OK to run WOT for a long time?

[joetheis]

This is on a 1991 Evinrude 70 2 smoker, has VRO hooked up and working.
This may be a silly question, but it's eating at me...........................
So, I was on the St Lawrence this past weekend. Was glass Friday and Saturday, which is a rare up there, no wind, nothing.....
I got a REAL chance to see what the motor and boat can do.
I usually run @ 4,000- 4,500 RPM with a 4 blade 13X15 prop.
Motor topped out @ 6000, maybe even 6500.
Can you usually run WOT well past 5,000 for a a LONG time without damaging the motor?
I come from a motocross background, so I had 2 speeds, idle and WOT for the entire race, but outboards quirks are still new to me!
Joe

 

[Chinewalker]

6500 is high for that motor. Should be propped to peak around 5800 or so.

As for your question, you're not doing it any favors by extended wide open throttle. I run mine for a minute or two long burst, but not much more than that. I find my cruising speed and stick to it - mostly.

 

[flyingscott]

6000 is the top rpm 6500 is to high for that motor run good a quality oil. I ran mine for 45 min wide open 6000 rpm because that storm was coming fast. I don't do it all the time, but if you have to you can but it will wear faster and your fuel mileage goes in the toilet.

 

[jimmbo]

Those engines were designed to run at WOT. The design life was 1000 - 1200 hrs @WOT. They will last 4 or 5 times that if throttled back by 25%. That was for 2 strokes. Auto engines rarely last 350 - 400 hr at WOT. I'm not going to comment on 4 stroke outboards except I doubt they will last as long as a 2 stroke

 

[joetheis]

I usually do a "Italian Tune up" (WOT for a minute er 2),when I get away from the no wake bouys, just to "clean it out".
I hear guys on both side of the fence.
I spent decades hammering 2 stroke motocross motors and know what a worn out, reed broken, piston melted, bearing fired, cylinder scorn motor looks like, (and most important- what it costs to get it back to life)!
I guess I'll keep it purring at my 4,000- 4,500 rpm and be happy!
Joe

 

[Faztbullet]

It will not hurt it to run WOT as long as its within RPM range,they are designed to run WOT. When I went to the OMC factory in 80"s (Waukegan) was shown a video of a 150 crossflow that had been running in a test tank at WOT for over 2000 gallons of fuel.!!! People would crap if they seen how the V-4 motors was assembled, would you take a HANDFUL of loose rod bearings and use 16 and no worry how many was dropped inside engine??

 

[bob johnson]

I thought about that sunday while I was paddling my Lowe Ultra Roughneck with a blown 115 V4 ocean runner hanging off the back.

Motor served me well for 6 years...I had always read from the guys in the know that those motors loved the high 5,000s and even the low 6,000 rpms...

I have gone through a ton of props but I always tried to get one that would ALLOW me to reach 5800-6000 rpms...even though the book said 5500 was WOT.

I had a new prop on it and it would rev to 6000 even.. and it was like glass sunday and I was in it to the max...but constantly watching the temps, just in case she didn't like that extended rpms!!!..water pressure was 25 psi!!! both heads were 130-135!!..life seems good until I heard a bang and a clunk.... throttled down and it stalled...started it up and it was noisey at first, then seem to quite , I was back in it because I wanted to get on the trailer!! but only at 5000 rpm...but she finally left go with another final bang... and locked up the flywheel... I am sure I through a rod or bent a rod or a rod cap..... now following this thread I think it was just the motors time!...but I cant help but think she would still be running if I left it at 4500 rpm and cruised back to the ramp!! that run at 6000 rpm was about 15 minutes only...but it was the longest I ever had the motor at WOT!

who know how many hours it had on it....its a 1995 model

I always used Johnson synthetic 2 stroke oil....


bob

 

[flyingscott]

Here is the problem about guys in the know telling you to overrev your motor they will never be there to pay when it breaks. Post #6 says it all stay in the factory recomended range and you will be fine they spend millions designing motors those are more than suggestions.

 

[interalian]

It will not hurt it to run WOT as long as its within RPM range,they are designed to run WOT. When I went to the OMC factory in 80"s (Waukegan) was shown a video of a 150 crossflow that had been running in a test tank at WOT for over 2000 gallons of fuel.!!! People would crap if they seen how the V-4 motors was assembled, would you take a HANDFUL of loose rod bearings and use 16 and no worry how many was dropped inside engine??

So you're saying assembly was sloppy and any extra bearings would just "flow through"? I would have expected more precision assembly techniques for something like this, but I guess if you're building them all day long you get sloppy. Isn't it 18 needles?

That said, my dad bought our '90 back in '83 and although it didn't get tons of hours, it spent a lot of its life running WOT. A few years back when my nephew, now 19, was 13 he was allowed to pilot the boat. He called WOT "ludicrous speed" - perhaps prescient of the Tesla car. In the last couple of years WOT RPMs got lower, and last year it would only do about 4400 but still sounded OK. Didn't find anything inside to explain it, althogh compression was a bit low.

 

[bob johnson]

So you're saying assembly was sloppy and any extra bearings would just "flow through"? I would have expected more precision assembly techniques for something like this, but I guess if you're building them all day long you get sloppy. Isn't it 18 needles?

That said, my dad bought our '90 back in '83 and although it didn't get tons of hours, it spent a lot of its life running WOT. A few years back when my nephew, now 19, was 13 he was allowed to pilot the boat. He called WOT "ludicrous speed" - perhaps prescient of the Tesla car. In the last couple of years WOT RPMs got lower, and last year it would only do about 4400 but still sounded OK. Didn't find anything inside to explain it, althogh compression was a bit low.

id bet that maybe the boats foam got waterlogged and the boats weight increases by several hundred lbs and that may be one reason why the rpms dropped.....I am certain that there were years in the 80s that boat builders were using two part foam and absorbed water easily!

I am going to remove and replace all the factory foam in my LOWE this summer just for that reason... the boat weighs about 500 lbs more than it used to!!!!!!!!!



bob

 

[interalian]

id bet that maybe the boats foam got waterlogged and the boats weight increases by several hundred lbs and that may be one reason why the rpms dropped.....I am certain that there were years in the 80s that boat builders were using two part foam and absorbed water easily!

I am going to remove and replace all the factory foam in my LOWE this summer just for that reason... the boat weighs about 500 lbs more than it used to!!!!!!!!!



bob

I've weighed my rig and it's on spec. It's a tin boat and there's no foam under the floor, it's all above the waterline - I replaced the decking a few years back and it's nothing but void underneath.

 

[joetheis]

Well, like, "Which oil is the best threads" , answers are from both sides of the fence...........
Historically, 2 smokers have roller bearings for bearings which can let them spin easier than babbet materal riding on a thin film of oil, (ala 4 smokers).......

I had a ATK 125 off road bike in then 90's. Great bike, the motor was a water cooled Rotax scooter engine.
These motors were built super tough, well over engineered, EXCEPT for the piston pin bearing!
You'd be WOT for a few races, pull the top end off, piston, rings would be perfect, but rod pin would be worn. I go throguht 2 sets of rings, same piston, but 6 sets of rod/rod bearings!
I tried to enlarge the oil hole on the piston, run a bit richer mix, nope.....
The top end would not get enough oil, or it'd burn off from the heat, (at the time I was using the BEST mix oil, (Spectro) they made for bikes).
I guess the CORRECT answer here is..............
You CAN run WOT for as long as the motor can handle it, but for the extra 5? MPH and the CHANCE you'll be running in on your trolling motor, (gas kicker or electric), or worse on the end of a tow line, why do it?
There are ALWAYS going to be time when common sense will take a vay-k and you have to stretch that throttle cable!
Joe