Topic: Cb350f fresh top end smoking like nuts!

[jag767]

Is it normal on a rebuild to smoke insanely on break in? I mean oil spurting out the exhaust. Only rode it 10 miles, not rough, varying rpm and throttle. I mean, it looks like something is wrong to me but i have not a clue as to what. It's new pistons with a 3mm overbore (rings are correct) new valves, guides, springs, etc, and decked.

Should i ride it more and see if it dies down?

[Pan1cReaper]

It is never normal for oil to be spurting out of the exhaust unfortunately. I would pull the rocker cover and see if one of the valve guide seals is not where its supposed to be, if you can see through the springs. If its not that, theres a chance its your rings not sealing and its got excessive blow by, I would probably start looking at internal stuff. Sucks!

[grcamna2]

They never do that after a rebuild,something inside is not sealing around the combustion chamber or as mentioned a valve guide seal possibly.

[jag767]

I know there's not chance the rings are seated yet, but for actual oil to be on the rear wheel, I figured something had to be wrong. I know the bore was done right because i was a pain about the proper clearance, and verified it afterwards. Rings have a proper gap, and the valves are new and they cut new seats. The exhaust valves do not have seals, just the intake on my head.

[jag767]

They never do that after a rebuild,something inside is not sealing around the combustion chamber or as mentioned a valve guide seal possibly.

This motor has been nothing but heartache. Guess back apart she goes. If its not the intake seals i havent a clue.

[calj737]

Pull your plugs first. See if you can identify a single offending cylinder. You might even run a leakdown test to understand which direction the leak is. Then proceed with better information.

[grcamna2]

I know there's not chance the rings are seated yet, but for actual oil to be on the rear wheel, I figured something had to be wrong. I know the bore was done right because i was a pain about the proper clearance, and verified it afterwards. Rings have a proper gap, and the valves are new and they cut new seats. The exhaust valves do not have seals, just the intake on my head.

I wonder if a piston ring was broken by mistake during assembly ?

[jag767]

Pull your plugs first. See if you can identify a single offending cylinder. You might even run a leakdown test to understand which direction the leak is. Then proceed with better information.

Will start with plugs for sure.

[jag767]

I know there's not chance the rings are seated yet, but for actual oil to be on the rear wheel, I figured something had to be wrong. I know the bore was done right because i was a pain about the proper clearance, and verified it afterwards. Rings have a proper gap, and the valves are new and they cut new seats. The exhaust valves do not have seals, just the intake on my head.

I wonder if a piston ring was broken by mistake during assembly ?

Anything is possible i suppose. They were a pain, but theres nohing to make me think one broke. I have a bunch of spares if thats it.

[Pan1cReaper]

Pull your plugs first. See if you can identify a single offending cylinder. You might even run a leakdown test to understand which direction the leak is. Then proceed with better information.

Good call calj. This way you arent just digging around blindly. I agree with the leakdown, all you need is a compressor for air pressure and a compression tester adapter to go into the spark plug hole to listen for where air is coming from. Without the leak down gauges you wont really have an idea how bad it is but it is pretty obvious if you hear air rushing out of somehwere its not supposed to.

Not to change topics, but you have more pics of the bike?

[jag767]

Pull your plugs first. See if you can identify a single offending cylinder. You might even run a leakdown test to understand which direction the leak is. Then proceed with better information.

Good call calj. This way you arent just digging around blindly. I agree with the leakdown, all you need is a compressor for air pressure and a compression tester adapter to go into the spark plug hole to listen for where air is coming from. Without the leak down gauges you wont really have an idea how bad it is but it is pretty obvious if you hear air rushing out of somehwere its not supposed to.

Not to change topics, but you have more pics of the bike?

Never did a leakdown test. I have the compression tester and compressor, im assuming do this at TDC?

Www.kinesismoto.com click on the 350f build, there's several more photos. Ill try to dig up the link on bikeexif to the bike for you too.

[HondaMan]

Do you know (for sure) what clearances were used on the pistons? And, on the valves, in their guides?

Here's some guidelines for the Baby Four's insides;

Piston clearance for cast pistons: 0.0006" - 0.0010"
Piston clearance for forged pistons: 0.0010" - 0.0016:
Valve guide clearance intakes: 0.0008" - 0.0014"
Valve guide clearance exhaust: 0.0014" - 0.0020"

If the valve guide clearance is more than 0.0022" in this engine (either intake or exhaust), it will spew oil into the cylinders and out the pipes, regardless of valve seals being new, or not.

If the piston clearance is more than 0.0022", it will have a real hard time trying to hold oil inside.

[jag767]

Do you know (for sure) what clearances were used on the pistons? And, on the valves, in their guides?

Here's some guidelines for the Baby Four's insides;

Piston clearance for cast pistons: 0.0006" - 0.0010"
Piston clearance for forged pistons: 0.0010" - 0.0016:
Valve guide clearance intakes: 0.0008" - 0.0014"
Valve guide clearance exhaust: 0.0014" - 0.0020"

If the valve guide clearance is more than 0.0022" in this engine (either intake or exhaust), it will spew oil into the cylinders and out the pipes, regardless of valve seals being new, or not.

If the piston clearance is more than 0.0022", it will have a real hard time trying to hold oil inside.

Mark i was hoping you'd respond! I know for a fact the piston clearance is .0008. When you say valve guide clearance you're referring to valve to guide clearance yes? I have brand new valves and brand new guides all oem honda that do measure to factory spec.

While on the topic let me ask. The exhaust guides do not have seals, which I found odd. Being that oil is coming out so liberally, of course my first thought is to that. Why did honda not use guides with seals in this motor, and could that be causing a problem?

[jag767]

The plus, alas, tell me very little. All 4 are wet and black and stink of burning oil. Numbers 2 and 3 have more oil into the threads, which I attribute to them both being helicoiled. The plugs them selves are equally as bad. The second photo is 1 and 4, the first is 2 and 3. I only put 1 plug for the pairs sonce they look identical.

[scottly]

With continuous smoke and oil spitting out the exhaust I would rule out valve guides, and suspect a problem with the oil rings. A compression and/or leak-down test will show how well the compression rings and valves are sealing, but won't tell if the oil rings are working properly. Are yours one piece or three piece?

[jag767]

With continuous smoke and oil spitting out the exhaust I would rule out valve guides, and suspect a problem with the oil rings. A compression and/or leak-down test will show how well the compression rings and valves are sealing, but won't tell if the oil rings are working properly. Are yours one piece or three piece?

One piece. I should point out at this point there is so much oil in the exhaust itself it will smoke no matter what. Also on a cold startup there is no smoke. I can verify that tomorrow

[HondaMan]

That piston clearance should be good: I finished a CB400F not long ago with the same clearance. The guides: it is not uncommon to run without exhaust seals, more often on racers than not, but even on the CB750 Honda didn't have seals until sometime during the K2. This doesn't cause the sort of oiling you are seeing, though, in any case. It has to be then guides in the +0.006" range of clearance before they start making a mess like that.

Next, I'd suspect something like seals that don't? They can leak into the chambers from the head gasket: on the 750 this often happens when the [in]famous oil galley O-rings don't seal like they are supposed to, or when the head gasket itself fails to seal around those same passages. This pumps the oil into the center 2 cylinders, and the misfire they suffer then causes the new rings in the adjacent cylinders to flutter and pull oil as well.

Uh...I just had a thought: the 350F/400F has little (often green-colored) O-rings that go underneath the guides. Many years ago I helped someone who had installed new (bronze) guides that ended up with a similar oily engine: it turned out that the O-rings were left out, and despite the tight fitting guides in the head, it was pulling oil like mad past the guides. I made a relied in the bottom of )new) bronze guides to fit the O-rings and he installed those: that fixed it. I honestly don't remember if it was the 350F or the 400F, but it was a aby Four, I do remember that much. Does yours have the reliefs under the guides for the O-rings? It is a shallow round-ish notch around the base, pinches the O-ring between that little flange and the head.

[jag767]

That piston clearance should be good: I finished a CB400F not long ago with the same clearance. The guides: it is not uncommon to run without exhaust seals, more often on racers than not, but even on the CB750 Honda didn't have seals until sometime during the K2. This doesn't cause the sort of oiling you are seeing, though, in any case. It has to be then guides in the +0.006" range of clearance before they start making a mess like that.

Next, I'd suspect something like seals that don't? They can leak into the chambers from the head gasket: on the 750 this often happens when the [in]famous oil galley O-rings don't seal like they are supposed to, or when the head gasket itself fails to seal around those same passages. This pumps the oil into the center 2 cylinders, and the misfire they suffer then causes the new rings in the adjacent cylinders to flutter and pull oil as well.

Uh...I just had a thought: the 350F/400F has little (often green-colored) O-rings that go underneath the guides. Many years ago I helped someone who had installed new (bronze) guides that ended up with a similar oily engine: it turned out that the O-rings were left out, and despite the tight fitting guides in the head, it was pulling oil like mad past the guides. I made a relied in the bottom of )new) bronze guides to fit the O-rings and he installed those: that fixed it. I honestly don't remember if it was the 350F or the 400F, but it was a aby Four, I do remember that much. Does yours have the reliefs under the guides for the O-rings? It is a shallow round-ish notch around the base, pinches the O-ring between that little flange and the head.

I know exactly what you are referring to and I will have to check with the machinist. Is there any way to see the oring without removing a guide? I feel like this may be the issue simply because it's the one thing I cannot be certain of. If this was an oversight will seats have to be cut yet again?

[jag767]

Took the head off. Nothing is jumping out at me. I will get to the valves later today

[grcamna2]

Took the head off. Nothing is jumping out at me. I will get to the valves later today

Did you speak with your machinist yet and see if he installed those small o-rings under new oem valve guides ?

[jag767]

Took the head off. Nothing is jumping out at me. I will get to the valves later today

Did you speak with your machinist yet and see if he installed those small o-rings under new oem valve guides ?

Called earlier and the guy who actually did it is at the hospital with his father, will have to wait to find out til tomorrow. My money is on he did not.

A little fyi, the amount of oil on the top of the pistons was insane.

[calj737]

Clean and degrease the head. Fill the intake ports with acetone and see if the seats leak. Or do it inverted. Then submerse the head inverted (just enough to reach the guide seats) and see if fluid bubbles up through the vale seats. You will have your answer pretty quickly.

[scottly]

A little fyi, the amount of oil on the top of the pistons was insane.

Guides don't usually cause massive amounts of oil pumping into the combustion chambers, at least in my experience. I still suspect a piston ring problem. If the second ring was installed up-side down, it would scrape oil off the cylinder upwards, instead of downwards, where it normally drains through the oil ring and the holes in the piston under the oil ring.

[jag767]

A little fyi, the amount of oil on the top of the pistons was insane.

Guides don't usually cause massive amounts of oil pumping into the combustion chambers, at least in my experience. I still suspect a piston ring problem. If the second ring was installed up-side down, it would scrape oil off the cylinder upwards, instead of downwards, where it normally drains through the oil ring and the holes in the piston under the oil ring.

I am completely positive the rings were not installed upside down. Unless all 4 were marked incorrectly from Cruzinimage which I highly doubt. If i remember correctly, The writing faces up, I believe the gray one is first. They are even in the right order in the little package they come in haha.

Didn't have a chance to play with the head, I will tomorrow. I'm going to cast a vote on no orings on the guides. I was absolutely meticulous putting this motor together, literally taking double the time I really needed just to verify everything, and it seems that whatever work is done outside of my control these days (aka someone else who doesn't care whatsoever) becomes my problem 100% of the time. Machinists in this area are abysmal. This is why my new project is with a 2014 cbr500r motor in a 1972 cb450 frame. It's easier to figure that mess out than to find good tradesman around here.

Ok rant over. If anyone wants to see what that looks like, here it is, still in its early stages.

[BomberMann650]

That cbr500 looks like it means business crammed into that little 400 frame.  Hope you have an appropriate length swing arm to keep the front end on the ground!