Topic: CB400F super four oil leak top end, through casting?

[barnshaw]

Good day SOHC4 people

Recently picked up a nice 1977 red CB400F which hasn’t been used on the road for over 15 years… low mileage (8000) with as many hours spent cleaning as it has being ridden!

It seems to have a very slight seeping of oil in the head which looks almost like the metal is porous in that area… just under the first fin, left side looking from the front.

Can anyone suggest a way of rectifying, rather than wiping with a rag after each ride!! Thank you

Thanks
Dan

[Mark1976]

   I have a 400f head apart, on the bench, when I get home later tonight I'll look a little closer at the casting. I've never seen an oil leak due to porosity in a 400f there before or anywhere on a 400f head. You'll more than likely going to have to pull the rocker cover to take a closer look.

[rotortiller]

I'd clean it really good and apply a thin coat of high temp JB Weld then paint over it after I was sure that it was leaking through metal porosity. I would not pull it apart at this point as it seems to have nothing to do with a gasket or seal.

[Mark1976]

   That area of the head has quite a bit of metal, if you're having an oil leak there you may want to investigate a little further. For porosity to exist there it would have to be a pretty significant defect, maybe it's related to the cover bolt hole in that area, a small crack or poorly installed heli-coil.

[Nurse Julie]

Hi Dan
As you're in UK, maybe consider joining us on the UK Forum as well.
www.sohc.co.uk

Never heard of porous cases on 400/4. Top end leaks are common though and usually not bad enough to worry about.

[barnshaw]

Thanks for all the helpful responses.

For now I will ride it and see how much of a leak it becomes. The JB weld isn’t something I’ve heard of, so will look into it if the leak isn’t too bad.

The image of the head was very useful, wasn’t expecting so much material thickness at that point!

Cheers all

[HondaMan]

Back in the 1970s, the Harleys were famous for porous cases. In my shop (yeah, the sales manager decided to also sell Harleys...   ) we were required (by Harley) to fix the leaks ourselves. So, we used [non-latex type] grey paint. We'd clean the site with carb cleaner and a cotton swab, then apply a smear of the paint into the leak. Then after that dried, do it again. And again the next day. Pushing the paint into the pinholes worked pretty well, if you realize that they were non-pressure leaks. This wouldn't work in a pressurized situation - but then. the old H-D bikes don't make much oil pressure, either: your 400F makes about 40 PSI hot in that top end.

[Tracksnblades1]

Back in the 1970s, the Harleys were famous for porous cases. In my shop (yeah, the sales manager decided to also sell Harleys...   ) we were required (by Harley) to fix the leaks ourselves. So, we used [non-latex type] grey paint. We'd clean the site with carb cleaner and a cotton swab, then apply a smear of the paint into the leak. Then after that dried, do it again. And again the next day. Pushing the paint into the pinholes worked pretty well, if you realize that they were non-pressure leaks. This wouldn't work in a pressurized situation - but then. the old H-D bikes don't make much oil pressure, either: your 400F makes about 40 PSI hot in that top end.

JohnDeere and International painted the insides of their trans and mainframes for years. Yellow and Red oxide respectively.
GE electric motor Glyptal paint works well and was Ole Smokey’s recommendation on a few..really pricey….though

[barnshaw]

After some vigorous riding I’m pleased to say the casing leak has subsided to a point where I won’t be doing anything to it other than riding.. the chain tensioner will need doing at some point so I’ll pay some attention to a fix then, thanks for the suggestions. As it’s not been used for over 20 years it’s not had chance to get hot/cold much, I’m hoping now it’s being used it won’t continue leaking, although that sounds backwards logic!

A picture to remember summer when the weathers gone bad 

[AMT]

Please post more pictures of this 400f. Appears to be in spectacular shape