Rebuilding a SRX700

S

sledneck1986

New member
Joined
Dec 24, 2013
Messages
17
Location
Québec, Canada
Hi everybody, I bought a SRX700 last winter and I falled in love with that sled. I had no major problems and I was planning on changing pistons before they blow. But I was lacking time this summer and didn't work on it, just started it two times in the summer.

So snow came early here this year and I started the sled. It was not running as strong as last year so I cleaned the carbs which helped a lot. But I was still feeling a flat spot near idle/low rpms. It was stretching the arms at wot, as always.

But the other day the engine blew, I heard a noise from the engine and it started backfiring. Back home I checked compression and from the clutch 130-130-0. I'll post pics, but on the exhaust side of the piston there is a hole on the side and the top of the piston is really damaged. Seems like it was running lean and it overheated a lot. I'm now in the process of rebuilding the engine and I found this forum where I think some people will be able to answer some questions I have.

When disassembling I recleaned the carbs, and the pilot jet from the carb of the faulty cylinder was clogged again...so heres the 1st question; Is a clogged pilot jet enough to blow an engine?

Also i found that on the faulty cylinder the power valve seemed to be stuck open and dry, the two others were moving freely and oily. 2nd question ; is the stuck open powervalve the cause or the result of the blown engine?? I mean, assuming it was probably stuck open before the piston break, can this be the cause of the blown engine? Or maybe this cylinder came so hot that the valve has jammed open...

I hope you can read me, English is my second language, anyway the pics are gonna talk by themselves!!
 
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Waiting on my clutch puller to take the engine out


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A new track is going there...


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...because the original one was shot


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The guilty


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Then the camera battery died...stay tuned
 
I don't know about a powervalve, but I'm sure a clogged pilot would contribute to a blown piston, Clogged pilot means less fuel so it runs lean.
 
I doubt powervalve could or would cause it. It being dry and stuck leans towards that cylinder carb issue. Pilot is primarily idle/low rpm range of carb circuit so honestly I wouldn't blame the plugged pilot. Plugged pilot does lean towards a problem in that carb. Partially restricted main jet? Top hat filter/screen clean? Next thought would be loose carb boot or crank case seal.
 
Sledneck, My sled ,a 2002 SRX, just did the same thing. The valve was stuck open and I totally destroyed the piston and cylinder. Sled was running strong.
 
By the looks of the top of the piston something foreign was hammering around in there. This could have been a piece of the ring or??????? Possibly a wristpin bearing let go? That is some serious damage to not have noticed something sooner. There must have been some serious power loss. I do not believe a stuck power valve could have anything to do with this problem. This is the exhaust side, it got very very hot. Either you have an air leak (crankseal, intake rubber not sealing, exhaust leak) or it was very very lean. However, usually detonation will blow a hole through the top of the piston.

you MUST pull the crank and clean/inspect the bottom end. Sorry for your luck.
 
Hi and thanks for the quick replies, I just don't want to waste that kind of time and money before knowing what caused that, so I appreciate your inputs.

Hammerdown you're right, this cylinder was not receiving fuel nor oil each time I closed the throttle, this is for sure not good.

Staggs yes I'm gonna take a close look at it and I'll change the two seals to make sure it don't suck air by the crankcase. Thats why I'm waiting on the clutch puller to take the engine out. And I think that I'm lucky in my badluck cause the rod and rod bearing looks just fine. Plus there is not much metal down there from what I can see.

Devilin ;
Top hat filter/screen clean? Next thought would be loose carb boot or crank case seal.
Click to expand...
Which filter/screen is that?? I can't see a filter on the fuel line so I guess it's inside the tank, I'll check it for sure! Carb boots were tight and in good shape as for the reed valves and reed gasket. I suspect crank seals, so I'll change them. But if they were worn, the three cylinders would have been lean, right?

The valve was stuck open and I totally destroyed the piston and cylinder
Click to expand...
Yes my clylinder is destroyed too. I'ts gonna be replated Nikasil. Hope they do a good job... Have you rebuild the engine yet? Found the cause of the failure?

Chris I think its the ring and maybe a piston chunk that made the damage on the top of the piston and also to the head, the wristpin bearing is ok but I'll change all 3 anyway. No exhaust leak. I had serious power loss when it started backfiring but just before it was running strong, especially past 4000 rpm. At lower rpms I noticed that it was not responding as it should, but it was nothing big, probably the clogged pilot jet. I'll have to check the fuel filter/ fuel delivery system.
 
Ok. I really don't think it is the pilot jet that would cause this problem. The pilot really only operates from 0 to 1/4 throttle. 1/4 to 3/4 is controlled by your needle and wide open is only the main jet. Is it the proper needle? Is the clip in the proper position on the needle? You will need a little ball style Allen key to remove the needle. What main jets are in there? Hope this helps....
 
The top hat filter or screen sits on top of the seat (float needle and seat) Its is very common for this to get gooed up with ethanol boogers and is a second line defense against anything the filter in the tank let pass through. To check/clean pop the float off remove the Phillips head screw and pull seat out. The screen has a plastic housing that snaps in place. If this is clogged up it would easily starve fuel on that carb through out rpm range.....especially the higher rpm
 
Even a small amount of water in carb could help cause lean condition, even a small amount of water in the carb can cause huge engine damage. That's one thing about the four strokes a little water won't hurt them but in the 2 stroke it can be catastrophic. I use that gas line antifreeze and stabilizer in every tank just for this reason. When your forced to get fuel from a questionable station or from a buddies gas can you always take the chance of water and dirt . Of course this is just my opinion and the precautions I take and to date I have never had to rebuild . Its cheap insurance considering what it costs to rebuild one of these triples.
 
I would disagree with chris and say that very much so the pilot jet can cause that damage, as the pilot jet even flows fuel at wide open. All carb circuits overlap. When the pilot jet is clogged and you run the sled, everytime you let off the gas, the needle drops and shuts off the main and midrange circuit, the cylinder goes instantly lean with no flow from the pilot jet. This causes heat ,which leads to detotnation, which then leads to your blown piston.
The damage on top of the piston is from the ringland being burned back and exposing the ring to the flame front in the cylinder. Once exposed to the heat, the ring turns orange, gets soft and peices of it break/melt off and begin to float around and mash up the piston and the head before exiting out the exhaust pipe.

Right in your first post you even say the pilot jet was clogged on this cylinder. The powervalve being stuck open was secondary, because of all the heat built up and debris causes the vale to stick open. A open valve will just make the cylinder lower on compression and make the sled run more doggy feeling down low, it wont blow up the engine.

always a hard lesson to learn that dirty carbs will take out a engine lickity split fast, your not the first and wont be the last.
 
Well yes I feel a little bit bad cause I already cleaned the carbs when I saw that something was wrong. I checked every jets and cleaned every passage with compressed air. In my mind they were now clean but now that the engine is blown i rechecked the carbs and found that guilty pilot. Something don't do its job of filtering the fuel. Didnt know about the top hat filter, thank you, maybe i'll have a surprise when i get there. Jetting is 146-146-148. I think pilots are all 42. I didnt check the needles, but as I said last year it was running perfect and this sled has not been modified much, so I dont think someone played with the needles, but I'll check.

Tonight I was not partying for the new year, I was installing my new track. Man this is a big job when you don't really know how to do this. I mean, when the chaincase is removed, removing the track = 30 min. Installing the new track = 4 hours lol. But I got it. Just waiting to install the chaincase so I can adjust the tension. Pics to come tommorow. Thanks everybody for the help.
 
Thanks for your help mrviper. We can always keep learning and EVERYTHING you said makes sense 100%. That is why I love this site!

Installing a track the first time is a lot of work but it will take half the time in the future!
 
"Something don't do its job of filtering the fuel. Didnt know about the top hat filter, thank you, maybe i'll have a surprise when i get there."

A lot of guys don't know about these "top hats" or "screens". There was recent thread on a Viper where the owner had replaced all sorts of parts in the end it was running out of gas because all 3 were plugged up. If that screen is plugged up letting little to no fuel into the bowl the rest of the carb don't much matter. As far as crap getting threw the filtering......I feel its more of a elcrapo fuel we are forced to use (even when they call it premium/supreme) It passes threw a filter as a liquid then gels or crusts up in the carbs. Even in carbs I don't find ethanol booger/jelly balls theres usually a white chalky residue.....almost like a salt dust.
 
Hi, the two other pistons seems good to me, no signs of heat/detonation.

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The two other cylinders looks good too, we can even see the machining marks on the walls.

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Fell free to let me know what you think, I can't wait to ride it on this beautiful snow again!

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Update! Lot of things done today!

Stuff including clutch puller, chaincase seals, crankshaft seals, etc.

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New track

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Find the mistake! :) That arm has been repaired dy welding in the past

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This is how I removed the clutch, no grease or water, just a lot of torque

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Then I found that ugly thing ; these are the rivets that hold the front heat exchanger! I've seen that cause when I was turning the handlebar left and right the whole thing was moving! I can't believe...

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I'll take care of that later, now let's take a look at that rusty magneto. 6 or 7 years ago at the mechanic school, I made that ``steering puller``, worked well for that mag too


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Those are the only metal flakes that were in the crankcase, not that bad, I guess almost everything passed in the exhaust


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Cleaner now


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Sorry for the mess on that table, hummm... so after disassembly, cleaning, bearing inspection, crankshaft seals replacement, etc. Bam

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That thing is magic, perfect for the crankcase, I'm sure no leak


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I found those marks on the crankcases, anybody knows what it means?


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Now this is my solution for the heat exchanger, I drilled the old, loose, worn pop rivets and replaced them by those beautifull little bolts you see on the right. These are good quality blots, very tight, should hold very good.


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Two more here

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More to come soon
 
I don't like the idea of right stuff for the cases but it's yours not mine. Those markings on the cases are so you know you have the matching set. You can't mix up case halves, they need to be used as a set.
 
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