compression/vacuum test question

rshaffer3 · Dec 2, 2008

I looked through the old posts but couldn't find an answer to my question so here goes.

If I'm using a set up that connects the tubing to the spark plug hole do you have to remove the rings to pressurize or vacuum test the bottom end crank seals? This would seem kind of self defeating because then you'd have to pull the cylinder off to put the rings back in but I don't understand how the air gets past the rings without doing this.

Or should I forget the spark plug hole and try to go through the impulse line? The saw is a Stihl 460 and I've got an 028 super that I want to check.

Thanks

Lakeside53 · Dec 2, 2008

Block off the exhaust, carb and impulse. Then your plug access is fine. No, you don't need to remove the rings - just put the piston at BDC (or any lower than the transfers).

tomdcoker · Dec 2, 2008

I think the air would leak past the rings and work O K, but I am new at pressure/vacuum testing, so I may be wrong. I use the impluse opening on the saws that have a fitting. If I am wrong someone will be along and correct me. Tom

Lakeside gave you the answer while I was typing. What ever he said is right. he is more knowledge than I am.

Ax-man · Dec 2, 2008

What Lake said. The only thing I can add is if you do use the plug hole make sure it isn't leaking through the threads or at the base of the adapter. That is the first place to check if the saw flunks the pressure /vac test.

Sometimes you run into saws have a pulse port in the intake manifold and don't have an actual pulse line to hook up to. If this is the case you have to use the spark hole to pressure and vac test. It is nice to be set-up both ways especially for the older saws.

Larry

rshaffer3 · Dec 2, 2008

Aha, I forgot that at during a certain point of the piston travel that the rings sit below the transfer ports, that's what I was missing. Thanks for the tip Mr. Lakeside.

I just got a new jug kit from Baileys today so I'm looking forward to re-assembling my 046 and checking for leaks.

alpinecrick · Dec 3, 2008

Question for you guys: How are you sealing off the intake and exhaust ports on your saws when pressure/vacuum testing through the plug hole?--Specifically I'm thinking about the old Macs.

Casey

Modifiedmark · Dec 3, 2008

Most the time I cut a piece of steel flat stock to size and drill two holes in it and bolt it over the ex port or the intake port with a piece of bike inner tube for a gasket.

Works for me that way, only takes a minute to make up a block of plate.

stihl only · Dec 3, 2008

You can make a "gasket" for the carb out of rubber with no center hole and bolt the carb back on. Do the same for the exhaust too. This will save the time it takes to make block off plates BUT in some cases, I like plates. Gives you better visibility to check around the base of the cylinder, etc.

compression/vacuum test question

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