherwise you wouldn't have known and it would have been a 50/50 roll of the dice. Piston to cylinder clearance on a fresh bore is typically around .0015" to .002", clearance of .004" is time for a oversize bore
 
Here's my update - Proving the above suggestions that you should check everything and not believe the boxes they come it: My cylinders were not NOS and were actually overbored to 0.25 OS! Machinist was able to hone cylinders into spec and says they are good to go but that the piston lost enough material to need replacement. I was able to find a NOS replacement piston (that I'm definitely going to take back to him before installing to "verify!") on ebay but now I'm searching for an 0.25 OS set of rings (or at least the oil control ring).
Machinist suspects that cylinder is running lean - my plugs look ok to me but I'm going to make sure no air infiltration is happening at carbs. i did have a free-er flowing aftermarket exhaust on it for the first ~1000 miles after rebuild and could never quite get it to run right so ended up finding a good used stock set which immediately made it idle and run better. I wonder if that period of time is when this damage occurred.
still moving forward and hoping to leave later next week for this trip, haha!
 
You want to replace all of the rings, not just one. Look also for .050mm oversize as an option. Those mean you'll have to file the ends down some but at the same time it also means you can set the ring gaps to exactly what you want. Since this is a street engine I'd split min./max.
 
Theoretical question that has come up in my mind bc I have access to a set of std rings: could one use standard rings on an oversize piston if the ring gap was within spec?
 
You could, but it's not likely to be in spec and if it is it will probably be right at the max allowable
 
There's no way a set of Std. rings will even come close to spec with a .25mm overbore. Even the technically correct rings will be close to max gap right out of the box. I went thru 3 sets of rings to get less than max on my 350 1mm overbore.
 
LongDistanceRider said:
There's no way a set of Std. rings will even come close to spec with a .25mm overbore. Even the technically correct rings will be close to max gap right out of the box. I went thru 3 sets of rings to get less than max on my 350 1mm overbore.
Click to expand...

wow, that's terrible! the 0.25 OS set that were currently on the bike are really close to the minimum! perhaps they were actually 0.5s or something- well, i was able to find a set that should get here Saturday or Monday- so I theoretically have time to get this all together and I'll let you know how the gap looks at that time.
 
I'm interested what your machinist finds when he measures the I.D. of the cylinders and the O.D. of the pistons you plan to install;the factory spec clearance does seem 'too tight' according to some machinists.. but it's better to have it 'within spec' according to the Honda factory manual.
What type of engine oil are you running;are the oil filter and pump in good condition ?
 
bilbikek411 said:
I'm interested what your machinist finds when he measures the I.D. of the cylinders and the O.D. of the pistons you plan to install;the factory spec clearance does seem 'too tight' according to some machinists.. but it's better to have it 'within spec' according to the Honda factory manual.
What type of engine oil are you running;are the oil filter and pump in good condition ?
Click to expand...

I didn't get the actual numbers but he said the damaged pistion was .008 below the bore- thus requiring new. depending on when i receive parts I was going to try to get him to measure before assembly and i'll get numbers then if possible. I was running castrol edge or something 20-50w and as far as i can tell my oil pump seems in good shape -is there a good way to check it? and centrifugal oil filter was cleaned at last oil change and i'm sure is slinging oil around. It really appears my issue was that the one cylinder was running lean- it's what the machinist said it looked like and it checks out on the spark plug- i had not checked it for a few hundred miles due to some loose threads that were worrying me would strip the next time i torqued it. at least this forced me to fix that- and off the bike which is much easier! I'll be rechecking for air leaks and cleaning jets during reassembly bc i'm not exactly sure why that cyl was running lean.
 
petalboat said:
I didn't get the actual numbers but he said the damaged pistion was .008 below the bore- thus requiring new. depending on when i receive parts I was going to try to get him to measure before assembly and i'll get numbers then if possible. I was running castrol edge or something 20-50w and as far as i can tell my oil pump seems in good shape -is there a good way to check it? and centrifugal oil filter was cleaned at last oil change and i'm sure is slinging oil around. It really appears my issue was that the one cylinder was running lean- it's what the machinist said it looked like and it checks out on the spark plug- i had not checked it for a few hundred miles due to some loose threads that were worrying me would strip the next time i torqued it. at least this forced me to fix that- and off the bike which is much easier! I'll be rechecking for air leaks and cleaning jets during reassembly bc i'm not exactly sure why that cyl was running lean.
Click to expand...


Ok,I would make sure both cylinders/pistons 'fit' measure well within the new spec clearance between cyls./pistons clearance,even if you need to bore it to the next size over to accomplish that. ;)
 
bilbikek411 said:
Ok,I would make sure both cylinders/pistons 'fit' measure well within the new spec clearance between cyls./pistons clearance,even if you need to bore it to the next size over to accomplish that. ;)
Click to expand...

I appreciate this idea and I think this is great advice that i do intend to follow, but if i have the chance to get it together before i can catch up with my machinist, i'm not going to get measurements. I'm really trying to get it all back together to leave for a trip next week! If i do get measurements, i'll post them. life on the edge, haha - ultimately, i guess i'm willing to live with the consequences if necessary
 
Got it all together this morning. didn't have time to get measurements on piston/cylinder. Went together without a hitch- or even any leftover parts. :) I used the those guys in Houston cam chain replacement with the tool they sell along with the press fit master link- there was a bit of a learning curve/ deciphering instructions/ figuring out a different way to do it. If anyone else needs help figuring it out, i'm happy to share what i did and hopefully it won't come apart anytime soon! i think I'd rather have a clip type master link even though that seems to be what failed on me earlier.
It started at first kick- ran for a few minutes and then changed oil. I put 25 miles on it slowly using more and more throttle up to maybe 3/4 and it sounds/feels great. I pulled the new spark plugs after that and they both look really clean and if anything on the lean side. With that in mind i lowered the clip on the needle from the 2nd to the 3rd slot. going to retorque head and do general check, put maybe 25-50 more miles on it, change oil/ clean oil filter, and pack up to head out tomrrow morning for a several hundred mile trip over several days.
 
Hopefully you've gotten it back to reliable so you can enjoy your ride. Post some pics from the road if you're able, and of course be safe.
 
Thanks to all for sharing your knowledge and spending your time troubleshooting with me!

ancientdad said:
Hopefully you've gotten it back to reliable so you can enjoy your ride. Post some pics from the road if you're able, and of course be safe.
Click to expand...
Me too! I'll post some pics upon my return!


bilbikek411 said:
Sounds ok.
Did the new piston seem to fit correctly?
Click to expand...
I almost included in the post that I couldn't tell a difference between the known good piston and the new one as far as size and fit go. But I can't possibly tell the difference of .004" anyway, haha. fwiw, it fit really well by my biased eye! :)
 
petalboat said:
Thanks to all for sharing your knowledge and spending your time troubleshooting with me!


Me too! I'll post some pics upon my return!



I almost included in the post that I couldn't tell a difference between the known good piston and the new one as far as size and fit go. But I can't possibly tell the difference of .004" anyway, haha. fwiw, it fit really well by my biased eye! :)
Click to expand...


Where are you traveling to 'petalboat' ? To Alabama ?

I lived North of you in Toccoa for almost a year back in 2011' and used to travel down to Athens to see the doctor and to get allergy shots.

Does Partzilla still have their headquarters there in Athens ?
 
they both look really clean and if anything on the lean side. With that in mind i lowered the clip on the needle from the 2nd to the 3rd slot. going to retorque head and do general check, put maybe 25-50 more miles on it, change oil/ clean oil filter, and pack up to head out tomrrow morning for a several hundred mile trip over several days.
Click to expand...

If you lower the clip, that raises the needle and makes it more lean. Have a safe trip!
 
Last edited by a moderator:
I returned to Athens yesterday after putting 600 miles on the bike in ~5 days. I, of course, snapped the clutch cable on the first day right when leaving, so was forced to replace with bicycle cable with the end wrapped around a bolt to hold it. I think Honda planned for this with the small hole located underneath the proper mount on the bottom of the clutch lever. Then, on day 2, I left a campsite and rode a mile away to a grocery store. When I came back to the bike it was sitting in a puddle of oil! I discovered the clutch shaft seal had blown out and felt very very lucky that it didn't happen on a long ride when i wasn't looking for it! Anyway, I pushed it back in, filled with oil, and was able to ride the rest of the time with only minor anxiety about it - checking for oil leaks about 1x per mile, haha. Aside from those 2 minor incidents, the bike handled the trip like a champ - many climbs in the mountains and lots of memories and miles. I'm having trouble posting photos for some reason but will try again in a bit.
 
petalboat said:
I returned to Athens yesterday after putting 600 miles on the bike in ~5 days. I, of course, snapped the clutch cable on the first day right when leaving, so was forced to replace with bicycle cable with the end wrapped around a bolt to hold it. I think Honda planned for this with the small hole located underneath the proper mount on the bottom of the clutch lever. Then, on day 2, I left a campsite and rode a mile away to a grocery store. When I came back to the bike it was sitting in a puddle of oil! I discovered the clutch shaft seal had blown out and felt very very lucky that it didn't happen on a long ride when i wasn't looking for it! Anyway, I pushed it back in, filled with oil, and was able to ride the rest of the time with only minor anxiety about it - checking for oil leaks about 1x per mile, haha. Aside from those 2 minor incidents, the bike handled the trip like a champ - many climbs in the mountains and lots of memories and miles. I'm having trouble posting photos for some reason but will try again in a bit.
Click to expand...


How does your engine compression,etc. feel ?
 
bilbikek411 said:
How does your engine compression,etc. feel ?
Click to expand...

Battery seems to be on last legs as my electric starter has weakened. I just checked point gap and timing and gap was on the small side and timing was advanced about 1/2 inch before the F. Otherwise it starts strong with a kick and is running good so I think compression is fine. Spark plugs look as they should without evidence of oil or of running lean.
 
You must log in or register to reply here.
Back
Top Bottom