What am I doing wrong? Compression testing

[rxpx40]

Went to look over a 2011 Husq 460 rancher this week. No gas in the tank so I couldn't hear it run. Pulled the starter and it felt like it had pretty good compression. Pulled the plug and tested the compression with my gauge. Yanked on it until gauge stopped climbing. Read 38 psi. Pulled the muffler and the piston looked good. No scarring or scratches. Tested compression with the throttle held open, compression release valve in both positions. WTH?
Seller claims the saw ran great when he put it away last. Everything about this sale/person/area seems sketchy at best. Is there a trick to testing compression I am missing?

 

[angelo c]

You might be missing the part where you just pull the muffler and look at the P/C for scoring...sometimes your eye is the best tool available. I always carry a T27 scrench with me...

yes there is quite a bit of sarcasm in my post...but don't trust a tool before you trust yourself.

I always let the owner/seller start the saw...if he can't get it to run then its anybody's guess as to why it wont run...and price it accordingly.

 

[Guido Salvage]

He pulled the muffler...

What type of gauge are you using? Does it have a Schrader valve?

 

[angelo c]

He pulled the muffler...

What type of gauge are you using? Does it have a Schrader valve?

my bad.

 

[Guido Salvage]

OP, do you have a screw in tester or are you trying to hold a tube in the plug hole? You also need a good O ring and to seat the tester.

 

[Brian VT]

Need Schraeder valve in tip of tube that screws into plug hole.

 

[cedarshark]

was the decomp valve open ?

 

[Guido Salvage]

was the decomp valve open ?

Said he tried it both ways...

 

[Jason280]

Start with the basics, will the saw run? If it will run, then you know the compression is certainly better than 38psi. Personally, I don't get too concerned about compression unless there is a cranking or running issue, and certainly wouldn't buy a saw I couldn't hear run....unless it was priced accordingly.

 

[rxpx40]

Said he tried it both ways...

Hey!
I'm not that kinda guy!

Seriously- Brand new compression tester with 3 different types of threaded spark plug hole adapters (and new o-ring). Includes a quick connect for the gauge. Yes, it has the Kenny Schrader valve. I have a release button to relieve the pressure.
I've used it twice. Connected gauge to my air compressor and read exactly what the output gauge on the compressor showed, so I know it isn't the gauge. I agree. If I can't hear it run, it doesn't run unless otherwise proven. Of course, buying a saw here would fall under the 'I can't hear it run' category, but I believe most of you'se guys are stand up kinds of sellers.

 

[cedarshark]

The fact that the seller did not have mix is a red flag. Try to start the saw. If it runs...you have better than 80-90. If it doesnt, you get to practice on your rebuilding skills.

 

[lone wolf]

Went to look over a 2011 Husq 460 rancher this week. No gas in the tank so I couldn't hear it run. Pulled the starter and it felt like it had pretty good compression. Pulled the plug and tested the compression with my gauge. Yanked on it until gauge stopped climbing. Read 38 psi. Pulled the muffler and the piston looked good. No scarring or scratches. Tested compression with the throttle held open, compression release valve in both positions. WTH?
Seller claims the saw ran great when he put it away last. Everything about this sale/person/area seems sketchy at best. Is there a trick to testing compression I am missing?

How many pulls did you do ? Did you keep pulling till the numbers stopped rising? I just did a compression test a day ago on a seized 034 it had 100 lbs. Pulled it apart the rings were seized at the exhaust side. Try again keep pulling till it stops.

 

[slovcan]

Went to look over a 2011 Husq 460 rancher this week. No gas in the tank so I couldn't hear it run. Pulled the starter and it felt like it had pretty good compression. Pulled the plug and tested the compression with my gauge. Yanked on it until gauge stopped climbing. Read 38 psi. Pulled the muffler and the piston looked good. No scarring or scratches. Tested compression with the throttle held open, compression release valve in both positions. WTH?
Seller claims the saw ran great when he put it away last. Everything about this sale/person/area seems sketchy at best. Is there a trick to testing compression I am missing?

How many pulls did you do ? Did you keep pulling till the numbers stopped rising? I just did a compression test a day ago on a seized 034 it had 100 lbs. Pulled it apart the rings were seized at the exhaust side. Try again keep pulling till it stops.

If it doesn't run it's a parts saw. Remember on our other forum rxpx40, a non-running Magna is a parts bike.

Your spidy senses said this whole thing is sketchy. I'd keep looking elsewhere.

Cheers,
Glenn

 

[sunfish]

Put the saw down & walk away...

 

[Big_Wood]

I have a feeling you are using an adapter that is increasing the combustion chamber size. The valve for bleeding off pressure is no the Schroeder valve either. A compressor can overcome the added area of the adapter but a saw be tested cannot. Some of the thin ring saws would almost lose all tension on the cylinder walls over time and they still blew higher then 35psi. Over 100psi actually.

 

[lone wolf]

I have a feeling you are using an adapter that is increasing the combustion chamber size. The valve for bleeding off pressure is no the Schroeder valve either. A compressor can overcome the added area of the adapter but a saw be tested cannot. Some of the thin ring saws would almost lose all tension on the cylinder walls over time and they still blew higher then 35psi. Over 100psi actually.

I have one that just tested at a hundred and the rings were seized on the ex side.

 

[Big_Wood]

I have one that just tested at a hundred and the rings were seized on the ex side.

I just did one a week ago that still ran but very poorly. Rings were stuck in the piston as well. Free'd them up with the deep fryer and all is well. Was an old 162se thin ring.

 

[a. palmer jr.]

Hey!
I'm not that kinda guy!

Seriously- Brand new compression tester with 3 different types of threaded spark plug hole adapters (and new o-ring). Includes a quick connect for the gauge. Yes, it has the Kenny Schrader valve. I have a release button to relieve the pressure.
I've used it twice. Connected gauge to my air compressor and read exactly what the output gauge on the compressor showed, so I know it isn't the gauge. I agree. If I can't hear it run, it doesn't run unless otherwise proven. Of course, buying a saw here would fall under the 'I can't hear it run' category, but I believe most of you'se guys are stand up kinds of sellers.

Try using it without any adapters. I've found that some adapters leak and will give a lower reading..

 

[Little Al]

A sort of "redneck" compression check to give a very rough idea as to if you have enough compression, I have found that if it passes this "test" it will usually run, with the saw complete ( inc. bar & chain) hold the recoil handle & let go of the saw, check how the saw descends on it's starter cord if it sinks slowly with a series of stops & goes on each compression stroke, it will usually have enough compression to start & run. If it goes down with little or no hesitation it's a strip down job, not conclusive by any means but will give you a start point.

 

[cedarshark]

Is this saw now your problem ?