Topic: Burning oil, or unburnt fuel?

[PeWe]

I can too, several times.
My K6 has been rebuilt several times plus numerous redones

And some extra cylinders with new bores and matching pistons ss spares. Plus heads.....

Easier with frame kit....

[HondaMan]

With just 20k miles on those bores, new rings will then work for a while, maybe 10K miles or so, in my experience. The #1 and #4 bores will be slightly egg-shaped now, which happened while the steel liners were destressing with the heating cycles and the increased airflow around the outside front corners of the cylinder fins. This one fact will prevent new, round rings from seating fully if they are just installed, but it will work well enough for casual riding. For the 100,000 mile future version, bore the cylinders to fit new pistons and rings, using 0.0008" piston clearance.

The cam cahin tunnel wear: I have seen that in engines that received the 'bad' aftermarket tensioner. It came (still does) with an incorrectly clearanced pivot bushing where it mounts at the base of the arm, and this burr (which is on both sides of the 'notch' that is cut to locate the oiler holes upward in the pivot tube) wore the center pivot tube so that the tensioner arm could wiggle left-and-right whenever the cam chain got a little bit loose. This then caused the chain to become very difficult (if not impossible) to properly adjust for tension, so it remained loose after adjustment. This causes teh wide wear on the front cam chain guide that you see in your parts now.

If you have the OEM tensioner arm, even an old, worn, OEM hard one, it actually works better than the new [off brand] version in most cases - heck, mine (OEM) went over 125k miles and still looks usable despite the top end being off 3 times (mostly to repair fin damage in various accidents I had)! The front chain guide can be either the aftermarket or the Honda version, and it will work fine if the tensioner roller and its pivot are correct. This left-right wandering of the tensioner roller (due to the quickly-loosened pivot) makes the chain attack the guide ridge in the center of the aftermarket rollers, causing the damage you are seeing there. The rubber was suspected for a while in the aftermarket tensioners, but I finally tracked the real problem down to the damage of the pivot bushing, caused by poor stamping of the 'notch' in the tensioner's arm at the pivot.

All this said: the cam chain ground up the rubber bits, so they should probably have ended up in the oil sump, under the pump, or in the pump's screen. The chain can't "hold" them inside of itself. The bits that made it back thru the scavenge pump could possibly have found their way into the pressure regulator of the pump, so I'd suggest removing those 2 plugs (regulator and check valve) and cleaning out the tunnels there, in case those bits might still be around. This can cause the oil system to lose pressure to the transmission and/or cause the oil tank to slowly drain thru the check valve from these points not being sealed well.

[The Lone Builder]

If I've followed you correctly Mark, the problem is with the parts I've circled, and its a badly cut hole in the tensioner that causes the problem. So if I'm renewing the tensioner and roller, I need to renew parts numbered 9, 10 & 11 as well as these will now be worn.

I still have the original parts, so I could put those in, but then I should still replace 9, 10 & 11?

So it seems my options are:
      To go the whole hog – rebore and replace pistons and rings, with new cam chain parts – or
      Just hone the cylinders and replace only rings, and reuse the original cam chain parts, keeping the new OE ones for when I do replace the pistons.

[HondaMan]

If I've followed you correctly Mark, the problem is with the parts I've circled, and its a badly cut hole in the tensioner that causes the problem. So if I'm renewing the tensioner and roller, I need to renew parts numbered 9, 10 & 11 as well as these will now be worn.

I still have the original parts, so I could put those in, but then I should still replace 9, 10 & 11?

So it seems my options are:
      To go the whole hog – rebore and replace pistons and rings, with new cam chain parts – or
      Just hone the cylinders and replace only rings, and reuse the original cam chain parts, keeping the new OE ones for when I do replace the pistons.

Yep, it sounds like you've got it: those rubber blocks can shrink ever-so-slightly with higher miles (like 15k+) or if someone accidentally used the ones from the sandcast series engines, which have a smaller outboard "head" on them - this lets the pivot shaft wiggle more if installed in the later engines. That can make for a rattling noise: I didn't realize WHERE those differing rubber inserts were coming from when I've found them in some rebuilt K1 and K2 engines before ( I assumed they were some errant aftermarket parts, but now I've changed my opinion about those). Apparently someone who was in those engines before me used the wrong parts when they replaced them.

The aftermarket tensioner roller's arm also often has a burr where the notch was punched out, making the whole arm not move very easily forward-back: it cab be simply filed so it isn't there anymore. Check whatever tensioner arm you do install to make sure it it flops easily and annoyingly forward and backward, just far enough to get in the way as you try to lower the cylinders on the pistons & rings!

[The Lone Builder]

👍

I've measured the cylinders and there doesn't seem to be any wear:

Would you still recommend a rebore?

[Tracksnblades1]

The bottom of the cylinders measure larger than the top..?

Have I read that right..?

A reverse taper..?

[The Lone Builder]

Demonstrating my ignorance here!  It never really occurred to me that the taper had a direction, but now that you point it out, it's rather obvious!!

That's what the measurements say. I'll redo them.

If confirmed I guess that makes the decision about reboring for me?

[Tracksnblades1]

Demonstrating my ignorance here!  It never really occurred to me that the taper had a direction, but now that you point it out, it's rather obvious!!

That's what the measurements say. I'll redo them.

If confirmed I guess that makes the decision about reboring for me?

Usually the bore ID increases from virtually no wear (original bore diameter) at the bottom of the sleeve where no piston rings travel occurs  to the increased bore wear caused by the rings and piston as they are subjected to the ever increasing pressure near the top of the cylinder, primarily during the compression/combustion …..The taper is usually a slight funnel shape with the big end up…

However the very top of the cylinder, where the top compression ring doesn’t travel on, should measure the same as the very bottom of the cylinder. This top of cylinder small area is sometimes referred to as the ridge. Its usually covered in carbon that needs to be removed before precision measurements can be achieved. Do not measure this part of the cylinder to determine taper… always measure a little below this unused top portion of the cylinder to determine cylinder wear. Sometimes it’s hard to measure below this area without a bore gauge or an instrument designed to..

Some used to use a ridge reamer to remove this area at the too.  So the “ridge” wouldn’t interfere with the new top ring…
But re-rings are another oil thread…most builders would bore if they could feel the difference. If you can catch your fingernail on it then it was obvious what was needed and similarly that’s the only time the ridge reamer would work well.

[scottly]

Demonstrating my ignorance here!  It never really occurred to me that the taper had a direction, but now that you point it out, it's rather obvious!!

That's what the measurements say. I'll redo them.

If confirmed I guess that makes the decision about reboring for me?

The worst case taper is less than .001", well within specs. There is nothing wrong with your cylinders.

[The Lone Builder]

I dropped the sump today and the contents are shown in the pics; some of the bits were metal as can be see from the magnet just visible at the top of the 2nd pic.

The oil pump is clean, but one thing puzzles me; the oil leak valve has a step in it, and not expecting this I didn't notice which way it went in - narrow end first or the other way. More confusing as any pics I've found online don't show a step in the valve. Any thoughts on which way it goes?

[PeWe]

Rubber in the narrow part that goes in first.
Here when I did one pump.

Had to use heat to get it out. Cleaned inside with drive chain cleaner and rubbed the valve clean with used grit 400 paper or simular so it could move by ease inside pump.

Important to check the relief valve too.
So it sit right, can move and correct part outside against/into spring. I think oil pressure will be way too high if flipped wrong.

[The Lone Builder]

I have the relief valve out too.

Both valves look in good state and are within spec, so OK there. I'll consider replacing the rubber too; I have a pump rebuild kit so I'll compare it with a new one and see.