compression tester comparison

[BILLSMOWERS]

just bought a echo compression tester from a friend in the states so poped down a friends shop and did a comparison with his stihl gauge

echo 120 psi stihl which has a 10mm thread but has a adapter to convert to 14mm but only got 60 psi ? His stihl gauge is only a week old but this is the first time out of it's box now he thinks there is a problem with the stihl gauge the only thing that is different is the stihl has not got a shrader valve in the end

any ideas

[BILLSMOWERS]

looks like the stihl gauge is us 60 psi difference we checked it against a second gauge which also reads 120 psi same as echo so stihl gauge out the window my friend not very happy as first time out of the box he is sending it back

[spudulike]

just bought a echo compression tester from a friend in the states so poped down a friends shop and did a comparison with his stihl gauge

echo 120 psi stihl which has a 10mm thread but has a adapter to convert to 14mm but only got 60 psi ? His stihl gauge is only a week old but this is the first time out of it's box now he thinks there is a problem with the stihl gauge the only thing that is different is the stihl has not got a shrader valve in the end

any ideas

 

That is a loaded question. Compression gauges typically either have a schrader valve or a rubber ball valve in the end. The rubber ball type typically make a reading very fast 1-2 pulls where the schrader valve types take around 5-6 pulls.

 

The schrader valves are not the type you get in car tyres but have an extremely low spring rate and are the type used in gas sniffer meters. So......the type of valve can influence the reading - the only place I have managed to get the valves from is Snapon as I was blowing them regularly on the ported saws I do.

 

It is always good to do a couple of slow pulls when using a schrader type compression gauge.

 

Me being me have found a presta type valve that has a low opening and sealing force and have converted my gunson to take it and reads as it should, these last much longer and don't break even with my ported portfolio. I have a Pickvant Sykes unit and it reads low and some car types won't even get a reading on small plant like this.

 

I have heard that a 14mm gauge stepped down to the 10mm size will lose around 20psi down to the volume of the combustion chamber being increased by the size of the adaptor internal bore - my experience sort of follows this theory.

 

You asked:lol:

[GardenKit]

I did not know Stihl did a compression tester, so learned something today!

 

Without a Schrader valve it would not work on a 2 stroke engine anyway.

The volume of the hose will be added to the swept volume of the cylinder, and thus dilute the reading, which anyway could only be read whilst the engine was being cranked. But the volume of the hose is much higher in relation to the engine size of our small kit than it would be on say, a 4 cyl 2000cc engine where its volume will not affect the reading too much

 

Likewise, the one with the valve will be diluted on the first few pulls, but as the valve will trap the pressure it will build in the hose and gauge until it can be topped up no more, thus reading the compression generated by the piston.

 

Does this make sense?

[BILLSMOWERS]

stihl & echo are for 2 stroke engines stihl has 10mm plug thread screwed in to a 14mm adapter the echo is the opposite way 14mm down to 10mm there must be a valve of some type as the stihl holds the pressure 55 psi first pull then up to 60 psi second pull then no more echo has the schrader in the end of the hose

echo takes 5 pulls to get the 120 psi the only thing i can think of is the stihl made for a specific series of engine?

[BILLSMOWERS]

stihl & echo are for 2 stroke engines stihl has 10mm plug thread screwed in to a 14mm adapter the echo is the opposite way 14mm down to 10mm there must be a valve of some type as the stihl holds the pressure 55 psi first pull then up to 60 psi second pull then no more echo has the schrader in the end of the hose

echo takes 5 pulls to get the 120 psi the only thing i can think of is the stihl made for a specific series of engine?

 

stihl part number is 5910-850-2000

for series 4180 power head there lies the problem it looks like the gauge is made for this series only

[GardenKit]

Stihl, like other manufacturers do not suggest compression testing as being accurate on two strokes and only suggest compression figures on a 4 stroke.

 

However, I find compression figures a good guide on a 2 stroke as to engine condition.

 

The thing with not having a valve in the end of the hose is that the hose volume is added to the unswept volume, vastly increasing it, so lessening the compression that can be achieved as the volume of the hose is being compressed every time the engine turns and released every time to.

The one with the valve traps the pressure and adds to it every rev "pumping it up" until it equalises the compression in the upper cylinder.

 

But I cant quite figure why it should work on a 4t?

[NFG]

Hi

 

Is it possible that the gauge lost its calibration during transit? As I understand a simple pressure gauge is a bourdon tube in a spiral that tries to straighten when pressure is applied thus moving the needle, thats right isnt it Spud?

 

So if you could calibrate it against some known pressure - scratch head for something at or around 150 or 200psi - then you should be able to re-adjust accordingly.

 

N

[adw]

Husqvarna do a compression tester part no. 531031686

[GardenKit]

Just found a pic of the Stihl one. It does not have a hose, just a solid tube which I guess is of small bore so not adding much to the unswept volume.

 

Reckon you have just got a faulty gauge then Bill.

 

I use a couple of Draper ones now, they seem to outlast all the others.

 

Top tip though. Remove all fuel before testing compression. I did one last year with a brand new Gunson gauge on its second use. The engine flooded and compressed petrol into the gauge which killed it instantly.