I hope it helps 
How To Do A Compression Test
- Thread starter Vintage Engine Repairs
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Good video... Quick and to the point!
Thanks!
And every time you pull the rope you are drawing in mix into the cylinder.
I hope it helps
Thanks Tom, much confusion abounds on cold or hot test
full or no throttle , and rate of climb on the guage
I,ll go with what you have !
Glad you enjoyed it! I’ve had great tuition and guidance from members on here over the years so it’s nice to be able to make videos that others can learn from now.
Yep
Good stuff as usual,
Tom one thing that was not mentioned.... As you go up in elevation the compression reading is going to be lower. So at sea level your 170psi is going to be much lower at 6,000feet elevation.
Cheers, Patrick
Tom one thing that was not mentioned.... As you go up in elevation the compression reading is going to be lower. So at sea level your 170psi is going to be much lower at 6,000feet elevation.
Cheers, Patrick
Thanks for the advice! I didn’t even think of that. Feel free to mention it in the comments and I’ll pin it for others to know!
Another fine video. Just one addition from personal experience - if you must use adaptors, make sure they have a shrader valve in the end that screws into the cylinder. The ones pictured do not have the valve and will reduce compression reading due to increasing the cylinder displacement, more so on smaller cc engines.
Attachments
Very good:
I have TWO small engine compression testers. One is homemade from info about such on this site and If one reads low I get a second opinion from the other.
I've seen good automobile mechanics give a wrong diagnosis of a chainsaw because their automotive compression tester read really low and most generally when I tell them their gauge is not reading correctly for a small CC engine:
They usually say their high priced Snap-On, Mac compression gauge reads correctly because I test it on my air compressor as right on. It's really an expensive gauge and always reads correctly.
Thanks for the video.
I have TWO small engine compression testers. One is homemade from info about such on this site and If one reads low I get a second opinion from the other.
I've seen good automobile mechanics give a wrong diagnosis of a chainsaw because their automotive compression tester read really low and most generally when I tell them their gauge is not reading correctly for a small CC engine:
They usually say their high priced Snap-On, Mac compression gauge reads correctly because I test it on my air compressor as right on. It's really an expensive gauge and always reads correctly.
Thanks for the video.
AMEN
do not have the valve and will reduce compression reading due to increasing the cylinder displacement,
These type on small cc engines WILL usually reduce the read compression even after several rope pulls and the reading taken will act lazy and weak on each increase pull of the rope.
I've taken spark plugs and braze in a tire valve adapter brass center section for use of the SPECIAL weak spring schrader vavle. A regular automotive schrader tire valve will also result in low compression readings on a small cc engine.
kshansen
ArboristSite Operative
Any suggestion on where to purchase the weak spring schrader valve?
Yikes..... iffin ya got some time to kill....
https://schrader-pacific.com/wp-content/uploads/2023/02/Valve-Core.pdf
https://schrader-pacific.com/wp-content/uploads/2023/02/Valve-Core.pdf
kshansen
You asked:
Any suggestion on where to purchase the weak spring schrader valve?
Link to a video about small engine compression testing6/23
https://www.arboristsite.com/thread...-04&utm_content=daily_newsletter#post-8020777
http://www.arboristsite.com/community/threads/compression-tester-issues.310133/
I got 3 of the Napa 700-9556 compression gauge Schrader valves today after the local NAPA ordered from their warehouse. The come 5 in a box and you can buy them each @ approx. $2.20 each. They worked A-ok. One was defective out of it's sealed package, was not spring loaded on back check due to a broken spring, noticed immediately before attempting install for test..
3 /2018
Napa #700 9556 is obsolete.
Here is a special low pressure schrader valve for compression gauges Milton and Lisle part number's and I seen them on flea bay as still available.
Milton 1251-2 @ about $5 each
Lisle 20100 @ about $7
Update info 12/20
Possible good compression gauge for chainsaws at $40, STANDIX 1023
Mentioned at this link 12/20
https://www.arboristsite.com/commun...mpression-gauge-and-tested-a-few-saws.348043/
You asked:
Any suggestion on where to purchase the weak spring schrader valve?
Link to a video about small engine compression testing6/23
https://www.arboristsite.com/thread...-04&utm_content=daily_newsletter#post-8020777
http://www.arboristsite.com/community/threads/compression-tester-issues.310133/
I got 3 of the Napa 700-9556 compression gauge Schrader valves today after the local NAPA ordered from their warehouse. The come 5 in a box and you can buy them each @ approx. $2.20 each. They worked A-ok. One was defective out of it's sealed package, was not spring loaded on back check due to a broken spring, noticed immediately before attempting install for test..
3 /2018
Napa #700 9556 is obsolete.
Here is a special low pressure schrader valve for compression gauges Milton and Lisle part number's and I seen them on flea bay as still available.
Milton 1251-2 @ about $5 each
Lisle 20100 @ about $7
Update info 12/20
Possible good compression gauge for chainsaws at $40, STANDIX 1023
Mentioned at this link 12/20
https://www.arboristsite.com/commun...mpression-gauge-and-tested-a-few-saws.348043/
And more:
In one of the posted links to this site you will see about modding a spark plug and also how I made some of my own low pressure schrader valves by cutting the spring on the long body type schrader valves. But the long body type schrader valves cannot be installed/used in some of the adapters due to their body length
Compression tester homemade and Schrader valves
Good Schrader valve is the NAPA 700-9556 at about $10 for a 5 pack. Obsolete now, NLA
Link to instructions
https://www.arboristsite.com/community/threads/compression-tester-issues.310133/
When you are checking compression on a 427 big block it's not going to make much difference where the Schrader valve is. But when your piston diameter is, say, 37 mm, adding the volume of the "pass through" hose before you get to the Schrader valve makes a huge difference. When checking chainsaw compression your Schrader valve MUST be at the spark plug hole. Here's my solution. This is for those who just like to make their own tools and/or are on a tight budget. As you will see, these homemade goodies will serve not one but two purposes. This seems like a lot of work, but it's not that bad - the instructions are long because they are detailed. Many of you will only need to make one of these. Materials: one sparkplug, the size used on your saw; one short piece of copper tubing, about 1/4" diameter; one discarded tire valve; one low-pressure Schrader valve; JB Weld. Items #1 and 3 could be had free at a small engine repair shop and tire shop, respectively. When you cut away the rubber from a tire valve, you are left with a brass tube into which a Schrader valve can be placed (see first picture). Grind the small end of the valve to reduce the diameter. If needed, drill and expand one end of the copper tubing. The two pieces just need to mate up nicely, they're going to be glued anyway (second picture). Once dry, fit the Schrader valve and note where the top thread is. Remove valve and cut away to just above that point. You want the plunger to stick out above the housing. Cut the ground electrode off the sparkplug. You'll have to remove the center electrode and ceramic from the plug, and it helps to grind away the crimp just above the hexagonal nut. Use a hammer and punch to do the rest. Fit the dried assembly into the plug - you may have to drill out the plug a little. Use enough JB Weld to seat the assembly with about 1/16th inch of the valve housing above the bottom edge of the sparkplug (third picture). When dry, fill in between valve housing and plug at the bottom and fill the rest of the void at the top. Find a nice O-ring to replace the plug gasket. Now for the two uses: with the Schrader valve in place attach your compression tester; with the Schrader valve out attach to your Mityvac for crankcase P and V test.
Another link for buying a tester
Its a Strandix 1023. 39.99 on ebay
https://www.arboristsite.com/commun...mpression-gauge-and-tested-a-few-saws.348043/
In one of the posted links to this site you will see about modding a spark plug and also how I made some of my own low pressure schrader valves by cutting the spring on the long body type schrader valves. But the long body type schrader valves cannot be installed/used in some of the adapters due to their body length
Compression tester homemade and Schrader valves
Good Schrader valve is the NAPA 700-9556 at about $10 for a 5 pack. Obsolete now, NLA
Link to instructions
https://www.arboristsite.com/community/threads/compression-tester-issues.310133/
When you are checking compression on a 427 big block it's not going to make much difference where the Schrader valve is. But when your piston diameter is, say, 37 mm, adding the volume of the "pass through" hose before you get to the Schrader valve makes a huge difference. When checking chainsaw compression your Schrader valve MUST be at the spark plug hole. Here's my solution. This is for those who just like to make their own tools and/or are on a tight budget. As you will see, these homemade goodies will serve not one but two purposes. This seems like a lot of work, but it's not that bad - the instructions are long because they are detailed. Many of you will only need to make one of these. Materials: one sparkplug, the size used on your saw; one short piece of copper tubing, about 1/4" diameter; one discarded tire valve; one low-pressure Schrader valve; JB Weld. Items #1 and 3 could be had free at a small engine repair shop and tire shop, respectively. When you cut away the rubber from a tire valve, you are left with a brass tube into which a Schrader valve can be placed (see first picture). Grind the small end of the valve to reduce the diameter. If needed, drill and expand one end of the copper tubing. The two pieces just need to mate up nicely, they're going to be glued anyway (second picture). Once dry, fit the Schrader valve and note where the top thread is. Remove valve and cut away to just above that point. You want the plunger to stick out above the housing. Cut the ground electrode off the sparkplug. You'll have to remove the center electrode and ceramic from the plug, and it helps to grind away the crimp just above the hexagonal nut. Use a hammer and punch to do the rest. Fit the dried assembly into the plug - you may have to drill out the plug a little. Use enough JB Weld to seat the assembly with about 1/16th inch of the valve housing above the bottom edge of the sparkplug (third picture). When dry, fill in between valve housing and plug at the bottom and fill the rest of the void at the top. Find a nice O-ring to replace the plug gasket. Now for the two uses: with the Schrader valve in place attach your compression tester; with the Schrader valve out attach to your Mityvac for crankcase P and V test.
Another link for buying a tester
Its a Strandix 1023. 39.99 on ebay
https://www.arboristsite.com/commun...mpression-gauge-and-tested-a-few-saws.348043/
https://www.arboristsite.com/community/threads/compression-tester.336165/
A good compression tester for small engines:
Actron CP7828A Professional Compression Tester Kit with 10mm, 12mm, 14mm, 14mm Long Reach, and 18mm Adapters $45 or so
Amazon link for reviewing:
https://www.amazon.com/gp/product/B00020BM28/ref=as_li_ss_tl?ie=UTF8&linkCode=sl1&tag=howtomotorepa-20&linkId=cdbd6f22890e891c57a50a4c630c7756
A good compression tester for small engines:
Actron CP7828A Professional Compression Tester Kit with 10mm, 12mm, 14mm, 14mm Long Reach, and 18mm Adapters $45 or so
Amazon link for reviewing:
https://www.amazon.com/gp/product/B00020BM28/ref=as_li_ss_tl?ie=UTF8&linkCode=sl1&tag=howtomotorepa-20&linkId=cdbd6f22890e891c57a50a4c630c7756
The three adaptors shown in the link above will increase combustion chamber volume and reduce compression readings - affects smaller cc (e.g. 37mm) engines more. None have a valve in the end that screws into the spark plug hole. I can't tell about the long solid tube adaptor. The hose does have a valve in the end.
