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Thread: Lotus twin cam breathing

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    Racer Decade Plus User wildo105e's Avatar

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    Lotus twin cam breathing

    In a bid to stop rocker cover leaks on my twin cam I have replaced the rattly filler cap with a shiny billet one from Burton. This fits nice and tight. But I have been thinking that maybe the old TC one was rattly as a vent for equalising crank pressures. The TC head has a vent to the block over the fuel pump but my crankcase isn't vented. I have been here before on cross flows but they vent the block. Will this give me more leaks than I started with ? I am going to fit a an electric pump shortly so could fit a breather in the blanking plate possibly. I am not keen on fitting a breather in my lovely rocker cover though.


    cheers

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    Re: Lotus twin cam breathing

    The original filler cap wasn't vented. If it was it would leak at times.

    Normally on Twincams the crankcase breathes through the hole above the fuel pump aperture into the head, which then breathes into the airbox via a horizontal tube - the air is then drawn into the carbs so is a basic crankcase ventilation system. If you don't have something similar to this you will likely have problems.

    I would either fit the proper rubber tube between block and head (which to do properly requires the head off which I'm guessing you want to avoid!), or vent the crankcase to the carbs or a catch tank but if you decide to vent straight to the carb you will need some kind of baffle or restriction to stop oil going into the intake system. The standard Twincam system has a few turns so that oil becomes trapped before it can get to the inlets, and if any does make it through there is a final gauze filter in the horizontal breather tube already mentioned. Only gasses should get through, no oil.

    What was the reason for not using the rubber tube between block and head?
    Last edited by HonkyWhiteTrash; 24-03-2016 at 14:28.

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    Racer Decade Plus User wildo105e's Avatar

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    Re: Lotus twin cam breathing

    Quote Originally Posted by HonkyWhiteTrash View Post
    The original
    I would either fit the proper rubber tube between block and head (which to do properly requires the head off which I'm guessing you want to avoid!), or vent the crankcase to the carbs or a catch tank but if you decide to vent straight to the carb you will need some kind of baffle or restriction to stop oil going into the intake system. The standard Twincam system has a few turns so that oil becomes trapped before it can get to the inlets, and if any does make it through there is a final gauze filter in the horizontal breather tube already mentioned. Only gasses should get through, no oil.

    What was the reason for not using the rubber tube between block and head?
    sorry my poor description. I have the rubber tube between block and head fitted so the head and block are connected with crank case pressure, When you mentioned the pipe that feeds to the carbs I think there is a 1/2 inch hole or so in the breather box on the head (I assume that is where the pipe fits).

    So if that is the case I am venting directly out of this hole to atmosphere, I suppose I can fit a pipe from this to a catch tank I was being really fussy. If this hole is there then I have not closed the system up.

    does that make sense ??


    thanks


    Dave
    Last edited by wildo105e; 24-03-2016 at 15:21.

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    Re: Lotus twin cam breathing

    I see! That's not so bad then! I've seen Twincams built by well respected engine builders without the tube from block to head so thought you might have had an engine built by one of those culrpits! But now I seem to remember yours is a Nick Stagg engine (?) so I would guess he would have fitted one as he's bob-on with everything he does.

    Yes you're right the system is open if that hole is unplugged. You can buy a long draught tube (original fitment in very early cars) with a right angled connector that goes into that hole on the side of the head - this just draughts to the road like pre xflow cortinas and anglias etc used to do.

    If your cam cover is leaking the first thing I'd do is check it for flatness as it's quite a distort-able unit and the cams manage to fling oil everywhere. Is it leaking in one particular area or just like the Exxon Valdez? :-)

    What does this filler cap from Burton look like?

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    Racer Decade Plus User wildo105e's Avatar

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    Re: Lotus twin cam breathing

    cheers thats put my mind at rest. The old cap was so loose and the new one is nice and tight thought i might have sealed the engine with no breathing. Cap is this one
    http://www.burtonpower.com/catalogse...ller+cap+lotus

    now hopefully the cap leak is cured the others seem to be the rear half moon seals. I will re do the seals etc and see if it improves. Read about a guy who does it with just silicone and no gasket. I also have new valve cover nuts as they seem to go slack all the time.

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    Re: Lotus twin cam breathing

    If you use Seloc washers under the cam cover nuts you can use Nyloc nuts on the studs rather than the domed type that come un-done.

    Remember not to overtighten the cam cover - it needs fastening down until it just seals. The oil should make the cork swell to keep it tight.

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    Racer Decade Plus User wildo105e's Avatar

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    Re: Lotus twin cam breathing

    ok so time will tell re sealed the 1/2 moon seals with red hylomar then the cam cover. Used dowty seals from burton, or as i call them rubber washers then a normal steel washer then nyloc nuts just nipped up so the washers couldn't move and no more.

    we shall see.

    as an aside found this picture on ebay of an air box which shows the breather into the backplate.


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    Re: Lotus twin cam breathing

    Finger crossed it works! They're hard to keep oil tight at the best of times!

    That airbox was at £720 when I looked this morning!

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    Re: Lotus twin cam breathing

    Quote Originally Posted by HonkyWhiteTrash View Post
    That airbox was at £720 when I looked this morning!
    £983 now glad I don't need one.

    Ran the engine up yesterday to full temp and all seems good for now

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    Re: Lotus twin cam breathing

    People really are stupid - you can buy reproductions of the air box and backplate which in total come to about £500. I'd prefer repro over used any day - surely marked/scratched originals can't be worth that much if putting them on a mint car (and if you have that much money to spend on an airbox you must have got an expensive/mint car) as they'll let the car down?! Those parts wouldn't suit a concourse car so it doesn't matter that they're original Ford!

    Good news with the engine! I love a twink!
    Last edited by HonkyWhiteTrash; 31-03-2016 at 10:26.

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    World Champion Decade Plus User meXEco's Avatar

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    Re: Lotus twin cam breathing

    Jesus glad I dont have to buy anything for mine to make it original or bufty lol.


    '68 1100 Deluxe-bog stock soon to be a twincam rep.


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    Re: Lotus twin cam breathing

    Hi who does the repos on the backing plate and cover please as I need both

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