Welcome, Guest. Please Login or Register

Author Topic: Piston and rings life. 2T vs 4T?  (Read 297 times)

0 Members and 1 Guest are viewing this topic.

Offline Mapog

Piston and rings life. 2T vs 4T?
« on: February 06, 2019, 09:26:29 pm »
When buying a new 250 2T Yamaha, I believe you get a spare piston and ringset with.?
I dont know whether its the same for the 2504Ts with slipper pistons?

What I would like to know is how do pistonlife of a 2T compare to a 4T of similar capasity?

Everybody always talks about the simplicty of the 2T and how cheap to rebuildt, but surely their engine life is much lower than a 4T?
 

Offline GeenSand

  • Senior Member
  • ***
  • Bike: AJS (all models)
    Location: Eastern Cape
  • Posts: 720
  • Thanked: 26 times
Re: Piston and rings life. 2T vs 4T?
« Reply #1 on: February 06, 2019, 09:33:51 pm »
Depends on the type of use.. we had a aircooled Dt175 on the farm that did 48k km on the first set of piston and rings it came with.. downhill from there.  (aftermarket parts= useless)

Sent from my Armor_2 using Tapatalk

Take nothing but photos
Leave nothing but tracks
Kill nothing but time
 

Offline Dux

Re: Piston and rings life. 2T vs 4T?
« Reply #2 on: February 06, 2019, 09:37:40 pm »
I presume you are talking enduro or mx , the 2 strokes suffer slightly because of the ports which will give increased wear , 4 strokes have high rpm , a typical 250 - 2 stroke revs to about 8500/9000 whereas a 250 - 4 stroke enduro bike will pull 12 500rpm with mx models usually 1000 rpm higher .
Having said what I did about 2 strokes a typical KTM 250/300 will have a recommend piston replacement at 100 hours , but then again the 4 strokes are also recommended to replace at 100 hours so no difference .
Where the big difference does come in is cost of repair when things let go , there the 2 strokes score big time .
So in my mind no cause for concern buying a 2 stroke .
Motoworx
motoworx1@gmail.com
073 232 5389
Unit 6 Viben square
8 Viben Road , Brackenfell
 

Offline Mapog

Re: Piston and rings life. 2T vs 4T?
« Reply #3 on: February 07, 2019, 12:25:03 am »
Dux, but surely the premix wouldnt give the same level of lube as the oil only in 4T?
 

Offline Dux

Re: Piston and rings life. 2T vs 4T?
« Reply #4 on: February 07, 2019, 07:49:38 am »
Dux, but surely the premix wouldnt give the same level of lube as the oil only in 4T?

Modern oils are exceptionally good and far superior to the stuff available 20 / 30 years ago , to give you an idea , guys racing classic 2 stroke GP bikes are getting 3 to 4 times the durability out of pistons and crankshafts , the only difference between then and now is the oils that are used .
I see bikes with in excess of 200 hours where the motor has never been opened . One KDX200 had run 4 years , practically every weekend , when the top end was opened the clearances were still within spec but a new piston was installed anyway .
Motoworx
motoworx1@gmail.com
073 232 5389
Unit 6 Viben square
8 Viben Road , Brackenfell
 

Offline Bill the Bong

  • CRF450X for the win
  • Senior Member
  • ***
  • Bike: Cagiva Elefant 900
    Location: Northern Cape
  • Posts: 3,846
  • Thanked: 61 times
Re: Piston and rings life. 2T vs 4T?
« Reply #5 on: February 07, 2019, 09:23:44 am »
I work on quite a lot of KTMs.  The 300 2T rings tend to last better than the 4 strokes (130 hr +), the 250 and 200s about the same (90 - 110) and the 125s less.  I'm sure the golden thread is revs on the 2 strokes.  All are for race bikes.
 

Online Welsh

  • BMW R1150GSV
  • Bachelor Dog
  • *****
  • Bike: BMW R1150GS
    Location: Gauteng
  • Posts: 16,590
  • Thanked: 204 times
  • Thunder Twonk. The two legged Twat Monkey.
Re: Piston and rings life. 2T vs 4T?
« Reply #6 on: February 07, 2019, 09:31:50 am »
Fundamentaly, a two stroke piston has a harder life than a four stroke piston, from a wear perspective, due to the large ports in the cylinder it has less support for the piston than a four stroke cylinder. In addition the ports cause some uneven thermal expansion which must be catered for with increased piston clearances, resulting in more wear. The simple fact that the intake and exhaust are carried out in the cylinder not in the head also results in differential temperatures in the cylinder, which must be again be catered for with increased piston clearances, resulting in more wear.
The flip side is the higher revs of the four stroke, this does not necessarily result in more wear, just fairly catastrophic failures if it does let go, hence a piston swap is not a bad idea.  :biggrin:   
Duirt me leat go raibh me breoite. Courtesy of Spike
 

Offline Tman21

  • Senior Member
  • ***
  • Bike: KTM 990 Adventure
    Location: Gauteng
  • Posts: 1,043
  • Thanked: 10 times
  • The I was like braaaap!
Re: Piston and rings life. 2T vs 4T?
« Reply #7 on: February 07, 2019, 09:44:51 am »
How long is a piece of string.

Mate has done 220hrs on his KTM 250 2T on one piston, rings were pretty sharp and compression on the low side but they still had a few hours left in them.  Others break a ring in less than 100hrs.  Maintenance has some influence here as well as your mixing ratio and oil used.  In my opinion if you are not racing and revving this bike all the time 120-150hrs is easily achievable without any harm.

My 250 Husqvarna 250FE 4T did around 250hrs before I opened the motor.  Mechanic insisted there is nothing to change but due to the hours I wanted at minimum the rings to be changed, couldnt find a set of rings so did a piston and rings combo.  Bike ran with that top end to over 600hrs in total without missing a beat and at the Roof in 2017 I put a hole in the casing and limped back to the DSP with oil pissing everywhere after a nice tumble off a terrace on one of the passes.  Did an insurance claim which included strip and assemble, with the bike shop not knowing the history they opened, inspected and said everything was still in perfect nick so assembled with new seals and gaskets everywhere.  I sold the bike to a mate that has now added at least another 100hrs on the same top end (so close to 500hrs) and the bike is still running strong.

On my 4T the oil never ever spent more than 12hrs in the motor but mostly changed the oil after every 3rd ride regardless of hrs, (roughly between 7-10hrs every round) with an oil filter every 3rd change and a new oil screen every 2nd filter.

My 2C here is that if you on the 2T now do a piston and rings every 120hrs, its relatively cheap and can save you from a 10K complete rebuild exercise.

Cheers
T