base gasket leaks

[SuperRat2110]

So I finally tried a leak down test on my 01 today and it went miserably. The base gasket has two primary leaks pretty much in the center of the front and back. Not sure where to go from here. I'm assuming i have some sort of warping going on? Where should I go from here? Can I try doing anything with the gasket?

Shaun

[thrownchain]

Is it leaking at the gasket or case seam?

[SuperRat2110]

Thats a good question, if it's right in the center then I guess it could be the case seam? Do I need to tear apart and re-seal?

[thrownchain]

Most likely.

[SuperRat2110]

The only other thing I noticed was that little hole in the center of the case halves actually goes all the way through the case. Is that normal?

[thrownchain]

I've never seen one all the way thru.

[dcooke007]

I always apply a dab of automotive RTV / silicone sealer where the two case halves meet before installing the cylinder base gasket. Noticed several engines displaying that leak over the years....even with good cases and gaskets. Just do it automatically now. Working on many Hodaka engines and testing you kind of learn where all the grimlins are.

Danny

[viclioce]

Danny. Are you saying put a dab of RTV on the surface where the cases join? Just curious. Victor

[dcooke007]

Hey Victor,
Yes, on top of the engine cases where the two halves meet under the cylinder base gasket. Lots of automotive applications where junctions like this occur and it is recommended to apply a dab of sealer to prevent leaks. Do not allow RTV to cure, assemble immediately. Doesn't take much....just a small dab.

In this case the cylinder studs are on the outer edges applying clamping pressure. Gasket just does not always deform enough to fill the very small opening. Also possible base of cylinder is not perfectly flat and contributing to the issue. It is easy to lap the cases flat but not so easy to lap the cylinder base flat. Cylinder liner / extension kind of gets in the way.

Danny

[SuperRat2110]

Danny, how long after applying and torquing it a down do you wait to do any kind of leak down?

[viclioce]

Thanks for the explanation Danny! I’ll try it with my Combat Wombat rebuild! Victor

[SuperRat2110]

Danny, thanks that fixed my leaks around the base gasket. Still a slight leak from one one of cylinder bolts and around carb flange studs. But that took care of the big ones. Thanks!

[thrownchain]

Teflon thread sealer will help those. Unless it's leaking thru the gasket and coming around the studs. I put a light coat of gasket sealer on both sides on those gaskets to get a good seal.

[SuperRat2110]

I got the small leaks fixed too but I still don't have a passing test. I've sprayed around all the critical spots multiple times and can't see or hear anything that would indicate the pressure loss I have right now. Not sure where else to look? I"m almost ready to stick the motor on the bike and keep moving forward, not sure if running it would help seal things up or not. Im assuming there are a lot of old bikes that run around with failing leak test.

[SuperRat2110]

I did use teflon around the studs on the flange and I smoothed out the washer on the cylinder bolt that was leaking. Both seemed to do the trick.

[thrownchain]

How fast does it leak down?

[SuperRat2110]

From 6 to 4 in less then a minute...

[thrownchain]

Head gasket is solid, have you sprayed the crankcase vent?

[Bullfrog]

Leaking down from 6psi to 5psi in one minute is a FAIL. 6 to 4 in less than a minute is a severe fail. Still need to find the leak(s).

The comment about the transmission breather vent is a good one. I often try to plug the little hole on the side of the vent fitting with the tip of a finger AND spray the soapy water on - this helps assure that the soap film covers the opening and bubble show up if there is a leak there. A leak at the transmission vent often means the clutch side crankshaft seal is leaking - but that should be confirmed BEFORE splitting the cases, since the leak could due to something else too.

Ed
PS: Some sealant on the threads at the bottom end of the cylinder studs is highly recommended. There is a potential "leak path" directly from the crankshaft cavity to the threaded stud holes . . . and up the stud passage on the alloy cylinders . . . over to the threaded stud holes for the intake manifold. Sealing the cylinder studs at their bottom ends greatly reduces the leak possibilities.

[SuperRat2110]

I did take the reed out and discovered the gasket was split but I know it wasn't prior to that. I'm pretty sure I sprayed heavily around it. So right now I need a new gasket and then I can check on some of those other things. Thanks for the all the advice, Ed.

[SuperRat2110]

Clutch side seal was replaced with all the other seals and bearings.

[SuperRat2110]

I did spray around the breather before I mangled my Reed gasket but didn't notice anything. I will keep trying though. Thanks for all the advice.

[Bullfrog]

Hang in there, you'll get it.
Ed

[SuperRat2110]

So I was able to seal up Reed gasket and I'm still getting the same leak time. I've sprayed around everything so many times I lost count. I even sprayed my leak system and checked it on the 98 to see if it was part of the problem. I've check the breather also and that shows no signs of leaking so my seals must be good. What else could it be? I've sprayed the the cylinder nuts and spark plug. I tiny bubble here or there but nothing suggesting the leak that is showing on the gauge. I cant even hear anything.

Ughhhh!

[Al Harpster]

Long shot here, but have you sprayed the seal under the stator? The flywheel side.

I believe you said both crank seals were replaced.

I once connected my "air input hose" to a small compressor set at 10 psi and looked for leaks.

This gave me a whole bunch of time to look AND listen. At 10 psi the compressor never runs if it's tank's full. Nice and quiet.

I eventually put a hose thru the transmission filler, put a funnel on it and listened. Like an old fashioned hearing aide sort of.

This may sound crazy, but I was loosing my mind trying to find this particular leak. Took me days to find it.

Keeping pressure on over time gives more time to look, look and listen. Some guys might say 10 psi is too much. Worked for me.

I gotta admit, I was at my wits end on that one.