cb350f PLEASE HELP

Hi all, new here from RI

I picked up an all original 72 cb350f a back in march with 40k miles. Had a local shop here rebuild the top end and crack the cases.. rings.. cam chain...valves.. carb rebuild.. fresh plugs.. wires..coils..and electrical.. brakes.. cables.. new everything.. really went through the whole bike. Put a dyna-s ignition in and a few other things. Bike runs awesome... have about 550 miles on it since the rebuild.. will do 90 mph+ easy.. I did a few cosmetic changes and cleaned her up real nice. I have SOOO much money and time into this bike and I know ill never get the value back.. but ive been looking for a 350f for 10 years.. and finally found the one i wanted. Countless hours polishing up the engine covers and components.. this bike is like my second wife at this point


problem is .. im getting a lot of oil smoke coming out of the right side exhaust.. after the bike gets hot I also get A LOT of smoke from the crank case vent. So much from the crank case vent.. especially when I was idle at a stop light...a police officer actually pulled up next to me and was concerned the bike was on fire! The shop kept telling me it was normal and to keep putting miles on it. After bringing the bike by the shop about 15 times they finally agreed to pull the top end off. I thought for sure that an oil ring had cracked allowing the blow by. Compression was perfect in all four cylinders.

Here is a picture of the pistons after they just opened it up.. they told me there is nothing wrong with the rings and everything looks great... take a close look at that far right piston.. it looks fried to me.. anyone have suggestion. The shop told me to order some new rings just to be sure.. but maybe it is the valve seals.. or lap?

I was getting a tiny bit of smoke out of the left side exhaust.. very very minimal.. but the right side would be huge poofs that only got worse as the bike warmed up... and the crank case vent looked like a 2-stroke scooter exhaust. Any help would be great thanks in advance! I have included some pictures of the bike. Don't hate on the clubmans.. im still a young and sprightly 30 years old

Don't let your first wife hear you say that.....

Smoke out of the breather pipe? There shouldn't be hardly any smoke at all.....are you sure it's just not a lot of steam? And what do the plugs look like? Of your #4 plug is covered in burnt oil and it's not the piston rings, I'd look at the valve guides / seals.

It is heavy blue white smoke. The if i touch the bottom of the breather tube I get oil on my finger

After a highway ride (30-40 miles) Ill pull off the highway and stop at a red light and the bike will stall out and have trouble starting again.. at this point there is a TON of burning oil coming out of the crank case vent. I am positive is is oil and not vapor.

Also when i start to get the heavy breather smoke, If i open the oil dip stick smoke will come out also..

But as far as the breather tube.. think of a two-stroke scooter exhaust and that's about how much I am seeing come out... and also from the right side exhaust pipe. It is blue-white.. without a doubt oil.

Ok, just making sure.

Something is going on for sure - there's no way it should be burning that much oil. I still say look at that #4 piston / valve set.

No.4 piston is telling the story. Too much carbon there for normal. With the amount of oil smoke you are describing my bet would be oil coming down from the top through the valve stem seal as opposed from up past the rings.

Did this oil burning happen from straight after the rebuild. Did they forget the valve stem seal.

Hot500 said:

No.4 piston is telling the story. Too much carbon there for normal. With the amount of oil smoke you are describing my bet would be oil coming down from the top through the valve stem seal as opposed from up past the rings.

Did this oil burning happen from straight after the rebuild. Did they forget the valve stem seal.

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Yes prior to the rebuild.. besides a BAD cam chain and low compression... it ran strong with no smoke what-so-ever. The smoke was a bi-product of the rebuild.

It's more than this but this could be compounding it: have you checked to make sure the crankcase doesn't have too much oil?

carnivorous chicken said:

It's more than this but this could be compounding it: have you checked to make sure the crankcase doesn't have too much oil?

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yes I changed the oil several times.. and tried different types of oil.

Was always filled just about half between the marks

The last time i changed it, i left it on the lower side.. just to rule that out as a problem

Seconding valve diagnosis.

Another possibility is that oversize rings were used and the end gap was cut down to spec. Blow by that bad, sounds like a ring issue. Compression being good is a bit of a puzzle in this case. I intentionally removed the valve seal umbrella on a hopped up 450 Honda for one cylinder to smoke. It was a rat bike, meant to look and sound bad. The high lift cams made a little noise which added to the scam as well. There was no blow by from the crankcase however.
Oversize, say 1mm, cut down rings won't fit the bore well, which could be the problem.

Crank case smoke usually means over pressure. Possible i have a bad oil pump? The rings are stock bore

If this was my bike I would be taking that head home from the shop and dismantling those valves myself. Making sure that valve stem seal is in place.
The problem has clearly arisen from the rebuild the shop did. They fcuked up somehow.

If No.4 rings are OK, not broken, no serious scoring of the bore, then the oil must be coming from the top. Your compression test tells that the rings must be OK.

I would be pulling that head down with a camera and a witness present and then giving that shop an exhibition of cranky old man syndrome.

It's hard to imagine that you can get much blow by from the tiny clearances that the valve stems have. Exhaust smoke yes, but severe blow by? Oil pump bad, will cause a piston failure. Your mechanic doesn't sound like the sharpest tool in the shed.

Just spoke to the shop today. I guess when they first pulled that piston out it was COVERED in WET OIL. I will be going down there today with a friend that is a Harley mechanic to look at it for a second opinion. This shop has been a nightmare ALL SUMMER. Stay away from them!

Hot500 said:

If this was my bike I would be taking that head home from the shop and dismantling those valves myself. Making sure that valve stem seal is in place.
The problem has clearly arisen from the rebuild the shop did. They fcuked up somehow.

If No.4 rings are OK, not broken, no serious scoring of the bore, then the oil must be coming from the top. Your compression test tells that the rings must be OK.

I would be pulling that head down with a camera and a witness present and then giving that shop an exhibition of cranky old man syndrome.

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So this is what I think happened. Im sure you are all familiar with piston rings and how they are like a giant c-clip. There is a quarter inch slot that is open in the ring (they are obviously not solid all the way around). I think the guy installed them on that number four with all the slots aligned instead of 180 stagger.. allowing massive amounts of oil to seep in.

The rings looked perfect to me in person. They still had some of the shine around the edges which shows they were not even fully broken in.

I took the head and the cylinder block to an independent machine shop to have it all re-worked even though I have invested about 2,000 USD into the rehab/restoration of this bike. I have so much money in it I mind as well spend another 150 bux for another hone, pressure test on the head and cylinders, remove the valves, new guides and seals again... and lap them...

Then this retard (sorry but he is) of a mechanic will put it all back together for me at no cost.

1000 for the bike
2000 for the motor rehab and other restoration

I've never spent this much time or money just getting a bike to drive down the road before..
Literally giving me grey hair and ulcers.. Hopefully this will cure it.
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1/4" end gap? are you serious? Should be about .025", not .250" no wonder it had blow by. Even staggered that's way to much.

Scooter trash said:

1/4" end gap? are you serious? Should be about .025", not .250" no wonder it had blow by. Even staggered that's way to much.

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I think he's looking at the rings outside of the bore. It should be about 1/4" if that's the case.

At least I hope that's the case - no shop in their right mind would assemble a motor with that much ring end gap and expect it to run......

I wouldn't be so sure, why would free state even come up? I have pulled engines apart that had the rings lined up, and they didn't have blow by issues. I've also seen on one occasion were a group of mechanics at a shop call .25" twenty five thousands. They were adjusting the slack on a cruise control chain and the apprentice called them out on it. He was out voted, so he was wrong.