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Thread: Conrod bearing failure xflow

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    Conrod bearing failure xflow

    Is it likely that running an engine that had slight piston to valve contact would cause the conrod bearing to completely fail? When I stripped engine there was nothing left of it, marks on pistons though where valves had been making contact.
    Initially thought lack of oil lubrication but had a new oil pump installed when engine was built.

    just trying to see what could of caused issues before I start the new build.

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    Re: Conrod bearing failure xflow

    its possible, but just because you had a new oil pump doesnt mean all is well? did you prime the oil system before stating it? and why did it have vale/piston contact thats something which should of been checked at the build stage. how many cylinders have had contact, if its only on the failed cylinder that may of been due to the bearing failure not the cause

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    Re: Conrod bearing failure xflow

    The engine was purchased from eBay and was installed as it was.
    I fitted a new oil pump and primed it. Oil pressure was present (well the light went out anyway) the car had done 20 miles before it blew.
    Piston to valve contact on cylinders 2 and 3 and not all 4 suspects me to believe the timing was out?
    From memory it was either cylinder 3 or 4 that the bearing disintegrated on. I guess it could of been a number of things.
    I was pleased I got to the mot station and passed though
    I have a new block been cleaned, bored, cam bearings fitted and crank been ground. I will start an engine build thread when it's back. Hopefully avoid anymore expensive parts colliding

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    Re: Conrod bearing failure xflow

    if the valve/piton contact was due to a timing error it should of happened on all 4 cylinders, the engine must of had an issue with differing piston or valve heights, did the pistons have valve cutouts? what cam was fitted?

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    Re: Conrod bearing failure xflow

    Engine was a 711m block (211mm height)
    85mm powermax pistons
    5.23 rods
    244 cam

    pistons looked to have had machining to allow for wider valves but not deepened. I'm building a new engine with another 711m block, +110 pistons with the deeper valve pockets, standard rods and 2737 crank as the 711m was un salvageable. I will buy another high volume oil pump too as I don't want any metal from other engine getting into new one and hopefully rule out dodgy pump.

    what oil pressure should be present to indicate healthy flow around engine if I was to measure with a gauge?

    in hindsight I should have taken the head off purchased engine to check before installed.

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    Re: Conrod bearing failure xflow

    244 cam MUST have valve pockets deepened, its unlikely the failure was simply low oil pressure, especially not if it only did 20 miles on the road.

    x/f dont have particularly high oil pressure 50-60psi is plenty, in fact for road use they dont even need that much

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    Re: Conrod bearing failure xflow

    85mm pistons means you must have a 1760cc engine if it's on std 1600 crank which means your bores could be very thin if using an unlinered block so beware.

    Back to your problems which is noting to do with thin bores. I have seen a few nasty blow up engines in my time with valve to piston contact and not one has ever had any crank bearing damage. That doesn't mean to say that's not the case with your engine.

    My first concern is that you have bought it off fleebay and why was it there? did the seller know something was wrong and you did n't? Never rely on a std oil light to make you think your engines in fine health, you need to install an accurate gauge into the main oil gallery in the block where the switch screws in. Secondly don't assume a new oil pump is not going to be at fault, you need to have it stripped dowm and inspected. There's a lot of crap on the market, even sold by a certain company with a Seal of quality!

    As for your valve to piston contact you need ideally between 80 and 100 thou clearance when pistons are at tdc with the valves on overlap to ensure you don't have any contact at high RPM.

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    Re: Conrod bearing failure xflow

    85mm pistons means you must have a 1760cc engine if it's on std 1600 crank which means your bores could be very thin if using an unlinered block so beware.

    Back to your problems which is noting to do with thin bores. I have seen a few nasty blow up engines in my time with valve to piston contact and not one has ever had any crank bearing damage. That doesn't mean to say that's not the case with your engine.

    My first concern is that you have bought it off fleebay and why was it there? did the seller know something was wrong and you did n't? Never rely on a std oil light to make you think your engines in fine health, you need to install an accurate gauge into the main oil gallery in the block where the switch screws in. Secondly don't assume a new oil pump is not going to be at fault, you need to have it stripped down and inspected. There's a lot of crap on the market, even sold by a certain company with a Seal of quality!

    As for your valve to piston contact you need ideally between 80 and 100 thou clearance when pistons are at tdc with the valves on overlap to ensure you don't have any contact at high RPM.
    Last edited by Forest_rallying; 28-07-2019 at 08:13.

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