hadfield4wd
New member
I would do a rebuild if any of my bikes had 100 psi
I'm stumped
- Thread starter pscook
- Start date
Jakobi
Super Moderator
I'd rule out that particular compression gauge before tearing it down again. If it's one that uses the length of tubing (or even an adapter) it's very easy to get 'low' readings given the small trapped volume of the engine.
A couple of cc's extra volume can add a significant drop in compression ratio. Add that to an engine running a large squish (already low comp), some hours, and a bleed port coupled with soft/slow kick overs, a cold engine, etc and you can have some low figures.
As stated earlier it really needs to be used as a baseline and comparison with all other variables remaining the same. Then you can draw conclusions regarding wear on the engine. Without, it's just stabbing in the dark.
On larger engines, the difference between trapped volume and trapped + adapaters/tubing is less, and even then on multi cylinder engines you're typically looking for variance between cylinders rather than measuring compression. There is a reason why some gauges are cheap and chips and others cost the buku dollars.
A couple of cc's extra volume can add a significant drop in compression ratio. Add that to an engine running a large squish (already low comp), some hours, and a bleed port coupled with soft/slow kick overs, a cold engine, etc and you can have some low figures.
As stated earlier it really needs to be used as a baseline and comparison with all other variables remaining the same. Then you can draw conclusions regarding wear on the engine. Without, it's just stabbing in the dark.
On larger engines, the difference between trapped volume and trapped + adapaters/tubing is less, and even then on multi cylinder engines you're typically looking for variance between cylinders rather than measuring compression. There is a reason why some gauges are cheap and chips and others cost the buku dollars.
Zman
Platinum Level Site Supporter
I agree with the comment on the compression test tool. From my recent experience with the Harbor Freight compression tester it reads very low compared to higher quality compression testers.* When testing a GG125, I read 60 psi with the harbor freight and 185 with an older Craftsman and a Milton made in the USA.** I did a quick calibration check on the Harbor Freight and while it was off a few pounds on a constant pressure source it still reads low when doing a compression test.** I believe it may be related to a slow check valve and maybe it does not respond to the quick pressure pulses of a 125cc engine.
compression
A friend let me use his OTC compression tester on my 2007 gg ec300. I did it with a cold engine, kicked it about 10times and had 175-180 psi.
Released air did it another 10 times got the same reading.
Looked in sparkplug hole, shiny in the middle with some carbon build up in a circle around the shiny middle of piston. I did have some very bad carb issues so for about 4-5 rides ran like crap. Could not make a 50 mile ds ride with running out of gas. Now carb great and did 65 miles and still had gas left.
My questions is rebuild or not. She runs good but I bought it a few years ago and have no idea the hours on it.
Thanks
A friend let me use his OTC compression tester on my 2007 gg ec300. I did it with a cold engine, kicked it about 10times and had 175-180 psi.
Released air did it another 10 times got the same reading.
Looked in sparkplug hole, shiny in the middle with some carbon build up in a circle around the shiny middle of piston. I did have some very bad carb issues so for about 4-5 rides ran like crap. Could not make a 50 mile ds ride with running out of gas. Now carb great and did 65 miles and still had gas left.
My questions is rebuild or not. She runs good but I bought it a few years ago and have no idea the hours on it.
Thanks
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