Right and Left cylinders.. Piston damage??

[yz400ex]

I recently picked up a Carls 685 motor. This was done on an 06 motor. When looking it over yesterday I noticed that 1 cylinder was marked M and the other was P. I am assuming this meant Mag side and PTO side. I have never seen this before. I checked another 600 that is sitting here and it has the same thing. I checked the other 600 sitting here and it does not. all 3 600's are 06's. On this 685, the upper part of the pistons on the very right and exhaust side of each one, look like they had been smashed a little. This also caused the top of the pistons to have a small lip in these spots and also scaring across the rings. The damage on each piston is hard to really see in these pictures, but it is easy to tell where it is. I have never seen this before. The pistons are perfect everywhere else. Its just this small spot. The cylinders and perfect. I dont see how this could happen. I dont see that it had hit the VES guillotine or anything. The cylinders on this motor are switched around where the M is on the PTO and the P is on the Mag side.. Could this cause an issue? Is there really a left and right side? I looked at the parts fiche and cant see that there would be any different parts #'s. I am going to replace the pistons, but want to make sure this doesnt happen again.. Anyone have any ideas?

 

[diamonddave]

I've worked on quite a few of these now, I see what you are talking about. I don't think it's too big a deal but I would tear it down to make sure. As for the cylinders being marked, some (like me) like to mark what side the jugs came off of. It's not mandatory but I like to keep everything the way it was before I work on something. That way the sealing surfaces on the bottom and top of the jugs match the way they were before teardown. Keeping the jugs on the same side also helps for future diagnosis in case of a problem but like I said it's not mandatory simply being professional IMO.

The 685 uses the highest quality piston made IMO (PRO-X). I think what you are seeing is a little blow-by between the exhaust boost port and the exhaust. I would perform a hot and cold compression test on it, then tear it down and if you have any questions, call Chris Kasel at Carls. He is a very helpful person.

 

[yz400ex]

Yea, I am seeing blow by, but it is caused because the piston is actually smashed right there. It is smashed up against the rings and actually creates a small lip on the top of the piston. I will see if I can get a few better pictures. When doing a rebuild, I always mark which cylinder comes from where also, but these were not done by someone.. They are factory stamped on 2 of the 3 motors I have sitting here. I will snap a few pictures of that also.. I appreciate your help..

 

[sled_guy]

The important part is to keep all the pieces together for each cylinder. I mark everything when I take one apart (pistons, wristpin bearings, cylinders and valves). On the 685 or any big bore for that mater, the valves are matched to the cylinder. If someone were to switch P to M then you might have an issue with them contacting the pistons.

sled_guy

 

[yz400ex]

It took awhile to get the time to grab a few more pictures, but here they are.. These are factory stamped. The other motor I have has identical stamping. I checked the valves and there was no indication of anything making contact with the piston. Also the damage is only at the top, barely past the rings. I would think, if it was the valves there would be damage the entire length of the cylinder.. Any thoughts on this or the M and P cylinders??

 

[louisal]

Id set a dial bore gage and check to see if the bores are out of round. I think the tolarance new is .002. The stamping looks like I stamped the jugs are you sure they have never been apart?

 

[yz400ex]

I dont know if either have been apart.. In have bought all 3 of my 600HO motors used from all different people all at different times.. 2 of the 3 motors I have sitting here have identical M and P marks on the cylinders of them.

 

[firecat99]

The important part is to keep all the pieces together for each cylinder. I mark everything when I take one apart (pistons, wristpin bearings, cylinders and valves). On the 685 or any big bore for that mater, the valves are matched to the cylinder. If someone were to switch P to M then you might have an issue with them contacting the pistons.

sled_guy

I have for years mix matching parts from my motors from pistons to valves you name it cylinders and all, As long as you keep an eye on everything you wont have a problem, like when i install my clyinders i rotate the motor a bunch to make sure rings and stuff dont touch anything.
I wish you had better pics on the 685 motor, I know my cat motors the pistons always show light scraching on the pistons even after being new ran the ripped down again nature of the motor i guess. but the blow by where it is cant be good i would check the bore and the pistons you might have a tight ring thats letting that happen I had the same problem last season on my D&D 720 but could not tell i was losing power till to got a weird backfire then decided to check comp as I was running the motor flat out since it was built didnt even give it a break in time but flat out for 1200miles and only had a few rings fade was pretty good for me.

 

[yz400ex]

I wish I had better pictures too.. I dont have a good enough camera to take close up pics like that and have them come out very clear. The blow by is because the piston is smashed right in that spot and actually smeared the piston over the ring a bit, stocking the ring to the piston so it cannot expand onto the cylinder. It really isnt that bad and I wonder if it could be removed and filed a little.. the rings are still good.. its just the piston is smashed and smeared a little just at the very top. I will check cylinder clearance in the very top compared to the rest of the cylinder. It did not even scratch the cylinder though.. not even a little.

 

[diamonddave]

Those are NOT factory stamps.

 

[yz400ex]

I just wondered because I have 2 motors here with identical stamps. They both came used and from 2 different people.. I didnt figure the factory would stamp because they have the same part #, but thought it was odd to have 2 of them with the same markings..