Reccomend a Compression Tester

Mountain Mike

Mountain Mike

I frequent the IBA Motel
Joined
Apr 28, 2008
Messages
655
Location
Bellingham, MA
Bike
ST1300
STOC #
7966
I'm told I need to test the compression on my bike. Before I just order any old one on Amazon, does anyone have a recommendation? Must have feature?

I read complaints about some kits not having the right size adapter, what size do I need? 0.8?

EDIT: I now know you need a compression tester with a "long reach 10mm". This can be found on Amazon or I am willing to loan mine.

Loan thread - https://www.st-owners.com/forums/showthread.php?112959-Compression-Tester-for-ST1100&highlight=

Equus 3614 Compression Tester - 6 Piece Kit
http://www.amazon.com/Equus-3614-Compression-Tester-Piece/dp/B000EVU8JS/ref=cm_cr_pr_product_top
 
st1300r said:
Plug threads are m10x1.0

Or do you mean leak down tester orifice?
Click to expand...

I have one cylinder that we suspect of not carrying its own weight. It has spark, balanced the carbs, carb boots fine, no more clogged jets, next test they say is a compression test for a possible sticking valve.
 
Hopefully the motorheads will chime in but as I understand it there are two tests.

-A compression test screw a gage in the spark plug hole crank and measure the pressure.

-A leak down test, screw two gages into the spark plug hole with a restricting orifice between them, pressurize with a compressor and measure the difference between the two gages. If there is flow (a leak) the orifice will cause a pressure drop in the second gage. Sometimes measured in percent. The orifice is sized to the size of the engine. I think a car is about .040".

Op asked about .8 I'm assuming millimeter which would be .033" so I'm guessing leak down test.

ifaik 10% leak down really doesn't mean anything as its realative to the orifice size and engine size. It would be in the ball park and would give relative numbers between cylinders.

Some of the elcheapo ones assume some restriction in the gages themselvse and don't bother with an orifice. Avoid them.


Usually this is done at top dead center at higher pressure but you can rotate the engine and check for leaks along the cylinder wall etc.
 
Karen said:
Hey Mike, want to use ours?


(I am about 90% sure Mike has one.)
Click to expand...


I'm building my own collection of tools and would like to have one of my own for the future, but I might lean on you for a tutorial.

st1300r said:
Hopefully the motorheads will chime in but as I understand it there are two tests.

-A compression test screw a gage in the spark plug hole crank and measure the pressure.
...
Op asked about .8 I'm assuming millimeter which would be .033" so I'm guessing leak down test.
Click to expand...

I'm pretty sure its the first one, I want to make sure I get a kit that threads correctly into our spark plug holes and .8 was the only measurement off the sparkplugs that seemed relatively close to the sizes mentioned in the kits.
 
You usually use a compression tester to test for major engine wear or severe mechanical damage, such as a blown head gasket, severely worn rings, or broken piston. To use, warm up the engine, then remove all spark plugs and thread the tester into one hole. Open the throttle up completely and crank the engine over several times. Write down the pressure. Zero the gauge and repeat on each cylinder. Besides wanting all the cylinders to be within factory spec, you also want all cylinders to be no more than about 10psi off from highest to lowest. If one cylinder is a lot lower than the rest, you have located a bad cylinder.

Next you need to find out what is wrong with that cylinder, or where is the air going? Using a fitting with the same thread as the spark plug (you can even make one using an old spark plug if you have some mechanical ability) and an air compressor, rotate the engine until that cylinder is at TDC. Apply about 50psi of air pressure to that cylinder. Now you need to listen. Listen at the air intake. If you hear air, you have an intake valve problem. Listen at the muffler for that cylinder. If you hear air, you have an exhaust valve problem. Remove the oil filler cap. If you hear air there, you have worn rings or a damaged piston, or possibly a bad head gasket. Remove the radiator cap. If that is where you hear air, you have a bad head gasket.

Jim
 
nhdiesel said:
You usually use a compression tester to test for major engine wear or severe mechanical damage, such as a blown head gasket, severely worn rings, or broken piston. To use, warm up the engine, then remove all spark plugs and thread the tester into one hole. Open the throttle up completely and crank the engine over several times. Write down the pressure. Zero the gauge and repeat on each cylinder. Besides wanting all the cylinders to be within factory spec, you also want all cylinders to be no more than about 10psi off from highest to lowest. If one cylinder is a lot lower than the rest, you have located a bad cylinder.

Next you need to find out what is wrong with that cylinder, or where is the air going? Using a fitting with the same thread as the spark plug (you can even make one using an old spark plug if you have some mechanical ability) and an air compressor, rotate the engine until that cylinder is at TDC. Apply about 50psi of air pressure to that cylinder. Now you need to listen. Listen at the air intake. If you hear air, you have an intake valve problem. Listen at the muffler for that cylinder. If you hear air, you have an exhaust valve problem. Remove the oil filler cap. If you hear air there, you have worn rings or a damaged piston, or possibly a bad head gasket. Remove the radiator cap. If that is where you hear air, you have a bad head gasket.

Jim
Click to expand...

Great Info Jim! Thanks!
 
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