Low Compression???

[lukewozniak2000]

I did a compression check today on my stock blaster and it showed about 90psi. Now, when i went to the book it says to warm the quad up first but i didnt do that. So is 90psi when its cold good compression or is it time to do a ring job...havent checked the compression when it is warm. Any input??

 

[sheeblast]

i have never warmed them up before checking. but did you hold the throttle open while checking? did you kick till the needle stopped moving? was the tester in correctly, like was it in far enough?

 

[YFS101]

checking it when cold is fine. hold the throttle open and kick until it stops going up.

90psi is low. rebuild it now before its starts to cause damage. you might just need a new set of rings or piston kit.

 

[lukewozniak2000]

I think that the tester is a pile. I checked it again and it was 90 but when i put the spark plug back in is seems like there is more compression cause it kicks harder......i will buy a new tester and test again. The compression should be at 120 right?

Also, if there is a need to replace the rings ect... is it a easy job that I could do, or is it a pain in the ass. It doesnt look that hard but you never know.

 

[sheeblast]

rings are easy, just need to have the walls rehoned, and new gaskets.

 

[lukewozniak2000]

so I dont need any special tools? I just take the bolts off and take the cylinder to my mech. and he can clean it up and then all i do is put it back together?

 

[lukewozniak2000]

im not sure if the top end has been rebuilt in the past, so what would be my safest bet on bore size and piston size?

 

[sheeblast]

no clue, only way to know is to take it apart and measure it out.

 

[scotj77]

any machinist should be able to tell ya if your cylinder is out of specs if you take the cylinder and piston to a shop

 

[lukewozniak2000]

ok. when i get the tester and actually works right, what is the proper psi?? 100-120 right?

 

[sheeblast]

is your motor stock? if so 110 -120 is good on a stock motor.

 

[cole454]

110-120 psi

edit Dang it again sheeblast

 

[sheeblast]

dude you were 3 minutes late.

 

[cole454]

I'm watching TV right now. I'm slow lol

 

[lukewozniak2000]

yeah the motor is stock. I bought a good tester and it still reads 90 so it looks like im gonna have to buy a rings kit along with gaskets

 

[sheeblast]

wait to buy the rings till you tear the motor apart so you know which size to get.

 

[Whitty21]

you shouldnt need a bore, just a hone, prolly 10-15 dollar shop service

installing the top end is easy as long as you install the wrist pin clips correctly you should have no problem.

there is a video stickied in the engine section done by ken oconnor, definately check it out and educate yourself

 

[sicivicdude]

If you re-ring the same piston you shouldn't even need to pull the wrist pin clips out.

You can determine if the piston to cylinder clearance is out of specification if you have a basic set of machinist tools available at any discount tool supply house.

$32 for the tools and you'll never have to disassemble your top end to take it to a machine shop again, you can measure the piston and cylinder clearance using the instructions in the manual.

6 Piece Technical Measuring Set

6" Digital Caliper

 

[YFS101]

130 is for a great engine,
120 is ok
below 120 it needs attention asap

dont just assume it only needs rings. carefully inspect it or take the piston and cylinder to a local shop and have them measure it.
if its within specs... (.003") and no no damage to the piston/cylinder then you can re-ring it. However if the cylinder and piston are worn to the max allowed. by the time you re-hone the cylinder it will be out of specs and will need to be bore .010" over and new piston kit installed.
Also it is a really good idea to replace the piston pin and bearing EVERY time you either replace the rings or piston. Of all the bearings it has the most heat, stress and wear.

 

[sheeblast]

not sure where you are getting your numbers, but stock 120psi is good. 110 is ok and below 110 is low.