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Thread: Cosworth oil pressure doesnít seem right

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    Bodger longy's Avatar

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    Re: Cosworth oil pressure doesnít seem right



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    Re: Cosworth oil pressure doesnít seem right

    Looks like there is different bearings, oilholes differs.
    But that dont explain why all is ruined. Did you assemble the crank and rods? On the nearest bearing in the picture you can see the surface been drawn in to the oilhole, is the tab on the bearing ok or has it been mounted the wrong way around?

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by HonkyWhiteTrash View Post
    Those shells look odd - one pair has oil feed holes in the middle, and the other three pairs have them offset! I take it that is just an optical illusion?

    Have the rods been installed with the front faces towards the front of the engine?

    I've just found a crank - big end bearing - failure on a pre crossflow I bought and it looks like the rod bolts weren't tight on one con rod, which looks like it caused low oil pressure and then eventually bent a con rod due to everything being so tight due to the melting bearing!
    Were the rod bolts tight when you undid them? It's possible clearances between big ends and bearings were quite big. Have you mic'd the crank up? Might be difficult if it's marked but still worth checking.


    Iíve just checked there all the same them end two are just the wrong way round and a bit of camera trickery well spotted though

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    Re: Cosworth oil pressure doesnít seem right

    nothing yet has explained the situation, you defiantly should check the core plugs behind the aux shaft seal housing

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by longy View Post
    I’ve just checked there all the same them end two are just the wrong way round and a bit of camera trickery well spotted though
    Glad to hear I was wrong!

    Surely can only be down to big clearances in the big ends now as main bearings are fine.

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by HonkyWhiteTrash View Post
    Glad to hear I was wrong!

    Surely can only be down to big clearances in the big ends now as main bearings are fine.
    not so sure, mains dont get the same hammer action and dont forget its still being run in, but that said right now i suspect issue is the ends have been ground but std shells used, as i said earlier its rare for a crank to be undersize on the mains but not the ends

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    Re: Cosworth oil pressure doesnít seem right

    Thanks everyone I checked the two front core plugs today as I fitted new ones but no there perfect. Engine is completely stripped now only damaged is big ends and pump rings bores mains all good and the cams

    Funny you should say that graham bloke at the machine shop said it’s strange how the big ends wasn’t machined with the mains.

    Shells were fitted correctly all tabs still in place hadn’t spun. All I can think off now is I fu#$ed up big time I should of plastigaged it. Even though the engine shop I was using back then wrote the sizes of the mains and big ends on the crank with a marker lol

    There going to measure up at the machine shop to see if it’s standard size or not

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by Graham View Post
    but that said right now i suspect issue is the ends have been ground but std shells used, as i said earlier its rare for a crank to be undersize on the mains but not the ends
    Even going 10" under and std shells that would make one hell of a big end rattle would it not ?

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by prox View Post
    Even going 10" under and std shells that would make one hell of a big end rattle would it not ?
    not necessarily with cold thick oil and running in on a low compression engine, as your only talking about twice the clearance of a worn old high mileage but not knocking engine
    Last edited by Graham; 15-10-2020 at 16:56.

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by Graham View Post
    not necessarily with cold thick oil and running in on a low compression engine, as your only talking about twice the clearance of a worn old high mileage but not knocking engine
    There is no way that 0.25mm is going to be taken up with "thick oil" and keep some sort of oil pressure for 200 miles

    The clearance in the manual states 0.013mm to 0.067mm so we are talking nearly 4 times the max clearance if std shells are used on a -0.25mm

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    Cosworth oil pressure doesnít seem right

    When I put the wrong shells on my Xflow the bearing damage looked similar to these but not as bad since I didn't drive it before discovering the problem.

    It sounded perfect on idle, you'd never tell.

    I was suspicious about the low oil pressure though before discovering it knocked when revved above 4000 rpm when cold, and above maybe 2500 rpm when hot.

    Stripped it down to discover similar results to the OP.

    Had bought the engine second hand in bits and didn't know it needed oversize bearings.

    Produced good power though once up and running.

    Sent from my Pixel 4a using Tapatalk

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by prox View Post
    There is no way that 0.25mm is going to be taken up with "thick oil" and keep some sort of oil pressure for 200 miles

    The clearance in the manual states 0.013mm to 0.067mm so we are talking nearly 4 times the max clearance if std shells are used on a -0.25mm
    yes i know its 4 times, but thats 4 times the clearance of a NEW engine, a well used engine can run with a couple of thou wear on the crankpins and even more worn off the bearings and not knock, so in that instance you are talking about twice the specified clearance

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    Re: Cosworth oil pressure doesnít seem right

    I have known Engine Machine shops get their tolerances wrong on more than one occasion so be aware of that one. Who reground the crank, them or another source?

    When you are satisfied and have rebuild the engine make sure you use a new oil pump of good repute and have the correct gasket fitted between the pickup pipe and pump. You'll have to pay North of £200 for a decent 4x4 oil pump. The best of luck.

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    Re: Cosworth oil pressure doesnít seem right

    And of course prime the oil galleries by using a drill to spin the oil pump drive with the distributor removed, you should see full oil pressure on the gauge by using this method.

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by prox View Post
    There is no way that 0.25mm is going to be taken up with "thick oil" and keep some sort of oil pressure for 200 miles

    The clearance in the manual states 0.013mm to 0.067mm so we are talking nearly 4 times the max clearance if std shells are used on a -0.25mm
    That -0.25 mm is on outer diametre, so the "extra" clearance on one side is half that.

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    Re: Cosworth oil pressure doesnít seem right

    Hi thanks everyone
    It was S.E.P kegworth who did all the original work to the crank. Old school place I would if took it back but they had my crank and block for nearly a year lol.

    It’s at a different place now as soon as they ring me I’ll go fetch it and see what they have to say about it

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by longy View Post
    Hi thanks everyone
    It was S.E.P kegworth who did all the original work to the crank. Old school place I would if took it back but they had my crank and block for nearly a year lol.

    Itís at a different place now as soon as they ring me Iíll go fetch it and see what they have to say about it
    Been in the "Motorcycle engine work" business since 1987, S.E.P used to have a very good Rep, a few years ago they had a management / owner change and have since gone very downhill with some appalling work, some i have personally had to put right.

    Please do keep us posted on what the new place finds.

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by Graham View Post
    yes i know its 4 times, but thats 4 times the clearance of a NEW engine, a well used engine can run with a couple of thou wear on the crankpins and even more worn off the bearings and not knock, so in that instance you are talking about twice the specified clearance
    I have to agree to disagree on this one, i would say it would knock with that clearance.

    Hopefully the OP will get to the bottom of it

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    Re: Cosworth oil pressure doesnít seem right

    Quote Originally Posted by prox View Post
    I have to agree to disagree on this one, i would say it would knock with that clearance.

    Hopefully the OP will get to the bottom of it
    disagree all you like my friend, but we have come across it before

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    Re: Cosworth oil pressure doesnít seem right

    A low comp engine with thick oil and easy breaking in does
    Not nessetivetly knock. I had a 11 litre diesel with one sice ground crank and standard bearings and we opened it just because low oil pressure. And a diesel has higher comp. Some others had overhauld it. So I agree with both of you.

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