When to change piston? (2-stroke)
ar...@ecs.umass.edu
250 2-stroke Question:
How often should a piston be changed?
On my 89 KX250 I would change the piston during the winter and replace
the rings once during mid season. I've heard of guys not replacing the
piston that often but just changing the rings regularly.
This question applies to my 94 KTM 250 which has about half of a season
on it. Should I do rings or piston and rings?
BTW: I ride at least 6 hours/week of enduro type trails.
Any body use Wiseco piston's recently?
Thanks for the help,
Al Ross
Mark Ingersoll
Hi Al,
as far as 2-stroke pistons go, the type of bike you own and how hard you
ride it seem to be the governing difference. I ride a MX bike hard so
I'll just give you my thoughts ($.02) for pistons and rings.
1. Cheapest way to horsepower. Keeping a fresh piston and rings will be
the best way to keep your bike fresh and snappy versus new pipes, etc.
2. On my bike, I do rings every 25 hours and a piston at 50. I ride a
Suzuki RM250, which tends to be hard on pistons/rings. My buddies with
CR's say they can go 50 hours for rings, 100 for pistons.
3. The best way to judge change time is to measure compression. When you
have a fresh piston and rings, break it in (1-2 hours) and check
compression. Then as it wears, you can get a feel for the compression vs.
performance to judge for yourself when it's time. On my bike, I get a
feel for the compression when kicking it over and this usually correlates
with ~25 hrs. For trail bikes, I'd guess 50/100 for your rings/piston.
4. Keep your filter clean and don't skimp on pre-mix ratio. If book says
32:1, stick with it. Skimping on pre-mix is the quickest way to kill a
motor. If bike runs "rich", focus on jets and plugs. I ran 32:1 Bel-Ray
and at 300 hours, bearings were still like new with near zero play.
Hope this helps!
Mark
Elizabeth City MX
MERRILL C. HOEKSTRA
>> 250 2-stroke Question:
>> How often should a piston be changed?
>>
>> This question applies to my 94 KTM 250 which has about half of a season
>> on it. Should I do rings or piston and rings?
>> Al Ross
>Hi Al,
>as far as 2-stroke pistons go, the type of bike you own and how hard you
>ride it seem to be the governing difference. I ride a MX bike hard so
Mark is right, the type of bike you own is important. KTM's pistons are
forged, not cast and the result is that they are more expensive, but they
last _alot_ longer. Unless you are contesting the AA or expert/pro class,
you can ride a KTM all season or two or three without changing the piston
and rings.
>I'll just give you my thoughts ($.02) for pistons and rings.
>1. Cheapest way to horsepower. Keeping a fresh piston and rings will be
>the best way to keep your bike fresh and snappy versus new pipes, etc.
>3. The best way to judge change time is to measure compression. When you
>have a fresh piston and rings, break it in (1-2 hours) and check
>compression. Then as it wears, you can get a feel for the compression vs.
>performance to judge for yourself when it's time. On my bike, I get a
>feel for the compression when kicking it over and this usually correlates
>with ~25 hrs. For trail bikes, I'd guess 50/100 for your rings/piston.
Probably best to use a compression gauge here.
>4. Keep your filter clean and don't skimp on pre-mix ratio. If book says
>32:1, stick with it. Skimping on pre-mix is the quickest way to kill a
>motor. If bike runs "rich", focus on jets and plugs. I ran 32:1 Bel-Ray
>and at 300 hours, bearings were still like new with near zero play.
Yes, A KTM with a clean filter and proper jetting will go a long time on the
original top end.
>Hope this helps!
>Mark
>Elizabeth City MX
<KTM marketeer mode off>
Merrill Hoekstra
91 and 94 KTM 250's
Ken Murphy
: > 250 2-stroke Question:
: > How often should a piston be changed?
: > On my 89 KX250 I would change the piston during the winter and replace
^^^^^^^^
Cast Piston (OEM)
: > This question applies to my 94 KTM 250 which has about half of a season
^^^^^^^^^^
Forged Piston (OEM)
Forged pistons are supposed to last much longer than cast pistons. Keep an
eye on the compression, and an ear on the motor. If it begins slapping, you
should have replaced it last month. ;)
: 1. Cheapest way to horsepower. Keeping a fresh piston and rings will be
: the best way to keep your bike fresh and snappy versus new pipes, etc.
This can be a bit spendy on a Katoom though. Piston/rings/gaskets for
a forged piston is >$150
[other good advice deleted]
: Hope this helps!
: Mark
: Elizabeth City MX
--
O Ken Murphy aka ke...@array.com RMEC
<M>erfMan DoD #0479 '94 YZ 250 NRA COHVCO
_/ \_ BBCFORR #2 406077 AMA
Disclaimer: _I_ don't believe what I said, why should you? 0005 FOLMA