Yamaha F80-F100 cylinder #4 connecting rod breakage: known issue?

dandreye

Petty Officer 2nd Class
Joined
Oct 19, 2007
Messages
141
Hi All,

Is it a known issue where Yamaha F80-F100 series outboards get their cylinder #4's connecting rod broken, damaging the crankcase? If so where can I find tech bulletin and/or any other docs with further details incl the root cause? Been reading a thread about it on a different forum and trying to help. Most of those who report it claim they were cruising at ~5000rpm when it happened, and that it's more likely to happen with low-hour engines (~200-300 hours). Some claim Yamaha replaces damaged blocks in Europe (during warranty I suppose), making me think it's a known defect indeed.

The same issue is also reported for Mercury 90hp 4-strokes (same block).

Apologies in case of any mistakes or inconsistencies as I am a happy user of a 2-stroke Merc 90hp myself and have never owned any of the above. Tried searching before asking but nothing came up, probably 'cos I'm not using the right terminology to describe the symptom.


Many thanks in advance!
 
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99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
could it be water entrusion up the exhaust when backing down or a quick stop of motor when a wave comes in from the back due to motor sitting low?
 

dandreye

Petty Officer 2nd Class
Joined
Oct 19, 2007
Messages
141
99yam40:

Implying subsequent hydraulic impact? That's one of several possible "user caused" reasons voiced early in that thread. The owner claims there were no preceding events like that though: basically that it occured all of a sudden as he was cruising normally at ~5000rpm. Another forum member reported exactly the same with his own one a few years earlier. If it were caused by water entering through the exhaust I'd expect it to happen pretty soon after if not immediately... besides that, I'd expect similar issues reported now and then with all sorts of outboard makes and models while this seems to be reported specifically for Yamaha 4-strokes. I just thought perhaps it's a known design issue of some kind, e.g. like the one where Yamaha 350hp crank is exposed to high risk of snapping if the flywheel is not replaced every couple of hundred hours (!), which Yamaha reportedly also does for free:
http://www.thehulltruth.com/boating-...ankshafts.html
 

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