gavgav
Well-Known Member
hey guys looking at bore kits for my motor and there are 2 different kits one is a normal kit and one is a scut kit just wondering whats the difference and benafits
pistons scut vs normal
- Thread starter gavgav
- Start date
Help Support Mini Dirt Bikes & Pit Bikes Forum:
china boy788
Well-Known Member
any info on the kits???? more then jst the name??? info on motor?
coolmodee01
VCM B Grade 2013 Champion
i think the scut piston only has 2 rings insted of 3
but not sure dont know enough about em
but i've seen a 178 scut on a yx motor and the thing fly's
but not sure dont know enough about em
but i've seen a 178 scut on a yx motor and the thing fly's
gavgav
Well-Known Member
ive got a yx160 motor
Cactus Jack
Master Spanner Spinner
- Joined
- Jan 18, 2007
- Messages
- 2,742
- Reaction score
- 53
S-cut stands for "short cut piston skirt" ... The reasons for running a short skirt would be to clear the crank counterweights in a motor that has been fitted with a longer stroked crank than stock or to lighten an over-sized piston to get the weight back to that of the smaller stock bore piston ... With the reason being that the piston weight is critical to maintaining the original factory balance , smoothness and reliability ...
In the case of the S-cut kits for pit bike engines ... You can only bore any engine out to a certain size before a bigger cylinder sleeve is needed ... When you fit a bigger sleeve , you also need to strip the engine down and have the hole in the cases bored to allow for the bottom part of the new bigger sleeve to fit into ... Boring the cases out weakens them by minimising the amount of metal between the cylinder studs and the sleeve ... To get around that problem , the piston skirt has been shortened to the point where it clears the top of the cylinder base gasket deck surface on stock cases , therefore eliminating the need to bore the case bore larger than stock ... The Short Cut piston combined with a sleeveless ceramic or nikasil plated cylinder allows anyone to bolt on the biggest sized bore kit with the max bore size that will fit inside the cylinder stud spacings ... As a result ... the piston can be a lot bigger than the sleeve bore in the stock cases ... and the cylinder studs maintain their maximum strength ...
As I stated before , when you add a lot to the diameter of a piston ... you have to remove metal from somewhere else to maintain the stock piston weight and engine balance ie shorten the skirt ... A shortened skirt will also help reduce friction ... but it will increase the pistons' tendency to tilt at TDC and BDC rock over ... A potential problem I can see with the S-cut BBK's is that oil can get trapped in the step between the new over-sized cylinder bore and the smaller stock case bore (IF the cylinder bore is bigger) ...
In the case of the S-cut kits for pit bike engines ... You can only bore any engine out to a certain size before a bigger cylinder sleeve is needed ... When you fit a bigger sleeve , you also need to strip the engine down and have the hole in the cases bored to allow for the bottom part of the new bigger sleeve to fit into ... Boring the cases out weakens them by minimising the amount of metal between the cylinder studs and the sleeve ... To get around that problem , the piston skirt has been shortened to the point where it clears the top of the cylinder base gasket deck surface on stock cases , therefore eliminating the need to bore the case bore larger than stock ... The Short Cut piston combined with a sleeveless ceramic or nikasil plated cylinder allows anyone to bolt on the biggest sized bore kit with the max bore size that will fit inside the cylinder stud spacings ... As a result ... the piston can be a lot bigger than the sleeve bore in the stock cases ... and the cylinder studs maintain their maximum strength ...
As I stated before , when you add a lot to the diameter of a piston ... you have to remove metal from somewhere else to maintain the stock piston weight and engine balance ie shorten the skirt ... A shortened skirt will also help reduce friction ... but it will increase the pistons' tendency to tilt at TDC and BDC rock over ... A potential problem I can see with the S-cut BBK's is that oil can get trapped in the step between the new over-sized cylinder bore and the smaller stock case bore (IF the cylinder bore is bigger) ...
wogtaz ryder
Well-Known Member
i read with the scut kits you cant get replacement pistons , and they tend to blow pretty quick.
Cactus Jack
Master Spanner Spinner
- Joined
- Jan 18, 2007
- Messages
- 2,742
- Reaction score
- 53
Yes that sounds quite right ... Since a short skirt piston tilts hard in the bore at TDC and BDC rock over ... they'll quickly develop ring seal problems and piston slap due to accelerated piston and bore wear ... So they'd need to run a tight piston to cylinder wall clearance ... IF the bore wore even slightly and you put a new S-cut piston into it ... it wouldn't last too long and you'll find that's the reason why they don't supply pistons on their own ... You have to replace everything as a unit since each piston is carefully fitted to the bore by the machinist who made it ...
I can envision S-cut kits blowing smoke in a very short period of time ...
I can envision S-cut kits blowing smoke in a very short period of time ...
sonerson83
Well-Known Member
So once the piston is worn out on your 178 Takegawa $1300 kit, you just throw it away????
wogtaz ryder
Well-Known Member
Yes pretty much , putting in a well used skirtless piston would be a pretty stupid thing to do ^^
Do it right the first time , bore your cases and get a full skirt piston .
Your probably reffering to the klx110 178 kit too .. which is i think 67mm and 195cc with the klx stroker crank which is abit ridiculous ..
way better off going for a full skirted piston around 64/66mm piston with the 55mm stroker crank which ends up as 177/188cc i believe with a good +r or v2 head you dont need anymore power then that.
55mm crank 60mm HC piston and good ported v2 head and carby was probably my favorite setup = 155cc
This thread is years old btw lol.
Do it right the first time , bore your cases and get a full skirt piston .
Your probably reffering to the klx110 178 kit too .. which is i think 67mm and 195cc with the klx stroker crank which is abit ridiculous ..
way better off going for a full skirted piston around 64/66mm piston with the 55mm stroker crank which ends up as 177/188cc i believe with a good +r or v2 head you dont need anymore power then that.
55mm crank 60mm HC piston and good ported v2 head and carby was probably my favorite setup = 155cc
This thread is years old btw lol.
The_GDFP
Master Spanner Spinner
Done right, S-cut works. Tak does it right. The plating holds shape much longer than other brands who tried it.
Clearance is key. Tak piston is barely smaller than bore. Loose, they rock, so service is critical. YX needs to have the case opened a bit, so you may as well bore to 70mm and run the $194 TB 67mm skirted kit. Same 201cc as the Tak, cheaper rebuilds, longer skirt, price in line with a Chi-lump.
Clearance is key. Tak piston is barely smaller than bore. Loose, they rock, so service is critical. YX needs to have the case opened a bit, so you may as well bore to 70mm and run the $194 TB 67mm skirted kit. Same 201cc as the Tak, cheaper rebuilds, longer skirt, price in line with a Chi-lump.
