Lotus Elan

Measurements for head to block rubber tube

PostPost by: david.g.chapman » Fri Jul 07, 2017 12:41 pm

Can anyone tell me the head and block hole diameters that the rubber breather pipe fits into on the twin cam?

I plan to make up something in metal this winter using the VW adjustable pushrod tube as a basis. At the moment everything is together so I can't do the measurements myself.

Dave Chapman.
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PostPost by: john.p.clegg » Fri Jul 07, 2017 12:58 pm

I can't tell you the diameters off the top of my head but I went down the same route a few years ago and found it V difficult as the hole in the block has an angled surface to it....I gave up..

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PostPost by: david.g.chapman » Fri Jul 07, 2017 1:55 pm

Hi John,

The block is the main area of concern for me. I have taken the plunge and bought a pushrod tube. it is designed to fit into 22mm dia holes in the VW engine.

There is a threaded gold part which I plan to fit into the head. The head hole diameter looks to be about 26mm (a guess), so I will make up a metal washer to glue over the top shoulder of the gold section, and then use a home made rubber washer on that to make the seal.

The hole diameter of the block is critical. If it's too small the shoulder on the blue anodised lower section will not fit and it could be game over. Too big and I can do the same as the gold end with my washer, plus a spacer to get rid of lateral play.

If it's about right (22 to 23mm), then a thick O- ring on the lower shoulder of the blue tube should seal ok on the exterior block face around the hole. I am relying on the compliance of the O-ring to take up the surface angle on that face and general roughness on the cast finish (fingers crossed).

Once I have the hole diameters and if it is practically possible I will post my idea of a way forward, and then post again when I fit it this winter.

Dave.
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PostPost by: john.p.clegg » Fri Jul 07, 2017 2:12 pm

Good luck

keep us posted

John :wink:
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PostPost by: oldchieft » Fri Jul 07, 2017 7:35 pm

This is one of a number of ideas that have been tried.

http://elantrikbits.com/lotus-elan-blog ... iner-tube/

Jon the Chief
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PostPost by: Craven » Fri Jul 07, 2017 8:09 pm

Hi,
Hole in block appox 20mm with small lead in at 21.5.
Ron.
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PostPost by: david.g.chapman » Sat Jul 08, 2017 11:16 am

Thanks everyone.

Please find attached a sketch I have done to show an idea on how to use the pushrod tube. I think it has to be used "upside down" with the gold tube on the bottom, as the hole in the block is too small otherwise.

I have exaggerated the slope on the block hole face, but some nifty filing will have to be done to the shoulder on the gold tube to match the slope. With a thick O-ring and maybe some RTV I do not think you have to be that accurate though. So I think it is doable.

As for the hole in the head I think you can see the issue there. Again something can be done with a ring spacer if required.

I will have a go this winter. Feel free to beat me to it if you want to! :D
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Downtube sketch.doc
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PostPost by: Craven » Sat Jul 08, 2017 11:56 am

Hi,
IMHO, you are trying to seal the bottom of the tube in the wrong place! ?O? ring would be better placed on the part of sleeve that?s pushed into the block. Unfortunately the hole is not machined at all just a rough cast finished.
Have not looked at other suggestions but I would use the original rubber tube, cut off top and bottom and use these parts as the seals, makeup possibly in plastic, a tube that can be pushed up and then down into the lower part, or fit rubber part first and then expand.
If the diameter of tube is slightly over size will be gripped by the rubber or use a spot of Super Glue.
FWIW
Ron.
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PostPost by: david.g.chapman » Sat Jul 08, 2017 6:29 pm

Thanks Craven.

An O-ring inside the block hole would be better if the surface is good enough. I seem to remember that my hole signed signs of having drill marks, not a cast finish. I just can't remember. There may not be a need to file a slope on the gold shoulder as well, although I do not want the tube assembly to be thrown off laterally by the slope.

I won't really know until I try it.

Dave.
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