Chainsaw Compression Question

[Vintage Engine Repairs]

Can I get an accurate compression test of an old ms 180 without the air filter and carb attached?

Thanks!

 

[pioneerguy600]

Yes. Compression is part and parcel of the piston, rings and and cylinder.

 

[Vintage Engine Repairs]

Yes. Compression is part and parcel of the piston, rings and and cylinder.

Thanks just realised the piston passes the air intake and thus that’s where the compression is created... rookie question!

Got this from Supercheap Auto, which here in Australia is basically a car parts shop. It doesn’t work.. reads like 25psi on my brand new saw and the exact reading on my old one that has half the compression ! It’s going back tomorrow and have ordered one front “All mower spares” it’s twice the price, but hopefully works!!

 

[HarleyT]

Thanks just realised the piston passes the air intake and thus that’s where the compression is created... rookie question...

No, the guys here will still fight over this topic!!

 

[jltrent]

Just pull the recoil and if it has good resistance they are usually okay. I can usually get within 5-10 lb. of compression by doing it that way. I have 4 gauges laying around here and all will give just a little different final results, but from the gauges you know if you have bad, good or great compression. North of 160 lb. is great compression, 140-160 lb. is good and below that usually down to 120 they will run okay, but off on power.

 

[Huskybill]

Wide open throttle, compression test. No carb or air filter doesn’t matter.

Some I see hang the saw by the pull cord. If the saw drops the compression is low.

 

[HarleyT]

Throttle fully closed!!!
Air filter on!!!

 

[Deleted member 117362]

Attach the gauge and start pulling until gauge needle no longer rises. Easy deal.

 

[Huskybill]

Your not getting a exact compression reading with the throttle closed.

Do one reading throttle closed and one reading throttle open subtract the larger reading from the lower reading(reading #1). Add both readings together then split reading one in half add it to the combined reading.

I won’t go a hot saw reading or oiling the rings.

 

[Deleted member 117362]

Nonsense. Do you close or open exhaust so air cannot get in?

 

[Huskybill]

Did I confuse you? Just funnin

 

[Deleted member 117362]

Nope, how do you stop air from coming in through exhaust port?

 

[HarleyT]

Wide open throttle

Why did you say this? It doesn't matter, you pull it over until the gauge stops rising,
don't you?

 

[Huskybill]

I didn’t know there’s an on going discussion about throttle wide open or closed during a compression test. With the throttle wide open the compression may max out with less pulls.
Someone is going to test the theory of both ways to do a compression test?

 

[farmguywithasaw]

Yup

 

[HarleyT]

I didn’t know there’s an on going discussion about throttle wide open or closed during a compression test. With the throttle wide open the compression may max out with less pulls.
Someone is going to test the theory of both ways to do a compression test?

Not me......

I am just trying to start trouble........

 

[pioneerguy600]

Thanks just realised the piston passes the air intake and thus that’s where the compression is created... rookie question!

Got this from Supercheap Auto, which here in Australia is basically a car parts shop. It doesn’t work.. reads like 25psi on my brand new saw and the exact reading on my old one that has half the compression ! It’s going back tomorrow and have ordered one front “All mower spares” it’s twice the price, but hopefully works!!

I have tested a good many with no muffler, carb and most body panels removed. The compression begins when the piston closes off the exhaust port on a chainsaw cylinder.[/QUOTE]

 

[HarleyT]

I have tested a good many with no muffler, carb and most body panels removed. The compression begins when the piston closes off the exhaust port on a chainsaw cylinder.

[/QUOTE]
So you are a throttle closed or open guy?


I am [bi-throttle]........
{Another way of saying that it doesnt matter}

 

[pioneerguy600]

It doesn`t matter and there is no throttle when the carb is off...LOL

 

[HarleyT]

So you are "pan-throttle"????