Is my P220g knocking or am I imagining it?

[Justinc 8]

 

Took a short video of the wheel horse yesterday. Been sitting in the garage for about 3 weeks not started (grass stopped growing) but I needed to move it around so I figured i'd let it warm up and run for a little bit. Heard what I think may be a knocking sound, something I dont remeber hearing before. Tractor has approximately 963 hours on it, never rebuilt and I highly doubt its even been decarboned or had the valves adjusted. When throttled up it doesnt change its tone but its more pronounced when you dethrottle. After uploading the vid I noticed you can barely hear what i'm talking about until I dethrottle it. Drove it around, threw the blades on to chop some leafs and I didnt notice anything out of the ordinary.

 

Any thoughts?

 

No smoke, no miss, no backfire and it dosent seem like there is a power loss of any kind. Am I just being a worry wart?

 

Thanks in advance.

 

edit. just watched the video again and what I hear in person is almost non-existent in the video.... I'll try to take a better one this evening

Edited November 4, 2013 by Justinc

[DoctorHfuhruhurr 132]

Hmm, hard to say through the video but I don't hear anything obvious. I would check the easy stuff first like the spark plug and check the oil for filings with a magnet.  Maybe try to rotate the engine manually while the spark plug is out to see if you feel/hear anything binding.   I'm sure others with lots more experience will comment shortly. 

[MalMac 1,328]

Sounds like you have a little something there. I am no expert on the Onans. Mine sounds similar but I tracked it down to a loose baffle in the muffler. Sure someone will chime in here that knows Onans.

[MaineDad 85]

Sounds like a valve tick to me

[Justinc 8]

As in time for adjustment, MaineDad?

 

I guess I've been needing something to do now that its colder out.

[Justinc 8]

Well guys i probably bit off more than i can chew, i tore her down tonight, figured i might as well decarbon it while im there. I just hope i can remember where all the little bolts and screws go. Call me crazy but i think someone has been in there before, almost every bolt was hardly tight. Vavle seats seemed to look alright. Ill grab some pics in the morning.

[dbartlett1958 96]

Justinc,

 

Better that the bolts were a bit loose, than stripped or broken!  Never-Seize and Loc-Tite are your friends!

Edited November 5, 2013 by dbartlett1958

[JackC 616]

It is overdue for a de-carbon and valve check and adjustment.  A compression test might be worth doing and may provide some information on the situation.  You could also check to see if both cylinders are running at close to the same temperature with a digital infrared thermometer or temperature probe.

[JackC 616]

Be careful putting it back together.   The block is aluminum and it is easy to strip threads.

[Justinc 8]

Well here's the business ends.

Front Cylinder

 

Rear Cylinder

 

Rear valves

 

Front Head

 

Rear Head

 

Didnt break open the valve covers yet, gonna decarbon everything nice and clean then i'll see where the valves are. Looks like I may get another 963 hrs from the old girl. The bores looked clean, no scouring or marks and the valve seat looked tight. No signs of rear cylinder overheating either, that I could see anyways. I think i'm going to chop off the bottom of the rear cylinder shroud so it wont collect grass and dirt, just fall out. Should stay nice and cool afterwards.

[MalMac 1,328]

Be careful on modifying engines shrouds. They help direct the flow of air for cooling purposes. Thats why it's important to keep them clean. Removing them will allow the air flow to be directed in the wrong direction and not past the fins as intended.

[WH nut 553]

Don't cut the shrouds, they are designed the way they are for maximum cooling

[Justinc 8]

Thanks for the advice, I guess I didn't think about that. No cutting of the shrouds will be done.

 

What should I do with the valves, if anything? I really dont feel like buying a spring compressors and messing with them, would I be safe to just decarbon the face of the valve and just go about re-installing everything or should I go deeper? I honestly didnt plan to go this far but figured what the heck.

[posifour11 723]

I'd say do it while you're in there. My compressor was less than thirty bucks. You already have it apart, it may prevent future issues. Buy once, cry once.

[Justinc 8]

Got my de-carbon gasket kit coming from onanparts.com, hopefully it'll be here by the weekend so I can get her back up and running. Borrowing a spring compressor tonight so I can do the job the right way.

[dbartlett1958 96]

Great Photos!  The plug in the rear head looks a bit more fouled than the front one. Could just be the angle of the shot, but something to consider.

[Justinc 8]

I'm pretty green when it comes to tearing down an engine so please disregard my lack of knowledge. I got the valve spring compressor and plan to remove them tonight, however, aside from having them ground or lapped, what else should I be replacing when i'm in there? Seals, guides, tappets? Or can i just get away with a good lapping and re-install? I guess my question probably depends on whats out of spec, but lets assume everythign is within spec, just remove valve, lapp and re-install without replacing anything else?

 

Thanks for all the help and advice so far.

[sorekiwi 761]

Do you have a copy of the service manual? 

 

What I would do is remove the valves, clean them up on a wire wheel and look for any obvious signs of burning.  Check for excessive slop in the valve guides.  If everything looks ok a light lapping with fine paste.  I think there are just valve stem seals on the inlet valves, replace them.

 

Clean as much carbon as you can out of the ports and combustion chamber.  Try hard not to let all that loose carbon get into the bores and around the rings.  I never touch the carbon on the top of the piston (unless its there in big chunks), but that's just me - there is always debate about whether you should disturb that.  I would also check that the cylinder heads are flat, and if need be lap them on some wet and dry paper on a piece of glass.

[Fordiesel69 214]

You can clean the carbon from the piston top as long as you put a layer of grease around the gap.  Put piston to TDC.  The grease will now be jammed into the ring area.  When done move the piston down in 1/2" increments to expose the greast / carbon particles.  Wipe them away and keep repeating until no more grease comes off the cylinder.  There you have it, a protetive layer of grease keeping the carbon from finding its way into the rings.  Upon startup this grease will just burn off harmlessly. 

[ARK 9]

Just for YI, carbon, coke will build up and change the compression ratio thus the over all compression will rise.  Also as you have noticed this carbon covering affect is everywhere within the combustion chamber.  Clean out the carbon-yes, examine the valves-yes, the seats, angles and any carbon build up.

 

Don't want to get a spring compressor then with a brass pick, brass tooth brush and a set of feeler gauges rotate the engine by hand watch the valves lift off their seats, stop, with a bright light examine the seat angles and reflect light off them, may have to splash Seafoam or carb cleaner to get remnants of carbon off if brushing doesn't work.  Check the springs for breaks, cracks, and marks., 

 

De-coking is about 500 hrs but I simply remove the spark plug just before an oil change and pour Seafoam into the cylinder, let sit for a few days, examine if the Seafoam leaked into the oil sump, check the oil level, crank the engine with plug out to remove any Seafoam, then gap and insert plug, start and idle 'till warm, then dump the oil.

 

The exhaust will be black smoky then clear, the Seafoam in the oil will clear oil passages.

 

New oil, check torque of head gasket and good till next year.

 

There really is no substitute for actually doing the PM, but there are times we just want a short cut.

 

The head bolts will loosen when compression rises, re-torque in sequence and check 6 months later.

-

[Justinc 8]

Thanks for all the advice guys.

 

Valve to tappet clearances were WAY out of spec, long overdue. The carbon on the heads wouldn't come off with simply a scotch brite pad and brake parts cleaner, so I got the dremel out and found a few mini waffer pads and very carefully sanded the carbon off, made them look brand new. Also checked the gasket surface on the head for level/smoothness and all was good there. Moved to the piston, nice layer of grease around the bores while at bottom center, put back to top and took a utility knife blade and carefully scrapped all the carbon from the pistons, the blade worked really well for this. Little polish with the scotch brite afterwards then moved to valves, no grooves, burn marks so I cleaned them up and slapped it all back together and now it starts much easier than it did and purs like a kitten. Ran it wide open Saturday for 2.5 hrs straight chopping leafs, never skipped a beat, changed the oil before hand of course and added a little marvel mystery oil in the gas and oil. Seems to be a little easier on fuel too. The only thing i hate about the tractor is the constant clogging of the flywheel screen but there's nothing you can do about it. Hopefully She has another 1000 hrs in her.

 

Now to the steering slop fix.

 

 

[Fordiesel69 214]

Did the slight knocking go away?

[Justinc 8]

It's weird, it was still there at first but after I changed the oil and ran it for a few hrs I didn't hear it again. One thing I noticed was before I changed the oil, the level was kind of overfilled. Don't know how that happened, I rarely have to add any oil but I could have just went a little too heavy the last time. Not sure if that had anything to do with it or not, however, a friend of mine overfilled his newer 4 stroke dirt bike once and blew the sight glass out and smoked the motor.....

[JackC 616]

"Valve to tappet clearances were WAY out of spec, long overdue. "  You may have avoided having the engine destroy itself.  The de-carbon and valve maintenance is important for the longevity of the engine.

 

"The only thing i hate about the tractor is the constant clogging of the flywheel screen but there's nothing you can do about it."  I use a baffle under the motor and above the deck to keep the grass that flies out from under the front of the deck from getting sucked up into the flywheel screen.

 

"One thing I noticed was before I changed the oil, the level was kind of overfilled. Don't know how that happened,"  Hard starting could cause excess un-burned fuel to enter the cylinders and leak into the crankcase raising the level of the oil.

 

Good to hear the engine starts and runs better and the noise is gone.  There is the proof of the value of the maintenance procedure.

[MaineDad 85]

Well done!