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  #11  
Old 6 Days Ago
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Ferrous Head Ferrous Head is offline
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Most of the gauges around have a "green zone" a "yellow zone" and a "red zone".

But at the top they will have percentages which will go from 100 per cent down to 0 Per cent. Most of the "tired engines" I see run around 0-30 per cent. But they are really tired engines. I aim for 5 per cent or less with my race engines. 10 is good for a street engine.

Tell me the procedure you used, especially where you calibrated (zeroed) the gauge.
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  #12  
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Yes, the piston needs to be at / near TDC for testing as Ferrous Head mentioned.
It takes less air to fill the cylinder for testing.
But others have had success with the pushrods out. As always, there are more ways to skin a cat.
But unless you are use to these tests, it's probably best to keep the piston up.
There will always be a certain amount of air that will leak past the rings even on a fresh engine.
You can simply induce air on a slow rate into the plug hole and stick a length of hose into your ear and the other end at various places, carb, head, exhaust... timing plug hole (with the plug removed).
You can remove the rocker box and place the hose around the valve stems.

Here are the Sportsterpedia pages on;

Compression testing
http://sportsterpedia.com/doku.php/t...:ref:svcproc20

and Leak Down testing
http://sportsterpedia.com/doku.php/t...:ref:svcproc21

You said you had the piston at TDC and locked, that's good.
20% leakage is at the threshold of problems (Less than 20% acceptable for pre-86 engines) but I'd double check the testing to make sure it's accurate before tearing down.

edit:
You've got app 5% difference between the cylinders, not bad.
The actual numbers are not as important as the relationship of each cylinder.
As long as both juggs are close to each other, don't sweat the actual readings. There are lots of variables that can affect those readings.

Make a note of the reading and the date you took it, check it again after a few rides and see if it reads the same using the same equipment.

In theory, you want both cylinders to wear about the same, this is normal.
One cylinder can throw a red flag by being more than 10% or so from the other.
But, there will come a time when the rings won't seal and the problem will have to be fixed on all of our engines.
All mechanical things fail in time.
Supposedly, HP loss will start at about 25%.

Mickey, have you done a compression test?
Generally a compression test will tell you if you have an air leak problem and a leak down test will tell you where the air is going.

I'd also suspect 80% leakage will look something like this.


I'm with Ferrous Head, I'd retest before I got worried.
Do read those links I gave especially on setup.
Matter of fact, I'd do a compression test and go from there.

Oh, and if you keep all this on one thread instead of multiple ones, it's easier for us to help you.
That way all the diagnosis is in one thread,
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Last edited by Hippysmack; 6 Days Ago at 07:13..
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  #13  
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Quote:
Originally Posted by mickey t View Post
I wish but from the gauge it looks like in not...it has the Mark's on it like food moderate and poor on gauge tha/ reads cylinder leakage...mine is in the red,poor. Which is upsetting because I got it kicked over 5 times...with 11 kicks involved by changing startup technique...took for a run down the street in the rain only to 2nd gear even w the bad clutch n thought I turned the corner w this problem

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How did it run?
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use a piston stop
i would not side load the wheels
the only way i would use the wheels is if it had a detent made for that like the old bsa thumpers.
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You don't even need a gauge to do a leakdown test.

Just a rubber tipped blow nozzle and your ears (or someone with good ears).
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Quote:
Originally Posted by Hippysmack View Post
I'd also suspect 80% leakage will look something like this.
Nope. that would be firmly in the 100% leakage category.

A leakdown tester measure the pressure drop across a fixed orifice, that hole is bigger than the fixed orifice.
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Quote:
Originally Posted by ryder rick View Post
Nope. that would be firmly in the 100% leakage category.

A leakdown tester measure the pressure drop across a fixed orifice, that hole is bigger than the fixed orifice.

With that one you don't need a compression gauge - you just put your finger over the spark plug hole.


Don't laugh, years ago I had a guy bring me a nice looking 60's IH he had just bought. Seller told him it need the carburetor "tuned" or maybe the tining done as he had ridden it and it was OK.

On my first kick I knew he had a problem. I used the finger test on the front cylinder.
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Quote:
Originally Posted by ryder rick View Post
Nope. that would be firmly in the 100% leakage category.
This is true.
But I didn't have a busted piston pic with a smaller hole on hand.
The point I was trying to make was that 80% leakage is more a 'little' problem.
The more volume of air loss lowers the pitch of the air escaping.
The op said he didn't hear any air.
I guess I should have just said it's impossible to have 80% air loss and not hear the air escaping.....
Listening with a stethoscope, gas hose etc is part of the process anyway unless the problem is obvious.

edit:
For grins and giggles, I setup a dual psi gauge at 92 psi, opened the outlet full hose, with the readings recorded in the second pic.
This left an inlet side 60 psi and outlet side of 48 psi while flowing from a small peanut air tank. It was more of a lower high pressure sound than a hiss just like opening the tank with no valve on the hose end.

Setup.


Testing.
As you can see, with the hose end open to atmosphere, I did not get 100% leakage.



I did that to approximately simulate what the readings might be with a hole in a piston.

Keeping that visual and looking at this pic with carbon buildup slightly holding a valve open, it's easier to understand that the readings can be more subtle than a big air loss and still be problematic when taking a leak down test.
And a compression test may show this cylinder to be the problem.
Whereas with a leakdown test, you can hear air going thru the motor even if their isn't a problem.
And if you're not used to hearing what normal air sounds like, you can drive yourself nuts chasing ghosts.

Last edited by Hippysmack; 5 Days Ago at 00:23..
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  #19  
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Quote:
Originally Posted by IronMick View Post
+1.
This is how I do mine. I do not like the lock the flywheel technique.
I understand your concerns about putting pressure on the flywheel face,

But it's not that much force. If it shifts your wheels your nuts are too loose.

Built up cranks actually do flex. We know this from catastrophic results. Pre unit Triumphs are prone to splitting the cases horizontally right through the bearing centers.
On Nortons the pistons can hit the electrode tips on the plugs and close them up enough to cost you a race. I've seen it.

You might think it's all rod stretch but the problems are resolved with billet cranks.

They don't flex.

If your tapers are good and the nuts done up correctly and you don't swing on the end of your 3/4 drive ratchet like a big ape, it will all be fine. The force is being applied pretty close to the crank pin.

If you have the piston at TDC the force is trying to compress the rod. not push it to one side. Most people think near enough is good enough when going for TDC. Use a dial gauge.

Although I could always be wrong and all of my engines will vibrate and explode any minute now.

(Gawd, I hope not. I'm off to Lakeside in the morning)
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to each his own i guess. the wheels are easy to fracture and even the fsm warns so when doing alignment.
all cranks can flex if they did not, they would break. the old insert bearings on the brit machines were a weak point and yep seen them spit out bottom end parts.
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