Compression Tester for 2-strokes

[Turbo]

I have one of the compression testers for cars but it gives low readings on 2-stroke chain saws.

Saw this YouTube video that explains why.

Basically you need a schrader valve in the end that screws into the plug hole.

He recommends a mityvac one but it's outside my budget.


https://www.amazon.co.uk/dp/B0002WS...8d1c3d96998389093a11c546&tag=stevessmall0e-20

So can anyone recommend a suitable tester at a more reasonable price?

There are units out there that can do both pressure and vacuum testing. Are they accurate?

 

[Migmac]

Yep, you can retro fit a valve into them.

 

[Turbo]

Yep, you can retro fit a valve into them.

How?

 

[Migmac]

Tom is this video shows you how to do it

 

[keithski122]

When I rebuilt my scooter engine I borrowed a friends pressure tester, it was a couple of bungs for the exhaust and intake, a gauge and a hand bulb like a blood pressure tester. It worked well and told me I had nipped the crank seal when refitting.

 

[Turbo]

Tom is this video shows you how to do it

Been looking into this and you need to source special schrader valves with a weaker spring than the standard car ones. Only source seems to be snap on and not easy to find.

The compression has to overcome the opening pressure of the schrader valve and the strong spring leads to low compression readings.

 

[Migmac]

Been looking into this and you need to source special schrader valves with a weaker spring than the standard car ones. Only source seems to be snap on and not easy to find.

The compression has to overcome the opening pressure of the schrader valve and the strong spring leads to low compression readings.

I’ve a friend who’s done it, I’ll ask where he got the valves from.

 

[Erie Fred]

When I rebuilt my scooter engine I borrowed a friends pressure tester, it was a couple of bungs for the exhaust and intake, a gauge and a hand bulb like a blood pressure tester. It worked well and told me I had nipped the crank seal when refitting.

Sounds like an aircraft leakdown tester.

 

[dobbslc]

@Turbo that's a good video!
That would explain why I only got 75psi on a freshly rebuilt Stihl saw that ran well.
I'm looking for a new suitable tester now

 

[Turbo]

@Turbo that's a good video!
That would explain why I only got 75psi on a freshly rebuilt Stihl saw that ran well.
I'm looking for a new suitable tester now

I was testing an unknown 2 stroke engine that wouldn't start and got a low reading.
For a comparison I tested all my good running saws and got low readings on them too! After googling I found that video that explained why.

 

[Migmac]

Been looking into this and you need to source special schrader valves with a weaker spring than the standard car ones. Only source seems to be snap on and not easy to find.

The compression has to overcome the opening pressure of the schrader valve and the strong spring leads to low compression readings.

Pal tells me it’s the red shrader valves you use

 

[JOEPRO]

I was testing an unknown 2 stroke engine that wouldn't start and got a low reading.
For a comparison I tested all my good running saws and got low readings on them too! After googling I found that video that explained why.

Probably a dud compression tester to be honest. I don't see any significant difference on the tester for 4 stroke VS 2 stroke engines.

 

[Kram]

Small displacement engines will be harder to test.

I got significantly worse readings with a cheapy china compression tester. Recommend the one in the LSE link, tho it doesnt have a 10mm adaptor.

Compression Tester - Genuine Husqvarna Part - 531 03 16-86

Compression Tester for Husqvarna Machines Genuine Husqvarna Part. OEM No. 531 03 16-86

www.lsengineers.co.uk

Post in thread 'Today I acquired...........'

Jan 17, 2025

View attachment 480877
Got one of the compression testers Kram linked to above, decent enough for £13. I’ve got a stihl kombi motor that runs okay - ish but I think it could do with a bit of tlc

Hi, Im sorry to say my test results are not great, it appears to read around 50psi lower than my other one and often more with a lot of inconsistancy, I
dont think these can be trusted. My comparison is against the Husqvarna recommended one here

Compression Tester - Genuine Husqvarna Part - 531 03 16-86

Compression Tester for Husqvarna Machines Genuine Husqvarna Part. OEM No. 531 03 16-86

www.lsengineers.co.uk

I did buy it primarily for the 10mm thread adaptor, as I...

• Kram

• 
• 

 

[Keithmac]

On the 4 stokes I do a compression and leak down test.

On the 2 strokes compression testing is hit and miss, for the time it takes taking it to bits and inspecting barrel and piston is more beneficial.

 

[premmington]

Probably a dud compression tester to be honest. I don't see any significant difference on the tester for 4 stroke VS 2 stroke engines.

LV = low volume engines - can't move enough air to fill the pressure tester.


Thus the need for a "one way valve".

 

[dan.taylor.1]

The husqvarna one listed by kram is what I use too, that and a Stihl one with a fixed brass stem rather than the flexi hose. Though my old gunson tester from 20 years ago worked fine too till I broke the hose in half...

 

[Keithmac]

As rough as it sounds on a 2 stroke if you pull the spark plug and put your finger over the hole and crank the engine if it pops your finger off when cranking it's normally enough to run an engine.

 

[Turbo]

Pal tells me it’s the red shrader valves you use

Seen a way of comparing the spring rate on a valve. You press the valve onto a set of digital scales and see how many grammes it measures when the valve opens.
Obviously you will need an original low pressure valve to compare it to.

 

[Turbo]

Looked at the price of a thread tap for a schrader valve. They are not cheap!
I guess you could strip the rubber of a tyre valve and loctite the brass bit into the end of your compression tester to hold the schrader valve.

 

[Turbo]

Small displacement engines will be harder to test.

I got significantly worse readings with a cheapy china compression tester. Recommend the one in the LSE link, tho it doesnt have a 10mm adaptor.

Compression Tester - Genuine Husqvarna Part - 531 03 16-86

Compression Tester for Husqvarna Machines Genuine Husqvarna Part. OEM No. 531 03 16-86

www.lsengineers.co.uk

Post in thread 'Today I acquired...........'

Jan 17, 2025

View attachment 480877
Got one of the compression testers Kram linked to above, decent enough for £13. I’ve got a stihl kombi motor that runs okay - ish but I think it could do with a bit of tlc

Hi, Im sorry to say my test results are not great, it appears to read around 50psi lower than my other one and often more with a lot of inconsistancy, I
dont think these can be trusted. My comparison is against the Husqvarna recommended one here

Compression Tester - Genuine Husqvarna Part - 531 03 16-86

Compression Tester for Husqvarna Machines Genuine Husqvarna Part. OEM No. 531 03 16-86

www.lsengineers.co.uk

I did buy it primarily for the 10mm thread adaptor, as I...

• Kram

• 
• 

My tester is the Sealey badged version of the Chinese tester.

Might add that Husky tester to my next LSE order. I can use the 10mm adaptor off the Sealey one.