how to find air leak?

[awesomeame]

i had the left piston/cylinder seize up on me. not entirely sieze up, but it needs to be bored over in any case. the right piston/cylinder look great.

 

so, what happened? i figure it must be sucking air somewhere, or there's no fuel at the carb. i can't find any leaks between the carb and the cylinder.

 

would a bad crank seal cause air to get sucked in? is there some way to pressurize the case to see if there are any leaks in the bottom end? there's no oil dripping anywhere. how much pressure should i put into the case?

 

--matt

[black sunshine]

Do a search on here for RNBRAD, he has a detailed post on how to build a leakdown tester. It should hold 6psi for 6 minutes. This will pressurize everywhere that you can obtain a leak.

 

I would post it up as a hyper for you but I am dumb... :shrug:

Edited November 13, 2007 by black sunshine

[theshee]

When my 421 had an airleak, I found it without a leakdown it was so obvious. It was leaking on the front of the cases where they go together, I found it because mixed fuel was running down the front of the cases, only below the seam though.

[Dgrey]

http://www.bansheehq.com/forums/index.php?...c=49835&hl=

 

Here is the link on the leak down tester. I should make myself one of those - although I have not had any air leak problems its still a good idea.

[Dave I.]

Here is the leak down tester I made. It worked good also.

 

1 1/4" PVC sprinkler pipe (Home Depot)

1 1/4" Caps (Home Depot)

1/4" barbed fitting (Home Depot)

Valve stem of your choice (Auto parts store)

Vaccum/Pressure gauge (Sears or Auto parts store)

1 1/2" Rubber expansion plugs. (Auto parts store)

 

Drill and tap one cap for the barbed end, Drill and install valve stem in other cap, Glue caps on pipe. I also chamfered the end of the pipe a little to help it into the intake boot.

 

[2strokespirit]

Its possible that its the crank seal at the flywheel side.

[awesomeame]

great ideas, thanks guys!!

 

--matt

[dajogejr]

If you don't feel like hunting down the parts, here's a good kit from a great guy, and a fellow member on here (machwon)

 

I know the picture only shows partially for one cylinder, I assure you it's for a twin cylinder banshee....

 

http://cgi.ebay.com/ebaymotors/Banshee-Pre...sspagenameZWD1V