Topic: CB400/4 Replacing Crank Seal (behind points)

[Calumjs]

I have searched and found a few posts regarding the replacement of the engine seal behind the points cover with out splitting the cases. I’m assuming this is the original seal with the lip on the inside, will this be something I can easily extract with oil seal removal tools? Or will it end in tears and requires the cases split?

I do think I have a bit of blow by, could this be causing the leak? Or does the crank case breather take care of the increases in crank case pressure due to blow by?

[Deltarider]

I don't have the answer. What I do know, is that not all oils are equal in keeping rubber parts supple. I have good results with Castrol oils in general and the 15W-40 GTX High Mileage in particular. When I had the full synthetic Mobil 1 in, I had to replace the oilpump seals in Spain. Also I recommend not to top up to the max mark. Halfway the max and min mark is good enough and can make a lot of difference in the crankcase breather spew out as CB550 owners with that poorly designed blow-by gas recirc system can testify.

[bryanj]

To do it properly its split the cases and remove camshaft to get enough lift on the crankshaft to fit seal

[Deltarider]

First I'd try an oil additive for this, you will find in auto stores, like Bardahl. Recently a friend of mine was about to take his XS650 engine apart to replace the lower cylinder packing that annoyed him. I advised him to use the same Castrol oil I use and, behold, it worked. When an engine has been inactive for a long period of time, it's not unusual to have some minor leaking that will cure itself after the bike is used regularly again.