Home Forums General Technical Help Comprression Dropping Now!

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  • #80955
    brianw
    Participant
    Club Member

    In the olden days of 2018 I recorded compression 145 – 175- 175 – 165 PSI . Head off & ground in the valves Which improved No 4 but not No 1. I noticed a small piece 1mm square of metal welded to the top of No1 piston. Since then, 6000 miles covered. But now over the last 200 miles definitely it has become quite 3-cylinderish . . Tapet clearances good, No sign of bubbles in the water , but a fare bit of engine breathing out of the oil filler if I take the cap off.
    I did the compression test again 2 3 & 4 are ok but No1 Cylinder gets a depressing 30 PSI . I put a couple of squirt of engine oil in & it came up to only 40 PSI .
    Is this rise proof of rings failed or is this only small rise a sign the valve is leaking ?

    #80957
    JAN
    Participant

    Generally, a minimal rise with oil in the cylinder denotes valve problems; with worn pistons and rings this usually bring the compressions up to the level of the others. This would not necessarily apply with broken rings, and the square of metal might be significant. Broken rings usually rattle, so if this is the situation, the engine should be noisy.

    #80958
    brianw
    Participant
    Club Member

    Thanks JAN, At one point there was a higher pitched tinkleling sound for a few minutes. But that seems to have stopped. I see, if the rings are bust up , no amount of oil is going to help. Another sign it could be rings is the short engine has covered 182,000 miles since its rebuild which I am quite pleased with! Respect to the guy who built it, & Alas he doesn’t do it anymore.

    #81405
    brianw
    Participant
    Club Member

    So whats the best way to get a working standard 1200cc engine? ( probably short engine , as head ok)

    I have one engine which broke its piston rings & started with a knocking noise & low oil pressure at 110K miles. I have taken this apart. it as visible wear on mains/big ends & little ends, cam shaft worn away & broken cam followers. In its favour it was never rebored.
    Do I take the bits along to a machineist get the parts ground / honed & ask what size pistons & shells to buy & try to put it together my self ? or is that too likely to go wrong ?

    Bolting the engine together my self has the problem that I wouldn’t know if it wasn’t fitting right.

    Is it better to just take it along get an engine built ?

    Either way how do i pick a good machineist?

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