2 stroke testing equipment.

[jdgaborist]

I want to be able to test the compression and rpms on my 2 stroke equipment. If you have experience with those 2 tools for saws, weed eaters, ATVs and such, please share.
Does an automotive pressure tester work fine for the small engines or would I be better off with a tool specific to small engines.?
Also, if there are other tools that can test the health of these 2 stroke motors I'd like to know.
Thanks in advance for your time and experience.

Specifically I have a echo 355T that wont start and is less thana week old. I'd like to have some understanding about it before it goes back. I know how to test spark and such, but I want the other test equipment so I .have a better idea the health of all my 2 stroke equipment.

 

[Homer6679]

A lot of people will recommend buying a compression tester designed for smaller equipment. I use the harbor freight set that I bought many years ago and get similar results to other “small engine” specific testers. Just test a known good running saw beforehand so that you know how much psi to expect from your gauge. Typically anything over 100 will run but 100 is still borderline.

For RPM I went and bought a cheapo inductive tachometer from Amazon. Seems to work fine in my experience.

 

[J D]

What fuel/mix were you running? If your saw is a week old & under warranty take it back. A lot of new saws (including Echo) come tuned lean out of the box. This can cause cylinder/piston damage that will wreck the saw in short order.
Compression tester needs to have a shrader valve in the fitting that screws into the cylinder & ideally a short hose up to the gauge. A good way to ensure this is to buy one for small engines.
You can usually get a good indication of compression by lifting the saw by its pull chord... if it will hold the weight of the saw or unwinds very slowly compression is usually acceptable.
Tacho can be a cheap inductive combination hr meter type or a more expensive non contact high accuracy. I use a cheap one but I tune by ear & only use the tach as a confirmatory tool. If you use one with a wire that has to wrap around the plug lead bare in mind having the top cover off will affect the air intake on some saws so set RPM may change by a few hundred when you replace the top cover afterwards. Usually they will still work if you coil the wire & place it over the spark plug outside the cover. YMMV.
If you are going to make any significant repairs to 2 stroke equipment a pressure/vacuum gauge is a must

 

[Coralillo Lo Pro]

The Stens 752-311 is a top quality small engine tester, but at $75 or so was a bit rich for me so I bought a Lang TU-21 for $28 that works good. Previous to that my new Bosch automotive tester was useless on two stroke engines, always read about 50 psi low. The idea you just need something that gives you a good comparison is all well and good, but sometimes I want to know my actual compression numbers, not just know whether it's acceptable or not. Mityvalve 8500 pressure/vac gauge a must if you plan to work on older small engines much at all to sort out crank seal issues and carburetor issues, like JD says for any major repair, not as important to minor tinkering with new engines. I generally tune by ear to the slightly rich side of things and not real fussed with testing no load RPM's as many performance-heads seem keen on doing.

 

[stihltech]

Less than a week old? Do you tech a favor. Don't touch it. Take it back and tell them EXACTLY what the saw is doing.

 

[Coralillo Lo Pro]

Less than a week old? Do you tech a favor. Don't touch it. Take it back and tell them EXACTLY what the saw is doing.

Agreed. More repair knowledge you have the better but don't practice it on new under warranty saws. That's what the dealer is there for. It's their responsibility for selling and guaranteeing working saws. The only new saw I've ever owned, my MS780, I haven't had to do any troubleshooting in the five years of owning it and milling with it, even letting it sit for long periods of time. Only had to replace a worn out spur sprocket, which gives you an idea it saw some use in that time. Otherwise it coughs on choked second pull each time, and starts on third. Most of my saws stay about that reliable. I think one of the worst mistakes people make is not keeping their saws clean. The limiters on the jets on new saws should theoretically make it hard to tune them so lean they burn out quickly though not always the case. But air filters can get coated in no time. All the broken saws a tree service guy brings me are coated in oil and dirt, with dust-caked air filters. Never ever cleans them. A blower attachment on an air compressor is your best friend for keeping your chainsaws clean and running well.

 

[heimannm]

stihltech - I saved this from my working days, I am sure you could probably add a few tips. #1, #7, and #8 are particularly applicable.

How to get better service on your machine

1) Do not call for service until everyone concerned has had time to form an opinion as to what is wrong. Allow each person the chance to correct the problem, whenever possible all control and adjusting screws should be turned all the way.

2) After several days, when the machine malfunction has become a major emergency place an urgent call for service. Friday afternoons are best, but anytime after 4:00 P.M. is O.K.

3) Alert all personnel so that each can give their version of what is wrong. Suggestions on how to fix the machine will be welcomed by the service man.

4) Hide the manual that came with the machine, claim no manual was ever received. Make several references to the service man that was here for exactly the same problem last time.

5) Have at least three graduate engineers available to ask highly technical questions which are in no way related to the immediate problem. Non English speaking is preferred but any strong accents are acceptable.

6) The minute the service man arrives, ask what caused the delay. Make it clear that he was to arrive two days ago (regardless of when the request was made). Before he can answer, ask him when the machine will be back in service.

7) The machine should be as dirty and greasy as possible. A mixture of used motor oil and pencil sharpener shavings works well. If the machine has electrical components, add staples or paper clips.

8) Assign someone to supervise the repair. Anyone who has never seen or operated the machine would be preferable. Poor hygiene and dental habits are a big plus.

9) Ask again when the machine will be ready.

10) Be sure the lights are off in the area where the machine is installed, a good service man can fix the machine blindfolded.

11) Ask if the machine is ready yet. If the service man is looking at a schematic diagram, ask him if he knows what he is doing.

12) When the repair is completed, tell the service man he did a swell job. Tell him that the job should be swell, it took long enough.

13) Try to talk the service man down on the bill, they are very fond of negotiating. Remind him big companies make too much money anyway.

14) After the service man is gone, call his boss and tell him the machine is now worse than it was before. Follow up with a letter and send a copy to the companies’ home office.

Mark

 

[Coralillo Lo Pro]

Lol. When i was looking up T435 problems for another thread, I came across a Husky tech who experienced some of that kind of thing with the local fire chief who wasn't happy with his diagnosis of user error tearing the intake boot on the saw. Even though out of warranty, the fire chief threatened to start buying all Stihl if the saw wasn't repaired for free with new P&C, and told the tech's boss that his mechanic was a "hack" who didn't know what he was talking about.

 

[jdgaborist]

stihltech - I saved this from my working days, I am sure you could probably add a few tips. #1, #7, and #8 are particularly applicable.

How to get better service on your machine

1) Do not call for service until everyone concerned has had time to form an opinion as to what is wrong. Allow each person the chance to correct the problem, whenever possible all control and adjusting screws should be turned all the way.

2) After several days, when the machine malfunction has become a major emergency place an urgent call for service. Friday afternoons are best, but anytime after 4:00 P.M. is O.K.

3) Alert all personnel so that each can give their version of what is wrong. Suggestions on how to fix the machine will be welcomed by the service man.

4) Hide the manual that came with the machine, claim no manual was ever received. Make several references to the service man that was here for exactly the same problem last time.

5) Have at least three graduate engineers available to ask highly technical questions which are in no way related to the immediate problem. Non English speaking is preferred but any strong accents are acceptable.

6) The minute the service man arrives, ask what caused the delay. Make it clear that he was to arrive two days ago (regardless of when the request was made). Before he can answer, ask him when the machine will be back in service.

7) The machine should be as dirty and greasy as possible. A mixture of used motor oil and pencil sharpener shavings works well. If the machine has electrical components, add staples or paper clips.

8) Assign someone to supervise the repair. Anyone who has never seen or operated the machine would be preferable. Poor hygiene and dental habits are a big plus.

9) Ask again when the machine will be ready.

10) Be sure the lights are off in the area where the machine is installed, a good service man can fix the machine blindfolded.

11) Ask if the machine is ready yet. If the service man is looking at a schematic diagram, ask him if he knows what he is doing.

12) When the repair is completed, tell the service man he did a swell job. Tell him that the job should be swell, it took long enough.

13) Try to talk the service man down on the bill, they are very fond of negotiating. Remind him big companies make too much money anyway.

14) After the service man is gone, call his boss and tell him the machine is now worse than it was before. Follow up with a letter and send a copy to the companies’ home office.

Mark

Doing service work for 30 years, I can relate.

 

[jdgaborist]

Agreed. More repair knowledge you have the better but don't practice it on new under warranty saws. That's what the dealer is there for. It's their responsibility for selling and guaranteeing working saws. The only new saw I've ever owned, my MS780, I haven't had to do any troubleshooting in the five years of owning it and milling with it, even letting it sit for long periods of time. Only had to replace a worn out spur sprocket, which gives you an idea it saw some use in that time. Otherwise it coughs on choked second pull each time, and starts on third. Most of my saws stay about that reliable. I think one of the worst mistakes people make is not keeping their saws clean. The limiters on the jets on new saws should theoretically make it hard to tune them so lean they burn out quickly though not always the case. But air filters can get coated in no time. All the broken saws a tree service guy brings me are coated in oil and dirt, with dust-caked air filters. Never ever cleans them. A blower attachment on an air compressor is your best friend for keeping your chainsaws clean and running well.

Good info. Thank you.

 

[jdgaborist]

Less than a week old? Do you tech a favor. Don't touch it. Take it back and tell them EXACTLY what the saw is doing.

Agree. Just wanting to have some info about the saw so that I understand that the dealer is giving right info to me. 1st time dealings with this shop.

 

[stihltech]

I (we all do) get the repair order that says"It don't run right". Some are Left hand saws
I try to call the customer to get more info.
We cherish the customer that will actually talk long enough to give us symptoms.
It not only decreases diagnosis time, it shows us a customer that will give a little trust in us.

I can't speak for the rest, but this is the customer I want in my shop.

 

[jdgaborist]

I want to be able to test the compression and rpms on my 2 stroke equipment. If you have experience with those 2 tools for saws, weed eaters, ATVs and such, please share.
Does an automotive pressure tester work fine for the small engines or would I be better off with a tool specific to small engines.?
Also, if there are other tools that can test the health of these 2 stroke motors I'd like to know.
Thanks in advance for your time and experience.

Specifically I have a echo 355T that wont start and is less thana week old. I'd like to have some understanding about it before it goes back. I know how to test spark and such, but I want the other test equipment so I .have a better idea the health of all my 2 stroke equipment.

 

[buzz sawyer]

Here are photos of the compression tester adaptor that caused false low readings for me. First shows the adaptor as received - no shrader valve in the end. This effectively increased the combustion chamber volume and low readings. Next to the adaptor is the brass tire valve I machined to fit in the adaptor. 2nd is the adaptor with the valve installed. Make sure the shrader valve is meant for small engines and not a standard tire valve. 3rd is the adaptor screwed onto the hose. This change took my reading from 90 to 130 psi in my Stihl 181.
Also recommend the vacuum/pressure testing equipment.

Here is an example of a compression tester that will NOT give good results on small engines. None of the adaptors have the shrader valve. https://www.amazon.com/dp/B00SKSAB8U?ref=ppx_yo2ov_dt_b_product_details&th=1

 

[Automan]

No compression gauge has a tyre schrader valve.(unless some bozo put one in)
Small engines will show low if the valve is anywhere away from the cylinder.
Valves on compression gauges should be near 2 psi or less.
Tyre valves are near 15-20psi.

Tyre valves will automatically subtract 15-20 psi off.
Valves up near the gauge will add combustion chamber volume from the hose.

cliff

 

[MudgeHollowBeaver]

No compression gauge has a tyre schrader valve

Then how does the gauge retain the peak pressure so that you can read it without holding the piston at TDC?

 

[MudgeHollowBeaver]

That is why there is another valve to release that stored pressure

 

[J D]

They have a schrader valve, but I believe they're not the same as a standard tyre schrader valve

 

[heimannm]

As has been noted (read the whole thread) the Schrader valve used in the compression tester must open at very low pressure, perhaps 2 PSI or so. The valve used in a standard tire application may be 10+ PSI or perhaps even a bit higher. I believe they are color coded to help identify the "pop off" pressure; the ones that I bought from Snap-On are white.

Mark

 

[Automan]

Sorry, my over/under statement on the schrader type valve.

as heimanm said tyre valves are way higher pop-off pressure.
gage valves that pass and hold cyl. pressure are approx. 2psi

Both I would think as schraders.