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Thread: Smokey Cosworth after overrun.

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    Part of the furniture Decade Plus User Hugh's Avatar

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    Smokey Cosworth after overrun.

    I've posted this on the RSOC BB but am more optomistic about getting a good answer on this board.

    I was hoping that the new turbo fitted last week was going to cure all my ailments but alas no.

    I drove the car fairly sportily yesterday for about an hour down back roads (never going above 5000rpm though) and after letting the car overrun for a few seconds (whilst going down a hill, foot off the accelerator) at about 3000rpm the very next touch on the throttle unleashes a whopping puff of smoke from the rear.

    Please please please can someone tell me why it is doing this as I am now rapidly falling out of love with my car again!


    Cheers
    Hugh

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    Re: Smokey Cosworth after overrun.

    I'm suer some one here will have a clue - your mail is almost a challange

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    Re: Smokey Cosworth after overrun.

    Hi sapphy not sure of the cars spec or what you've had done but an idea would be the valve stem oil seals, cruising with your foot off the accelerator will give you a negative pressure in the cylinders which could pull oil down the valve stems which is then burnt when you accelerate again.

    Just an idea to start the ball rolling.

    Steve

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    Re: Smokey Cosworth after overrun.

    Hugh this is normally associated with a worn engine BUT new engines can do the same if they havent got the correct breather setup, BUT at 330HP if you engine is the original I would suggest its a bit worn, BUT this isnt too much to worry about.
    <br>
    <br>The other magor cause of this along witht he breater issue is using a oil that is too thin, I recomend a 10w at the absolute mininum and pref a 15w oil.
    <br>
    <br>Hope this helps, If you want to call me I can try and diagnose further.

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    Part of the furniture Decade Plus User Hugh's Avatar

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    Re: Smokey Cosworth after overrun.

    Thanks chaps, I forgot to give the more detailed information!

    The car has done 81k, is running a Stage 1 power engineering chip from Power Engineering and RR at 259bhp. It is all on the original components except the usual stuff like Head Gasket (WRC multilayer), Turbo (Standard Replacement). I have a friend who has a 50k engine and is running 330bhp with no breather system and his is fine without an upgraded breather system.

    The smoke only appears after some quite 'high revving' overrun, and 'coughs' out when I next touch the throttle. It is considerably worse once the oil has got up to full operating temperature (30-40mins of driving).

    I wondered if the breather system must be cacked as I don't think it can be the rings as blow by would surely occur whilst on-boost?

    I had wondered about whether it may be the valve stem seals, is there anyway of checking this without pulling the head off?

    Thanks for your number Clint , it is now stored in my phone. I will ring after I have had a chance to do a bit of further investigation on it this weekend.

    Cheers all for your help, keep it comming!
    Hugh

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    Re: Smokey Cosworth after overrun.

    Not sure Sapphy, but it sounds exactly like the way my 3dr was behaving, before the engine rebuild.
    The valve guides were shot in that and I would guess that was causing the bulk of the problem.

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    Re: Smokey Cosworth after overrun.

    I'm really interested to see if you find the problem. I have the same snag. In order to try and find out what is wrong I have had the head off twice and did the seals first time and the guides second time. Then had the turbo rebuilt with twin oil seals at the back end. I think thicker oil cures it a bit and now use Mobil One Motorsport. Everything on the engine checks Ok and it has now done 88k so I wonder if it is a bit of piston ring bypass when the cylinders go from boost to high vacuum then boost again. Anyone else any good ideas?

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    Re: Smokey Cosworth after overrun.

    There is a vent into the inlet manifold from a standard breather system, you can replace it with a grub srew available from GGR for a couple of quid. Your system could be a little blocked (the flame box and non return valve are crap) and forcing some oil into the inlet manifold. Something to investigate anyway. Just a suggestion

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    Re: Smokey Cosworth after overrun.

    It was worn bores / rings. It has had a full rebuild since

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    Re: Smokey Cosworth after overrun.

    Sapphy,

    Make sure your intercooler is clean of oil. Remove it and leaving it standing over night (or as long as possible) on one end so any oil can run out of it.

    Also check all your breather system for blockages.

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    Re: Smokey Cosworth after overrun.

    Thanks Daz, but this post was over a year ago!

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    Re: Smokey Cosworth after overrun.


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    Re: Smokey Cosworth after overrun.

    Nevermind then!

    I never bothered looking at the date just posted out of habit!

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    Re: Smokey Cosworth after overrun.

    Well 15 years later I've got the same problem Only happens on the over run and the engine was sat for 4 years so I'm guessing the stem seals will be my first port of call !!! Mine dosnt breather to the inlet at all and has two breather pipes from each side of the block to atmosphere via a tank,
    Wondering if any one has used a 15w oil as suggested and did it help the situation ???
    Cheers paul

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    Re: Smokey Cosworth after overrun.

    Replacing the stem seals will work for a short while but in my own experience with this problem I ended up having to fit new guides and valves!
    It's sucking oil down the guides due to the sloppy fit and massive overrun vacuum.
    Last edited by davemk1; 20-08-2018 at 23:10.

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    Re: Smokey Cosworth after overrun.

    Quote Originally Posted by davemk1 View Post
    Replacing the stem seals will work for a short while but in my own experience with this problem I ended up having to fit new guides and valves!
    It's sucking oil down the guides due to the sloppy fit and massive overrun vacuum.
    agreeed

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    Re: Smokey Cosworth after overrun.

    Thanks for replys guys . Was hoping that since the motor been sat a few years i would get away with seals .
    job for over winter me thinks, while heads off I might as well get the guides done aswell
    Cheers paul

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    Re: Smokey Cosworth after overrun.

    It was guides on mine that caused this issue to

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    Re: Smokey Cosworth after overrun.

    Watch wheeler dealers cosworth episode. This is exactly what they did. on theirs

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    Re: Smokey Cosworth after overrun.

    Quote Originally Posted by wildo105e View Post
    Watch wheeler dealers cosworth episode. This is exactly what they did. on theirs
    �� I rember that one now you mention it

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    Re: Smokey Cosworth after overrun.

    Almost certainly valve guides as mentioned above - new seals might mask it for a short time. I had all 16 guides replaced along with several valves that had gone out of spec before refitting the YB in the mk1. No smoke at all.

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