Author Topic: Tappet cover sealing washer/"O" ring  (Read 362 times)

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Phil C

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Tappet cover sealing washer/"O" ring
« on: 20 February, 2018, 13:38:11 »
When I took off the (hex-head) tappet covers on my 1965 B40F, they had flat fibre washers and goo.  I decided to replace them with new ones, but on enquiring was told they should be "O" rings, so that's what I bought. On fitting them this morning, I found that anything more than extremely gentle spanner pressure causes the ring to squash out of the side of the cover. There is no groove for the "O" ring. I am a bit concerned that the covers are not on any where near tight enough to be secure, but also that if I tighten the cover any more then the ring will distort out of the side of the cover. Should they be "O" rings or flat fibre sealing washers?  Phil (novice.)

AWJDThumper

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Re: Tappet cover sealing washer/"O" ring
« Reply #1 on: 20 February, 2018, 14:44:08 »
They should be flat sealing washers. There would have to be a bevel in the mating surfaces to allow an O-ring to be used.

Phil C

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Re: Tappet cover sealing washer/"O" ring
« Reply #2 on: 20 February, 2018, 17:25:26 »
Thanks.

Phil C

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Re: Tappet cover sealing washer/"O" ring
« Reply #3 on: 22 February, 2018, 17:54:53 »
They're hard to find. Make some out of gasket paper I suppose?  Phil (novice.)

AWJDThumper

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Re: Tappet cover sealing washer/"O" ring
« Reply #4 on: 22 February, 2018, 17:58:21 »
They need to be fibre washers - I don't think they are hard to find:

https://www.ebay.co.uk/itm/PAIR-OF-40-0182-BSA-C15-B40-B44-ROCKER-INSPECTION-CAP-WASHERS-/272916031800

Phil C

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Re: Tappet cover sealing washer/"O" ring
« Reply #5 on: 22 February, 2018, 18:31:11 »
Many thanks - I've ordered them. Out of interest, why would home-made paper gasket ones not be suitable?  Phil (novice.)

AWJDThumper

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Re: Tappet cover sealing washer/"O" ring
« Reply #6 on: 22 February, 2018, 18:57:29 »
A paper gasket is not strong enough to take the shear forces involved in tightening up the rocket caps - a fibre washer is.

Phil C

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Re: Tappet cover sealing washer/"O" ring
« Reply #7 on: 22 February, 2018, 19:18:48 »
Fair enough, thanks. So (please be patient with me), why then is a paper gasket sufficient on the rocker inspection cap, ie the oval-shaped cap held on with a central Phillips head screw? I mean, why do the two tappet inspection caps need to be so much tighter than the oval rocker inspection cap? I'm not doubting what you say, of course, and I am obviously very grateful for your help; I ask just in order to learn. Phil (novice.)

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Re: Tappet cover sealing washer/"O" ring
« Reply #8 on: 22 February, 2018, 19:39:14 »
It's simply that the rocker caps are rotating when they try to compress the gasket - this produces a shear force in the paper gasket which will tend to tear it apart (the shear force tries to move the top of the paper one way and the bottom of the paper the other way). The gasket under the oval inspection cover is not subject to a shear force but just a simple compressive force. 

Phil C

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Re: Tappet cover sealing washer/"O" ring
« Reply #9 on: 22 February, 2018, 21:07:45 »
Okay yes I get it.

AWJDThumper

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Re: Tappet cover sealing washer/"O" ring
« Reply #10 on: 23 February, 2018, 07:49:58 »
Any screw in plug needs a much stronger sealing washer to be used, be it fibre, plastic, copper or aluminium.