Should oil scraper rings be this TIGHT?

[stanleyoutdoors]

I'm putting a new Pro-X (japanese) piston and rings into my KTM (Austrian) 525 dirtbike.

Bore is freshly honed.
Piston and bore diameters in spec (on loose side)
Both compression ring and oils scraper ring end gaps are within spec (on loose side)

The oil scraper rings are the type where there is a wavy spring in the middle, flanked by 2 thin rings. The inner diameter of the wavy spring has a crimped ridge that makes the rings touch the ridge rather than the OD of the piston groove (effectively forcing the oil rings outward)

I am very sure I am installing it correctly, but it seems that the wavy spring is pushing the rings out too much. With the (much larger) compression ring, I can easily squeeze it with my fingers to get the gap to close and shove it in the bore. With just the compression ring, it slides nicely. But with the (much smaller) oil rings, I can not squeeze them hard enough to close the end gap, due to the wavy spring pushing them outward. Using a ring compressor tool, I managed to get the piston in the bore, but it was really difficult to make it slide up or down. (I had oiled it up really well)

Is it normal to be that tight? Most of my other experience is with 2 strokes (no oil rings, only compression ring(s)). And the last time I rebuilt this engine, I kept the stock piston and used new rings, but the stock oil ring is 1 piece plus a coil spring. I don't remember it being nearly this tight.

THANKS!

 

[oldmxracer]

I have done hundreds of four stroke dirt bike engines.

Sometimes the scraper rings snag the expander ring and it takes a bit to get them correctly installed on the piston.

When they are correct You will be able to compress them with Your fingers.

Sorry, but I would pull the cylinder back off and look for bent scraper rings.

 

[stanleyoutdoors]

I have done hundreds of four stroke dirt bike engines.

Sometimes the scraper rings snag the expander ring and it takes a bit to get them correctly installed on the piston.

When they are correct You will be able to compress them with Your fingers.

Sorry, but I would pull the cylinder back off and look for bent scraper rings.

I pulled it back out and there is no snagging, no bends. I've re-installed the rings on the piston probably 20 times and always the same: I can squeeze them a little but the expander rings just wants to expand it REALLY hard. Seems too hard to me.

When the piston was in the bore, I estimate it took about 50 lb of force to move it.

 

[tonydanzah]

Did you install the piston without the scrapper to see a difference in cylinder movement?

 

[Tig Master]

I pulled it back out and there is no snagging, no bends. I've re-installed the rings on the piston probably 20 times and always the same: I can squeeze them a little but the expander rings just wants to expand it REALLY hard. Seems too hard to me.

When the piston was in the bore, I estimate it took about 50 lb of force to move it.

Put the rails by themselves in the bore and check the end gap the same way you check compression rings. Something is not correct there.

T

 

[oldmxracer]

Glad, We got to talk on the phone, wished YOU lived closer to Me so there was no need to take it to a dealer !

Just did this motor today, A '08 YZ450F Cylinder Works bore with a Vertex piston.

 

[kerrynzl]

If this is a re-ring on the same piston.... have you scraped the carbon [coking] out of the ring grooves?
A broken ring is the best tool, but wear gloves because the edge of the ring causes cuts.

 

[stanleyoutdoors]

Thank you everyone who replied- especially oldmxracer, who called me up on the phone.

I took it into the dealer where I bought the piston and they showed it to one of their mechanics. He agreed that there was definitely something WRONG with the piston and or oil rings. My best guess is that either the groove in the piston is too shallow or the wavy spring that shoves the ring out is just a bit too long. The Piston was made in USA- I expected better.

So they exchanged the Pro-X for a Wiseco (plus $50). I considered OEM but they wanted $400 for a KTM piston and I just can't stomach getting bent over by KTM like that.