Cheap compression testers?

[bertsmobile1]

>What you should be doing is taking compression readings at regular intervals like servicing or every season end etc

That was my hope. And even if the gauge is off, but consistently off it should be OK for me since it would still show a relative decline.

As for my extreme budget tester.... I found a video that was helpful to strip out the ceramic insert in the plug. I didn’t have a holesaw that would fit, but I found that a hacksaw around nut did the trick!

That will work fine
It will work better if you put the same amount of oil into the cylinder for each test say 3 to 5 drops from an eye dropper so the rings have the same oil seal each time.
When I ran a fleet of light vans & motorcycles we did compression tests bi- monthly.
That way I could catch the wear early and we got 3 to 4 sets of rings out of each piston & bore .
Might sound tight fisted but we ran 8 x 4 cylinder motorcycles and a set of rings & gaskets was under $ 100
A rebore was $120 and a set of pistons $ 200 so it added up quickly.
It also meant that the bikes always ran crisply which is important if you are riding all day every day in capital city traffic .
Did the same thing with the vans but being water cooled, the ring wear was substantially less ( the riders vs Drivers also contributed more than a little )

 

[Scrubcadet10]

On small engines i keep it cranking or pulling it until it stops rising.

 

[Hammermechanicman]

On small engines i keep it cranking or pulling it until it stops rising.

Correct. On any engine you crank till it stops rising. At a certain point it will stop rising and just bouce a couple PSI.

 

[bertsmobile1]

On small engines i keep it cranking or pulling it until it stops rising.

Try it by pulling the rope then by spinning the crank.
You will not notice it going up 0.5 psi ( or less ) from 90 to 190
There was a sub 50cc kart class down here a while back & one of the cart tuners showed me that .
On bigger engines you are incresing 1 to 20 psi each pull but on small ones easy to see a very small rise as a "bounce"

 

[longhike]

Ok I’m sure it’s not accurate, but for a proof of concept it’s “kinda” OK. I already had the abandoned .97¢ tire gauge, the old spark plug, and a couple drops of 5 minute epoxy... so there’s no loss.

It’s an old edger that hadn’t been started in many years after the fuel lines crumbled that I picked up at a garage sale as a challenge to see if I could learn a little more about small engines. After a new carb, fuel lines and some new gaskets my edging looks much nicer

But even though it runs great, from pulling the starter the compression felt light (most likely my lack of experience). And putting my thumb over the hole didn’t seem accurate. It’s only a 22cc engine but the edger works great so I’m assuming it’s OK. Although I am still curious about finding a good tester for small gear.

Here’s the mini tester V1 ... at least I’m learning along the way and thanks for all the helpful tips/info! If I find a more accurate tire gauge maybe there will be a V2?

 

[bertsmobile1]

Enquiring minds need to be fed .
And thanks fr sharing.
Good compression testers cost big bucks
Mine was around $ 250 ( Aus ) and even then I have suspicions about it's accuracy .
OTOH from using it over the years I can be fairly sure if an engine won't pull 90 or better then it is not going to run .
However I rarely use it now days and have gone to leak down testing which is a lot easier and works on all engines .

 

[Hammermechanicman]

Enquiring minds need to be fed .
And thanks fr sharing.
Good compression testers cost big bucks
Mine was around $ 250 ( Aus ) and even then I have suspicions about it's accuracy .
OTOH from using it over the years I can be fairly sure if an engine won't pull 90 or better then it is not going to run .
However I rarely use it now days and have gone to leak down testing which is a lot easier and works on all engines .

I am with you on the leakdown test instead of compression test on 4 stroke engines. I still like to do compression test on 2 strokes. My good automotive compression tester died a few years back and i picked up a cheapo asian one (big mistake) not realizing where the Schrader valve was located. Not that i need one but i think the china cheapo is going in the bin and going to get a better one.
Strangely enough had a Shindowa 488 in the shop last week and felt low on compression. Sure enough i measured 95psi. I though it would be a dog if i even got it started. Fixed the fuel line problem and it fired right up and had good power for a 48cc saw. Spec is 140-156psi. I have tested a lot of saws with my good tester and i have measured other saws at 90psi that barely ran. Just when i think i know 2 strokes i find out i don't.

 

[bertsmobile1]

The Shindawa is a 2 ring piston
Two ring engines will run at lower compression ratios than single ring engines
Usually a 2 ring runs a couple of k slower than the equivalent single ring.

 

[Hammermechanicman]

The Shindawa is a 2 ring piston
Two ring engines will run at lower compression ratios than single ring engines
Usually a 2 ring runs a couple of k slower than the equivalent single ring.

Good to know. Of course both my hopped up kit saws run 2 ring pistons and the 60cc turns 13500 and the 92cc turns 13000 WOT. But they aren't stock either. Always fun to show up with a chineese knockoff kit saw to cut and buck storm trees and cut rings around the guy with the same model Stihl brand $1500 saw.

 

[bertsmobile1]

Good to know. Of course both my hopped up kit saws run 2 ring pistons and the 60cc turns 13500 and the 92cc turns 13000 WOT. But they aren't stock either. Always fun to show up with a chineese knockoff kit saw to cut and buck storm trees and cut rings around the guy with the same model Stihl brand $1500 saw.

A stirrer after my own heart
I run a couple of old WWII motorcycles, bored & stroked from 500cc to 760cc & 860cc .
They live in a lean to on the side of the shed so look really tacky and I really love sitting right on the back wheel of a pristine over restoration then retard the ignition & glide past them on long hills as they shuffle back through the box.