Smack's Piston Peril

Well, not long ago I mused at what would be the next thing to break on my beloved steed. Life was definitely listening, as it didn't take long...

On a road trip, 200km from home, at 6500rpm, I start hearing a rhythmic tick-tick-tick-tick, and out of my peripherals, see white smoke in my rear views, coming out of my pipes. about 3 seconds later, the bike loses power. I pulled the clutch, the engine ran, but holy handgrenade it was rough, so I used the ignition kill switch as I was still doing 80kph, and glided onto a side street.

I checked the obvious, leaks. There were none, anywhere. Next I checked the fuel line, and yes, fuel was flowing when I switched to prime. Fuses all looked good, no other obvious damage. So I waited until the whole thing cooled down, and attempted a start (troubleshooting, I wasn't about to start riding). #2's exhaust manifold stayed dead cold. I swapped 2 and 3's spark plug wire to rule out the coil, and #2 stayed cold.

I had some tools, but nothing that would allow me to pull a spark plug, and I was in the middle of nowhere. So I called a friend with a truck to come rescue me.



It was dark when we got home, so today I got crackin on troubleshooting. Pulled the spark plug and it was drenched in oil... not a good sign. Pulled the other plugs, they were all okay, so I disabled the ignition and hooked my compression tester up to number 2. Didn't even make the needle think of moving... uh oh....

Rotated the crank to get #2 at TDC, peeked through the spark plug hole and confirmed my horror, a chuck of piston was missing. Well, at least I have a project now.



That's probably not gunna buff out....



Gunna find a nice chunk when I drain the oil.



So now I am gunna check the cylinders and get some new pistons, rings, and gaskets to replace stuff. No damage to the cylinder, or head. Though the piston does have some scrape marks on the leading side, like I said, there was no damage to the cylinder.

But now I am trying to figure the cause. Valves are in spec, fuel levels at 2mm, running stock jets, pilots colortuned at 2.5 turns out. Age? Running the wrong plug? I use D8EA's since I don't need the extra 5k of resistance because the boots and dyna's put the numbers perfectly in spec. Would running DR8EA's have made a difference?

 

Ouch, how many miles on your bike?

 

That's too bad, just wonder if it was time for that piston to give it up. Glad that you are getting after it right away. I would guess you have even cooler weather this week then we do here in WI, good to doing indoor projects.

 

How are you using d8ea plugs? Don't xj's use bp7es or in Canada bpr7es or for 85xj700, 750 bpr8es. My mistake you have a 550 d8ea is right plug or for Canadian bike dr8ea cause we use 5k ohm plug caps.
Is there any possibility of that carb being a cause,clogged jet , bad vacuum diaphragm, etc

 

Based on the pictures, it does not look like detonation was the cause. Usually a mixture problem will burn a hole, and that hole is from a fracture. Yamaha used cast pistons, and somtimes a cast piston will have an inclusion that grows into a fracture, and finally a piston failure.

Did you see any balls of aluminum on that sparkplug?

 

Almost too clean a piston top , fuel washing the cylinders of oil and causing severe scuffing on that piston ? What do the other 3 look like?

 

61,370km. Did the engine rebuild at 40,000. It did sit in the PO's yard, uncovered for 15 years though.

I haven't checked the carbs yet. Well, not internally. I did check the fuel levels and they're all still at 2mm.

Nope, just oil on that plug.

You can kind of see what #1 looks like,little bit of carbon on the dome of the piston. The other 3 look the same, though for peace of mind, I'll just replace all 4.

 

I'm looking at the first pic again. Maybe she was running lean, but not for a long time. What I think is that the carb was doing its job, but there was a vacuum leak that showed up while at speed.

 

Definite bummer. Might as well inspect the carbs again, I'm gunna be waiting a while anyways.

 

We've got the ring sets and a piston in stock!

 

You must not have been using synthetic oil because I recently heard these engines can do over 300k without even needing to adjust the valve clearances!

 

Let's all play nice. No need to troll other users, particularly in refrence to discussions from other threads.

 

That had to be like k-moe said, a fracture, it was just time for that piston to give up the game. Hope no other damaged happened and that you can get her back on her feet soon.

 

Thanks for the support Len! First place I checked was your stock, and I already found a set of pistons from a Canadian supplier... my only qualms about sending an order from you is how terrible our exchange rate is at the moment...

Not even going there. Have a nice day.

Thanks! When I started it for troubleshooting it seemed to idle, lumpy it it idled and had just enough juice to get up the ramp into the truck, and then again into my shed. Nothing else sounded wrong. Quick inspection with a boroscope on the inside of the crankcase didn't show anything else crazy going on, but when I drain the oil, I'll also pull the clutch cover to make sure there aren't any chunks where chunks shouldn't be.

 

I know, we're working on that.............

 

Live with it. Its a fact.

 

Please start a thread and provide evidence so we can have a discussion about your claims.
Many XJ owners also use approved synthetic oils and have not experienced your results.

 

Fortunately when you see this sticker in the mail you know your day just got better....



And with that, the pistons are installed. Gaskets should be here before the weekend... I hope....

 

Did you manage to find the broken bits?

 

I only respond in defense of childish remarks and I have no need to start a thread and prove myslef. Originally someone asked how far an engine has lasted withouy any valve adjustment. My answer still stands.
If I had to rebuild an engine with anything under 150 000 km i would be ashamed at how I treated that machine.