Pressure test

[StihlNAlberta]

OK ... here are a couple general questions that could relate to any model/make.

1. After the installation of a new top end (P&C), i wanted to do a pressure test to ensure a good crank/carb seal. Rings are not seated yet but this should not effect the test I am assuming. Where should the piston be to get an accurate reading, or does it matter? I still can't get the case to hold pressure.

..... I have tried soapy water everywhere and cannot find an air leak. It pressures up and slowly drops off. Think I'm gonna try and remove and plug the decomp. valve hole even though the decomp. valve is brand new. May take a bit to get a bolt with the correct threads.

2. Bearings. Seems like most if not all OEM crank case bearings are open not sealed, and by this I mean you are able to see the ball bearings and are able to grease or service these. Most companies who manufacture bearings (IE 6202) now come with a plastic sealed non serviceable bearing .... any reason NOT to use these in your case? My thinking is that it may give you the potential for a better case seal.

 

[bluestripes]

Deffinately try it with the de-comp out and aplug installed. Even new de-comps leak some.

 

[jockeydeuce]

Could be the decomp leaking......I use an old fish tank and dunk the whole saw sometimes to find the leak.....As long as there's pressure in the case, no water can enter.

 

[spindrift7mm]

How much pressure are you using,if too much pressure is used it will push by seal lips.Some bleed off is acceptable in a used saw,if the saw will hold pres/vac for 30 seconds the refresh rate of the saw running will overcome this and it's still tuneable. It's not ideal but if the saw owner needs to finish up a job or the season the saw may run well for years. My 064/066 will only hold pres/vac for 1min bleed off after a complete build i've went back in 3 times and checked /changed things,It is truly a beast and holds tuning very well so I've come to the conclusion there's a slight crack somewhere I can't find possibly the bearing insert in the clutch side case and I'm not going to worry about it unless it gets worse.
Becareful with sealed breaings, if sealed on both sides remove the inside seals as they will seal out your fuel mix and there won't be any lube getting to the bearings.
Throw Chips not Dust Ken

 

[lone wolf]

What he said put it in an aquarium and you will find the leaks!:msp_thumbup:
Oh an empty one w/o fish ok.

 

[heimannm]

You do realize you have to seal off the intake and exhaust, don't you. You cannot rely on the rings along to isolate the crank case from the top end. If you don't want to go to the effort of making plate that bolt on, at least seal the openings with some Gorilla tape.

Plus, as noted you must install the spark plug and compression release if so equipped, or else block the compression release port with a 10 mm screw, I normally use a short screw with an o-ring to make sure there is a good seal.

Mark

 

[lone wolf]

You do realize you have to seal off the intake and exhaust, don't you. You cannot rely on the rings along to isolate the crank case from the top end. If you don't want to go to the effort of making plate that bolt on, at least seal the openings with some Gorilla tape.

Plus, as noted you must install the spark plug and compression release if so equipped, or else block the compression release port with a 10 mm screw, I normally use a short screw with an o-ring to make sure there is a good seal.

Mark

:msp_ohmy::msp_ohmy::msp_ohmy:

 

[fossil]

:msp_ohmy::msp_ohmy::msp_ohmy:

I have tested quite a few saws that hold prssure quite well but will not hold vacuum. If that is the case, it's generally the crank seal(s) that are leaking. To answer you question it does not matter where the piston is or even if it's there. You must seal the whole saw up and make sure all your seals (exhaust port, intake (seal below the carb but above the adaptor / boot) are not leaking. I don't know what type of saw you are testing but if it has an impulse line you should pressure / vac test through that to make sure it is OK as well. If it does not, I generally go through the the spark plug hole. It is a good idea to roll the piston over to make sure the crank seals are good in all crank positions. If the saw has a rubber intake boot, look at that carefully to make sure there are no cracks ot tears in the boot.

Mark makes a very good point that the decomps all seem to leak a bit and should be removed and the hole plugged with a bolt.

 

[StihlNAlberta]

Aquarium? Now that is a great idea .... maybe the bath tub would work too. LOL

I've got a couple pieces of old bike tube plugging off the exhaust port and the carb. intake. Got the De-compression hole plugged as well and it seems to pressure up quicker but doesn't hold. 5/16 - 24 bolt I had to trim w/yellow t-tape. The leak is coming through the spark plug hole as this is where I am pressurizing the case (no impulse line on this saw). The little rubber cone that came with my kit doesn't seat very well in the spark plug hole and by process of elimination, this is the next visible leak. All else seems to be good but I want to be sure. Popped of flywheel & clutch .... bearing seals look good.

5-10 pounds is what I am trying to achieve.

Anyone have a tool they built to spin in the spark plug hole and attach the pressure tube to? Old spark plug may work somehow but need a way to attach the hose.

CHEERS!!

 

[lone wolf]

Aquarium? Now that is a great idea .... maybe the bath tub would work too. LOL

I've got a couple pieces of old bike tube plugging off the exhaust port and the carb. intake. Got the De-compression hole plugged as well and it seems to pressure up quicker but doesn't hold. 5/16 - 24 bolt I had to trim w/yellow t-tape. The leak is coming through the spark plug hole as this is where I am pressurizing the case (no impulse line on this saw). The little rubber cone that came with my kit doesn't seat very well in the spark plug hole and by process of elimination, this is the next visible leak. All else seems to be good but I want to be sure. Popped of flywheel & clutch .... bearing seals look good.

5-10 pounds is what I am trying to achieve.

Anyone have a tool they built to spin in the spark plug hole and attach the pressure tube to? Old spark plug may work somehow but need a way to attach the hose.

CHEERS!!

Try using grease to seal the rubber plug first.

 

[fossil]

Aquarium? Now that is a great idea .... maybe the bath tub would work too. LOL

I've got a couple pieces of old bike tube plugging off the exhaust port and the carb. intake. Got the De-compression hole plugged as well and it seems to pressure up quicker but doesn't hold. 5/16 - 24 bolt I had to trim w/yellow t-tape. The leak is coming through the spark plug hole as this is where I am pressurizing the case (no impulse line on this saw). The little rubber cone that came with my kit doesn't seat very well in the spark plug hole and by process of elimination, this is the next visible leak. All else seems to be good but I want to be sure. Popped of flywheel & clutch .... bearing seals look good.

5-10 pounds is what I am trying to achieve.

Anyone have a tool they built to spin in the spark plug hole and attach the pressure tube to? Old spark plug may work somehow but need a way to attach the hose.

CHEERS!!

I just knocked the guts out of an old spark plug and pulled a tire valve through it. I use an "O" ring instead of the plug gaskets to seal the pressure plug off. Works good.

 

[BIG JAKE]

I knocked the guts out of an old plug and jb welded a brass hose barb into the center. Whatever is suitable for the hose you want to use-works great:msp_thumbup:

 

[ROWDY]

I'd like to see a video of this being done if possable!

 

[StihlNAlberta]

Well I will see if I can dig up an old spark plug, brass fitting and some JB Weld tomorrow and MacGyver something together prior to starting this old saw.

I'm with Rowdy .... if anyone has a pic of this thing-a-ma-jig I'd love to see it!!

:tongue2:

 

[nmurph]

Here's the SM quote for an 044. Most other saws are similar.

Pressure-

Pump air into the crankcase until the
gauge indicates a pressure of
0.6 bar (8.7 psi). If this pressure remains
constant for at least 20 seconds,
the crankcase is airtight.


Vacuum-

Pull out the pump piston until the
gauge indicates a vacuum of 0.4 bar
(5.8 psi).
Note: When you release the pump
piston the non-return valve automatically
seals the suction hose.
If the vacuum reading remains constant,
or rises to no more than 0.3 bar
(4.25 psi) within 20 seconds, it can be
assumed that the oil seals are in good
condition.
However, if the pressure continues to
rise (reduced vacuum in crankcase),
the oil seals must be re placed, even if
no leaks were detected in the pressure
test.

 

[torence 20]

i just took a spark plug knocked out the guts, drilled and tapped it an put a brass barbed fitting in there and rtv siliconed it

 

[StihlNAlberta]

In doing a little more reading on AS apparently Husqvarna pt #503 84 40 02 called plug adapter is also available for around the price of a plug.

Homemade is likely still cheaper but it's either that or waiting for the JB Weld to dry!!

Thanks for the picture!! Looks like a great tool that would do the trick.

Some great options. THX!!

 

[cedarshark]

I am not sure I understand the reason to modify a spark plug to become a pressure/vacumn port. Even if you successfully modify the plug (without leaks), you now have to plug the impulse line and make sure it does not leak. I am a strong advocate of pressure testing under water. Not only does it locate a leak easily at the crank seals(points straight to the bubbles) but it also checks all your test seals at the exhaust,carb port, intake boots, impulse lines and decomp ports. I just dont see why you would do it any other way.

 

[lone wolf]

I am not sure I understand the reason to modify a spark plug to become a pressure/vacumn port. Even if you successfully modify the plug (without leaks), you now have to plug the impulse line and make sure it does not leak. I am a strong advocate of pressure testing under water. Not only does it locate a leak easily at the crank seals(points straight to the bubbles) but it also checks all your test seals at the exhaust,carb port, intake boots, impulse lines and decomp ports. I just dont see why you would do it any other way.

Works for me every time I test in an aquarium. It saves days of guessing just don't drop it in the aquarium to hard or it will crack the glass ask me how I know . And half the time the leaks are your intake or exhaust blocked off improperly.

 

[fossil]

I am not sure I understand the reason to modify a spark plug to become a pressure/vacumn port. Even if you successfully modify the plug (without leaks), you now have to plug the impulse line and make sure it does not leak. I am a strong advocate of pressure testing under water. Not only does it locate a leak easily at the crank seals(points straight to the bubbles) but it also checks all your test seals at the exhaust,carb port, intake boots, impulse lines and decomp ports. I just dont see why you would do it any other way.

A lot of the older saws don't have impulse lines (just passages through the carb adaptor) and pressure / vac testing through the spark plug hole is quite a bit easier than making up fittings to go through the exhaust or intake ports.
I agree 100% if you have an impulse line to go through it instead.