Burndown Root Cause

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BarrySRX

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I just disassembled my 99SRX engine and split the case. the cause for the teardown was a burndown on the Mag cylinder which will need a new piston, rings etc at minimum. I also am hearing a good rattle from the mag side crank bearing which I expect is from piston material working into the rollers. When I look at the three pistons they appear progressively better as I move away from the mag side, the center is showing a little wear that is really just superficial, and the pto piston looks pristine. I think thisis due to a lack of lubrication, but I don't know why. There is oil in the reservoir and it appears the oil pump is working because my pto piston looks great, but it's clear the center and mag were getting less lubrication, or seeing higher temps. Does this sound like too little oil, Or loss of coolant? Alsonis there a way to troubleshoot for either of these causes? Just like to know why it happened before I invest time& $$ into a rebuild just to have it happen a second time.

Thanks
 
if you lose oil the lower end is usually the first to go, the mains and the lower rod. so that rattle could be from low oil over time. i just dont think the burn down would be from no oil, its usually a seize up at that point. a picture is worth a million words!
 
X3 on pics, Based JUST on description I would lean towards leaking crank case seal on mag side or a problem in that carb. Pics may tell an entirely different story.
 
From my own personal experience the most popular cause of a burn down is a lean condition caused by either a lack of fuel or a bad gasket/seal causing air to leak or get drawn in.Pics should help narrow this down for you,there's enough guys on here that can give you a cursory diagnosis but if your in the teardown mode and have free time on your hands look over your carb boots very closely for cracks or tears in the rubber.While Doo has a very bad reputation for this particular area of failure it's certainly worth looking at on a Yamaha whenever your doing this kind of work.Crank seals would also be an area to scrutinize for an air leak and I don't know what your budget is like but if you have any notions of reusing your old ones it's entirely up to you but replace them if you can.

While your at it tear into them carbs and clean them religiously and thoroughly,you could have a main jet that's kind of gummed up and leaning out the mag side cylinder.If you leave gas in the system for any lenght of time the ethanol will cause numerous issues in the carbs,clogging up jets and passages.I've always drained my gas tank for storage and run the carbs dry and knock on wood I've never had and build up in my carbs,but I always take them apart every fall anyway.

Some food for thought for you anyway.
 
OK, got some pictures. I positioned the pistons just how the came out of cylinders, mag side right, pto left. the engine did seize in the mag cylinder. When I was taking the clutch off it actually freed up. The mag piston and cylinder are now junk. the middle one looks worse than it really is, but all seem to have a good amount of residue. trying to figure out if its a pump thing, or if my carbs weren't getting enough mix to the cylinders in order to lubricate. does the oil pump even lubricate the cylinders? thought the mix out from the fuel pump into the crabs did that. also worth noting when i took this apart, the mag and center crank arms were visibly dry of oil, while the pto side looked well lubricated.
 

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Im not real good with SRX's but that Mag piston/cylinder looks like a cold seizure to me. Being wiseco pistons i know they need a good warm up before taking off. From looking at the pistons you can see a little wash on the rim of the PTO cylinder and none on the other two. I would say you were running a bit lean also. IMO not a oil/lubrication problem, dirty carbs or bad jetting. Who did the rebuild the first time? Ill be watching to see what the real experts say.
 
DUDE ( super 1c ) I THINK YOU HIT THIS PERFECT IN YOUR POST. THE WISECO,S WERE THE GIVE AWAY. COLD SEIZE FOR SURE AND LEAN ON TOP. WITHOUT A DOUBT UP JETTING FOR STARTERS. MAKE SURE THERMOSTAT WORKS AND GIVE ALOT TIME FOR WARM UP WITH WISECO. 3:16 (yammie tony)
 
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YAMMIEGOD3:16 said:
DUDE ( super 1c ) I THINK YOU HIT THIS PERFECT IN YOUR POST. THE WISECO,S WERE THE GIVE AWAY. COLD SEIZE FOR SURE AND LEAN ON TOP. WITHOUT A DOUBT UP JETTING FOR STARTERS. MAKE SURE THERMOSTAT WORKS AND GIVE ALOT TIME FOR WARM UP WITH WISECO. 3:16 (yammie tony)
Click to expand...


"WITHOUT A DOUBT UP JETTING FOR STARTERS."<-- what does that mean?

So it sounds like the sled wasn't warmed enough long enough before taking it out. anyone know how long exactly i should warm them up next time? i didn't know different pistons would require longer times. I have two good stock pistons that i may replace the two wiseco pistons with. any issue mixing piston manufacturers as long as i warm up for worse case? not sure how the lean condition happened, i cleaned and adjusted the carbs METICULOUSLY.
 
top of your pistons in your pictures shows a lean WASH. two things going on. silver grey/ dry is lean. go to bigger main jets. let the sled idle in your yard this season and go back in house and get ready. when ya come out you should be good. also check and see your thermostat is working probley. wiesco,s take longer for warmup than oem. 3:16 (YAMMIE TONY)
 
You don't want to mix pistons. Either run all oem or all aftermarket. aftermarket pistons take longer than the oem's to warm up.
 
wiseco and oem pistons are made from different compounds. Not exactly sure what but what happens is if not warmed up properly the wiseco's absorb heat faster then the jug and the piston expand faster then the jug sleves hence the seizure of the piston. This can happen with OEM pistons also if not warmed properly. Its that the wiseco's take a longer warm up to allow the sleves to catch up before you put the hammer (heat) to it. Then when everything cools and shrinks back down the piston will normally break free and show the marks yours does. As far as jetting there is tons of good info on jetting and wash for SRX's on this site via search. You can read for day's. Mrviper700 has a bunch of articals on this in threads and tech section. YAMMIGOD and blue also have tons of great knowledge on these srx's.
 
Another reason not to mix pistons is they are different weights between aftermarket and oem.
 
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lots of good stuff here, thanks for the help. looks like a'll have a good summer project on my hands
 
I think the wiseco pistons are thinner/lighter than the oem and therefore expand more rapidly with heat. Also the other reason i believe is becasue the wiseco pistons are forged rather than cast like the oem's
 
If you want to stick with Weisco pistons I have 2 in my spare parts box that I ran for not quite 2 seasons.I replaced them with OEM when I did a rebuild after a lean burndown so it's doubtful I will use them.They are coated too.Shoot me a pm if your interested.
 
That is exactly how we have been warming up our sleds for years works well never had any issues. Start it and go in and get ready.
 
I have seen this before. Check the thermostat! If it was ever over heated than it could be stuck open, thus allowing coolant through way too soon. You are doing the right thing though in figuring out why this happened. So many guys just toss a piston in and figure it was "just time".
 
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