After 17 years, it had to happen sometime ...

[Craig380]

Was out for a good ride this morning, on the way home, wound up the wick to around 90 and .... a little cough from the engine and then wuuurrrgghhh. Left cylinder not firing. Oh dear. Oh deary me. Bugger.

No ominous rattles from the motor, so limped 10 miles home on 2 cylinders. Removed the left plug, it's covered in grey gunmetal deposits. Shining a torch down the plughole reveals a nice new spark-eroded extra port in the piston crown

A timing check showed it hadn't slipped, it was spot on where I always keep it set. Half-full fuel tank so not running onto reserve, and I regularly run it hard with no ill effects. Just one of those things, I suppose.

Not sure I even want to start thinking about a full engine strip and rebuild just yet, but that's what it will need, as there will be molten piston crown in the bearings. Time to start saving the pennies, then.

[Coyote]

I'll bet you knew exactly what happened the moment she went. Gut wrenching feeling. I think I would have said a little more than oh deary me.

[rngdng]

I'd bet you developed an air leak somewhere...maybe base gasket. If the timing's not off, something made you very lean. Sorry it happened.


Lane

[oldjapanesebikes]

Sorry to hear, but as you say it does happen. Definitely one of those 'Oh S**t' moments though. Looking at the bright side, think how many more years you'll get from it once its been made right again !

[Craig380]

thanks guys ... an open question to you, I really should do a full rebuild, right?

The engine was spinning at around 7,000 when it happened, so god only knows where the molten bits of piston crown have gone.

[oldjapanesebikes]

thanks guys ... an open question to you, I really should do a full rebuild, right?

If you've had it for 17 years, then the short answer I think would be 'yes', but that's a tough pill to swallow as it isn't cheap, especially if you have to have someone else do the work.

[tricky1962]

As an alternative approach, how about flushing the crankcase with diesel until nothing "foreign" come out, then running it and see what state's it in.

Worst case, the crank shaft seals have been damaged and you would replace those during a rebuild anyway.

I holed a piston because I cocked up setting the timing. I removed the heads and barrels, flushed the crankcases through with diesel which I filtered with coffee filters. Once the diesel could be filtered with no visible detritus in the coffee filters, I popped the new piston on, cylinders etc and have run it for 2000 miles with no problems.

If you encounter a problem subsequently then you've not lost much cash.

This all assumes you don't require absolute reliability from your bike - if you do then I would agree, full rebuild for safety's sake.

[tz375]

It's time for a new set of crank seals and there is no way to get the detrius out without a full crank strip. Good news is that it should be good for another 17 years or more.

The question is what caused it. It needs to be fixed, so do a leakdown test and see where it's leaking from.

[tricky1962]

IF it needs new crank seals, then that needs to be done first and the leak down second

[ConnerVT]

No harm in doing a leak down test before tearing into it, but whatever the result, it will be inconclusive.

If it fails the leak down, did a seal give up before the piston melted, causing the failure? Or did the debris from the failure damage the seal?

If it passes the leak down, then you still won't have a likely cause for the failure, and the crank should probably be rebuilt anyway, as you don't know what damage that debris has/will cause. A tear down gives an opportunity both to inspect and clean.

Sorry to hear of your loss. But as you said, 17 years, it had to happen sometime.

[Vintageman]

One possibility the top of the piston(s) had been wearing and rotting over time... finally let go when you stressed it a bit more.

So maybe not that much stuff when it did come through. I have had that happen more than once… flush crank area well …have to take engine out unless drain plug or remove SRIS check valve and good to go. Check rod side shake etc. Crank should turn smooth ... no bent rod

Well you will have to take off top end . Then you can pour a little pre mix each side at a time see if it leaks down to see if you need new seals.

Not everyone has cash to do a full rebuild, and you can always do it later. Top end rebuild is quick

So of course you can do a full rebuilt and make her new… been there done that too. Sometimes just want to get it going and many times it proves just fine! You'll no more once you pop the top.

Jet up little next time also if you run her hard for a long time think about one plug step cooler. But, again it something that may have just been happening slowly.

[titan performance]

I have holed 2 pistons on 500s. Both times in the early 80s when I was even poorer than I am now. In both instances I flushed with petrol/2T mix and then fitted a replacement, used, piston. I'm happy to say, no adverse effects at all in either case. One of those bottom ends, has still never been apart, the other was split when the kick start mech broke, but there was zero debris to be seen.

[Craig380]

Thanks everyone -- I'll lift the barrel in the next few days and see what I can see down there.

Luckily I had the one-piece head cut into three individual heads a couple of year back, which makes the investigation job a bit easier ....

[Coyote]

I don't know about the 380, but I imagine it is much like the 550. You can't see anything due to the balancing wheels in the crank.

[Cliff]

Took me 40 years to hole a piston in mine but I did it last summer! First time EVER the bike has been in the back of a pick up! I removed the cylinder and piston, blew out the crankcase with compressed air, replaced the piston/rings, put her back together and drove 1000 miles the next weekend!
Cliff!