BRed 2011 - Blowing smoke. Causes? [SOLVED]

[fmjnax]

I have another thread about my newly acquired 2011 MUV700 having shift problems. While playing around with it and doing drive tests, it started blowing smoke. At idle, even after warmup, it kicked out a moderate amount of smoke. Under any sort of throttle, it really billowed out the clouds. Light blue smoke. Oil was replaced with Valvoline ATV 10w40. Oil level was correct (even tried slightly overfilled and slightly underfilled). No engine light or any other indicator of problems (no frothy oil, no oil in the coolant, no visible leaks). I should have checked the oil pressure, but I did not.

During teardown, I noticed that the air filter was missing entirely and there was some dirt in the box. I suspected that some dirt got in the engine and wore the cylinder or rings. I should have checked compression before pulling, but I did not. I have pulled the engine entirely and currently have the cylinder and piston off. Piston actually looks ok to me. A little bit of "grime" around the ring grooves. One small scratch, but doesn't catch a nail and almost can't feel it. No damage to the rings. They were loose, not catching, and easy to remove. No scores in the cylinder walls, but a little bit of buildup at the bottom end. Can't see the machining at all, but no scratches to be felt. I couldn't find my feeler gauges so I didn't check valve clearance but I have some on the way and will check as soon as they arrive. Gaskets were all in-tact and looked good. Spark plug is very black and feels oil-fouled but could be carbon as well. Black transfers when rubbed but doesn't entirely wipe off of the plug.

Cylinder mic's out at 101.88mm so within the service limit of 102.05mm
Piston mic's out at 101.83mm, within the limit of 101.90mm
Cylinder/Piston clearance mic's out at 0.05mm, within the 0.19mm service limit
I'm not a machinist so I don't have mic's able to check taper and round, but as far as I can check I seem to be within service limits.

I plan on replacing the rings for sure and I'll have the cylinder honed since I'm still within specs. I think the piston looks good enough to re-use, but I may go ahead and use a new one anyway since it's already out.

What else could cause it to blow smoke?

 

[HondaTech]

Piston skirt shows dirt ingestion, obviously from the missing air filter. All of those vertical scars in the piston are evidence of debris rubbing it. Also with thr cross hatching not visible, shows the dirt has polished the cylinder walls until the rings cant seal. The oil rings were probably worn out from this as well. I'd bet if you put the rings down in the cylinder the end gap is massive.

If this were at my shop, it wouldn't go back together without a complete crankcase split to clean the entire lower end and to look at the oil pump for damage. Id also replace the cylinder/piston, etc. Also mic the cam lobes for wear and check the lifter buckets for wear.

These engines are picky on clean oil with the trans using it to operate.

 

[fmjnax]

Thanks HondaTech. That's basically the same suggestion you gave me in the other thread. I am working through it to do a complete split to clean the screens and really get a feel for the condition on the internals. Sounds like I suspected correctly with the dirt invasion. Let me put some rings in the cylinder and mic the gap. I'll reply shortly with that. I didn't notice anything obvious on the lobes or lifters, but I'll spec those as well.

 

[fmjnax]

Yeah, ring gap is WAY out of spec. They were so out of spec that I checked them numerous times to make sure. HUGE gaps on all the rings at all positions in the cylinder. 2-3x the service limits!
Top ring = 1.15mm (service limit 0.5mm)
Second ring = 2.64mm (service limit 0.7mm)
Oil ring = 1.74mm & 2.4mm (service limit 0.9mm)

Would you over bore the cylinder to .25 and use the larger piston/ring set or do you think I have enough service limit to hone and use a standard piston/ring set?

 

[HondaTech]

You have less than a millimeter left before the service limit on the cylinder. We'd replace the cylinder, but you could probably go oversize.

 

[906UP]

I'm w @HondaTech on this one, an overbore is possible but you need to find a reputable machine shop. I did a quick search and you can get a new OEM cyl for about $260, at that price why risk it. Go with all new OEM parts and she'll be good as new

 

[fmjnax]

Agreed with you both. Full top end kit and a new jug on the way.

Thanks guys!

 

[Smitty335]

Agreed with you both. Full top end kit and a new jug on the way.

Thanks guys!

You looked into the injection/carb, had to go through that to get to the motor? Really don't know what the Big Red had, but it had dirt from appetite to a hole. Not good.

 

[fmjnax]

You looked into the injection/carb, had to go through that to get to the motor? Really don't know what the Big Red had, but it had dirt from appetite to a hole. Not good.

It's injected. The intake was indeed dirty and the entire assembly will get broken down and a good cleaning. The fuel tank has been drained and cleaned. All lines will be replaced or cleaned. And most importantly, all of the missing air cleaner parts have been ordered.

 

[Smitty335]

It's injected. The intake was indeed dirty and the entire assembly will get broken down and a good cleaning. The fuel tank has been drained and cleaned. All lines will be replaced or cleaned. And most importantly, all of the missing air cleaner parts have been ordered.

Sounds like your doing it right! Great! It's the fastest way!

 

[fmjnax]

Problem solved. Closing out this issue for any future readers that stumble across it. Here's the synopsis of what I did.

- Broke down engine and fully cleaned
- Replaced both oil pickup and strainer screen
- Replaced cylinder, piston, rings, wrist pin, circlips
- De-carbed and cleaned head/valves
- Drained and cleaned fuel tank and lines (probably wasn't necessary based on findings)
- New spark plug and wire
- New Honda GN4 oil and filter
- New air cleaner

She smoked for a while on the first start, maybe 20 minutes tops, but now runs like a champ. Thank you everyone for the input and assistance.