Strato compression readings

[radio]

Recently I purchased a Husqvarna 545. A compression test showed about 110 psi. My tester is a MityVac and I used the 14mm to 10 mm adapter. I have read that using adapters throws the compression off. I would like to know why. Since the MitVac hose has the schrader valve at the tip, adding less than an inch of an adapter should not significantly change the readings. And yes, using the hose (14mm thread) correlates with another gauge that I have.

I also purchased a 576xp and compression testing without the adapter and using the 14mm hose with schrader valve at the tip, yields similar results.

So ... do strato saws not show expected results when doing a compression test?

 

[Simondo]

The 14mm to 10mm adapter adds to the volume of the cylinder above the piston at TDC when it has the valve further up than at the tip into the plug hole . Cant answer the situation over the 576 as having the valve at the tip is optimal for tests. I no of no issue with strato saws and compression testing.

 

[Landmark]

The 14mm to 10mm adapter adds to the volume of the cylinder above the piston at TDC when it has the valve further up than at the tip into the plug hole . Cant answer the situation over the 576 as having the valve at the tip is optimal for tests. I no of no issue with strato saws and compression testing.

I cant tell it adds or decreases cylinder volume when looking at it. So i am still unclear to why there is compression reading problems.

 

[Simondo]

This is how I see it Dave.
For the same reason that reducing the space left above the piston when changing squish will give you a lift in compression .... the adaptor is affectively giving you a bigger volume combustion chamber if the valve is not at the end.

 

[Landmark]

This how I see it Dave.
For the same reason that reducing the space left above the piston when changing squish will give you a lift in compression .... the adaptor is affectively giving you a bigger volume combustion chamber if the valve is not at the end.

It appears the valve is flush at the end of threads in my cylinder. Here's another pic but its not as good.

 

[Simondo]

It appears the valve is flush at the end of threads in my cylinder. Here's another pic but its not as good.
View attachment 25943

Yea...the threads of the brass adapter are flush but the valve isnt . The valve would need to be plugging the hole right at the cylinder wall for the volume not to change.

 

[Tor R]

The valve should be on the tip of the adapter, as longer distance there is from the combustion chamber to the valve the more lower reading you get.
Do your schrader valve work propleby? 110 psi is so low that I would check the valve, even with the adapter.

I've never checked compression on 550/560/562, but my snap-on hose is long, on all my saws I have to pull at least 20 pull before I get correct reading.

 

[Simondo]

The valve should be on the tip of the adapter, as longer distance there is from the combustion chamber to the valve the more lower reading you get.
Do your schrader valve work propleby? 110 psi is so low that I would check the valve, even with the adapter.

Tor....I get only 90psi from near new Dolmar Ps 420 on the 14mm to 10mm adapter without a shrader valve at its tip. The same tester without the adapter screwed onto the 14 mm end and put into a 42 special reads 165psi ..... Posable Daves valve is fine and its down to the adapter only.

 

[Tor R]

Tor....I get only 90psi from near new Dolmar Ps 420 on the 14mm to 10mm adapter without a shrader valve at its tip. The same tester without the adapter screwed onto the 14 mm end and put into a 42 special reads 165psi ..... Posable Daves valve is fine and its down to the adapter only.

try to see if you can make one adapter where the valve is on the tip of the adapter Simon and see what you get in reading result.

 

[Simondo]

The valve should be on the tip of the adapter, as longer distance there is from the combustion chamber to the valve the more lower reading you get.
Do your schrader valve work propleby? 110 psi is so low that I would check the valve, even with the adapter.

I've never checked compression on 550/560/562, but my snap-on hose is long, on all my saws I have to pull at least 20 pull before I get correct reading.

"
Do snap on address the issue of the shrader valve at the end of "each " screw in adapter Tor ? ...if not then it seems odd . I just cant find any testers that have ALL there parts set up right !

 

[Simondo]

try to see if you can make one adapter where the valve is on the tip of the adapter Simon and see what you get in reading result.

Iv looked into it Tor and getting a tap a seating tool are not cost effective . Think a bodge up with glue is the option ...I Hate A Bodge !!!

 

[Tor R]

Simon, there was a thread about it here
http://opeforum.com/threads/accurate-compression-testing-on-10mm-cylinders.2880/

 

[radio]

Do your schrader valve work propleby? 110 psi is so low that I would check the valve, even with the adapter.

Yes, the 14mm hose shows expected readings on 4 other saws as well as my air compressor.

 

[radio]

Ummm ... er ... oops ...

... the compression release valve on the 576 is pushed in ... doh!

I have not yet fueled or used the saw. When I have time I will pull the compression valve and reset it and re-test.

I looked at the 14mm to 10mm adapter and yeah, there can be enough space in there to throw the readings off.

 

[mdavlee]

If you add 2cc to the chamber that will throw it off big time.