Comperssion Test

[StevoRevo]

Just wondering what the best way to tell if my engine still has good compression..??

I think i know how and i think i have good compression but just wanted to hear what everyone else had to say...

Thanks in advance

 

[Metalhead Matt]

Well, it should have some pretty good "thump" to it when it's warmed up. Get it warmed up, kill it, then turn it over by the fly wheel. It should have close to the same resistance as it does cool. Not totally the same, but fairly close. Don't burn yer digits!

 

[StevoRevo]

With the glow plug still in place..??

 

[Foolproof]

With the glow plug still in place..??

Yeah Thats the only way it will have compression. The pinch creates the seal and w/o the plug in the pressure would just go out the top.

 

[Metalhead Matt]

With the glow plug still in place..??

 

[StevoRevo]

So in other words if the sleeve starts to get slack the flywheel will be easier to turn cause all the air will be pushed out the bottom..??

 

[MotoGod]

Pretty much...yeah. If you want a good idea of how much pinch is left, yank the piston and sleeve and manually slide the piston into the sleeve. See how far it goes up without much force. If you are close to the top without much force....it's probably time for a pinch or a new piston/sleeve ;-)

 

[StevoRevo]

Pretty much...yeah. If you want a good idea of how much pinch is left, yank the piston and sleeve and manually slide the piston into the sleeve. See how far it goes up without much force. If you are close to the top without much force....it's probably time for a pinch or a new piston/sleeve ;-)

But if i took the glow plug out and spun the flywheel isnt that the same thing as yanking the piston and sleeve out and doing it manualy..??

Whats the difference..??

 

[Metalhead Matt]

The piston only goes so far up in the sleeve when it's attached to the crank.

 

[MotoGod]

Matt is correct. The connecting rod limits how far up the sleeve the piston will travel. If the taper is gone over that travel distance...your engine will run erratic, or not at all, or will start to flame out when it gets up to operating temps and the sleeve expands.

 

[StevoRevo]

The piston only goes so far up in the sleeve when it's attached to the crank.

Makes sense
Didnt think of that..

Thanks guys.. extremly helpful as always