CB175 piston ring weirdness

M

mbone83

New Member
Hello everyone,

Recently started a top end rebuild on my 1973 Honda CB175.

Purchased some new standard size ring sets for the pistons and noticed both the compression rings are the same profile.

Anyone ever experienced this with a CB175 ring set?

Thanks!

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Done many 175 builds. If they are the NOS Honda rings it to hard to tell by the naked eye but they are different. They are marked right by the ring gap. One will have 1 marking (ie a dot)the other will have 2 markings (ie a dot and a T). The one with 2 markings is top the other is second ring the last is oil. Remember markings go up.
 
The rings were purchased from a US Ebayer.

He says they are NOS Honda Nippon brand.

They are marked with a "IN" by the gap.

Both the compression rings look like top rings.

What's your thoughts on that?

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I think I have a similar set in the shop. Will check when I get him but I think one of the rings has a faint 1 or t on it. When I get to the shop tonight I'll looks and double check. The mark is very faint though
 
I pulled out a 30x loupe and inspected the rings. Both are identical.

The rings I removed had a definite profile difference.

I guess I'll know if I'm hosed when I start the motor. :/

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The rings I have in a red Honda ring box have an r and an r1. R1 being top of you are saying you have 2 rings with "in" then those would be top if the others have no markings. If all 4 have "in" then they were packaged wrong. All rings have ID markings that denote direction and order.
 
Yea. I guess at this stage, I'll run the rings and see what happens.

What a bummer, I tried to purchase from a US source so I could bypass the 2 week shipping time from Thailand.

I guess some things are better sourced from across the pond.

On a side note.

I had 85 and 90psi compression on the cylinders before rebuild. I'm now sitting at 120 both banks on a cold motor with no break-in. Hoping for 150 after break-in!

Wish me luck!




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mbone83 said:
Yea. I guess at this stage, I'll run the rings and see what happens.

What a bummer, I tried to purchase from a US source so I could bypass the 2 week shipping time from Thailand.

I guess some things are better sourced from across the pond.

On a side note.

I had 85 and 90psi compression on the cylinders before rebuild. I'm now sitting at 120 both banks on a cold motor with no break-in. Hoping for 150 after break-in!

Wish me luck!




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Click to expand...
Good luck.
 
mbone83 said:
Yea. I guess at this stage, I'll run the rings and see what happens.

I had 85 and 90psi compression on the cylinders before rebuild. I'm now sitting at 120 both banks on a cold motor with no break-in. Hoping for 150 after break-in!

Wish me luck!
Click to expand...

Keep hoping!

Luck won't help.
 
You have the WRoNG RiNgs!!! Might as well take the engine and throw it in the trash because that's where it's going to end up in a few hours of running.
 
Well, I ended up getting a different set of piston rings to go in the motor. They were clearly marked this time.

Got the motor up and running to discover oil was puking from the head gasket seam.

Torque of 14.5lbs is on spec with the manual.

Decided to remove the head yet again. The gaskets crush rings are not crushing at 14.5lbs and because of this it's not sealing on the rest of the gasket well.

Just ordered OEM NOS gasket.

Anyone ever encountered a gasket like this? It's a NOS SCM brand.

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I have worked on a couple of these motors that customers have installed the wrong size o-rings on the upper oil drain dowels. That will cause the head to not torque flat hence the oil leak. If you can measure the squeeze ring on the head gasket see if the front (exhaust side) is smaller than the back. That would mean it's torquing on the orings and not flat on the head gasket.Never seen a head gasket squeeze ring not seal properly if everything is correct. Glad you sorted the rings out.
 
I'll definitely check the squeeze ring thickness in those two locations.

As far as the o-rings causing the torque to be uneven- I would it's not that considering the rings were also supplied in the top end gasket kit.

The only discrepancy that comes to mind about this particular gasket. The kit said it was for a K3-K4 model. I have a K6 serial number on my 73 (which technically should have had a K7 serial).

The gasket kit says it fits cb175 and cd175.

Perhaps those models had a ring impression on the deck surface?

Only speculating..

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The cb/cl/sl/cd all use the same piston sleeve and cylinders. The head on the cd is different but only in the fact that it uses 1 carb not 2. Some have different cam journal blocks but that's not what we are dealing with. The mating surfaces are identical. It's not out of the realm of possibility of your original idea that the squeeze ring is a solid ring and won't squeeze down,Sealing off the head gasket and allowing oil to come out of the oil feed dowels. It was running you said so it had compression which leads me to believe the head gasket squeeze rings sealed in some way. I measured the new ones I have and they measure .052-.054". I also measured ones that I use to check piston to head clearance and they measure .046-.048". Oil can only come from the feed holes ( back right and left stud) or the opening for the cam chain. Since you said it cam pouring out i would lean on the oil feed lines.
 
Von Braun,

Thanks for all of the very informative posts!

Where to begin.. OK.

The gasket kit I purchased originally was an aftermarket NOS kit from 1971. Company logo on the packaging is "SCM". I myself have never heard of that gasket manufacturer but I figured it being older it should have been a decent kit.

That SCM head gasket had some very thick squeeze rings that just wouldn't compress well. The head literally was suspended by those rings and barely any of the composite gasket surface was doing its job if sealing. Believe it or not, the majority of my oil leaks were from the exhaust side opposite of the oil feed dowels. I think the o rings were keeping those possible oil leaks at bay. I am going to go out on a limb and say that I was getting the majority of the oil leaks from the cam chain gulley via crankcase gases.

I think there was so much blow by with that bad gasket, I was getting a lot of oil in the right cylinder.

Yes I know that sounds crazy but I could literally hold a flash light at the corners of the head gasket and see light between the cylinder head and the deck of the cylinders.

I received a NOS Honda head gasket in the mail today and right away noticed the quality was quite a bit better. Squeeze rings were half the size of the SCM brand gasket.

I put the new gasket on this evening brought the torque up to 14.5LBS. No gaps between the cylinder head and deck of the cylinders was noticeable using a flash light like previously.

I'll be putting the motor back in the bike tomorrow night. I'll let you know how it goes!


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Well I'm glad it looks as though it's been sorted. It's a major problem in our hobby of companies trying to reproduce parts and not knowing their head from their feet. It unfortunately takes a person to order the parts to find out they don't work for the rest of our community to learn. The 1st penguin in the water gets eaten by the Sea Lion syndrome. Definitely use a GOOD oil and if at all possible a zinc additive In That bike. I've seen more than my fair share of destroyed cam journals and wiped out cams because of the "stellar" oil system. Good luck with the rest of the build and happy riding.
 
What do you consider good oil? I was going to run Castrol 10w-40 non synthetic.

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Redline and motul are some of the better off the shelf ones. Motul is a true synthetic ester oil. Redline is also very good but not a true synthetic. I use zddp additive in all the 175 motors. I use brad penn oil in my Vw bug with zddp as well. My personal 175 has redline and zddp. Zddp is the zinc additive btw. You can use non syn oils and in all reality any oil will work but the motors were not designed from the factory to last near 10000 miles. If you change your standard oil every 500-600 miles you may not have an issue. That also includes cleaning the sludge cup. I change mine every 1000.
 
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