Topic: CB750K mystery oil leak question

[HairyPotter]

I recently replaced the gasket on the valve cover (aka cylinder cover gasket). In doing so, the bolt on the right front corner (sitting on the bike facing forward) stripped out at the very end. I replaced it with another bolt that was 1/4” longer. Just to be sure, I also ran a 6mm x 1/00 tap into the hole to clean up the threads. Screwing the longer bolt past the stripped out point allowed me to get enough bite to tighten it down. Before bolting the cover back down, I peered into that hole with a high powered flashlight and also into the one just south of it. The latter seemed to have something stopping the depth of the hole. The hole that I put the longer bolt in didn’t have this “stoppage”.

First ride, I didn’t notice any serious leakage, just a little bit of splatter which I thought was residual oil from a previously mis-installed valve cover gasket. Now I realize that there appears to be a very small seepage leak from the vicinity of just below the valve cover bolt that I’d replaced with the longer one.

Question: Did I destroy some sort of seal when I inserted the slightly longer bolt? Note: The leak is not coming from the space between the valve cover and the cylinder jugs, or between the jugs and the lower case. It just appears to be coating the fins on the right side of the jugs with a bit of oil that eventually flies off and coats everything behind it with oil.

What am I missing?

[scottly]

I replaced it with another bolt that was 1/4” longer.

Is the longer bolt bottoming out in the hole before clamping the cover down? A washer or two may help.

[HairyPotter]

It didn't bottom out. I only put in a bolt long enough to bypass the part that was stripped so that it would tighten down the valve cover. When I look into the hole nearest to the one that was stripped, that is, the one closer to the rear of the motor, I could see some sort of "bottom" to the hole. On the hole I stripped, that was not present. The image is of the hole that has the longer bolt.

[calj737]

Clean the motor. Sprinkle Baby Powder on the motor in the areas of suspicion. Ride the bike. The oil will hit the baby powder and show you where you are leaking. Then, you get to figure out how to fix it 

[madmtnmotors]

Most of the valve cover bolt holes are "bottomless" in that they are bored clear through and the underside is exposed to the atmosphere. This means that only half the gasket is protecting these openings. Once the oil seeps as far as the bolt, then it can leak out through the threads. I use thread sealant on my valve cover bolts for this very reason.

Remove the suspect bolt and apply some thread sealer. Not thread locker, thread sealer. 

[flybox1]

Most of the valve cover bolt holes are "bottomless" in that they are bored clear through and the underside is exposed to the atmosphere. This means that only half the gasket is protecting these openings. Once the oil seeps as far as the bolt, then it can leak out through the threads. I use thread sealant on my valve cover bolts for this very reason.

Remove the suspect bolt and apply some thread sealer. Not thread locker, thread sealer. 

^ This.....and thread SEALER on the oil pan bolts too.  ARP makes a nice thread sealant.

[HairyPotter]

Thank you everyone! These are great suggestions!

[madmtnmotors]

Most of the valve cover bolt holes are "bottomless" in that they are bored clear through and the underside is exposed to the atmosphere. This means that only half the gasket is protecting these openings. Once the oil seeps as far as the bolt, then it can leak out through the threads. I use thread sealant on my valve cover bolts for this very reason.

Remove the suspect bolt and apply some thread sealer. Not thread locker, thread sealer. 

^ This.....and thread SEALER on the oil pan bolts too.  ARP makes a nice thread sealant.

Permatex makes a nice one too, available at almost all auto parts stores.