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Smack's Piston Peril

Discussion in 'XJ Technical Chat' started by PilotSmack, Apr 30, 2017.

  1. PilotSmack

    PilotSmack Active Member

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    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.

    [​IMG]

    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.

    [​IMG]

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

    [​IMG]

    Gunna find a nice chunk when I drain the oil.

    [​IMG]

    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?

    [​IMG]
     
    LeClairerog likes this.
  2. Stumplifter

    Stumplifter Well-Known Member

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    Ouch, how many miles on your bike?
     
  3. Timbox

    Timbox Well-Known Member

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    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.
     
  4. Toomanybikes

    Toomanybikes Well-Known Member

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    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
     
    Last edited: Apr 30, 2017
  5. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    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?
     
  6. Toomanybikes

    Toomanybikes Well-Known Member

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    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?
     
  7. PilotSmack

    PilotSmack Active Member

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    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.
     
    Alan63 likes this.
  8. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    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.
     
  9. PilotSmack

    PilotSmack Active Member

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

    chacal Moderator Moderator Supporting Vendor Premium Member

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    We've got the ring sets and a piston in stock!
     
  11. Paul Howells

    Paul Howells Active Member

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    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!
     
  12. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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

    Timbox Well-Known Member

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    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.
     
  14. PilotSmack

    PilotSmack Active Member

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    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.
     
  15. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    I know, we're working on that............. :)
     
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  16. Craig B

    Craig B Active Member

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    Live with it. Its a fact.
     
  17. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    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.
     
    PilotSmack, Timbox and Stumplifter like this.
  18. PilotSmack

    PilotSmack Active Member

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

    [​IMG]

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

    [​IMG]
     
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  19. a100man

    a100man Well-Known Member

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    Did you manage to find the broken bits?
     
  20. Craig B

    Craig B Active Member

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    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.
     
  21. PilotSmack

    PilotSmack Active Member

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    No big chunks. When I drained the oil I filtered it though a cheesecloth and had a ton of ground up bits of aluminum, and when I pulled the filter and cut the can I had the same ground up powder on the element. The total debris looks to be about the amount that I'm missing.
     
  22. a100man

    a100man Well-Known Member

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    Hmm. Might be worth changing oil and filter again after just 100 miles or so as an extra flush.. don't want that crap finding it's way onto
    bearing surfaces even if it is only aluminium...
     
  23. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    I'm sorry, but your claim of not needing any valve adjustments is beyond extrordanary. It is common to find used bikes (most models of XJ included) that have zero valve lash (shim over bucket) with as little as 25,000 miles on the odometer. Since you are unwilling to provide evidence, your claim cannot be expected to be believed.

    Please refrain from making this a pissing match, as we don't do that here.
     
  24. Craig B

    Craig B Active Member

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    I didnt try to start a pissing match.
    I made a post.
    Juvenile responses turned it into a pissing match.
    I did take your suggestion and opened a thread on the subject of my bike.
    http://www.xjbikes.com/forums/threads/the-marauder-1982-yamaha-750-maxim.113104/
     
  25. PilotSmack

    PilotSmack Active Member

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    Hey guys, sorry for the long time for an update. Work called me in to play with airplanes last week (oh darn hey?) and the gasket kit showed up so I was all kind of busy.

    Everything installed fine. I definitely noticed there was slightly more resistance when I turned the crank after I assembled, but I figured that was due to the new rings and honed cylinders. Compression test okay, put everything else back together. First 10 min test ride went okay, slight oil leak from the valve cover gasket that disappeared before the next ride. I am currently at 350 out of 1000km for the break-in. My goodness though, she runs soooo much smoother now! And even idles better and sounds better, and I'm getting an extra 8mpg. She consumed about 100mL of oil in the first 200, but hasn't consumed any since. And I did an oil/filter change at 150km, no more chunks in the oil or pan.

    I don't wanna get ahead of myself, but I think I got this one under wraps. If anything else changes I'll give you all a shout.
     
  26. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Congrats, sounds like a successful surgery!
     

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