2003 900 MC - Learning from my first seize?

[OutdoorJunkie]

This last weekend my motor seized 2 miles down the trail. I'm wondering what you all think of this, and hopeful to learn how to keep it from happening again. (This is my first...ugh)

What happened:
The sled was warmed up properly in the parking lot (5 minutes or so), then ridden slower (20-30mph) for the first mile then ~45mph the 2nd mile until it just quit on me (like I hit the kill switch).

When this occured, we looked at it and noticed a couple things:
1) the wire connecting to the temperature sensor (near the thermostat) had rotted and broke off at the sensor
2) power valve cable on the PTO side had worn through, exposing the cable
3) friend noticed that he thought the PTO spark plug wire wasn't seated right. When checking this out, we reseated it but it didn't seem to seat on the plug as tightly as I liked.

That said, we were able to re-start it, but it sounded rough. We tried the "pull the wire off the plug trick" on that PTO wire, and it killed the engine, so we figured that wasn't it and so back to the lot I headed. Well, 200 yards back it died again and it was seized.

Diagnosis from the cat dealer is that I need a top end, and that a failure of the o-rings or head gasket were the likely cause (due to finding dark coolant and "very flat rings and/or gasket"). The theory seems to be the exhaust got into the coolant and caused the coolant to fail. So, the mag cylinder needs replated, the PTO cylinder was ok just to be honed.

I gave them the go-ahead to do the work, which is a bummer given they're saying down for 4 weeks, but thought I'd see if we could learn something in the meantime to keep this from happening again:

- Does it make sense about the cause the dealer is thinking?
- For some reason I thought there was a kill feature to keep the engine from overheating, but that probably didn't matter given the broken temp sensor wire.
- Any other suggestions of work that should be done while in there?

There were definately some failures on my end in terms of maintenance (I had seen the darker exhaust for at least this year; I'd also know the PV Cable was wearing through). Any other learning suggestions for me to learn from here?

--Rob

 

[Idcatman1]

Your dealer is probably right. Bad o rings will let compression pressure into the cooling system and will blow the antifreeze out. Low or no antifreeze will let the engine overheat leading to seized pistons. Not having a working temp light leaves you with no notice of the situation. There is no automatic shutdown for overheating on these engines. They leave that up to the operator. On previous rides did you notice steam from under the hood or a sweet odor? That would have been an indicator of antifreeze getting blown out of the system. Bottom line is always check the antifreeze before riding. Power valve cable wouldn't have contributed to what happened, neither would the loose spark plug cap. But both can sure affect the way the engine runs, get them fixed. There has been a lot of talk here about the midrange lean spot on these sleds. I use a different jet needle in the carburetor to richen it up just a bit, the 9DFH02-58 part number 6506-200.

 

[M9M5]

Lean spot

You found the 900 lean spot. You can't just cruise down the trail at half throttle with the 900's. They'll burn down every time. You have to very the throttle position. Open it up let off just don't hold it steady. Your over heat light wouldn't have saved you on this one.

 

[OutdoorJunkie]

Thanks for the response idcatman1 and m9m5...good info.

The main part I'm questioning relating to the coolant being the cause is that I didn't smell a drop of antifreeze at all, ever, on this thing. That said, I did have to add some prior to riding the week before so maybe that's it. I normally check it before every ride, but can't remember for sure on this day.

You're comments on the half-throttle are making me wonder if running in the mid-range was partially the culprit as well, so I might increase that jet needle. Thanks for the tips. I've had this down the trail in a similar fashion a fair amount and no prior issues, but definately not worth chancing another meltdown.

We're getting everything fixed and hope to be back off trail soon...being here on a Saturday suckz, espec. with the new pow in the mountains. Hope you all got some good play time in!
--Rob

 

[snowmanx]

Too bad you didn't look at the pistons and cylinders? $ weeks? you can do a top end rebuild on those things in about 3 hours pretty easy.

First thing I was going to say was running down the trail at 45....mid lean burn down like stated. My wife did the same thing to mine 2 years ago. I let her ride it and she cruised about 45 down the trail for about 3 miles before I could stop her. Took out my cylinders and everything.

My vote in mid range burn down. ALWAYS vary your throttle when cruising down the trail. Good luck and let us know.

 

[Repoman]

I believe the mid-range lean spot is more for the EFI's... I have been running in the 6,000 to 7,000 rpm's alot for extended runs on my '03 1/2 1M carb with not issues. The lean spot is supposed to be 6,500 to 7,000 and then get better above that. The only thing I have different in my carbs is the ZR needles and proper jetting.

 

[snowmanx]

Mine was/is a carbed version.

 

[Flange]

Carbed sleds had the lean spot too. Sorry to hear about your misfortune.

I'd also suggest that you modify your warmup routine to insure you avoid a cold sieze. I had an 03 for a year, then an 04 King Cat until the beginning of last season. I had a temp gauge on it and I can tell you 5 minutes is not nearly enough time to warm these sleds up. The thermostat will not even be open yet, which can be verified by touching the rear exchanger. If its still cold, then the thermostat hasn't opened yet. Rarely could I get the thermostat to open without actually putting a small load on the machine. I would let it warm up for about 10 minutes, then start to move the sled putting minimal load on it. The temp would climb to about 130-134F at which point the thermostat would open, and I'd see the temp drop within a couple of seconds to 90F! I'd stop moving and let the temp climb again until the rear exchanger was nice and warm. I wouldn't want to be putting much load on it when that baby opens!

 

[Rixster]

Yep, good old cat 900 mid lean burn down. Are you stagger jetted ? The mag side of that motor ALWAYS runs hotter then the pto side. I ran at least 1 size bigger main in the mag side then the pto side. I know of guys running 2-3 sizes bigger. But, as stated above, running down the trail 1/4 throttle at 5000-6000 RPM will kill that motor EVERY time. Keep the throttle moving.

 

[finskspets]

OT

A bit O,T, but is it the same midrange lean spot on 800`s

thanks!

 

[M9M5]

ZR

I believe the mid-range lean spot is more for the EFI's... I have been running in the 6,000 to 7,000 rpm's alot for extended runs on my '03 1/2 1M carb with not issues. The lean spot is supposed to be 6,500 to 7,000 and then get better above that. The only thing I have different in my carbs is the ZR needles and proper jetting.

The only difference is ZR needles? That's why you can run at a steady midrange rpm. ZR needles fatten up the mid range because they're designed for low elevation riding.

 

[fishtank]

Was it making any funny smells? I had some overheating issues last season and again this year at times. You can definetly smell the engine getting too hot even when cruising at speeds. I could smell the bad smell before the warning light started to come on at which point I shut it down and found the bloody coolant cap to have come off

Need to go shopping for a new bottle this summer.

 

[OutdoorJunkie]

In my case it didn't make any funny smells at all.

 

[fishtank]

Same sort of "hot metal" smell you get when you overheat your car. Maybe im just used to it, blew the head gasket in my car a year ago, lol.

 

[HANDSOME]

Lean in the mid range and its worse on the 03 because of the timing curve being more advanced than an 04.

 

[HANDSOME]

post up some pics of your piston if you can .

 

[fishtank]

Someone mentioned the mid range lean to be 5000-6000rpm while someone else mentioned it to be 6500-7000rpm.

Does anyone know what it is and how much of a variance and how often are we talking?

I always vary from 5000-7000rpm on the trails but it gets tiring when your on a 20km ride in. I will usually only let it sit at one rpm for maybe max 10-15 seconds.

Is this too long? Is my variance ok? Ive never had any problems, just wondering if I'm overdoing it at all.

 

[Arctic Thunder]

Someone mentioned the mid range lean to be 5000-6000rpm while someone else mentioned it to be 6500-7000rpm.

Does anyone know what it is and how much of a variance and how often are we talking?

I always vary from 5000-7000rpm on the trails but it gets tiring when your on a 20km ride in. I will usually only let it sit at one rpm for maybe max 10-15 seconds.

Is this too long? Is my variance ok? Ive never had any problems, just wondering if I'm overdoing it at all.

Put a set of EGT's on it and find out.

It can depend on temperature, load on the motor, etc.

I have found around 6500 is the worst.

As for blipping the throttle all the time. It is a PITA. The other thing is I think doing this ALL day is really hard on the clutchs and belts. Everytime you hit it, the clutchs are taking a shot. So it is hard on everything when doing this.

Honestly I put the stock pipe and can back on mine and have jetted it fat enough to keep it cool. (Just because I don't ride that sled, the kids do now and I don't want to worry about them holding it at a steady RPM on the trails)

Thunder

 

[900kingkitty]

i got a new in the package set of zr needles if you want them?

 

[knightracer_08]

I had the same problem on my 700 carb on a day with good quality air, mid throttle, melted down, would run on one cyl but not another, I strongly recommend the aem af gauge, for the cost of an engine its cheap insurance.