How long should (or could) a 4 stroke motor last? (2023)

Hi Guys,

OK… I’m not trying to scare anyone from buying a 4-tech… and in reality, we don’t have a choice anymore. The EPA has made the simple, light, cheap, high powered 2-stroke a thing of the past. Also, there are a few lakes where 2-stroke PWC have been banned, so 4-strokes are here to stay.

I’m going to try to answer a few questions and comments in the order I read them.

Weaverama said:

So what's a guy to do to get to 400 hours and still have a reliable ski? Oil changes and flushing help but damn, I bought this because of the 4-tech and hate to hear that at 100 hours I am in a "danger zone" and no one would give decent money for one with over 200 hours.

Anyone got any good news?

Yes… flushing will help… and good oil. Since these are high reving engines… I recommend a synthetic oil, and change it at least once a season. Brand is up to you.

In the new world of 4-strokes… the dirt bike industry has gone though the same changes. The new 4-stroke MX bikes (not the old, low RPM air cooled engine) we have all the same problems. The number one thing to do is to check your valve clearance. I have said this many times on this board… but I kind of get brushed off. To make a 4-stroke rev… you have to loose weight in the reciprocating parts. One place is in the valve stems. On our Rotax engines, they are about 5 mm. (that’s thin) and to get them to open and close fast… the springs have to be strong. Eventually, the stem will start to stretch. If you are lucky… you will experience hard starting when this happens. But, unfortunately, with fuel injection, and a good starter, this may never happen. (when you kick start a bike, it’s easy to feel) OK… so, once you have a stem stretch… the next thing that will happen is the valve head will pop off. This happens when the engine is spinning at very high RPM’s, and one of the jugs will eat itself, resulting in a $3k to $5k engine replacement.

If you check your valve clearance every 20 hours or so… you will intercept this problem. When the clearance starts to close up… pop the head off, and replace the valve. That will cost you a head gasket, and a set of valves… and the engine will continue to run for a long time.

dsw222 said:

Maybe you guys can chime in on the life of 2 strokes too. I'd be interested to hear opinions from the vets like Honda.

Two strokes are more expensive to run with the oil use etc, and the engines need top end jobs more often than 4 strokes (correct me if i'm wrong)... but they're not too hard to work on so you can keep them going for not too much money when you run into problems

You’re wrong. (sorry, but you said to tell you) Well… I guess I will say you are only half wrong. (hope that makes us friends againHow long should (or could) a 4 stroke motor last? (1))

Your thoughts are coming from what you see, but you are comparing apples to oranges. OK… the 2-strokes you see are our PWC, and boats… and the 4-strokes you see is your car/truck. (if I’m wrong, tell me) In our PWC… they see full RPM a lot… and 75% of peak almost all the time. In your car… sure, you rev it up once in a while, but most of it’s life… it sits at 15% power. My truck going down the highway at 65 MPH is only spinning 1500 rpm. My ski going 65 mph, is spinning 7000.

From my example above… a 4-stroke dirt bike will require more top-end work than it’s 2 stroke counterpart. (apples to apples)

As you said, a 2 stroke is easy to work on… and WAY cheaper to fix. When I was racing SCORE in SoCal… I would freshen up the top-end of my WR250 race bike, once a season, and would take an hour to do. (a piston and rings, and no gaskets) total cost was $60. To freshen up the top-end of a WR-450 (it’s 4-stroke equi) will cost you $400 to $600 depending if the valve seats need replaced. (because you wore though the hard coat)

SabrToothSqrl said:

Well, if we look at the sheer number of parts and things to go wrong with the 4 stroke, especially the super charged ones... you would think the 2 was the way to go for reliability. No valves, no super charger, no push rods, no oil in the crank case, smaller size, WAY less weight. no electronics....

Exactly. Less parts means less to go wrong, less weight, and a lot cheaper to fix.

SabrToothSqrl said:

I've ridden the newer 4 stroke ones... there nice, and amazing and what not, I just wasn't that impressed, and it wasn't that much fun...

Yep… exactly.

Without a doubt, the new 255 hp supercharged skis are a RIOT, and will accelerate hard enough to put a grin on your face that you won’t be able to wipe off for a long time… but the “Regular” skis, are a little un-impressive. If you take out a 130, or 155 GTX… they are big, heavy, and only get to about 45 mph. (50 on a good day) OK… sure, my old Si will only get to about 48 mph… but it’s small, and only weighs around 350 Lbs. That makes that 48 mph a TOTALLY different ride. (it’s a good time)

TheChad said:

Actually if you figure in the fuel cost and cost of oil changes, the old 2-strokes cost MUCH less to run then the new 4-strokes.

The 2-strokes are much easier and ALOT cheaper to work on/fix.

Yes, on all points. The 2-stroke oil is expensive, but if you look at total operating costs… it’s cheap.

TheChad said:

I'm not sure the 4-strokes have been out/running long enough to get hard evidence on their lifespan when cared for properly, but 100-200 hours doesn't seem like a "Danger Zone" to me (Assuming all proper maintaince is performed).

I believe 90% of the time weather 2-stroke or 4-stroke the reason these engines blow isn't usually from being worn out, but due to lack of maintaince/proper care.

Yes and no.

Yes… they have been out long enough to know. (just not in seadoo) My favorite example for a boat is the GM Iron Duke engine. This engine has been put into EVERYTHING. Cars, trucks, jeeps, boats, generators, street sweepers, large tree chippers, and so-on.

OK… a 2.5L Iron Duke in a typical Jeep Wrangler (XJ/TJ era) will last 150,000 miles without a problem. At 65 mph… that will be about 2300 running hours. Take that same engine, and pop on a Mercury sticker, and put it in a small boat hull, and that’s your popular 120 hp Merc I/O. It’s projected life is around 400 to 600 hours. I’m sure you are asking why. It’s because of what RPM it spends it’s life. But it’s a great example based solely on RPM.

TheChad said:

I believe a properly cared for 4-stroke should last well over 400 hours, I don't have anything to back that up, but I just can't see the manufactures selling $15,000 ski's with an engine that is only expected to last 200 hours, then cost several thousand dollars to replace.

Look at the 4-stroke 4-cylinder motorcycle engines that run 15k RPM, they last long over 400 hours.


I would also like to think that they will last longer… but truth be told… if you are someone who puts on 100 hr’s every season, and ride aggressive… your ski will only last about 4 or 5 years. (if you take care of it)

As far as the bikes… that’s an illusion too. My shop is based on motorcycles, and I run track days. If you are talking a modern 600 cc bike up to 15k RPM’s all the time… you will get one or two seasons out of an engine. Truth be told… an aggressive street rider will only break 11k once in a while. Even on a 600… it will spend most of it’s life between 4000 and 7000 RPM, and at those RPM’s… yes, they will last longer than 400 hr’s.

Weaverama said:

This isn't my thread but I jumped in because it was a request from the OP about the 4-tec. I went with the 4 stroke, and the Seadoo, for any number of reasons but mostly for reliability and "couch-like" comfort on long distance runs. I did my research on Rotax motors and believe the Austrians do it right. 2 strokes are great, I would run nothing else on my boat because my personal setup does not allow ease of oil change and a 4 stroke is just too heavy with lousy hole shot.

So anyway, back to the thread....why is a properly maintained and operated 4-stroke a clicking time bomb after 100 or 200 hours? Don't take this question the wrong way but, do most of you guys beat your own skis to death and assume everyone does it? See my other thread re: Computer Printout. How can someone prove that their ski is not beat to snot????


I wouldn’t quite call it a “Ticking time bomb”, but if you are buying a used ski… you never actually know how it was treated.

Sorry this got so long… but I just wanted to throw out what was on my mind.

A final word….

OK… you guys have seen my water toys, and they are all older 2-strokes. It’s partly because I like projects… but I like the light weight, and ease of maintenance. I am more than able to go out and buy a brand new 4-stroke ski… but, until they ban 2-strokes… I probably won’t own one. I will consider a 4-stroke boat… but they are less likely to be abused.

Just my 2 cents… take it for what it’s worth.


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