Cylinder base oil leaks

[aharrett]

Does anyone have any advice on the best method of sealing cylinder bases?

The bike is a 1979 R100RT and I have lived with a oil leak from one rocker oil feed stud for several years. The engine was assembled with base gaskets to improve an previous cylinder base oil leak.

Recently I dismantled the top end again to cure this leak. Believing the gasket to responsible for a poor seal at the rocker feed I reassembled it without gaskets and used oversize cylinder base o rings as supplied by Motobins (UK), and the normal o rings around the rocker feeds.

The oversize o rings seem to be working well, and three of the rocker feeds are fine, but one (not the same one as before) is leaking badly. Before taking it apart again I thought I would just ask in case this is a common problem, although it's leaking so badly I fully expect to find something wrong with the o ring.

[Frog]

Pardon me if this information does not apply to your bike, as I do not know your specific model.

In my understanding, the pushrod tub seals are pushed into the engine case by a collar that is press fit onto the tub. In some cases, the collar is not positioned in board enough to exert enough pressure on the seal. There is a tool (that one can make) which is used to gently hammer these collars towards the seal.

Hope that helps

[mattcfish]

Pardon me if this information does not apply to your bike, as I do not know your specific model.

In my understanding, the pushrod tub seals are pushed into the engine case by a collar that is press fit onto the tub. In some cases, the collar is not positioned in board enough to exert enough pressure on the seal. There is a tool (that one can make) which is used to gently hammer these collars towards the seal.

Hope that helps

No, he's talking about the oil passages at the stud. Could we have a problem with studs that are pulling out? Sounds like they aren't holding torque. How do they feel when they're tightened?

[chasbmw]

Do you assemble with sealant?

BMW now suggest that you use 'drie bond' brand sealant
Also sold as 'yamabond'. Use a smear around the crankcase stud o rings,
This sealant works much better than the hylomar that I used to use

Charles

[Roy Gavin]

Sherlocks sell a rather expensive gasket they claim will cure all leaks.

Sounds easier than gasket cement and O rings, and I just dont like gasket cement around oil ways.

[aharrett]

Thanks for your prompt replies guys.
I don't think the studs are pulling - there is no visible evidence, and they torqued up normally.

Those gaskets from Sherlocks are what I used last time, and to be fair the bike was leak free for several years. However, I remember thinking on assembly, that they may well cure the base joint leak that I had, but it looked as though they would compromise the rocker feed seal, because with the gasket in place, the o ring has nothing firm to compress against (just the gasket material). Then when the leak developed several years later, that's what I assumed.

With this in mind, I decided to assemble this time, using the oversize o rings (to help the cylinder base seal which was my original problem), and allow the rocker feed seals to seat as intended in the recess since this had not previously caused a problem.

I used a good quality silicone sealant on the base flange to assist the main o ring, but was reluctant to put any on the small o rings for fear of blocking the oilways. Perhaps I should try again using this 'Driebond'. Is it better than silicone and where do I get it from? I also in the past used Hylomar, and I must say, with the exception of this BMW always had good results.

[lrz]

Though there may be some proprietary differences, I'd guess these sealers are fairly similar. I've used the Honda version, readily available at the local dealer, w/ good success.

The key is to use a light application to a clean surface paying particular attention to the area around the oil gallery.

[chasbmw]

You should be able to get dreibond from 'bins or from BMW dealers, otherwise the similar yamaha or Honda products.
I use a smear around the metal at the oil feed studs.
After it is all in one piece, take plugs out, ground them, take off rocker boxes and turn the engine over on the starter.
You will be amazed at the quantity of oil produced in a very short time.

[R90Steve]

I have been told by a very good source that some of the key ingedients have been removed and substituted in Three Bond and the other "bond" named products to meet California enviromental regualtions says he can tell the difference. My source has a well known, all brand MC engine machine shop and I tend to believe what he tells me.
He has used Three Bond products and is now looking at other products. FWIW

[aharrett]

OK, I'll reseal with 3 bond or similar. That's a good point about checking the oil flow before running the engine- I hadn't thought of that.
I can't help thinking there is something fundamentally wrong with the arrangement if it's necessary to 'help' an o ring with gasket compound though. In every other application I've encountered, an o ring seals perfectly adequately using compression. Is it that the recess is too deep, allowing insufficient compression, rather like the issue with the cylinder base o rings? If so, I could maybe try to source extra thick o rings?