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Author Topic:   Interesting 4-stroke reading
PFSQUAN posted 10-10-2002 09:12 AM ET (US)   Profile for PFSQUAN   Send Email to PFSQUAN  
There is a very interesting thread about 4-stroke outboards in the Boater's Forum on The topic is "4-stroke weak point" and has two additional links.

When I am in Ft. Lauderdale later this month for the boat show, I am going look into this further.

kglinz posted 10-10-2002 10:58 AM ET (US)     Profile for kglinz  Send Email to kglinz     
Any engine running 4 or 5k and stopping instantaneously is going to break something. Sounds like a case for aluminum props.
jimh posted 10-10-2002 01:18 PM ET (US)     Profile for jimh  Send Email to jimh     
This is one of the most obscure references I have ever seen. The thread mentioned refers to another thread. That thread quotes without citation others who mention another thread. This is one of those "a friend of a friend of a friend says his friend said.." stories.
newt posted 10-10-2002 03:42 PM ET (US)     Profile for newt  Send Email to newt     
Jim, I agree. But here it is in less obscure form!

newt posted 10-10-2002 03:45 PM ET (US)     Profile for newt  Send Email to newt     
Try this:

jimh posted 10-10-2002 04:08 PM ET (US)     Profile for jimh  Send Email to jimh     
Still not a shred of first-person data in that thread. It's all "I read somewhere" or "Someone told me."

I read somewhere that all that stuff ain't so. See how easy that was!

Bigshot posted 10-10-2002 04:44 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Quote:I read somewhere that all that stuff ain't so. complain about our grammer? :)

John W posted 10-11-2002 11:11 AM ET (US)     Profile for John W  Send Email to John W     
First hand or not, these are valid questions & interesting threads. I've been thinking if I repower it would be 4 stroke, but the issue of wrecking the powerhead by bending pushrods & valves if you hit something is worth further investigation, particularly for someone like me, a Florida flats fisherman who runs in very skinny water on a regualr basis and has the skeg scratches to show for it.

Even if this is a problem, I'm sure it's only a problem if you hit hard enough to cause significant lower unit damage...but that happens a lot on Florida flats boats, there are mechanics who make a regular income replacing/rebuilding lower units after oyster bar hits, particualrly in the Everglades. Rebuilding a damaged lower unit is a much smaller bill than replacing your entire new 4s motor.

I've been skeptical of the reliability of DFI outboards because of all the early Optimax & Ficht problems, but I may need to reconsider.

dgp posted 10-11-2002 11:35 AM ET (US)     Profile for dgp  Send Email to dgp     
JohnW, all of the current 4 stroke outboards are of the overhead camshaft design so there are not pushrods to contend with. Worst case scenario would be a broken crankshaft but I doubt that the c/s would be the weakest link in the drivetrain.
John W posted 10-11-2002 11:53 AM ET (US)     Profile for John W  Send Email to John W     
dgp, I guess you're right on the pushrods, but at least one poster on those threads contends that OHC engines would be more suceptible to valve damage than pushrod engines. I'm no engine expert so I don't know, but I tend to respect Dunk's opinions as he's been an outboard mechanic for many many years.

In any case the issue is, would impact cause valve timing to be off resulting in valve or powerhead damage on a 4 stroke? For most boaters this wouldn't be a major concern, but for those who boat in shallow and/or rocky areas, it's a valid question.

My uneducated personal opinion is that we probably won't see much of a rebuild market on 4 stroke outboard powerheads like we curently see on 2 strokes due to the complexity of these motors...when they're worn out they'll get replaced, not rebuilt...making valve & powerhead damage a possible ticket to motor replacement. So if the 4 strokes are more suceptible to impact damage I'd like to know about it.

jimh posted 10-12-2002 08:03 AM ET (US)     Profile for jimh  Send Email to jimh     
The topic, "Are 4-stroke engines more susceptible to damage from propeller strikes?" is a fine topic. I'd like to read more about it. I don't have one single problem with the question.

What I have a problem with is directing people to sources of information that are less than authorative.

I prefer to read sources that are direct, first-hand and qualified. If the thread linked above is the definitive source of information on this topic, then this is a topic in need of some reseaarch.

We should openly discuss this topic, but I don't see any need to be limited to or bound by what someone else says they heard from someone else and posted to another forum.

On the corollary issue, "Can 4-stroke engines be economically rebuilt?", I would suspect it depends on the damage. If it is just a blown piston, a rebuild might make sense. If it is a tangle mass of bent cracnkcases, cams, and valves, perhaps not a rebuilt candidate.

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