30cc Intake Leaks

[yknotrc]

While running my XB the other day it started to idle fast on the 4th. tank, a quick check with WD40 indicated a leak between the intake manifold and block


I worked on it yesterday and found that the lower bolt hole had not been tapped deep enough! Looking at the old gasket in was obvious that it was crushed more on one side the the other,I put both bolts back in the manifold and then checked the depth of the holes in the block with my caliper it seemed like they were plenty deep enough.


next I tried bolting the intake to the block without the gasket and bingo after backing out the top bolt the manifold was loose I was able to rotate it on the remaining lower bolt!The bolt was bottoming out and seemed tight but it was not clamping the manifold the way it should.


Not having a 5mm bottom tap handy I added a thick flat washer to each bolt and put it back together with teflon gaskets no more leak!


I did check the manifold on a piece of glass to make sure it was flat and it was


I have read on this and other forums about people having intake leaks on these engines so I thought I would pass this along, maybe a common problem or maybe I just got a bad one! anyway if you have a intake leak double check and make sure this is not what is causing your problem or just add a couple of flat washers just to be sure

 

[DemonRC]

Ya it's pretty common. Most people just chop 5mm off the end of the bolt. Be sure to screw on a nut, chop 5mm off the end of the bolt, file a bevel on the end of the bolt, and then take the nut off so you don't accidentally jack the threads up. I had a bad thread once and it ate the thread in the soft aluminum head.