BRed What are the causes of engine smoke and oil consumption?

[fmjnax]

I picked up this BigRed as a project. Completely tore it down, cleaned every part of the engine, replaced what was worn out, and built it back up. New cylinder, piston, and rings. New camshaft. New valve seals. The engine smokes like a freight train; lightly at idle and heavily under any throttle. I'm at a loss and am about to throw in the towel and let the Honda Powersports shop take it from here. First, I want to gather as many possibilities for the smoking and see if there is something I might have missed.

Here's what I have done and currently know:
- Brand new cylinder, piston, and rings. All were "matched"
- New gaskets
- Brand new camshaft
- All new air cleaner parts
- Valve clearances set (though they are probably out again since I have been messing with it)
- Spark plug was new at rebuild and is definitely carbon fouled now (matte black tip), but no carbon buildup in the combustion chamber
- Compression is at 100psi (which is higher than the manual states, but I believe the jug/piston is a plus-size)
- Using genuine Honda GN4 oil
- No oil in coolant and no coolant in oil
- Leakdown seemed to have a leak at the exhaust side so I replace all 4 valve seals (have NOT done another leakdown since the new seals, but will be doing that today)
- Have tried various timings between both extremes
- If I pull the plug and turn the engine over, I get a fuel mist out of the plug hole, but NO oil in the mist (paper-tested)
- Smoke is not blue. It's more of a thick gray, but it's definitely burning oil and coolant level has NOT changed
- It did NOT smoke at all immediately after the rebuild, but started to smoke slowly soon after. First it would smoke at idle and it would clear after running. Over time, it became worse to where it smokes at idle and even worse under throttle.

I'm really thinking that it is the rings. The cylinder still looks brand new (which it is brand new) and I have good compression, though, so that has me questioning it. This is probably beyond my shade-tree mechanic skill, but maybe I'm just missing something simple. Any thoughts?

 

[Admin]

 

[Jerryg]

Try running it without the exhaust to make sure that you don't have motor oil pooled up in it somewhere. Other wise the only thing I can think of is a malfunctioning oil ring.

 

[fmjnax]

Good call Jerry, but I did already do that (forgot to note it). Smoke comes directly out of the exhaust port on the head.

Any thoughts on how an otherwise brand new oil ring would malfunction? I had spaced all the rings properly and ensured proper installation. It seems to be perfectly fine for a while after the rebuild so I don't believe it was due to anything I did. Of course, the answer might be in the ring itself if/when I tear it down again.

 

[fmjnax]

On a slightly different note, is it possible to do a re-ring on these engines without fully pulling the engine from the chassis? That's the part I really don't want to do again.

 

[HBarlow]

Blue smoke and excessive oil consumption always means a damaged piston, worn or cracked piston rings, or worn valve guides or seals in an engine that has not been disassembled.

Your engine has been rebuilt with new parts and your posts sound like you're experienced and knowledgeable.

That set of facts suggests wrong or faulty new parts or a mistake in assembly.

I would take it apart again and inspect the piston, rings, and valves.

Have you done a compression test?

 

[fmjnax]

Thanks for the input Harvey. I appreciate the compliment! I'm not a pro by any means and most of my experience is with 2-stroke boat outboards, but the process is pretty much the same. It is certainly possible I made a mistake during assembly (maybe I put a ring in upside down). I thought I was using quality parts, but there's always the possibility of a faulty ring. The piston and jug still look brand new but will have to see what the rings look like on disassembly.

I suppose it could be worn valve guides. I did mic them and they were within spec, but that's all I did there. The seals are all brand new and are "performance" seals (allegedly upgraded vs OEM).

Yes, compression is good. Actually a bit higher than the manual states, but that may be because I have the overbored jug and plus sized piston. My gauge was tested against a regulated air supply so I know it's accurate.

 

[Jerryg]

Good call Jerry, but I did already do that (forgot to note it). Smoke comes directly out of the exhaust port on the head.

Any thoughts on how an otherwise brand new oil ring would malfunction? I had spaced all the rings properly and ensured proper installation. It seems to be perfectly fine for a while after the rebuild so I don't believe it was due to anything I did. Of course, the answer might be in the ring itself if/when I tear it down again.

If you take it back apart, pay close attention to the inner oil ring, the springy spacer thing. I had one on a GP engine that the little tiny tab end where it connects had one side broken off. But that was a real fluke, never seen anything like that again. So just give a real good inspection of the rings. Remaesure gaps and make sure they were not installed upside down or anything.

 

[Jerryg]

Thanks for the input Harvey. I appreciate the compliment! I'm not a pro by any means and most of my experience is with 2-stroke boat outboards, but the process is pretty much the same. It is certainly possible I made a mistake during assembly (maybe I put a ring in upside down). I thought I was using quality parts, but there's always the possibility of a faulty ring. The piston and jug still look brand new but will have to see what the rings look like on disassembly.

I suppose it could be worn valve guides. I did mic them and they were within spec, but that's all I did there. The seals are all brand new and are "performance" seals (allegedly upgraded vs OEM).

Yes, compression is good. Actually a bit higher than the manual states, but that may be because I have the overbored jug and plus sized piston. My gauge was tested against a regulated air supply so I know it's accurate.

It could be valve guides but usually you can re-ring at least once before you have worn guides. Replacing the guides might be a good idea anyway if you have to go back in. Just make sure you have the right tools to do that. Like the right size valve guide ream and seat cutter tools.

 

[Jerryg]

I'm really thinking that it is the rings. The cylinder still looks brand new (which it is brand new) and I have good compression, though, so that has me questioning it. This is probably beyond my shade-tree mechanic skill, but maybe I'm just missing something simple. Any thoughts?

Any time you put new rings in, you should hone the cylinder and put a nice new cross hatch so the rings will seat properly.

 

[fmjnax]

Thank you again for the input Jerry! Sounds like I really should let Honda Powersports handle this. I don't have the tools to do a head job (nor have I ever done one) and all I have is a flex ball hone for the cylinder. I might tear it down for my own edification and then have the shop build it back up.

I'm glad there wasn't a suggestion for something small and stupid that I missed. You guys have more-or-less confirmed my thought of it being the rings.

Oh, and as for the valve guides, if they were worn would you expect to see oil and/or carbon buildup on the shaft side of the valves/top of the valve heads? When I pulled the head, I specifically checked that to make sure it wasn't my valve seals leaking. All 4 of the valve shafts/heads were clean and no excess oil residue.

 

[Jerryg]

Thank you again for the input Jerry! Sounds like I really should let Honda Powersports handle this. I don't have the tools to do a head job (nor have I ever done one) and all I have is a flex ball hone for the cylinder. I might tear it down for my own edification and then have the shop build it back up.

Flex ball hone should be fine. If it's coarse you can always wrap some 400 wet snadpaper around it and run it up and down the cylinder a few times. I usually do that when I use coarse stone hones.

 

[Doogle]

Just glancing over this thread, my first guess is was it honed properly. Then doing a proper breakin per instructions with the new rings. It sounds like the rings aren't sealing. A couple other thoughts- a bad head gasket seal could allow coolant or oil into the chamber. Valve guides would need to be really bad to allow that much oil past new seals. Never put new pistons, rings, and cylinders on without going through the head. Especially with an unknown project bike.
Did you gap the rings to spec? And while you had the cylinder off, did you check for play from the connecting rod? When you have the motor down that far, check everything you can to prevent having to take apart again. New gaskets = $.

 

[fmjnax]

Thanks for the input Doogle!

Mistake on my part for not checking verifying the cylinder, etc when I received it. I purchased a full top-end kit from Powersports Nation. It is a remanufacture and included the cylinder, piston, rings, wristpin, circlips, and gaskets. They claimed that the cylinder was bored and honed specifically to the piston that I received. They also claimed the ring end gaps were checked for proper sizing prior to shipping. Dummy me took them for their word and didn't double-check so I cannot confirm nor deny. I DID check for play on the connecting rod, though, and that was within tolerance.

When I reassembled, I broke down the head, cleaned it up, and checked specs. Everything was within tolerances. That was the extent of the head work, though (other than the new valve seals and setting the valve clearances). I don't have the tools or knowledge to do the reaming/seating.

I just finished pulling the jug and piston out. Initial glance I didn't see anything major out of whack that would allow that much oil to be burned, but we'll see if anything pops out at me when I really look it over. I'll share pictures to see if ya'll see anything.

As far as head gasket goes, is there a tell-tale way to know if it's bad or not? I've actually never witnessed a bad head gasket so I don't know what I would be looking for. I assumed it would be obvious and the current one looks fine to me, but maybe it is shot and I just don't realize it.

Doogle, you may be on to something. The head has been on-and-off at least a half dozen times since the rebuild and now that I think back, the smoking issue didn't really start until I replaced the camshaft and adjusted the timing. I was having trouble starting up and replaced the cam due to the decompressor on the old one. While that solved my starting issue, I THINK that is also when the smoke issue really started. Maybe I got something in between the layers of the headgasket. Hmmm, more to investigate.

 

[fmjnax]

Here's some pictures.
Cylinder doesn't look terrible to me. There is a surface stain that you can sort of see in the pictures, and some vertical scuffing but nothing that catches a feeler gauge. I couldn't get it to capture on camera, but I can still see a faint outline of the crosshatching. Should be able to hone it all out (as long as it is still within tolerances).
Piston skirts are worn more than I would expect with less than 100 miles on it. Some issues at the top but nothing crazy. Rings look ok.
Are they in perfect condition? Absolute not. However, I'm not seeing anything here that would allow that much oil blow-by. I've seen worse pistons and cylinders in outboard that had absolutely no issues so I'm not totally sold yet. I'm going to start mic'ing everything and comparing to specs in the manual to get a better idea of the condition.

 

[fmjnax]

And specs all checked out fine, within tolerance (other than cylinder ID and piston OD, since those are plus size, but the cylinder-to-piston clearance is within spec). Cylinder is still true and in-round. Cylinder surface is still flat and unwarped. Rings are good. Guides and clearance look good. Wrist pin and connecting rod in spec. Unless I'm missing something, I don't see any indicator that the piston and/or rings are to blame for the abundance of smoke that I am seeing.

 

[Jerryg]

Here's some pictures.
Cylinder doesn't look terrible to me. There is a surface stain that you can sort of see in the pictures, and some vertical scuffing but nothing that catches a feeler gauge. I couldn't get it to capture on camera, but I can still see a faint outline of the crosshatching. Should be able to hone it all out (as long as it is still within tolerances).
Piston skirts are worn more than I would expect with less than 100 miles on it. Some issues at the top but nothing crazy. Rings look ok.
Are they in perfect condition? Absolute not. However, I'm not seeing anything here that would allow that much oil blow-by. I've seen worse pistons and cylinders in outboard that had absolutely no issues so I'm not totally sold yet. I'm going to start mic'ing everything and comparing to specs in the manual to get a better idea of the condition.

View attachment 285666 View attachment 285667 View attachment 285668 View attachment 285669

The piston skirt is a non issue, but measuring the cylinder is a good idea. Do you have a telescopic guage and micrometer?

 

[Jerryg]

Did you check the piston ring end gap?

 

[fmjnax]

Yes, sir, I checked piston ring end gap by inserting each ring into the bottom of the cylinder squarely and measuring the gap. All 4 rings (mic'd both of the oil seal rails) match the service limits on the dot (so I guess Powersports Nation filed them down to the EXACT service limit, which I'm not super happy about; would have liked at least a little more service room).
*EDIT* Actually, top ring did have some service room. It measure at 0.48 mm and the service limit is 0.5. The others measured spot on at the service limit

I measured cylinder round/taper using my telescopic mic in 12 places (4 directions at top, 4 directions at center, 4 directions at bottom). I'm still not super proficient with the tele's, but my results were close enough to be comfortable saying the jug is within spec.

 

[fmjnax]

Guys, I am an idiot!

I somehow mic'd the old set of rings. Must have grabbed the old piston off the bench. It looks like I do, in fact, have bad rings. First ring is fine. Second ring measures 1.42mm (which is TWICE the service limit). One of the oil rails is fine but the other measures at 2.45mm (which is nearly TRIPLE the service limit)! I've reached out to Powersports Nation to make sure those are not the intended gaps since it's an overbored cylinder, but I can't see how that would possibly be correct.

I don't see any damage or abnormal wear on the rings so not sure how they gapped out that far, but with that much gap I can certainly see how I would be guzzling oil and smoking like a freight train. Looks like I'll be re-ringing and I'll also get a new gasket set and take the head in to the shop to have them rebuild it for good measure.

 

[Doogle]

Could the rings be installed upside down. If they have bevels on them, they must go as per instructions.
Sorry it is disassembled already. I was going to suggest a leak down test. If you aren't familiar with them, compressed air is applied to the spark plug hole with the piston at top dead center. A gauge measures the leakage to see if it is at acceptable limits. And while you have the pressure on the cylinder, you may hear/see where you have abnormal leakage. Bad head gasket may have bubbles into coolant overflow or oil tank. Hissing sound out the intake or exhaust with leaking valves. Air blowing out any vent line. You get the idea.

That piston looks like it has wear on it for 100 miles. It's still in spec? During break-in did you ride short distances then stop and allow it to cool down. At initial start with new stuff there is a lot of friction. Pistons heat up and expand-possibly enough to not allow oil between piston and cylinder.