Hole in top of piston

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penchar

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Feb 11, 2010
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Age
51
Location
sudbury ontario
I am looking for a little help. I have a 1998 stock srx 700 and was out riding when one of my clyinders shut down. Pulled the plugs and found 2 of the the 3 plugs indicated very lean and the 3 plug was very damaged. Started looking for the problem and found a hole in the top of the piston from the cylinder with the damaged plug, which from what i have read indicates the machine ran lean.

Upon looking further for the cause i noticed the oil pump cable was stuck in the wide open postion causing the oil bottle to empty during the ride. My question is could the piston have blown allowing me to shut down and save the engine from seizing.
 

Simple questions to you...Didn't your warning light come on telling your that your oil level was getting down??Did you not check your oil level every time you go riding?? Maybe you have a leak somewhere and the hole in the piston was your warning ....sorry this had to happen to your motor.Now running out of oil should of just seized the motor solid at one point.But if you were to lean to begin with and the added heat would hurt you also.Do you have stock jetting for that year??Were the carbs cleaned and quality gas used??Lean condition for sure because more oil in the system leans it out..Piston can only take so much friction and heat..
 
The oil was full when I left on the ride and I was only 100 kms into the ride when the bottle was near empty, but as I said the oil pump cable was stuck in the wide open position. The oil light did not come, so maybe there was more oil then it appeared, and as far as fuel it has only seen premium. The carbs I believe are stock jetting and as far as cleaning it has been some time but to me it would seem strange all 3 carbs would go lean at the same time on the same ride condsidering the day before when I checked the plugs they were golden brown to dark brown but as you said the extra oil would cause lean conditions, but i always thought the more oil would be better.
Thanks for your help.
 
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Test the gas for water and remove the carbs ,look for any crud in the bowls that might have blocked the mains.When the oil cable comes out of the holder it will only get about 3/4 throttle wide open for the gas so i find it hard to belive it was the cause but you never no.


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yes that does seem strange ..but if something pulled the jets exactly at that time...a possible disaster.I always add a couple caps of seafoam with every fill up.It will help to keep things a little cleaner and helps if there was moisture in the gas as well.Check boots to airbox/carbs for loose or cracks..Maybe your crank seals??How many miles on the motor..You will now be opening her up..so change seals for sure and check crank for any fragments and damage as well.Sorry this happened especially when you think you have done everything correct..but the carbs may be the culprit..PS:check to make sure your oil bottle warning light works and check for leaks in the lines.Any puddle of oil down below.? Still hared to believe you would of drained the whole bottle.Let us know what is left in there if any..
 
So far the only thing wrong that I have found is the oil pump cable beiing pulled all the way to the open position at the throttle end. Looks like one of the times when I gave the machine a shot and let off, the cable got stuck which allowed the pump to run wide open for some time leaning out the engine but I am still looking incase there is another problem.

When I looked closer at the oil bottle I was not totally empty just very low. As far as the mileage on the engine it is around 7600 kms.
 
Too much oil and engine will run lean. Learned this the hard way with glo fuel engines in rc cars. I was adding extral oil to the glo fuel and it caused the engine to run too lean.
 
remember fuel cools oil lubricates what size main jets? check for intake leak boot off carb or crank seal just my 2 cents
 
The main jets to the best of my knowledge are stock. As far as the speed and rpm all I know is i was approx 100mph and not sure on rpm. Up until this the engine was running fine and as i indicated in a earlier post the spark plugs the previous day were a nice brownish colour after a day of trail riding idicating to me the jet size was ok, but when i removed them after the problem they were indicating very lean conditions.

Will lean conditions cause detonation?
 
Just wanted to say thanks to the help and suggestions. Started looking for the cause and so for the only problem found is where the oil cable makes the bend at the front of the air box it goes through a metal housing which has a plactic cover, the cable pulled out of the housing allowing it to stick open.
 
anytime you add more oil to fuel you LEAN out the engine. I know most people think more oil is better but its also leaner,the oil displaces the fuel so the engine runs leaner air to fuel ratio. Oil does not protect it from burning down. With todays new technology on synthetic oils you can run the oil/gas mixture much leaner and have very good bering protection.

I would say you ran it lean with that much oil and if the jetting was leaner then stock(you need to check the numbers on jets and needle clip placement) it wouldnt be hard to damage the engine these days with low quality low octane fuel with a stuck oilpump cable.
 
Jetting is stock but deffinatey ran lean, judging by the amount of oil used in 100 km ride. Now I am thinking it has been like this for most of the season as the oil consumption seemed high. Things you learn after it is too late. Now it is just deciding to rebuild stock or to do some engine work while it is apart.
 
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