[KelPas]

Did the top end of a customers(neighbor) 08 Honda Rancher 420 last summer. He said it worked fine for 2 months of steady driving by his son and then one day it started smoking pretty good and using oil. He drove it for the rest of the summer and fall. Took it out this spring and it's still burning/using oil so he brought it to me to check it out.

We thought maybe the valve seals took a crap but when I removed the head and valves the seals look fine and no oil on top of the valves. Oil breather system is clean and working.

Combustion chamber and top of piston is clean. Rotated the engine to BDC to check the cyl walls and the cyl is glazed and no cross hatch visible.

Now this engine was rebuilt properly and I have done probably a hundred. I take the cyl to an engine machine shop and they measure it and do a rough bore and then tell me what size of oversize piston and rings I need to order. When they are in I bring them to the machine shop and they do a final bore and hone after measuring the new piston.

I install the rings according to the shop manual after measuring ring end gaps and clearances.

Used Honda oil and the owner broke it in properly by warming it up and driving it somewhat hard and no babying it. full throttle but not reving to high then off the throttle and repeat several times to seat the rings. After 5 hours he changed the oil and the bike ran fine for 2 months and did not burn or use oil in that time then just suddenly started burning.

He's not hard on his stuff and if I messed up a ring or something it should have done this right away and not 2 months down the road. I've never had this happen before as I always use OEM pistons/rings/gaskets and not aftermarket parts. Engine had never overheated as far as I know. Picture doesn't really show how shiny it is but does show no cross hatching. Wierd thing is he brought this to me last summer for the same thing- burning/using oil and now it's doing it again

 

[fishfiles]

...my thoughts , the connecting rod has slack , the piston is wobbling and the bore is egg shaped ------ or you machinist did a bunk job ........ try G+H next time around , hard to beat them price wise and work wise

 

[wheeler]

I wanna know why the piston is so clean? I've never seen one that clean with the time frame u mention.... & yes the cross hatching isn't visible.

 

[Jeepwm69]

420 cranks don't hold up well at all. I'm with Fish on the bad crank/rod. ANY play at all in the wrist pin to small hole on the end of the rod? ANY up/down play in the rod at all?

 

[retro]

The piston crown looks like its been water blasted clean. I see the cylinder wall shows water scuff/burnished smooth evidence too. I imagine the combustion chamber looks the same...? water implosion carbon removal... very efficient. The piston ring will tell a more complete story if thats the case.

My guess is the kid has been back in that same water hole/creek that trashed the motor the 1st time. The rod might be bent or hammered at the top by now, so I'd replace that before fixing the topend. If the motor was sunk its gotta be yanked and split for cleaning and the crank rebuilt anyway...

 

[SlammedRanger]

My first thought was exactly what retro said. The grit in the water it sucked in sand blasted the piston top clean. No gas combustion is ever that clean. Thats like nitro engine clean. The same grit removed the crosshatching on the cylinder walls. You would have a hard time convincing me otherwise. My .02

 

[retro]

On liquid cooled motors the first thing to check for anytime you find the piston/chamber cleaned by imploding water droplets is a coolant leak. That could be from bad/warped gasket surface or blown gasket, a cracked casting, a porous (defective cast) casting etc. Whatever it was allowing moisture into the chamber looks like it was slow 'n steady... classic signs of a crack or porous leak somewhere.

Check the top piston ring for extremely sharpened upper & lower edges (sharp enough to cut ya like a new razor blade) and inspect the lower surface of that top ring land for evidence of hammering... the land will be sharp around its edge (chamfer hammered away) and in extreme cases that outer land edge might be rolled out slightly. The lower surface of the ring will look hammered and work-stressed with an uneven surface matching the hammered ring land. Sometimes the upper ring land surface will have a gazillion tiny pits (look like it was media blasted, like the top of the piston looks, only finer) caused by imploding water molecules. That ring land clearance will be very sloppy and way out of spec, of course, and the 2nd ring land will show signs of deterioration along its top edge... likely becoming sharp, but still having a more normal looking bottom edge.

Break-in/seating procedure of new iron or iron/moly rings & bores should be RPM limited to a max piston velocity of 1500 feet per second during the first hour of operation, with continually varying/alternating pressure loading & unloading of the rings. Unless a new flat-tappet cam & lifters were installed at the same time as the fresh bore, brief shutdown/cooldown periods of a couple minutes or less are advised during the first 15-20 minutes of life. Don't allow the motor to idle for long, or at all if possible in either case to keep the oiling supply high. Beyond thar' be evil 'n destructive dragons...

 

[fishfiles]

I find it hard to believe that a piston that is that clean is burning oil , did you clean it up before you took that picture ? ----- another thing I noticed is the mark at the top of the bore , it is kind of wider than I seem to being use to , is the piston coming all the way up to the top of the deck , if there is a bend in the rod , it won't come all the way up and make the mark wider

 

[Rocketman5144]

First thing I thought when I saw the picture is man that piston is clean.
I'm with the others its been getting water in it some how. Please let us know what you figure out.

 

[mrbb]

I think the OP went MIA on us here! LOL

 

[shadetree]

bad rod, and that motor has seen another drink of lake water..lol.

 

[ATC4ever]

Not using synthetic oil are ya?