SRX burn down with pics

tnc110

tnc110

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01 trail ported srx, clutched, jet hot coated oem pipes and bender can. Was on a trip to the UP. It was cold...-10f in morning, +5/+10 when it went down. I started off the day with a tank of 93 non ethanol. Rode 50 miles and topped off with 91 octane non ethanol. About 60-70 miles later she went down. It was on a long straight grade. I was off and on the throttle quite a bit as I was trying to notemy shift rpms. It started off revving up to 8800, maybe even 8900. I let her go up to 90 mph a few times. Then I noticed it was only revving to 8400. Then it developed a bog. Stopped and changed the plug on the dead cylinder and no dice...no compression. Tow it. Here is what I found.

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And here are the other two cylinders (mag and center, pto went down)

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So help me learn from all this. This is the third trip I have taken with this motor...running mostly 91 octane (probably 1500 miles) This day it was the coldest it has seen. Did it go down because of bad gas? Air too cold for 91 octane? A ported motor essentially runs less compression than a stock motor because the compression part of the cylinder is actually shortened correct? My brother rode my other 01 SRX, all stock, all weekend with no troubles. Almost 800 miles. Another friend had a bender piped viper. He ran the same gas and on the second day his burnt down the mag side. On an interesting note, his viper had both the ram air intakes jammed full of snow...he didn't notice it until riding it 200 miles that way. He cleaned out the intakes and 2 miles later it was toast.

How long does it take to melt a piston...is it possible that the only thing keeping his viper alive was sucking the warm air from under the hood instead of the cold dense air? What octane is required for piped viper?

Is it safe to assume that my crank is toast?
 
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Just from looking at what you have for pic's looks like a lean burn down. The other two piston domes and plugs are right on the edge also. You can hardly see any piston wash on the piston domes. The jetting is for the pro's as i run vipers but it looks lean especially for those temps. Yes gas could have been a factor as well. Those piped vipers need the best premium you can find and then some. Also jetting is key.
 
I could be mistaken but it seems like I have read that porting effects how you "read" pistons. I give an X3 if this was a stock engine but am unsure with the porting...waiting to hear more opinions.
 
Curtis
YooperWoods said:
I agree looks like a lean burn down. Wash is minimal on the two surviving pistons and non existent from what I can see of whats left of the burnt piston. Where did you get the 91 from?
Click to expand...
 
tnc110, I got your pm and since you said you want others to learn from this I will post my reply here for you.

When someone has a engine done I ask them what octane fuel they have available and are willing to pay/run in the sled and the engine is set up to those specs, and a set up sheet provided with jetting,clutching and general tips,which you said earlier that you recieved from the guy whom you bought the sled from who had the work done. As mentioned in earlier in my pm reply to you, the engines are designed to run on 93-94 octane PREMIUM fuel as the set up sheet indicates and the use of octane booster is always reccomended as also stated on set up sheets. Jetting is set up from 30 down to 0 degrees as most people dont ride colder then that. When guys from canada have them done and they ride in colder weather jetting is changed from the normal 0 degree but the fuel octane in which that jetting is set up to be safe must remain the same, going to less octane will not protect the engine and lean it out. The jetting is safe at those temps AS long as that level of octane fuel is used.
Octane is the fuels ability to NOT burn, which makes less heat and sustains detonation. Going lower on octane increases heat and starts detonation, thats why your pistons look so lean with no wash other then a tiny spot on 1 piston.

When you use a less octane fuel you produce more heat,more heat leads to detonation, that leads to burning the pistons crown edge. What actually happened is you burned back the crown and exposed the ring to the flame front and once it becomes orange and soft from the flame front it folds and gouges into the cylinder, busting the ringland off and ruining the head. There is a BIG differance between 93 octane and 91 octane especially in a performance engine, that engine is loaded harder then stock via performance clutching,engine mods. You cant make 91 octane into 93 octane by simply adding booster, as most boosters only raise it by tenths of a point, most people dont understand that.

Pretty much I can tell you that lower octane fuel and cold temps is exactly what did that to your engine. Its exactly the same thing that happended to the viper you were riding with as well. Your keen observation of the air inlets being plugged on the viper was his safety more or less as it was choking it down some, making it richer, you cleaned them out and then poof it burns down also. Viper is same thing as your srx is, high performance and the jetting it set up to a specific level and temp zone. Reading of the spark plugs,piston wash is required when outside of the zones in which the engines are set up and the jetting would need adjusted outside of those zones. Vipers are even a tad more prone to it because of the increased timing from the cdi box. Increased timing adds heat to the piston, couple that with low octane and you have a sure recipe for detonation.

In order to avoid problems in the future you have to set it up for where your going to ride it all the time, if that place is up in the lovely gods country of the u.p,( it for sure is awesome place) then youd need to jet it up richer to guard against the fuel quality and temps its ridden in. Raise the needles some and go up on the mains. It will likely be low on rpm and not make as much power when you ride it in the warmer temp section but you cant have it both ways without adjusting the jetting. Another thing that slightly helps is if it happens to plumet in temps like it does up there, turn on your carb heaters for a tad of protection it will richen the sled up slightly.
 
I forgot to answer your other questions:

1.) it was just the circumstances of this trip that did it, the lower octane fuel and low temps was just the perfect recipe for detonation, if you look closely at your other pistons youll notice the little tiny pick marks or tiny indentations on the rim, thats detonation starting to etch the piston.

2.) it can happen over time or all at once, just depends on how hard the engine is being loaded, mph doesnt have anything to do with it, its rpm/load on it. can ahappen at wide open in deep snow at 20mph or wide open in a lake at 100mph. actually anywhere in between that as well if its lean in the needle settings, cruising at 40-50mph has taken down more bone stock vipers then you can count.

3.) crank may still be good if the lower rod bearing isnt damaged, youd need to take apart further and see with cylinder/piston off.

4.) piped vipers also requires 93 premium fuel
 
Today's fuel blows. I had good luck running the freshest 91 I could get with 8 ounces of torco accelerator to 5 gallons. Used that for 4 years in my 780 motor without any issues down to about -10f here at 1200'. Ran same fuel at 8000+ as well. We typically ride from the garage and I mix all my fuel there but if I filled on the trail I dumped it in and gave the sled a good sloshing around before hitting the snow again. Now that I'm in the turbo game I run c12 and 91. Fuel is cheaper than motor parts.
 
Yes it was! Thanks for taking the time to post such a detailed explanation!
 
As far as the crank goes, I guess I need to split the cases to examine it closely? This sled has 6000 miles on it and I am absolutely in love with it. I rented a skidoo renegade this weekend since mine was down. Yeah it rides nice, but mine rides pretty nice too with the mono skid, boss seat and rx1 ohlins up front. The "hang on for dear life" feeling that this SRX gives me is priceless...and I still don't have the clutching dialed in yet!

What I'm getting at is that this sled is the one that I am going to hang onto for a very long time and I want it to be right....I'm guessing splitting the cases and have the crank checked and welded is in order here? New crank seals too.
 
I would split the cases and make sure no debris in the lower end, also replace mag and pto seals and check bearings for peace of mind.

As for gas you're going to have a hard time finding good 93 on the trail, even 91 in some of these small towns is going to be questionable in the UP. You might want to consider getting a gas caddy if you have a place to mount one then you could carry a few gallons of avgas to dump in when you fuel up on the trail.
 
Tore into it some more today. Looks like some metal got in the crankcases. I'm going to use a bottom end I had bought awhile back for just this reason, and then have this crank checked out in the off season. Here are some more pics. The two shots of piston bottoms are the un hurt pistons.

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TNC, I had the exact same thing happen to my prized SRX a few years ago for the reasons Mr Viper explained. The engine had 13000 miles on it and had not been opened since new. I was planning a rebuild in the off season, the burn-down/melt down cost me a lot more money to rebuild the engine. From the pic of the two pistons, the rings should have been replaced many miles ago. The brown and black stains on the sides of the pistons are the result of blow-by or combustion gases passing by the rings. When you rebuild this engine, the question you should continulally ask yourself is " how much would I pay to NOT have to rebuild this engine again?" By that I mean, don't skimp on the inexpensive parts ( seals, gaskets, o-rings, etc.), the time spent on cleaning and inspection and the time spent on details of the assembly. On every engine and spare crankshaft that I buy for spare parts, I always send the crankshaft out to a crank repair shop to have them thoroughly checked and repaired. During the detonation process, not only does the piston get hammered from the explosions but the wrist pin, wrist pin bearings and large end rod bearing get hammered. It may cost $200 to $300 to get the crank checked and/or repaired but it is money well spent to make sure your don't have to go through this process again. Get a copy of the Yamaha repair manual and inspect and measure (or have a local machine shop measure) as many parts as possible such as the cylinder dimensions. Take your time during the off-season, I actually enjoy rebuilding these engines as much as riding. Just my 2 cents.....use caution when putting new parts on the bottom end of an engine your bought UNLESS you know the history of the engine and the bottome-end was protected during storage with a liberal coating of oil then sealed in a plastic bag.

Jim
 
Also, make sure your carbs are spotlessly clean before running the rebuilt engine. Make sure every orifice, and jet is clean. Even if you put the sled away with clean carbs, it can't hurt to check them again at the beginnning of next season.

Jim
 
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