piston damage; Cause?

[dirk]

Hello folks

I'm going crazy with the KR-1S.
first I find (again) a hairline crack on the engine mount.
crap enough.
i wanted a better picture of the damage.
i have removed the exhaust.
what I find by the way?



i did not notice anything while driving.
what could be the cause?
the piston (mitaka) is 2500 miles old.

cheers
Dirk

[buzinc]

Exhaust port not chamfered properly! I think you need to whip the head off and take a peek inside!

Buz

[KR-1R]

.
.
there looks to be alot of crud in the ring grooves
oversize/worn barrels = piston/bore tolerances, lots of varnish on skirt
lubrication = choice of oil not burning completely - over oiled - meter pump, riding conditions

is the other piston any different?

[dirk]

good morning

@all
i know.
my English is creepy.
google translate helps me a little bit.
maybe it is sometime better..
sorry

thanks for the answers

@buzinc
how do i chamfer Nikasil cylinder?
is that possible with Nikasil?

@KR-1R
i have not looked at the other piston. (perhaps at the Weekend)
too much oil?
if you often have to drive across town or slowly over land, the muffler are always very wet.
when I move the bike fast, the exhaust is dry.
i need 1 liter of oil in 500km.
this is more or less the same consumption as my TZR.
the TZR is much leaner at part throttle.
"oversize/worn barrels = piston/bore tolerances"
?
the Piston and the pistonring were new.
the coating on the cylinder is so thin that it can not make much?
i have not heard rattling in the cold state
there is no cylinder pair.
a cylinder is stamped with "A" and the other "C".
Mitaka pistons are always "B"?
however ...strangely damage
imake new pictures as soon as the cylinders are dismantled.

regards
Dirk

[buzinc]

'@buzinc
how do i chamfer Nikasil cylinder?
is that possible with Nikasil?'

Usually when you have the barrels re-plated, chamfering is part of the finishing process. As the piston moves up/down, the ring 'bulges' slightly into the port. The chamfer just helps it back into the piston grove.
How old/miles have the bores done?

Like I said earlier you need to pop the head off and look at the ports for damage.

Buz

[dirk]

'@buzinc
Usually when you have the barrels re-plated, chamfering is part of the finishing process. As the piston moves up/down, the ring 'bulges' slightly into the port. The chamfer just helps it back into the piston grove.

Yes I do that with cast iron cylinders.
Nicasil
i'm afraid that the coating breaks down when I'm working with a file.

i do not know how old the cylinder.
the cylinders are from my spare engine.
the coating looked better than with my old cylinders.
my old cylinder are gone ca.10000km.
as my cylinder head was never sealed, I changed the cylinder

[dirk]

good evening

On the piston ring, the chrome layer is chipped.
The cylinder is not damaged by the piston ring.
for the few miles it has a lot of blowby.

damage piston ring:

back:

lhs piston:


Dirk

[dirk]

rhs cylinder:


lhs cylinder:



Dirk

[Professor]

You should not have chromed piston rings in a nicasil'ed barrel / bore.

Maybe Mitaka supplied you wrong rings with pistons?? you could try wossner.

The genuine barrels were graded size A,B,C, as were the pistons. But pistons weren't available to order in different grade sizes?! I think

I agree there is a lot of blowby, maybe check piston size / clearance