Which compression tester do you use?

trepetti

It's all good!
Elite Member
Site Supporter
Joined
Mar 23, 2012
Messages
1,599
Reaction score
834
Points
113
Location
Northern New Joizey
Visit site
With my 05 crossing the 70k miles line this last riding season, it's time I started keeping an eye on the compression. Also, it's 17 degrees outside today and I feel like buying a new tool :) .

I am looking on the web to see what is available, and I see thing like Harbor Freight (which I hear TERRIBLE things about) and the Amazon offerings (BangZoom, KaPow, and other onomatopoeic manufacturers).

Looking for a simple, reliable and easy to use tester. Let me know which one you have in your toolbox....
 

trepetti

It's all good!
Elite Member
Site Supporter
Joined
Mar 23, 2012
Messages
1,599
Reaction score
834
Points
113
Location
Northern New Joizey
Visit site
Thanks Scott. I have never used one, and the Internet is full of useful and useless information.

I see that OTC make a motorcycle set as well and the biggest difference I see it the length of the gauge hose... the 5606 is 26" and the motorcycle 5604 is 10". I see some internet dribble about the additional volume of air in the longer hose being a problem, but I am guessing not. You ever encounter a notable accuracy issue with the 5606 on smaller engines?
 

TownsendsFJR1300

2007 FZ6
Site Supporter
Joined
Feb 7, 2009
Messages
12,516
Reaction score
1,157
Points
113
Location
Cape Coral, Florida, USA
Visit site
I use mine mostly (95%) on small engines; chain saws, weed eaters, mowers, etc.

The 5606, as you can see, has many adapters. I've never come across an engine it didn't fit.

The longer hose isn't an issue with accuracy. There's o-rings if you hook up an adapter..

I'll check an engine W/O oil added in the top end and get a #. Then add oil and check.
The unit WILL show a difference however small or large, the # change (very accurate).

I can't speak about the MC style but I'm sure it'd be fine.

I do small engine repair on the side (more as a hobby) and have several commercial accounts (roofing company, tree service(lots of chain saws), Vermeer stump grinders, chipper/ shredders, several mechanics'-that don't work on small engines, mostly 2 strokes (Hilti engines, etc)as well as individual customers..

I'll use the leak down tester (same brand, OTC) should I find a unit with questionable compression:
 

TownsendsFJR1300

2007 FZ6
Site Supporter
Joined
Feb 7, 2009
Messages
12,516
Reaction score
1,157
Points
113
Location
Cape Coral, Florida, USA
Visit site
And, for an accurate reading, ALWAYS test with the throttle fully open...

Keep pulling/cranking until the pressure stops rising.. It may take several pulls/cranking..



Compression from the OLD McCulloch chain saw engine shown above (bad):

DSCN0503.JPG
 
Last edited:

Gary in NJ

Junior Member
Site Supporter
Joined
May 6, 2014
Messages
1,964
Reaction score
1,908
Points
113
Location
Amoungst the Twisty Roads
Visit site
A compression gauge is a great tool, but a leak-down test is an essential diagnostic tool. Both of mine are from Harbor Freight. There are some things you don’t buy from HF and some things you do…and these type of non-pro, seldom used tools are a good use case.

The compression gauge is easy to figure out (remove ALL of the spark plugs, connect the gauge to the cylinder, open the throttle and operate the starter until the needle peeks), the leak-down test a little less so.

In order to operate the LDT you need to get the tested cylinder at TDC and hold it there during the duration of the test. A helper on a breaker bar is very helpful. You add a reference psi to the cylinder- I always use 80psi because it is easy to hold and high enough to get a significant result. You then listen for the leaking air. If air is escaping from the exhaust, you have an exhaust valve problem. If air escapes from the throttle body (or carb) you have an intake valve issue. If it’s coming from the case breather it is the rings (it is rushing from the breather it’s likely a hole in the piston, but then you’d have 0psi during the compression check).

A healthy engine will hold 90% of the reference pressure (72psi). Below that value you should be investigating further.

When diagnosing an engine issue and you’ve ruled out fuel/air and spark, those two tools are essential. The compression gauge is something that should be used every time you change spark plugs. Make a note of the value and then track the changes over the life of the engine.
 

trepetti

It's all good!
Elite Member
Site Supporter
Joined
Mar 23, 2012
Messages
1,599
Reaction score
834
Points
113
Location
Northern New Joizey
Visit site
A compression gauge is a great tool, but a leak-down test is an essential diagnostic tool. Both of mine are from Harbor Freight. There are some things you don’t buy from HF and some things you do…and these type of non-pro, seldom used tools are a good use case.

The compression gauge is easy to figure out (remove ALL of the spark plugs, connect the gauge to the cylinder, open the throttle and operate the starter until the needle peeks), the leak-down test a little less so.

In order to operate the LDT you need to get the tested cylinder at TDC and hold it there during the duration of the test. A helper on a breaker bar is very helpful. You add a reference psi to the cylinder- I always use 80psi because it is easy to hold and high enough to get a significant result. You then listen for the leaking air. If air is escaping from the exhaust, you have an exhaust valve problem. If air escapes from the throttle body (or carb) you have an intake valve issue. If it’s coming from the case breather it is the rings (it is rushing from the breather it’s likely a hole in the piston, but then you’d have 0psi during the compression check).

A healthy engine will hold 90% of the reference pressure (72psi). Below that value you should be investigating further.

When diagnosing an engine issue and you’ve ruled out fuel/air and spark, those two tools are essential. The compression gauge is something that should be used every time you change spark plugs. Make a note of the value and then track the changes over the life of the engine.
Thanks Gary. I am pretty familiar with both leakdown and compression testing, just never done them myself. Appreciate the step by step....

I have a rule that I won't buy any Harbor Freight tool that has a motor, but it is always good to hear of a respectable mechanic that uses any specific tool. When the weather turns I plan to start trending my compression. Hopefully I won't need a leakdown test yet, but if I do I will add the Harbor Freight tester to my list.
 

Motogiro

Vrrroooooom!
Staff member
Moderator
Elite Member
Site Supporter
Joined
May 8, 2008
Messages
14,968
Reaction score
1,138
Points
113
Location
San Diego, Ca.
Visit site
Some things from HF are worth the dollar and some are trash. I bought a pop rivet tool that didn't pop the rivet but did pop it's internal mechanism. If your store is close and you're doing your own project you might say it's not a big deal. I bought a super cheap heat gun that's been great. I have an adjustable watch back spanner wrench that also came with different attachments that works great.
 

Gary in NJ

Junior Member
Site Supporter
Joined
May 6, 2014
Messages
1,964
Reaction score
1,908
Points
113
Location
Amoungst the Twisty Roads
Visit site
We had a new Harbor Freight store open about 10 miles from me. Prior to that I'd have to travel 40 minutes to go to HF and I didn't think it was worth the trip. With that said, things I have bough successfully from HF over the years:

SAE & Metric 1/2-drive Impact Socket (2005) - They have served me well and get used as just regular sockets all of the time
Compression Gauge & Leak-Down Test (2008) - Never an issue, great value
Front Wheel Chock (2014) - Does what it is supposed to do.
Rear Swingarm Stand (2015) - Does what it is supposed to do.
Wheel Balance Stand (2018) - It's excellent
24" 3/8-drive Breaker Bar (2021) - It's excellent
Hydraulic Motorcycle Lift (2021) - This is the $130 one. It's excellent. I've had a 270 pound engine sitting on it for two months...no problem
Blasting Cabinet (2021) - It's excellent
LED Lighting (2021) - So far so good
1/2 Air Hose and Regulator - So far so good
Nitrile Gloves - Great value, especially the 7mills ones

Things I wouldn't buy...
-Things with electric motors
-Abrasives (sand paper, grinding wheels)
-Things that my life depends on
-Hardware
-Batteries
 
Top