Just replaced changed pistons, now engine is making a hard knocking sound

[kidwoo]

Just replaced pistons, now engine is making a hard knocking sound

Just threw new pistons in an 04 summit x 800 as well as all the appropriate gaskets. Engine started right up on the second pull but after idling for about a minute it started sounding like something was bouncing around in the motor. I definitely accounted for all bearing rollers, all clips and spacers and was VERY careful covering the crank case while everything was open.

I did notice the reed boots looked a little beat, but the thing ran fine before I took it apart. Could this be the problem though, causing the engine to run lean? That's a suggestion I got from a buddy. Either way the noise is definitely irregular and pretty loud. Last time I started it, it also ran for a few seconds after I hit the kill switch.

Any ideas?

Thanks!

 

[m8magicandmystery]

sounds like your diesiling...???..timing is off..??..

 

[kidwoo]

sounds like your diesiling...???..timing is off..??..

Is it even possible that I could have affected the timing just from pulling the jugs and pistons though? Serious question.....I really don't know.

 

[m8magicandmystery]

no you really can;t...was your base gasket same thickness(port timing could be affected) ...etc...head gasket...oem parts..??...did you fill up from a jerry can...contaminated or old old fuel

 

[m8magicandmystery]

and definately no knocking before rebuild..??...are the pistons oem and wrist pins and wrist pin brgs..knock could be piston slap(if clearences too much )...wrist pin knock if clearences not right..)....but with the run on after sled is turned off im thinking problem is not with the rebuild unless gaskets really differant..but that the run on and knock is related..ps...it should idle on one cylinder so just pull the sparkplug cap off one and then the other...you may be able to isolate the nuisance cylinder if the knock stops eliminating the spark...

 

[kidwoo]

Yeah the thing really did run fine before the rebuild. Even the rings I went in to replace looked fine. All oem parts went back in.....pistons, bearings, pins, gaskets (0.6mm BTW).

Good thoughts on isolating the cylinders though. I already took the reeds off since the boot wear was the only thing that stood out when I tore it down and I'm going to replace them just for the hell of it. Am I barking up the wrong tree thinking I've got a vacuum leak through the reed gaskets causing it to run lean?
Either way I'll put it back together just to run each piston and see what's up.

I took plenty of care making sure the piston rings were seated.....if that's the case then there really shouldn't be any reason the piston is flopping around. The whole sled only had 1500 miles on it, I can't imagine the jugs are off.

Thanks for the help.

 

[INKEDRIDER]

piston

your piston rings are stuck in so what you are hearing is the piston slapping your cylinder just take it back apart and use some scotch bright on your rings and put back together

 

[kidwoo]

your piston rings are stuck in so what you are hearing is the piston slapping your cylinder just take it back apart and use some scotch bright on your rings and put back together

Familiar territory for you?


Judging by the sound, I could certainly believe that.


I'll definitely check it out.

Thanks man.

 

[MARCUSO]

arrows pointing towards exhaust on pistons?

The boots go bad on doos, I would replace ASAP before you become another victim, but I doubt it would be making it knock.

Make sure you check ring end gap if you tear into it.

I know it sounds obvious, but perhaps something was overlooked.

 

[DRD]

Why not pull the head and have a look??

 

[studboy]

Double check the piston part number. I had a 98 670x ho and got the wrong pistons and when it warmed up they would knock, as they were domed more and used for a 670 non ho.

 

[summit800]

are you sure its not idling to low and your hearing clutch noise

 

[PJ-Hunter]

Just guessing here, piston slap!

 

[kidwoo]

Pistons are in the right way, and it's definitely not the clutch (first thing I thought too, but I never touched the clutch anyway).

I'm going to wait till I get some new boots before I pull everything again. After reading a bit more and finding some pics, I do need to replace the boots regardless. The sled is in the garage at my office so I want to minimize the exploded snowmobile affect on my boss.

Right now the sticking ring sounds like the most likely problem. And I'll recheck the gap on them.

Thanks for the help guys. I'll report back just in case anyone else runs into this.

 

[Crasher]

Pretty easy to pull the head and take a quik look. Check your compression. Should be around 145.

I had a simalar problem on my 05 this year. Turned out that the end of one side of the ring over the location pin broke off and was banging against the head.

Make sure you installed the rings correct side up. I don't know if you could even get it together with them up side down but you know how sh^t happens.

 

[joshkoltes]

rave valves

your rave valve guietines could be in upside down, iv done that. they say "top" on them.

 

[pyxle]

Did you spill anti-freeze down the cylinders? Use too much oil during assembly will cause a knocking. Too much liquid will cause high compression and excessive smoke and noise.

Personally, I have rebuilt about 50 doo engines and this has happened a couple of times.

It will cause the engine to idle at a lower RPM and smoke like a s.o.b.
If it does not clean up after cracking the throttle and "cleaning it out" then it is something else, like bottom end, or cylinders are egg/taper shaped.

 

[kidwoo]

Did you spill anti-freeze down the cylinders? Use too much oil during assembly will cause a knocking. Too much liquid will cause high compression and excessive smoke and noise.

Personally, I have rebuilt about 50 doo engines and this has happened a couple of times.

Yeah both of these are certainly a possibility. Should I just change the crank case oil anyway? I dipped a paper towel into the oil and it did kind of look a little green. That sort of worried me.

Does what you describe literally sound like something banging around kind of violently...again, at irregular intervals?

I've got it apart right now and both rings moved freely on the pistons where I was kind of hoping I'd find a stuck one. I'm going to go ahead and run the scotchbrite pad on them just in case. They were right side up btw.

An interesting sidenote. The two boxes of the pistons have different part numbers.

One is 420889457 (what I ordered)

The other is 420890721 (covered up with a shop sticker I had to peel off).

Both of these are listed as 81,87 pistons but are listed this way

420890721 PISTON 81,87MM*PISTON-ASSY

420889457 PISTON 81,87 *PISTON-ASSY 81

The markings on the pistons are identical. Are these interchangeable?

Josh: never touched the rave valves.

 

[jdtech65]

When I was rebuilding a 02 800 skidoo this winter, one of the pistons I ordered from the dealer was not the correct piston as it was supposed to be. The part number on the box was the correct piston but the wrist pin slot was way way to big. The wrist pin would fall right through the hole in the piston. When I was ordering them, the pistons superceeded so many times it was impossible to keep the numbers straight. The easiest way to tell might be to call a dealer and see if the numbers superceed.

 

[kidwoo]

Just found the part number. The 8890721 piston matches an 07 and later 800 engine. And like I said, both markings on the pistons themselves match up. No wierd installation differences between them.
Should be fine right?