Nikaseal worn around exhaust port. YZ250 and YZ85

[Gibbit]

I just wanted to pick the brains of the 2 banger gurus on here.
I have the top ends apart on my YZ250X (166hrs) and my sons YZ85 (178hrs). Both show the same signs of wear.
I’m wondering if I should be getting more out of my cylinders than I am.
I’m very anal about clean air filters and run Castrol TTS Racing at 40:1.

What is causing the Nikasil to prematurely wear like this!

Yz250x bore.


YZ85 bore


YZ85 head.

[oldboy]

I have never been a fan of TTS. A mate children's bikes had repeated failures when their father switched to TTS due to sponsorship obligations (free oil). Went back to Motorex all good. I personally run ELF

[Gibbit]

I have never been a fan of TTS. A mate children's bikes had repeated failures when their father switched to TTS due to sponsorship obligations (free oil). Went back to Motorex all good. I personally run ELF

I like how the castrol burns so clean (as you can see from how clean the head on the 85 is).
I have done tests on motorex for 40hrs and castrol for 40hrs. The castrol piston was so much cleaner.
But maybe it’s luberication properties are not good enough.

[JJW]

I run $5/litre 2T oil and my cylinders don't look like that!

Are you sure it is the nikasil wearing? Does the mark polish off? ie is it definitely worn or is there melted aluminium coating the cylinder there? What is the mark at the top of the 85 bore?

Aftermarket pistons too tight?

What do the pistons look like?

It all looks too clean to me....jetting too lean? Even then I would expect to see some carbon cooked on.

I have no idea what the issue is but I think it is more than brand of oil.

[Nutty]

Classic lube-film failure, exacerbated by hot burn.

*Change to Motul 800T,
*Don't go any hotter than BR9EG in either bike,
*Don't use EIX plugs,
*Jet them a touch fatter on the MJ
*Change the PJ/needle-straight balance (PJ richer/NS leaner)
*Read the "Spooge ain't bad" thread.

http://www.dirtbikeworld.net/forum/s...ghlight=Spooge

Simple lubricant failure Gibbit, identical in both bikes...common demoninator? Oil. Not hard...

BTW, what premix ratio were you running?

[Chewy]

I used to get the same wear on my YZ250s at around 200 hours, however not to that extent. Using Rock Oil K2, mostly trail riding at low revs.

[Gibbit]

I run $5/litre 2T oil and my cylinders don't look like that!

Are you sure it is the nikasil wearing? Does the mark polish off? ie is it definitely worn or is there melted aluminium coating the cylinder there? What is the mark at the top of the 85 bore? Definitely worn. The mark at the top of the bore is the ring mark

Aftermarket pistons too tight? Only use Oem pistons matched to the bore size. A,b or C ect.

What do the pistons look like? Clean but have been a little hot

It all looks too clean to me....jetting too lean? Even then I would expect to see some carbon cooked on.

I have no idea what the issue is but I think it is more than brand of oil.

See above in Red

[Weird Rooster]

@JJW. What oil do you run? pm if you prefer. Cheers

[Gibbit]

Lube film failure, exacerbated by hot burn.

*Change to Motul 800T,
*Don't go any hotter than BR9EG in either bike,
*Don't use EIX plugs,
*Jet them a touch fatter on the MJ
*Change the PJ/needle-straight balance (PJ richer/NS leaner)
*Read the "Spooge ain't bad" thread.

http://www.dirtbikeworld.net/forum/s...ghlight=Spooge

Simple lubricant failure Gibbit, identical in both bikes...common demoninator? Oil. Not hard...

BTW, what premix ratio were you running?

Cheers Nutty. Your always on the money. I'll give 800T a go. I already don't use EIX plugs. I usually just go with the recommended plug temp.
I run 40:1 in all my 2st (even the TC50 and TC65) but change to 32:1 for Finke and any fast enduro's.

[Gibbit]

Nikaseal worn around exhaust port. YZ250 and YZ85

I used to get the same wear on my YZ250s at around 200 hours, however not to that extent. Using Rock Oil K2, mostly trail riding at low revs.

The 250 piston had done 57hrs of finke prerunning, plus the race, a Transmoto 6hr and a few other pretty fast WOT enduros. I change from a 178mj to a 190mj for any fast WOT stuff.



The 85 piston had done about 90hrs of reasonably easy trailrides and MX. My son is no Pro but keeps it in the powerband pretty well.

[380EXCQLD]

Just out of interest Gibbit, have you measured the wear on the pistons?

90 hrs is a lot for the 85:speechles

[Gibbit]

Just out of interest Gibbit, have you measured the wear on the pistons?



90 hrs is a lot for the 85:speechles

I don’t own a micrometer but checking the piston to bore gap the dodgy way with a feeler gauge, the 85 had a gap of .127mm and the 250 has .178mm.
Ring gap for 85cc is .4mm
and 1.2mm for the 250cc

[JJW]

@JJW. What oil do you run? pm if you prefer. Cheers

It's no secret....I run Gulf Western Air Cooled at 40:1 and jetted a bit fat - NOT for economy!

[andrew300]

I know it’s an old thread, but did the cylinder need replating with that amount of wear, or did you just put in a new piston & rings?

My KTM300 has similar wear, but only a quarter the size of the one pictured.


Sent from my iPad using Tapatalk

[Motoxfox]

Andy .....see my reply on your other post.

To fill in the dots.......any damage to the nikaseal or even scoring means
1/ the surface will 'flake' around the exhaust port where your cyl is damaged.
the flaking will immed score the cyl and piston which means your straight back where you started.
false economy to rebuild the top end with that cyl damage.

2/ a scored cyl also like you have will not allow the rings to fully seal on the compression stroke.
which is why you currently have low comp readings.

only true path is to rebore to remove the 'chip' / flaking.
That depth, re new bore diameter has to be assessed to ensure first that a piston sizing is
available to fit the 'new' finished cyl diameter once re nikaseal'ed.

welcome KTM 315 2T
GL