Author Topic: more puzzels  (Read 344 times)

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Offline tck

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more puzzels
« on: 04 May 2020 at 14:12 »
I  do seem to have a tiger by the tail with this engine although a Mk4 number it did have a plus timing cover with a rev counter and I had a struggle with the cap screws to get it off and then on the bench I found these 3 components two discs with 3 holes and 3 bumps respectively and a top hat pressing which I guess is like a gauze holder. (not the gauze or holder I was expecting), of course I have no idea of their relative positions so if anyone knows it would help .
Overall it seems I am in need of whatever 80-90+ documentation there is, who knows what else awaits me?

Offline douglas1947

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Re: more puzzels
« Reply #1 on: 04 May 2020 at 16:24 »
May be it belongs to my 90+ engine!!!???
(E.No.: 90/16)
I have fitted a standard MK4/5 timing cover on it.

Michael

Offline tck

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Re: more puzzels
« Reply #2 on: 22 May 2020 at 18:58 »
Since no one has come up with anything about this I wonder if its anything to do with a 90+ timed breather as the Mk4 engine did have a + timing chest.
I found this in the Technical section by Eddie
I don't have any detailed info regarding the timed breather - other than it was a disc with 2 windows that ran against the back of the revcounter drive adaptor plate, and was driven by a tongue that engaged with a slotted nut that held the magneto gear - an odd arrangement as it's timing would be affected by the amount the nut was tightened. I think I would be inclined to fit studs in the threaded extractor holes and make a drive plate to suit (especially as the rotation would be trying to undo the magneto nut!).
well this has 3 windows not two and I am not sure how it went together as when the case came off in a rush after resisting all efforts it deposited these 4 items in no order!

Offline eddie

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Re: more puzzels
« Reply #3 on: 22 May 2020 at 21:03 »
This was a short lived attempt to fit a non-return valve to the breather on the early Mark series. The 2 halves of the housing had a floating disc valve between them (missing from this photo) that only allowed the fumes to escape but not return. I think these valves proved troublesome in use, but no more effective than the more usual plain gauze found on the majority of Mark engines.

  Eddie.

Offline tck

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Re: more puzzels
« Reply #4 on: 24 May 2020 at 08:59 »
Thanks Eddie
The only question remaining is if the central bottom hole of the timing cover is the breather outlet why do so many concentrate on another  breather in the oil filler cap? some even put BMW reed valves in there
With all the engines I have dealt with one path to the outside from the crankcase however convoluted is all that is required -or do they block the timing cover one?

Offline eddie

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Re: more puzzels
« Reply #5 on: 24 May 2020 at 09:34 »
Hi,
     I don't understand why there is suddenly a need for extra breathers - if the original breather is not sufficient, then there is a problem with the engine (resulting in too many fumes). Adding extra open breathers just saps the power. During his experiments with the 'Plus' models, Eddy Withers found that a correctly timed breather gave a power increase of about 3HP at racing speeds. The timing of the breather is the critical part, depending on the revs at which the extra performance is needed, and the distance the breather is from the underside of the piston. As the piston descends, the pressure wave travels through the crankcase to the breather, and depending on the revs, the piston may be rising again by the time the breather valve needs to open. The timed breather on my DBD34 Gold Star does just that - it opens when the piston is rising!
  Of course, reed valves overcome the need to time the breather, but all the air that comes and goes from the crankcase has to be pumped - and that consumes power!

  Regards,
                 Eddie.

 

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