air leaks

[poleframer]

air leaks are mentioned often in saw problems. How do you check for them, without tearing the saw down?

 

[BostonBull]

You need to have a vacuum and pressure tester and some blocking plates.
Some disassembly is required.

 

[retoocs555]

You can check common leak places like intake boots easily with a visual. and sometimes you can feel really shot crank seals by hand.

Other than that pressure test.

 

[Justsaws]

Sometimes if the saw is running at a steady rate you can check for air leaks by changing the position of the saw engine. Lay it on each side if it speeds up or slows down that can be an air leak. Typically the saw will speed up and rev out. Fill the gas tank 3/4.

Also you can with the saw running spray WD40(do NOT use carb cleaner or brake cleaner) around the seals you can get to, this should also change the rpms if there is a leak on those seals.

If the saw is screaming fast do not do any of these as the over rev can cause expensive damage.

What saw and why do you suspect an air leak?

 

[Freakingstang]

Sometimes if the saw is running at a steady rate you can check for air leaks by changing the position of the saw engine. Lay it on each side if it speeds up or slows down that can be an air leak. Typically the saw will speed up and rev out. Fill the gas tank 3/4.

Also you can with the saw running spray WD40(do NOT use carb cleaner or brake cleaner) around the seals you can get to, this should also change the rpms if there is a leak on those seals.

If the saw is screaming fast do not do any of these as the over rev can cause expensive damage.

What saw and why do you suspect an air leak?

Good info saws, but to the first one, a saw that is running with a mis-adjusted carb will speed up or slow down if the saw is tilted. Not always an indication of an air leak, but a majority of the time it is. This becomes more prominant in modded saws if not tuned correctly as there is more fuel in the transfers

 

[poleframer]

What saw and why do you suspect an air leak?

Just a general mechanic question. Know some about bigger engines (listen for vacuum leaks, spray and listen). Please elaborate on the vacuum/pressure tests. Thanks

 

[HiOctane]

Just a general mechanic question. Know some about bigger engines (listen for vacuum leaks, spray and listen). Please elaborate on the vacuum/pressure tests. Thanks

To make a pressure test,you need to block the exhaust and intake with a plate and some rubber behind to make the saw "air tight".You connect a pressure gauge to the intake(usually) and you try to bring the pressure to around 9-10 pounds.The pressure has to stay stable at 9-10 for lets say a minute on your gauge,If the pressure is dropping,then you have an air leak by seals,gasket,etc.You squirt wd 40 or else then around the place where its susceptible to lose air like around seals,etc.You gonna see air bubbles coming out of the location of the leak.You replace the defective parts and check again after to be sure the engine is air tight.

 

[Lakeside53]

To make a pressure test,you need to block the exhaust and intake with a plate and some rubber behind to make the saw "air tight".You connect a pressure gauge to the intake(usually) and you try to bring the pressure to around 9-10 pounds.The pressure has to stay stable at 9-10 for lets say a minute on your gauge,If the pressure is dropping,then you have an air leak by seals,gasket,etc.You squirt wd 40 or else then around the place where its susceptible to lose air like around seals,etc.You gonna see air bubbles coming out of the location of the leak.You replace the defective parts and check again after to be sure the engine is air tight.

And.. same for a vacuum test - suck until you see about - 8psi... Seals will often leak under vac but not pressure.

Best thing for seein g leaks is soapy water, or if it's really hard to see where the leak is commingfrom, just drop the saw (under pressure, not vac) in a bucket of water.

 

[Jaxx]

So.. How do you find the vac leak?

 

[Lakeside53]

Vac leak is almost always a seal - it's "usually" the only thing in a saw that will hold pressure, but fail under vac, but sometimes a cracked boot or impulse line can behave the same way.


I flip the saw up on its side (seals exposed) drop some light oil into the seal cavity, and then pump up the vac. It will either "cure" the problem (it stops leaking temporarily) or suck in the oil. Be sure to rotate the crank - some seals only fail at a particular crank position.


When you do pressure or vac testing, be sure to prod or twist on the boot and impulse lines to check for cracks.