Need Help - Blown Engine!!!

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filo_bedo

New member
Joined
Nov 22, 2009
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67
Age
49
Location
Milton, Ontario
Hi Guys

I need some help.

Over the fall months I decided to change the rings on my SRX. I have had my sled for all of last season. I put approx. 1400kms on the lsed last season. The sled was in overall great shape but the sled had 10000kms and had compression around 116lbs in each cylinder. I figured because of the high mileage and low compression I would be proactive and change the rings. The pistons and cylinders all looked great so we simply chaged the rings ( I did this job with a friend who has more experience doing this work than I ). I never removed the carbs or touched them. All new gaskets were used on the heads, the base gasket ( confirmed it was installed correctly per the shop manual once we got back to the shop today ) and the powervalve gaskets. All the powervalves were pulled and cleaned. All bolts were torqued per my shop manual. Coolant was changed and bled. Of the full tank of gas, approx 30% was fuel from last year ( which has carb stabilizer in it ) and 70% was gas from this season. All gas was 91 octane ( premium ) or better. We oiled everything when we put it together. We made sure to align the rings when we put the jugs back on. The sled started and idled fine as it always did last season.
We took the sled for a couple short runs and checked the plugs which seemed to look OK. Finally yesterday we took it for an actual run thinking the sled was good and pistons 2 and 3 blew. Piston 1 was still OK although it looked to also run hot. I will load piston head pics shortly.

After we took the sled apart today, the first thing we checked was the carbs since we didnt touch them when we did the rings. All the main jets looks great and carbs overall looked good but the pilot jet in 1 and 2 seemed to be a little clogged and 3 was completely blocked. All blockages freed up when I blew them clean with my mouth.

So what could have done this damage? Could the small partical blockages in the pilots have done it? Could it be crank seals even though piston 2 blew?

During yesterdays run, 75kms were on the trails with no issues. 3 stops and starts with no issues and lots of power during that time. When we got on the lake I brought it up to 7000rpm ( never pinned it ) and then noticed the problem so we parked and checked it out.

I want to replace everything but I dont want to do it without knowing the cause or having the same thing happen.

Any and all help would be appreciated.

Thanks in advance
 

It was definitley lean...., thats why the front edge of the piston is burned off exposing the ring. I take from reading your post, with 2 things that pop into my mind, 1.) the fuel in the sled is stale and its not quite the ratio of good to bad you described and likely the octane is very low.
2.) In your carb talk, you dont mention if the jets are of stock spec?, you also didnt say if you removed the jets and checked that the circuits are open in the carbs as well as the jets.

even looking at your not blown piston, it was lean...........the lake running just sped up the process. hopefully the plating is still good in the cylinders. I can tell you plugged pilots will show up more on idle quality and poor low speed performance, usually they wont ruin the piston as shown,because you simply give it more gas and move onto the needle circuit and more throttle the mains. pilots do flow a small percentage even wide open, they contribute 2-3% but this isnt what took the edge of the pistons, thats the main load of the main and what i see as low octane fuel or stale ,bad gas.

I know you have already learned a expensive lesson that every season you need to perform a complete carb clean with the newer gas it doesnt stay good over summer storage and the carbs get fuzzy and goopy as a result. You should always drain the fuel out at end of season and put it in your truck or something, you just cant rely on it, not like it used to be.
 
wow that sucks. OK looking at the pics you posted i can confidently say that you were running lean due to both pistons being burned on the exhaust side. Pilots that are plugged could have done this but you should have noticed poor idle quality. Check your carb boots for rips and or leaks...how did you replace the rings and not remove the carbs? You need to check for vacume leaks around the base gasket, pinched fuel line, plugged fuel filter or restricted carb circuits...You definately ran lean now you need to figure out if it was an air leak or restricted fuel.
 
tid bit more info

I would also add that the reason the pto cylinder is still ok is because it has the larger main in it, but it too was lean, just hadnt started to have detonation yet like the other 2. I believe, the fuel is right on the edge, meaning low octane. I looked at the pics again and thats my first thought process going with your descrition of events and circumstances.

Good luck, hope the cylinders are good yet.

if it helps a 2001 srx should have 40 pilots and 148.8 mains in the center and mag cylinder and 150 in the pto.
(although a 42.5 pilot is liked by the 01 when ya got aggressive clutching in them.)
 
you didn't mention that it was getting oil.I was going to say did you bleed the oil line,but if you didn't disconnect at any time..then ignore my suggestion then.
 
I agree with everyone else thet this was caused by either poor fuel or lean condition[probably a combination of both].

Items that can cause a lean condition:

1]improperly jetted carbs
-post your current carb jetting-mains?-pilots?-needle clip + washer shim positions?
-low float level

2]dirty carbs
-ensure all jets,circuits,passages,+top hat filters are clean

3]inadequate fuel supply
-ensure tank fuel filter is clean
-ensure all fuel lines inplace, not kinked or loose
-don't run hard with low fuel!!!under 1/4 tank[the fuel pickup could become uncovered
and as the sled runs out of fuel it will go lean]

4]air leaks
-leaking/cracked carb boots
-air leaks around reed cage
-leaking crankcase seals or crankcase itself not sealing properly

5]improperly installed or modified airbox
-if the air box has been modified it will effect your jettin requirements

Just some ideas of what to look for...even if you find one issue...IMO...everything should be checked.

Bob
 
Did you check the ring end gaps before assembling the motor, or just snap on new rings, bolt it back together, and cross your fingers?
 
I will try and answer all questions as best I can

The main jets on the sled were 147.5 and 146.3. These jets match the stock settings in my SRX shop maual. Are they correct? Mr.Viper do you think I should use larger jets? I will need to look for the size of the pilots, I did not see any identification on them.

We did not measure the gap on the rings - I will do this on this install. I did use all Yamaha parts including rings assuming they would be quality parts within spec. My bad

Airbox is stock and not modified

Carbs appeared to be in overall good shape. There was no crap in the bowls, the only flaw we could see was the pilots somewhat plugged. The idle on the sled was always ok though.

Is there a way to test the base head gasket for air leaks?

All fuel lines were untouched from last season so no kinks and gas was topped and the tank was full although partially old gas from last season was still remaining. I will check the fuel line filter.
Could it be a bad fuel pump itself? The sled did run fine for 75kms with what seemed to be lots of power but could it still be a bad pump not pumping enough at higher RPM?
 
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I should also note that I did not put any oil in the fuel because I read it is not really good to do that, should I have done that? Do you think it would have helped?
 
When rings are installed, is there a right side up and down? I know the rings were aligned with the point on the piston they are supposed to be aligned with when putting the jug on, but I am not sure if he knew there was an up and down side to the rings themselves?
 
Bluemonster I can confirm on the 80km run oil level did drop, so it definetly got some oil, maybe not enough? I am thinking of changing the fuel pump altogether or at the very least rebuilding it. Does the oil get pumped via the fuel pump as well?
 
filo_bedo said:
When rings are installed, is there a right side up and down? I know the rings were aligned with the point on the piston they are supposed to be aligned with when putting the jug on, but I am not sure if he knew there was an up and down side to the rings themselves?
Click to expand...
should of been some kind of marking on ring's, either a #,dot,letter, that side faces up, think you had a combination of issues which caused your engine to go down, ring's , end gap, dirty carbs and jetting, fuel etc.... the pro's will chim in and help you along, do as they say, and you will have many trouble free smiles ;)!
 
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Oil pump pumps oil into fuel pump as well as crank case, the oil mixes with the fuel in the fuel pump and then fuel supply is like premix as it exits the pump to carbs.

There is a top side of the rings, only the top of ring has a "T" engraved/stamped on it.

Ensure you thoroughly clean those carbs including the "Top Hat filters under the needle + seat!

Bob
 
filo_bedo said:
I will try and answer all questions as best I can

The main jets on the sled were 147.5 and 146.3. These jets match the stock settings in my SRX shop maual. Are they correct? Mr.Viper do you think I should use larger jets? I will need to look for the size of the pilots, I did not see any identification on them.

We did not measure the gap on the rings - I will do this on this install. I did use all Yamaha parts including rings assuming they would be quality parts within spec. My bad

Airbox is stock and not modified

Carbs appeared to be in overall good shape. There was no crap in the bowls, the only flaw we could see was the pilots somewhat plugged. The idle on the sled was always ok though.

Is there a way to test the base head gasket for air leaks?

All fuel lines were untouched from last season so no kinks and gas was topped and the tank was full although partially old gas from last season was still remaining. I will check the fuel line filter.
Could it be a bad fuel pump itself? The sled did run fine for 75kms with what seemed to be lots of power but could it still be a bad pump not pumping enough at higher RPM?
Click to expand...
those jets are to small they are the 2000 jetting specs and caused lean burn downs in the right conditions,they should be 148.8 x2 and a 150 for the pto like mr.viper said. ring end gap should be checked but i have never had to adjust it on yamaha rings in a stock bore. i agree 100% with mr.viper, lean jetting and a little low on octane burned those pistons.
 
If the rings were installed incorrectly do you think this could have led directly to the problem? I dont ever recall my friend telling me to look for the T when we put them on so I am...... I just talked to him and he said he looked at them and could not find a difference so he assumed all the rings were the same. I am guessing it is highly unlikely that without looking for the "T" on the rings that all rings were installed correctly.
Do you think this could have directly led to this situation or not?
 
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