oil leak but not at gasket

[johnnytri-z]

anyone know why oil would seep up from the case on my tri-z and leak around one of the cylinder/case stud and stud nut. and what the fix is for this problem. all of the gaskets are new was rebuilt only has about 2hrs on engine.

[MTS]

Pretty common, Check to make sure that stud is not pulling the threds out of the case, pretty much just put the torque wrench on it make sure it isnt loose, iv run my case's deckd flat and stock, stock they have a rise towards the middle to pinch the gasket, and the base of the cyl will start bending around the studs after enough install's. anyways i use some anerobic sealer on both sides of the basegasket and problem solved loctite makes it along with wurth and a few other companys im sure, used it on many 2 strokes without a problem just need a very thin film of it,,not a big messy goop like yamabond or hondabond. Sprock also makes a fancy basegasket to solve the problem too, i use the anerobic on that also altho its probably fine without it, Offroad innovation carrys his stuff. about the only other way it could creep up the stud other than the basegasket would be a crack where the stud is installed or a crack in the jug itself.

[barnett468]

Hello


In addition to checking the items mentioned by MTS you can also do the following if you don’t find the stud to be loose or case to be cracked i f want.

ENGINE CASE CYLINDER SURFACE – The cases do NOT have an intentionally machined “rise” in them in the base gasket area. This would be an illogical engineering concept. If they were to do this they would have to do it in both directions which would be called a “reverse swail” or “crown” in some circles.

The two halves of the cases are machined separately and occasionally one half will not match another half as well as some so there will be a difference in height between the two of typically no more than .005”. The base gasket is designed to take up this much variance to prevent leaking.

The simple question s are, 1. Why did no other mgf do this?, 2. Why would they do this since the bottom of the cylinder is flat and it will warp the cylinder mounting flanges when it is torqued down and therefore be even MORE likely to leak if the sealing surface on the cases irregular by more than the approximate .005” production tolerance?

CYLINDER BASE SURFACE – This surface is machined perfectly flat. Occasionally the mounting flanges will get warped from over torquing and or mounting to cases that are warped and or machined higher on one half than the other etc.

SURFACE FLATNESS TEST – One can test the “flatness of both the cases and and the cylinder by simply placing an 8” or longer straight edge on them and looking for crowns or gaps etc. If there is a a gap totaling around .006” or more between the cases and cylinder base it will be substantially more susceptible to leaking than one that has less than a total of .005” or less.

If you have a gap of more than .005" between the two I suggest calculating to see if surfacing the cylinder base will be enough to reduce the tital amount of your gaps to .005" or less. If it won't then I suggest surfacing the cylinder base if it is warped and then simply using an additional base gasket and sealer which should "band aid" the problem temporarily.

[barnett468]

Hello

If the cylinder mounting flanges are warped and you have the cylinder base surfaced they need to surface the nut seating surface on the top of the flange also or it will no longer be square to the bottom side of the flange causing the nuts to dig into one side of the cylinder and possibly stretch the stud threads and/or allow the nuts to loose their torque in which case they would need to be continually monitored for proper torque as re-torqued as needed.

[barnett468]

Hello


Designing a "crown" into the base gasket sealing surface on the engine cases would also potentially create a leak in in the engine cases as the cylinder attempted to “flatten” out the crown in the engine case as it is tightened down.

[MTS]

Call it what you want, all the stock sets of case's i have had are no where near flat, and are not missmatched half's. Pretty much what i said the first time around.

[barnett468]

Call it what you want, all the stock sets of case's i have had are no where near flat, and are not missmatched half's. Pretty much what i said the first time around.

Hello

I certainly don't doubt that but you are simply attributing it to the wrong thing that's all.