KTM Owners Forum banner
  • Hey everyone! Enter your ride HERE to be a part of this month's Bike of the Month Challenge!

1 - 12 of 12 Posts

·
Registered
Joined
·
87 Posts
Discussion Starter #1
I am replacing the piston in my '07 250 EXC-F, simple enough task in itself, but I have have just retreated to a beer position from putting the rings in the new piston ....

The oil control ring is a piece assembly, two scraper rings that are separated by a "spring" ring. This central part is shaped to fit between the scrapers, and has a lip on the inner edge that fits slots in just behind the scrapers. With me so far ?

Putting them into the ring groove is proving such a 'mare...:frown: The "spring type ring goes in, no problems, one scraper goes on, again no problem. However as the spring type ring is fitted so its inner lip sits behind the scraper ring, the ends of the spring overlap. When the second scraper is fitted, this overlap prevents the 3 part assembly from fitting into the groove!!!! Is there a knack to this, anyone had this problem before, or is it a case of just keep trying and trying until it works ?

Yes I do know what I am doing, I have rebuilt engines before, this is my first 250 EXC-F; but do take this piss if it makes you happy ...
 

·
Registered
Joined
·
1,169 Posts
Oh dear i have just had the same problem, thought the oil/spring ring was too big. See "help" thread below. I have just stripped it again, may need o order new rings, waiting for a reply from the man in the know. that'll be kev.
 

·
Registered
Joined
·
1,169 Posts
just found this,
In four-stroke applications Vertex offers both two-ring and three-ring pistons. Three-ring pistons will have two compression rings and one oil ring. A two ring piston only has one compression ring and the oil ring. The oil ring on both types of pistons is a three piece design, consisting of two rail rings and one expander ring. On three-ring pistons, the two compression rings will go into the top two ring grooves and the oil ring will go in the bottom ring groove. The two compression rings may be different from each other. If this is the case then it is necessary to look at the profile of the rings to ensure they are located in the proper groove. Often one ring will have a taper to its profile. If this ring is installed into the wrong ring groove, it will not compress properly. It is also common for the second compression ring to be darker, because it may be made from cast iron. Ensure that any letters located at the tip of the rings are facing up. This is the same for two ring pistons except there is only one compression ring. When installing the oil ring, first install the expander ring and make sure the ends do not overlap. If you look closely at the expander ring, it has a shoulder/lip on both top and bottom that prevents the rail rings from seating completely against the piston groove. It is important that when installing the rail rings you do not allow them to sit on top of this should/lip. If the rail rings are not seated correctly on the expander rind then the oil ring will not fit in the groove properly. After all the rings are installed on the piston, make sure that each of the ring end gaps is about 120 degrees from each other.
 

·
Registered
Joined
·
87 Posts
Discussion Starter #5
Got it ..

I managed it, the Vertex info helped. The problem was that the first scraper ring put in position tends to drop down the groove, over the lip of the expander ring, pushing it to the other side of the groove and thus blocking the next scraper ring. It is like juggling cats, not enough hands and just when you think you have them all in place, one drops out the groove. Getting it all into the barrel was almost worse ...

Thanks for the link Scotty, that is a very concise rebuild pictorial. I like the idea of marking out the placement of the ring gaps. Old wisdom dictated that gaps should never be placed at the load points i.e. front or back of the piston, always to the sides. I note that your marking places a gap at the inlet side of the piston where the load would be placed ...
 

·
Registered
Joined
·
87 Posts
Discussion Starter #7
did you use a ring compresser to put piston in?
Nope, just the remainder of my thumb nails and gentle persuasion.

I just know that the rings are going to drop out when I wretsle the gudgeon pin clip into place. Still, practice makes perfect ...
Just need to make sure I don't forget the base gasket, and get it the right way up!
 

·
Registered
Joined
·
1,169 Posts
very hard to break these, it is fiddly, but a couple of small flat screwdrivers works wonders.Push one side in then kep it there with the driver then push the other side of the clip and it just pops in. I,m an expert now cos first i left the gasket off, then second I did'nt feed the cam guide through, then 4th 5th and 6th I,ve fucked the oil ring. On and off quite a few times, waiting for my new oil ring then I'll do it all again. Learning curve, so they tell me.
 

·
Registered
Joined
·
109 Posts
I'm with the little screw drivers on both the rings and the clips...

Fit all 3 parts into the groove (well close too, because they wont fit) spread the 'spring' with a couple of small screw drivers then seat them all properly, if they are well lubricated it makes it all a bit easier.

As for fitting the clip, i block the lower case off with a bit of cardboard which has a slot cut in it for the rod, you can then rest the cylinder assembly on it and it'll stay flat, wont drop, and you cant pull the piston out the bottom of the bore if you dont lift the cylinder off the card, oh and most importantly you cant drop the clip into the cases unless your REALLY unlucky, once the clips seated then slide the bit of card out, push the cylinder down and job done, dont forget the base gasket though eh ;)
 

·
Registered
Joined
·
87 Posts
Discussion Starter #12
As for fitting the clip, i block the lower case off with a bit of cardboard which has a slot cut in it for the rod, you can then rest the cylinder assembly on it and it'll stay flat, wont drop, and you cant pull the piston out the bottom of the bore if you dont lift the cylinder off the card, oh and most importantly you cant drop the clip into the cases unless your REALLY unlucky, once the clips seated then slide the bit of card out, push the cylinder down and job done, dont forget the base gasket though eh ;)
Great minds ... I had just been musing why not use a piece of card, when you posted that . Spooky !

As for the clips, I have small flat blade screwdriver with a gap in it for security screws; and now for gently twisting the gudgeon pin clips into the bore without any hassle... So stress free
 
1 - 12 of 12 Posts
Top