4-stroke engine lifespan.

[Chris142]

Whats the average life of a 4-stroke single cylinder quad engine?

Mines a kawasaki Mojave 250. It is water cooled.

When it was 6mo3days old (3days out of warranty)I had to bore it and put a new oversize piston in it. It ran great, didn't use oil untill about 6 months ago.

It slowly began to consume oil. Now it's at the point where I need to rebuild it again as the oil consumption is getting out of hand.

It has a box between the airfilter and carb that is where the crankcase vents into. It's filling this box up with oil. I assume that the blowby is bringing the oil into this box.

The quad is very low geared, 5th gear is an underdrive! So the engine is always screaming.

I do ride it alot and would not be suprized if it had somewhere near 20K miles on it.

 

[JohnBrowning]

Well I know people that have three wheelers and quads from the 1980 and early 1990's that are origanal. The carb's have been rebuilt more then once but the engines have not been touched! We have never been gentel with them either. Some of them all of the plastic pieces are broken and the racks look really bad etc...

It is all about maintence. If you ride them hard you have to step up maintence. I would say that you got a lemon though. THe only time I have heard of anyone wearing one out like yours is with a lot of raceing on it and either a turbo charger or NO2.

 

[Chris142]

I maintain it very well. It lived on Motul syn oil or Mobile-1 for most of it's life. Changed every 250 miles at the most untill the oil consumption got out of hand. I have 2 oiled foam airfilters that I swap out to keep them clean.

I don't really care for the airfilter setup. It's not your normal round filter thats held on with a hose clamp. It's a flat one that fits in a box and you must seal the sides with grease. I always made sure that it was well sealed.

I hope I can just hone the cyl and slap new rings on it.

Currantly running SAE60 oil!

 

[Chris142]

quote:

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Originally posted by JohnBrowning:
Well I know people that have three wheelers and quads from the 1980 and early 1990's that are origanal.

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I think I ride more than 90% of the bikes out there. "Most" people might ride in their back yard or the lot next door ocasionally and go to the sand dunes once a year. Prolly less than 50 miles a year?

For me A short ride is 50 miles and I may do a couple a week.

I ride to a restaurant on Saturdays for lunch. It's 38 miles each way if I just go there and back.

Went 97 miles yesterday

 

[Chris142]

UPDATE: I tore the top end down.

Looks great except for quite a bit of carbon buildup I assume from the oil that it's been drinking.

The gap specs for the rings are:

top and 2nd ring: .008-.014
Oil ring: .008-.028

My specs are .009 for the compression rings and .024 for the oil ring.

But the oil ring seems to have lost it's tension. It will actully fall down the cyl!

What causes that?

Also my intake camshaft is flat. I can't imagine that the valves were opening much! I've read on atv forums that this is a common problem with these engines and was hopeing that the synthetic oil would prevent it.

The cyl looks great. I can still see the hone marks and it has no ridge. No carbon buildup in the piston ring lands either.

Gonna hone it, put rings, a cam and follower in it and hope for the best.

 

[Hirev]

Have you considered the possibility valve guides might be shot? Has it been overheated before?

 

[Chris142]

quote:

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Originally posted by Hirev:
Have you considered the possibility valve guides might be shot? Has it been overheated before?

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It doesn't have a temp guage but it's never boiled over.

How would valve guides affect piston ring blowby?

I think the main problem is the loss of tension in the oil ring.

 

[Hirev]

When a intake lobe goes flat it leans out the fuel mixture. This in turn drive combustion temperatures much higher than normal. All the rings take to much heat and they lose much of there tension, creating blow by.

But the valves and valve guides also take to much heat. Not saying they are bad but you might want to check for excessive wear. Cause they will effect oil consumption.

 

[Chris142]

Oh ok. That makes sense.

 

[c_rossman]

I would look at the air filter setup, Make sure you arent sucking in any dirt anywhere. The mojave engine is very good. Maybe you could put a bigger sprocket on the front to keep the RPMS down. I have or had a 2000 Blaster two stroke still on the factory bore. A four stroke should last alot longer.

 

[Cujet]

If you search, you may still be able to find a nice performance camshaft for that engine. That will help out a bunch. Those engines respond very well to flow enhancements such as cams, porting and a good valve job. The last 250 mojave I built was a real powerhouse.

Also, those engines are known for low tension problems in the ring pack. That is due to (as the other post mentioned) high heat. There are a few things you can do (in addition to fixing the camshaft) to reduce the piston/ring heat issues. First is to use a low restriction exhaust system. I know that may seem odd, but it does solve problems. The second thing is to make sure the jetting is correct. Also take a good look at the cooling system.


Chris

 

[Chris142]

I just put it back together tonight. I honed the cyl and installed new kawasaki rings.

I also replaced the cam and rocker with new stock parts.

I removed the stock airfilter disaster and put a clamp on filter on the back of the carb. The crankcase breather is a piece of hose with a Ford crankcase vent filter!

I definatly need to play with the jetting, the quad has a supertrapp pipe. Any ideas on jetting? It has lots of bottom end power and is very responsive but has no top end.

Too lean now?

 

[Hirev]

quote:

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Too lean now?

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I would bet money that it is way too lean. Stock ATVs in general are really restricted on the intake and exhaust side. Unrestricting (opening) them up can really lean them out big time. The jetting should be richened up before you even start it up. You want to start rich and work you way down. Very lean conditions will kill a motor very fast Especially on the main jet.

 

[Cujet]

Yup, too lean is likely the problem. Get yourself some larger jets, and play with them. In a worst case, get some number drill bits 1-60 and drill the jet slightly larger, 1 drill size lower number and see what happens. Sometimes when carbs do not have a readily available selection of jets I do this. I even have soldered up jets to reduce the size.

Chris

 

[Seth_TJ]

Kawi mule at work has 4,000 hours on it

 

[tom slick]

quote:

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I definatly need to play with the jetting, the quad has a supertrapp pipe. Any ideas on jetting? It has lots of bottom end power and is very responsive but has no top end.

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sounds like the main jet is too small. will it rev to the redline if you try or does it sputter or miss?

 

[Chris142]

I raised the needle with some small washers. It screams now!