Dropped valve! Help! - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 5 (permalink) Old 07-28-2018, 07:26 AM Thread Starter
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Dropped valve! Help!

Hi all. Absolutely puzzled with this... I've just replaced the head gasket on the front cylinder. Engine timed back up correctly, all bolts torqued to correct settings, tested by cranking over a few times by hand, and reinstalled. Engine fired up and runs sweet for 10-15mins. I ride down the road for all of 20 yards and bang!
Engine back out, flywheel turned back to TDC, cams are in the correct place (holes line up) chain doesn't appear to have jumped any teeth... one of the exhaust valves has snapped & punched a hole through the piston, the other exhaust valve has snapped a tappet.. if timing was correct, anyone have any idea how this could have happened? Any advice appreciated. Thanks all
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post #2 of 5 (permalink) Old 07-28-2018, 08:08 AM
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the fact that it ran 10-15 mins would indicate that the timing was probably correct.

gonna say that the failure was just 'one of those things', or as my local nissan service center said after keeping the wife's car for 6 months waiting on a new airbag and upon getting it back finding the brakes where shot, 'a casualty of war'

wow, thats a run on sentence.. to clarify, if anyone wants to really know, wife's car had an airbag related recall, and the dealership gave out free loaners while they held the car (it was unsafe to drive, due to possible unwanted airbag deployment, and I got to drive a 2018 Maxima, which had 18 miles on it when I got the key). once new parts where in (which involved redesigning and manufacturing parts, thus the long time in storage), the brakes where shot.. they where fine when I took it in. the service manager said its a 'casualty of war' and wouldnt do anything about it.. to be honest they had at least 60000 on them and likely due for replacement anyway.

2005 VN750

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post #3 of 5 (permalink) Old 07-28-2018, 10:04 AM
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High revs, keepers falling out of place, metal fatigue in the valve stem or keepers, valve seat worn or out of place, sticking valve contacts piston.

Check the keepers and the valve seat. The connecting rod should be checked for straightness due to the piston damage.

Were the keepers removed during the previous teardown? Did you hear any clicks, taps, clicks, or backfires just before it happened?

Damage to both exhaust valves .... They both stuck? (#1 suspect) Check for varnish build-up on the valve stems. I would guess both valve stems will be bent.

Sometimes a flaw in the metal just finally gives way. Had a new camshaft break into three pieces, just after the minutes long break-in period, restarted the cold engine and KLACK-chunk! It was over. My four year old son was able to reach in and pull the third piece out.

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Last edited by Spockster; 07-28-2018 at 10:32 AM.
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post #4 of 5 (permalink) Old 07-29-2018, 11:32 AM
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Stuff happens!

Rebuilt the engine in my rallycross (original) mini cooper, loaded it onto the trailer and off to the track. Fired her up and backed off the trailer looking forward to the first heat. Wham!!! the differential let go the first time I turned the wheel, damn near ripped off my arms (front wheel drive). Winched it back on the trailer after some very colorful language.

'99 Vulcan "Victoria"
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post #5 of 5 (permalink) Old 07-30-2018, 05:02 AM
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I would concur with others "keepers failure" when fitting these little pieces wriggle them around as you undo the valve spring compression tool slowly to make sure seated firmly, I think you have been unlucky though, CRAP HAPPENS.

Vn 750 A2 1986 rebuilt engine, crank shaft, half casing,shell bearings,con rods,rear cylinder head,oil pump,water pump ,(had ceased bearing rusted up),tie bar upgrade,clutch basket drilled,front cylinder cam chains,toc springs,stator,shaved, rectifier,agm battery,solenoid ,starter motor (used) re-spray ongoing.
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