bottom end rumble

250 2c- the Wee-WeeVees

bottom end rumble

Postby mark2cv » 06 Sep 2020 17:19

Hi all, . checking out the clutch, I found that the rubber seal was missing from the oil pump, presumably starving the bottom end oil supply. I had ridden it about 10 miles before discovering that and replacing it. It has since developed a rumble on the overrun when hot, no noise on initial start up or hard acceleration Am I right to suspect big end wear?
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Re: bottom end rumble

Postby mbmm350s » 07 Sep 2020 14:50

Hi

Since the 250 2C has the deep groove ball bearing for the main bearings (unlike later 350s and 500s which have a plain bearing) then big end wear (plain bearings) is most likely with oil starvation.

Did you inspect the oil for any shiny grey particles.

Was the engine rebuilt? The proper seal is green and made of neoprene and is quite robust and dare I say it despite what
the manual recommends is re-usable after careful inspection shows it to be in excellent condition, free of any nicks, cuts or deformation etc and
is still compliant. Recently there has been a black neoprene tube as a substitute I wouldn't use it.

Mark
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Re: bottom end rumble

Postby mark2cv » 07 Sep 2020 20:10

Thanks for the reply Mark,
the egine is s I got it, no history. I didn't check the contents of the oil, but I am sure it is the big ends I can hear. Luckily I have a spare engine which I will put in on Wednesday. I will strip the engine in time. I haven't changed big end shells before, is it a straight forward job, and are they available. Thanks
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Re: bottom end rumble

Postby mbmm350s » 07 Sep 2020 20:47

Hi

Not difficult to change shells - just bear in mind that the workshop manual aka blue book the 250 refers to the 250T and not 250 2C,

The owners manual for the 250 2C gives the torque settings and clearances and method of checking

Mdina Italia should have the shells

Mark
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Re: bottom end rumble

Postby mark2cv » 08 Sep 2020 19:03

I fitted my spare engine today, (history unknown) and it seems to run okay, except from a little smoke from the rocker breathers. Anything to worry about? Also, how do I verify oil circulation.
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Re: bottom end rumble

Postby mbmm350s » 10 Sep 2020 11:29

except from a little smoke from the rocker breathers


more likely water vapour condensing, especially from a stored engine.

Mark
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Re: bottom end rumble

Postby MickeyMoto » 10 Sep 2020 11:51

Hi Mark, (mbmm350s)

Why would you not use the black oil pump tube? I have used one in my rebuild. Are the green ones still available?

Regards,

Worried of Knaresborough.
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Re: bottom end rumble

Postby mbmm350s » 11 Sep 2020 10:30

Hi Mike

I wouldn't worry, the seal is there and all is good.

Maybe I should have written I wouldn't use it unless I had no choice.

NOS green seal still available?, I dont know - not in the UK

The black tube is supplied by Ariete in the oil seal kit, I don't know what it is made of.

The green seal has decades of testing and is known to be good, tolerant of oils and temperature.
The green colour was used to identify the material composition, neoprene is a often a collective term.
The neoprene of this seal wont have the same properties as neoprene used for leggings, sports kit, wet suits etc.

The black tube is undoubtedly cut from a piece of tubing, its has flat ends.
We are relying on some limited compression of the tube to make a better seal than just a line contact.
This is unlikely as its the same height as the green seal.
The oil gallery is a conical surface and isn't well finished

Since the black seal is cut from 12mm tube the o.d of tubing is not a critical dimension for tubing,
only the bore is a requirement for flow rate calculations.

The main fault is that it is undersize and can be easily dislodged from the oil pump on installation.
may be it could be held with a little sealant.

So it is left to judgement as to whether to re use or fit the black tube, and all have to be satisfied that the seal is perfect
Those who have seen many seals are better to judge than I.
However I would use all of my used seals in preference to the black tube.

However if the seal is not perfect or lost then at least in the UK the black tube may be the only option.

Please look after the green seal, don't chuck it in a box where it gets mashed, or lose it in the degreaser.

Mark
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