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Author Topic: Oil feed to the crank...???  (Read 669 times)

Nitram

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Oil feed to the crank...???
« on: April 10, 2015, 09:31:34 am »
I was reading the other day about the relatively simple modification to improve oil feed to the big end (and being a plain bearing, its probably a case of more-is-better) which involves simply removing the bush that sits in the clutch cover and that goes over the end of the crank, and replacing it with a lipped seal. The bush, 'though in a blind hole, is pretty easy to remove and is identical in size to the seal where the gearshift shafe goes through the same cover: i.e. 24mmx14mm. So its pretty simple to put the seal in, 'though I also planned to put a thin steel retaining plate over it, screwed on with countersunk screws etc, just to make sure it doesn't pop out under oil pressure.

But it occurred to me to wonder the extent to which the bush is designed to support the end of the crank, (which after all is just outboad of the primary drive) rather than simply to facilitate oil feed to the crank....... It'd be a shame to have the crank snap some time when the clutch was dumped the mighty NF's power was unleashed through an unsupported crank....... ;).

I guess lots of motorbike engines don't have any support for the end of a crank , 'though some do. (I'm thinking here of Ducati singles which from memory have the crank bush (and oil feed) outboard of the OHC bevel drive gears- but my experience with fourstrokes is minimal)

Has anyone come across this mod on a NF, and had the bike run indefinitely afterwards without problems ?  ???

Any thoughts on the subject ?

Cheers,

Nitram

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banquo

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Re: Oil feed to the crank...???
« Reply #1 on: April 10, 2015, 01:56:54 pm »
Hi Nitram. Of course I don't have any experience of this, but the function of the bush will be to support the outboard loads on the crank (outboard of the main bearing that is), which in this case effectively is the drive side. The primary drive will attempt to bend the shaft, and its stiffness will be affected by the fact it's now cantilevered instead of supported at both ends.
That will result in about twice the bending stress if my memory serves me right (and that's by no means guaranteed these days) based on simply supported beams supported at one end (cantilevered) compared with at both ends. Of course it's a lot more complicated than that, as you have various different forces applied at different parts of the shaft, but the principle remains.
Needless to say, it wouldn't be recommended to modify anything mechanical to the extent that stresses were increased, but if the outboard crank is very over-engineered, with a factor of safety far higher than needed, then it's perfectly possible for it to work without any issues.
Only experience can answer that, and if there are many who have performed the modification without problems, then that would raise the comfort level.
I take it there's not enough depth to fit a shorter bush and a seal, which might be the preferred solution?

huub

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Re: Oil feed to the crank...???
« Reply #2 on: April 10, 2015, 05:23:29 pm »
if he engine has done some miles , there will be enough play to stop it from acting like a bearing.
and steel running in a alloy bush is a pretty bad bearing combination anyway.
having said that , a oilseal should be held in place firmly to stop it from popping under the 4 bar oil pressure available
with a extra metal plate to protect the oil seal, it is quite a common modification
« Last Edit: April 10, 2015, 05:25:09 pm by huub »

Nitram

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Re: Oil feed to the crank...???
« Reply #3 on: April 10, 2015, 09:33:09 pm »
Thanks Banq and Huub.
The crank certainly is, like all things NF, very solid on the drive side (i.e. probably over-engineered). And as Huub points out, if there's wear in the original bush then it wasn't contributing to supporting the crank anyway. Mine has about .5 mm wear (there must have been bugger-all oil pressure) so I'm thinking........I'll give it a go. And the additional oil pressure can only be a good thing for the big end.
Tony from UK says his is running fine with the mod, and if as Huub says its a common mod then not too much risk............hopefully.... ;)

Thanks again for your thoughts.

Nitram

banquo

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Re: Oil feed to the crank...???
« Reply #4 on: April 11, 2015, 08:58:57 am »
No substitute for experience. It did occur to me that the wear could have as much to do with run-out on the crank and misalignment than anything else.
The crank won't be perfectly straight, and there will be at least some run out when rotating, plus any whipping that may occur. Also, how could they guarante that the bush in the clutch cover aligns perfectly with the crank, when they are on separate castings? Maybe I'm missing something.
Look forward to hearing how you get on with the conversion. Some pix would be good too!

patentgeek

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Re: Oil feed to the crank...???
« Reply #5 on: October 23, 2017, 05:56:35 am »
Reviving this thread as I'm in the process of replacing the aluminum bushing in the right engine cover with a shaft seal. 

To extract the aluminum bush, I used a tap (I think 9/16-20 was closest) to thread the ID of the bushing.  I then heated up the engine cover around the bush with a MAP torch and threaded a bolt through the threaded ID of the aluminum bush until the bolt bottomed on the engine cover.  Continuing to tighten the bolt acted to extract the bushing.

I noticed the end of my crank (that will fit into the shaft seal) is somewhat grooved, which isn't an ideal surface for a shaft seal.  Other than dressing down the surface, I'm not sure what can be done about that.  I'm sure the shaft seal will seal better than the aluminum bush, and the modified Daytona oil pump I'm installing should have almost double the pumping capacity of the stock NF oil pump, so I'm not particularly concerned.  It might be possible to press a very thin sleeve onto the end of the crank and use a larger ID shaft seal if the grooves are problematic.

huub

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Re: Oil feed to the crank...???
« Reply #6 on: October 23, 2017, 08:22:44 am »
sounds like a perfect application for a speedi-sleeve.

Nitram

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Re: Oil feed to the crank...???
« Reply #7 on: October 30, 2017, 10:06:59 am »
In case anyone is considering this mod, I ended up putting the crank in the lathe to tidy up the grooves and scoring, but taking off the bare minimum to achieve a reasonable finish. The seal, retained by a thin cover plate and some small allen screws Loctited in has now been in place for about 6,000km without problems. I don't have an oil pressure gague so I don't know how much it helps but its got to be better than the sloppy bush that was in there before.
Good luck !
Nitram.  :)
 

banquo

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Re: Oil feed to the crank...???
« Reply #8 on: October 30, 2017, 12:37:46 pm »
Sounds good Nitram; did you take any pix?

patentgeek

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Re: Oil feed to the crank...???
« Reply #9 on: November 24, 2017, 06:27:44 am »
Huub suggested an SKF Speedi-Sleeve to fit over the grooved end of the shaft to provide better sealing.  I believe SKF part #99055 can be used for this application as the nominal shaft diameter is 14mm.  See the link below for technical specifications:

http://www.skf.com/us/products/seals/industrial-seals/power-transmission-seals/wear-seals-skf-speedi-sleeve/index.html?designation=99055

banquo

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Re: Oil feed to the crank...???
« Reply #10 on: November 24, 2017, 09:57:24 am »
Looks like a good solution to me, although dependent on the shaft being within the described tolerance band. I'd be concerned about run-out as well, as there's no mention of a spec. for that. When it comes down to it, I'm never comfortable with bearing supports on two different castings, unless they can be line-reamed to guarantee alignment. How can anyone be sure they are perfectly aligned? At least an oil seal has some compliance for misalignment, although it's a big ask expecting it to withstand full pump pressure?

huub

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Re: Oil feed to the crank...???
« Reply #11 on: November 24, 2017, 10:11:36 am »
the aluminium bush is not a bearing, just a primitive way to get some oil into the end of the crank

a oil seal is a more elegant solution , but needs a smooth shaft,( that is where the speedi sleeve could help.)
the morini twin has a similar layout, and a oil seal to feed oil into the crank.
on the morini the seal has a metal plate , to prevent it blowing out.
machining the original aluminium bush to incorporate a seal shouldnt be hard.
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banquo

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Re: Oil feed to the crank...???
« Reply #12 on: November 24, 2017, 11:43:00 am »
So the plate on the Morini is just a retainer plate, to keep the seal in place?
No problem with oil blowing past the lip due to pressure?

huub

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Re: Oil feed to the crank...???
« Reply #13 on: November 24, 2017, 12:58:20 pm »
a 15x24x5 seal , kept in place by a metal plate
( slightly beveled inside diameter , not to interfere with the seal lip) the plate is fitted with two screws
no problems with oil blowing by , the oil pressure adds to the sealing of the seal
http://www.ebay.de/itm/Moto-Morini-Kanguro-350-3-1-2-Motordeckel-Kurbelgehause-Deckel/282666203334?hash=item41d037f8c6:g:2wUAAOSwCU1Y2Nx4

on a morini the oil pressure pushes the seal out , on a NF if you machine the inside of the bush and fit the seal there , the seal cant be pushed out
morini's run pretty high oil pressures, compared to the NF
 

banquo

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Re: Oil feed to the crank...???
« Reply #14 on: November 24, 2017, 01:09:05 pm »
Thanks Huub; I'll take a look at the shaft condition when I have it out.