Pressure/Vacuum testing follies.

[Definitive Dave]

Yeah but how we can spot from where we have vacuum leaks ? for the pressure we have the soapy water what we have for the vacuum ?

a light bead of oil will get sucked into the vacuum leak, not as easy as a pressure leak but necessary and you can use a drop of oil on the end of the impulse line to check your impulse pulse by turning the crank slowly by hand
Dave

 

[TJ the Chainsaw Mechanic]

the 192 has two different types of seals for replacements - one is used if you are splitting the crankcase and the other are the push in style for when the crankcase will not be split they will not work properly when used for the wrong application, check ahead to make sure you have the right seals ordered for your job
Dave

The ones I have ordered are the ones that go in with the case split. There is a way to tell from the outside which one they are. I'll have to get a picture. lol Thanks for the head's up though! I noticed that when I went to order them.

 

[panteliss]

a light bead of oil will get sucked into the vacuum leak, not as easy as a pressure leak but necessary and you can use a drop of oil on the end of the impulse line to check your impulse pulse by turning the crank slowly by hand
Dave

 

[smokey7]

How many of you guys have done damage when you were learn g to pressure test or just in a hurry and made a mistake? I have done it both ways. I have pushed seals out from setting compressor reg for testing then needed blow gun turned it up and forgot to turn down. That time I shot the seal clear out of the saw.

 

[logeeland]

Many times a crank seal will hold going out but not in. I am not sure if I would dunk a saw fully underwater...

 

[TJ the Chainsaw Mechanic]

Many times a crank seal will hold going out but not in. I am not sure if I would dunk a saw fully underwater...

As long as the fuel tank is sealed off and you have block off gaskets covering the intake and exhaust ports, pressure testing is fine under water. Makes cleaning the saw a tad faster to. haha. I've done it with just about every saw with air leaks and had no issues, granted I do take the block off gaskets though and blow 200 psi worth of air through to cylinder just to insure no water got into the crank case.

 

[TALLGUY]

I was confused the other day fixing a Old Homelite 330. I resealed the whole case and wanted to vac and pressure test. I blocked off the intake which is huge when you don't have a boot, by the way. It wouldn't hold any vac and I could hear it sucking air. Pressure I could hear also. I finally figured out Homelite left a pin hole at the bottom of the crank case to drain excess fuel/oil? Once I put my finger over the hole everything tested out great.

 

[Lone Wolf]

Ok, SO I have pressure tested several saws that Hold pressure....confirmed by putting the whole saw under water and no bubbles... but they don't hold a vacuum. Any ideas?

Crank seals are known to fail vac but pass pressure due to the design of the sealing lip. To prove it is the crank seals load up grease all over them and vac will then hold. If so end of the story!

 

[TJ the Chainsaw Mechanic]

I was confused the other day fixing a Old Homelite 330. I resealed the whole case and wanted to vac and pressure test. I blocked off the intake which is huge when you don't have a boot, by the way. It wouldn't hold any vac and I could hear it sucking air. Pressure I could hear also. I finally figured out Homelite left a pin hole at the bottom of the crank case to drain excess fuel/oil? Once I put my finger over the hole everything tested out great.

That's interesting.

 

[JP56]

So what I should be doing is testing first with the decomp in and then using the plug if I have a problem in order to rule out the decomp. Would that be correct?
And Evanrude, I will deffinatly be picking up one of those test flanges. How much did it cost?

I paid $21.00 for mine including shipping, on ebay at dealzfordays

 

[JP56]

the 5910 850 420 can fit to the olders models but also can fit and to some new models but not big diference

I don't have direct knowledge, but have been told that some saws have a thicker shoulder or stud mount for the carbs, instead of the thin bolt/nut combos found on most and the difference in the 2 parts is that the back of the part has 2 countersink holes in it for the thicker mounting bolts. Most of the guys just drill there own counter bore into that side and then it can be used on all of the saws. Hope this helps someone.