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Thread: Normal amount of blow-by for a 2.25 petrol?

  1. #1
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    Normal amount of blow-by for a 2.25 petrol?

    Did an oil change on the Series II, and figured I'd take a look at blow-by while I had the breather cap off the draft tube.

    I noticed a (quite small) pulse of air coming out, it felt like it was lined up with the rate that one cylinder would be firing. Is that automatically bad news or is there some acceptable amount of blow-by for these? I could do a compression test but that's a bit more work than I wanted to do today.

  2. #2
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    Forgot to mention, engine was stone cold.

  3. #3
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    If you’re engine is running at 500 rpm each piston will fire 250 times per minute so that would be at least the minimum pulses you would have from each cylinder. Also as it is a four cylinder, two sets of two pistons go up and down together your getting the pulses of two pistons twice each revolution. In my experience if you have excessive blow by you will have a fair amount of oil mist on the engine surround after a trip and see a definite heavy pulsing during running. If it is a single cylinder at fault as in broken rings you will see a very heavy pulse usually with a miss due to oiled up spark plug. Hope that helps.

  4. #4
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    Thanks. I don't see either of those, and it's running fine - I just stuck my hand over the draft tube out of curiosity and noticed it. I don't suppose you know what's a "normal" thing to feel when doing that?

  5. #5
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    I've had a similar problem when the "baffle plate side cover front'" p/n 514423, listed in my parts catalogue but not shown, was missing. It sits between the oil filler pipe flange and the block.
    W.

  6. #6
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    Had another look at it tonight. I definitely have the baffle plate side cover, thanks BSF for the tip.

    After running it a little longer and experimenting a bit more, I don't think it's an issue - the "pulsing" was actually very minor. If I stuck my hand over the draft tube (trying to block it), I realised there was as much vacuum as there was pressure, it was just oscillating between the two. So that's clearly fine. That said, I'm still curious about how much blow-by would be OK here, just to tuck away in the back of my head.

    I think I'm just being paranoid since the engine was rebuilt a few years ago by me, and he's the dodgiest guy I know.

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