Bill Hoddinott - VA (guest) View all posts in this topic  
Sun Aug 05, 2007 8:07 pm
118,172 Miles on '88 250 Ninja - Maintenance Time        

Most readers are aware of my 100K mile road test report that is on the Wall of Shame in this forum. Some may recall my experiment with the replacement '01 engine to use 5w-30 non-synthetic car oil and run it until mis-firing or other symptoms of distress appeared. The '01 engine had 1700 miles when I bought it, and I checked the tappets at that time. It was installed in the bike March 25, 2004 with fresh oil and filter, and the oil has been changed twice a year since then, as has been my practice. Most use is highway riding, 65-75 mph which gives 70+ mpg on 87 gas.

A few days ago at 118, 172 miles, after several miles in traffic flowing at 75, I pulled up to a gas station to fill up. On re-starting, aha, it didn't want to fire up immediately as it always has, hot or cold. When it did fire, it mis-fired a little under load. That was all the clue I needed to know it was maintenance time. I believe what causes this symptom is that the spark plug gaps gradually increase, until they reach a critical dimension. The bike may run fine at 75 mph, with the system voltage around 14 giving a good spark that can jump the widened gap. BUT, when you crank the engine on the starter, the system voltage drops right down to 10 volts or so from the heavy load of the starter, AND, the sparks may not be hot enough to jump the wide gap.

Okay, now the engine has 32,902 miles since new and the plugs have never been touched. No reason to.

Back home, next day put the bike up on the (invaluable) air lift in the shop. Took off fairings, seat and tank and put in a safe place, tank propped up securely so it couldn't flop over and slop gas out. It is better and easier to take the tank off with minimum gas in it, but this time it was full.

Drain coolant, catching it carefully because it 'pees' so hard when you pull the plug. Pull the top cover and the coolant return fitting, remove RH coil and extract top cover out the right side carefully.

Removed oem NGK CR8HSA plugs and sure enough, the original .025" gaps were both right at .040" due to the sparking erosion to both the central electrode and the ground electrode. This was almost certainly the cause of the mis-firing. I could have carried on with the same plugs by just regapping them to .025", but I had a fresh set of NGK C8HSA plugs (these were new in box but may be obsolete now, albeit perfectly good) still left in the previous owners stash of tools and parts he gave me so put these in (after checking the gap was .025" - it was) with a light coat of anti-seize on the threads (available at NAPA and other autoparts stores). It is imperative to use anti-seize on replacement plugs otherwise you are gambling that they won't be permanently stuck/seized the next time you want to remove them.

BTW, the "color" of the old plugs was perfect, the central porcelain nice and clean and dry, but not dead white which might mean running too hot. There was just a slight build-up of deposits on the top of the ground electrode, a good sign which means it too is not running too hot. Evidently the plugs Kaw called out for their engine were running exactly right in the service I was giving it. I seem to recall a horror story on this forum a couple months ago where someone holed their piston at 80 mph, possibly through running non-approved plugs, which again possibly overheated and caused a typical pre-ignition failure classically displayed as a hole through the center of the piston crown. Detonation is another matter that results in piston damage at the edge of the crown, likely trapping the rings and killing the compression, or seizing the piston.

Using the Kaw tool (it might be tough to get anything else in there under the frame and all) I tightened the plugs carefully by hand at first to avoid cross threading and then used a box end wrench carefully on the Kaw tool as they tightened too much for fingers (some carbon and corrosion inevitably gets in the threads in service, and I see no practical way to get it out - I wouldn't want to put a 10mm plug tap down in there even if I could, since it would rain some debris down into the cylinder, maybe even metal chips. This is not necessary) . Tightening the plug down carefully until I felt the plug washer contact the head, when it starts to tighten for real. I found that it took about 3/4 of a turn after this point to get the plug washer fully flattened and sealed, when my calibrated hand told me the plug was fully tightened. So stop.

All right, you may say, what did the tappet clearances look like after 31,202 miles without inspection and running the 5w-30 non-synthetic car oil? Good question and I was waiting to see, myself. Having no metric feeler gauges, I did some higher math and determined that Kaw approves clearance of .003-.005" for intakes and .004-.007 for exhausts. One intake tappet was found to be .002" and the others were .004-.005". I corrected the tight one to .004", but at .002" it certainly was not tight enough to do any harm.

One exhaust tappet was found at .003" and one at .004" so I opened these both to .007". The other two were .005" so I left them.

I found everything immaculately clean and copiously oiled under the top cover, no sludge anywhere. The timing chain was nice and tight on the cam sprockets and there was no perceptible wear in the cam bearings when attempting to move the camshafts up and down. The original '88 engine did have some play in the camshafts at removal with 86, 970 miles, besides the dangerously slack camchain.

I did notice just the slightest witness of wear on the very nosetips of all the cams, but not enough to feel with the fingernail. I assume this is normal and not detrimental. We'll see how it looks next time.

I used Kaw's tappet adjusting tools, they ease what must be a very meticulous job and after disturbing the adjusters, you need to check the tightness of the locknuts two or three times. I check the clearance by turning the nut on the crankshaft end with a 9/16" socket wrench the normal running direction (counterclockwise on the left side) until the nosetip of the camlobe of interest is 180 degrees from the camfollower underneath.

Put everything back together, refilled with fresh 50/50 antifreeze coolant. Engine fired immediately and I continued to top up the coolant as it purged its air, until it was totally purged and full. Rode bike around the block, and all seems well. We'll see how it works on a normal duty cycle of 65 miles on the highway.

Whenever I do this kind of work I am reminded that every piece, part and fastener is important, and every operation has to be done with the greatest care, to get a good result. I spent about six hours on this project, with nearly 60 years wrenching experience, since model airplane days, because I want the utmost reliability, and I don't want to damage anything by hurrying too much. The socket head screws that secure the fairing to the tank, for just one example. You have to be extremely careful to get them started straight and not cross-thread them. After just short of 20 years and over 118K miles, these are still okay.

Novices can learn to do any of this work well if they want to, but even white-haired mechanics like your scribe have to be very meticulous to avoid making mistakes that can lead to trouble. Good luck and have fun.

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