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Oil Leak RHS Crankcase

Discussion in 'Technical and Troubleshooting Torque' started by lilster, Jul 12, 2011.

  1. Yesterday I went to change the oil on my Honda CB250 (2001 model). This is the second oil change I've done after an initial one when buying it at 15,000km.

    Now last time we changed the oil it went from red (motul oil pours out red) to almost black pretty quickly - within a week. Google searching suggested two things
    a) It's fine - Carbon turns stuff black quickly and this is normal, particularly with no oil filter in the CB250
    b) It's not fine - this is an indication of an oil screen that's never been taken out and cleaned.

    Not having a stake in the internet debate, I decided that this time I'd take out the oil screen to clean it to be safe. But on opening the RHS crankcase I found the oil pump had two extra pieces when comparing it to photo in the manual I have for a 1988 CB250. Also, giving one of the screws on the oil pump a turn (need to take it out to get at the screen) they wouldn't budge (screen had also obviously never been taken out), so I put the oil screen in the too-hard basket and didn't bother touching oil pump/screen etc. Figured I could live with oil getting dirty quickly, rather than risk something going wrong with the oil pump down the line and facing a hefty repair bill.

    Also, opening the crankcase discovered two things:
    1) It was very hard to pull off, required some light taps with a rubber mallet, but quite sure I was as gentle as could be.
    2) The plastic/rubber sealant around the crankcase cover was cracked and chipping - some came off with the crankcase cover, some was left on the casing still on the bike etc.

    So basically, without changing anything, put the RHS crankcase back on. Poured in the new oil, found it was seeping slowly but surely out of the bottom of the crankcase/crankcase cover (where some of the sealant had cracked off, no surprises.) So drained the oil into a storage container, then left it overnight for the rest to seep out.

    Today bought some silicone gasket sealant to fill the gap where the previous sealant had cracked off. Put a small amount of silicon sealant on, which is now poking below where the leak used to be. Opened up the crankcase and cleaned out the remaining pockets of oil so the sealant would adhere properly.

    Now, I'm leaving the sealant for 24 hours, but tomorrow putting the oil back in and checking for leaks. Is there anything else I need to check for? My brain also tells me that the silicone (small amount may feasibly be poking up at the bottom of the crankcase if it's sealed properly) and oil will not affect each other, and it's built to withstand high temperatures, but are there any risks with this stuff I should look out for?

  2. Try using a gasket, you silly duffer.

    Some sealants will not kindly to being exposed to oil, have you used one that's safe for oil?

    Also, if you are going to use sealant, use very little & be sure none will squeeze out inside the engine, you don't want that stuff getting in your oil galleries.
  3. I thought that's what I was doing? This stuff is silicone gasket sealant, not regular silicone.

    It's also safe for oil and up to 250deg (confirmed on link).

    There's a small chance some might be poking up on the inside of the crankcase because there's a very small bit poking out the bottom - but once you torque it down it has to go above and below the seal so that it's sealed - how do you avoid that?

    I would have bought a new gasket if you could find it easily, but the only one I found online was for the 1991-1993 model CB250, and I'm guessing even the most minor change renders it useless.
  4. It doesn't have to push out the sides to be sealed properly, in fact you need very little sealant as the surfaces are squeezed together quite a lot.

    I would have thought the CB250 had very little changes over the years, aside from going from a (twin to single), I would check with your local bike shop to see if they can shed any light on it. If it's a commonly replaced gasket, it shouldn't cost much, I would expect $5-$15.

    If you can't find a replacement gasket, buy some gasket paper (less than $5) & cut your own.
  5. You are going about it in a pretty bodgy manner. take the cover back off. Scape both surfaces completely clean and then apply a thin film of liquid gasket. Torque it up lightly and leave to set, then come back and torque it up fully.

    This stuff is not meant to be left in place.
  6. I bought a gasket a couple of years back and think it was about $20. I do remember thinking that was expensive. Certainly you need the surfaces clean before you put them back together oterwise a harder bit of sealan/gasket might form a high spot whch prevents a proper mating of the surfaces.

    I also took the sieve out but can't remember exactly how it was placed. I thought it just slotted into the sump and I simply pulled with pliers. I have a pdf file somewhere, not the right model, but as said they really didn't change that much in the engine department.

    Interesting. Never heard this technique before. I can see it should work but why wouldn't torquing correctly in the first place be equally good?
  7. Thanks for the response. We did check for a gasket but they didn't have any at Syd City Motorcycles. We took it apart, re-applied the silicon sealant very carefully this time, not torquing it down but just enough to keep it in place. Will check for any leaks tomorrow.

    Read this somewhere else online too - I think it's so that you don't end up pushing/squeezing the sealant into the inside of the gasket by tightening too far while it's still not set.

    Wish I knew that about pulling it out with pliers- the manual said to remove the whole pump. Wasn't keen.
  8. Won't swear to it. Been a while and the whole set up seemed odd to me. Somewhere I have a pdf file of the manual. When Iget some time I will look it up.