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Thread: low compression on my xflow - help

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    Bodger

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    low compression on my xflow - help

    I have a xflow 1660 with piper 285 cam and twin weber 40's and uprated stage 2 head ( 42mm in/34ex). in 2011 it was rebored and fitted with 1300 HC +60thou pistons and new rings the compression test showed
    Cylinder pressure test – Hot 03/09/11

    1 2 3 4
    173psi 168psi 173psi 170psi

    The engine has only done 5,000 miles since then . I had the head refurbished with new guides, recut valves /seats and skimed a few months ago. but it has been idling very rough so redid the compression test.
    Cylinder pressure test – Hot 02/01/18

    1 2 3 4
    120psi 112psi 115psi 118psi

    I have set the valve clearances as per piper spec and warmed the engine up and using the same compression tester in both tests.

    I was expecting 160/170 psi but these values are really low. Any ideas of what has gone so wrong?

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    Re: low compression on my xflow - help

    If the valve job is the only difference.......... how much do you trust the company that did the work? Sounds like guides fitted and either the valve re-cut has been bollux'd or the seats haven't been cut! If the bit that traps the air ain't doing its job then you get that result or you've killed your rings through a bad fuel tune?

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    Racer Decade Plus User Forest_rallying's Avatar

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    Re: low compression on my xflow - help

    Have you recently fitted an alloy rocker cover, I have known the rocker adjusters to foul on the sides of the cover giving symptoms as you describe with some alloy covers. You'll soon notice the score marks inside the cover if they are. Failing that double check your tappet settings and if all's okay there then I would be looking at a valve seating problem.

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    Re: low compression on my xflow - help

    are you doing compression test with WOT

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    Bodger

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    Re: low compression on my xflow - help

    was the new head gasket the same thickness? if yes i would test again with a bit of oil down the bores. if still the same valves need lapping in,leave tappets loose for check

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    Re: low compression on my xflow - help

    Was it the same gauge you used both times ?

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    Re: low compression on my xflow - help

    IF, its been used hard those 5000 miles have been done mostly in short distances with lots of throttle blipping ( which washes the bores) it could sadly be because its now actually worn, forget compression testers buy a cylinder leakage tester that will show true condition of rings and seats

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    Re: low compression on my xflow - help

    Quote Originally Posted by katana View Post
    If the valve job is the only difference.......... how much do you trust the company that did the work? Sounds like guides fitted and either the valve re-cut has been bollux'd or the seats haven't been cut! If the bit that traps the air ain't doing its job then you get that result or you've killed your rings through a bad fuel tune?

    Sorry for the delay. I have never used the company who did the work on the head but it did look ok. One thing which I did not mention was the car has been off road and sitting in my garage for the last 2 years and just refitted the head and started her up a few weeks ago . It has not been on the road at all since then so could the rings be tight?

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    Bodger

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    Re: low compression on my xflow - help

    Quote Originally Posted by fatboy slim View Post
    was the new head gasket the same thickness? if yes i would test again with a bit of oil down the bores. if still the same valves need lapping in,leave tappets loose for check
    Sorry for the delay , I set the tappets cold as per Piper instructions at 0.35mm both in/ex, The head gasket was the same as before (Payen). I have not tried loosening the tappets a bit b- certainly worth a try - but as I mentioned on the last responce the car has been off the road and standing for 2 years and just refitted the head and fired her up a few weeks ago- would this be an issue?

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    Re: low compression on my xflow - help

    Same Gauge - Draper DCT1

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    Re: low compression on my xflow - help

    Your low compression seems to be consistent across all four cylinders on your current test. You use the quote it has been idling very rough, what do you mean by that? I would n't expect an engine to idle rough with low compression, if it was too low you would find it very difficult to start.

    Maybe you have other problems besides your low compression which is leading you a dance. No mention of whether you have fitted an alloy Rocker cover.
    Last edited by Forest_rallying; 05-01-2018 at 16:22.

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    Re: low compression on my xflow - help

    Quote Originally Posted by Forest_rallying View Post
    Your low compression seems to be consistent across all four cylinders on your current test. You use the quote it has been idling very rough, what do you mean by that? I would n't expect an engine to idle rough with low compression, if it was too low you would find it very difficult to start.

    Maybe you have other problems besides your low compression which is leading you a dance. No mention of whether you have fitted an alloy Rocker cover.

    Hi sorry forgot to say - it was the same alloy rocker cover - had for several years and no sign of rubbing. The car has been off the road for 2 years now and only refitted the head a few weeks ago. Would this affect things , maybe the rings are not sealing?

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    Re: low compression on my xflow - help

    could be, as i said, best to stop guessing and do a cylinder leakage test, it tells you far more than a compression test as its not effected by cranking speed, throttle or even cam type all of which effect a compression reading

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    Re: low compression on my xflow - help

    Quote Originally Posted by Graham View Post
    could be, as i said, best to stop guessing and do a cylinder leakage test, it tells you far more than a compression test as its not effected by cranking speed, throttle or even cam type all of which effect a compression reading

    Thanks will do , have'nt got that but looks cheap enough on line so will go and buy one and try it out. thanks again and will let you know!

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    Re: low compression on my xflow - help

    Might need some miles driving to bed in the valves on the seats also ? (just thinking loud)

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    Re: low compression on my xflow - help

    Quote Originally Posted by racing escort View Post
    Might need some miles driving to bed in the valves on the seats also ? (just thinking loud)
    it might but it shouldn't

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    Re: low compression on my xflow - help

    No need to buy expensive cylinder leakage tester.
    Just knock out the centre of an old sparkplug( easier said than done, just takes time) and weld a bit of steel pipe in the hole attach a bit of air hose to it with the correct end to fit your compressor hose.
    Ensure piston on true TDC and valve closed. Plug in to compressed air supply and listen to the exhaust, air intake and dip stick tube. if you hear air coming out the exhaust and or air intake ( Throttle open) then its valves. You will always hear some blow back past the rings. But If the exhaust and inlet are quite then it points to the rings.
    This is also a good way to check for head gasket leaks (IE bubbles in the water)

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    Re: low compression on my xflow - help

    No need to buy expensive cylinder leakage tester.
    Just knock out the centre of an old sparkplug( easier said than done, just takes time) and weld a bit of steel pipe in the hole attach a bit of air hose to it with the correct end to fit your compressor hose.
    Ensure piston on true TDC and valve closed. Plug in to compressed air supply and listen to the exhaust, air intake and dip stick tube. if you hear air coming out the exhaust and or air intake ( Throttle open) then its valves. You will always hear some blow back past the rings. But If the exhaust and inlet are quite then it points to the rings.
    This is also a good way to check for head gasket leaks (IE bubbles in the water)

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    Re: low compression on my xflow - help

    Quote Originally Posted by Mike Bentley View Post
    No need to buy expensive cylinder leakage tester.
    Just knock out the centre of an old sparkplug( easier said than done, just takes time) and weld a bit of steel pipe in the hole attach a bit of air hose to it with the correct end to fit your compressor hose.
    Ensure piston on true TDC and valve closed. Plug in to compressed air supply and listen to the exhaust, air intake and dip stick tube. if you hear air coming out the exhaust and or air intake ( Throttle open) then its valves. You will always hear some blow back past the rings. But If the exhaust and inlet are quite then it points to the rings.
    This is also a good way to check for head gasket leaks (IE bubbles in the water)

    i have done what you say in the past looking for leaks etc, but a quick search on ebay throws up a leakage tester for £16! so hardly worth bothering plus a leakage tester will give a % of leakdown, so you have an actual figure to go by, by ear you are never going to know the difference between say 10 and 20 % leakage

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    Re: low compression on my xflow - help

    Just looked on E-Bay
    Its a no brainer at that price.
    Thinking back I must have made my spark plug ones some 35 years ago when a cylinder leakage tool was a great big over engineered box thingy costing a lot back then.

    Thank god for China and E-bay

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    Re: low compression on my xflow - help

    Quote Originally Posted by Mike Bentley View Post
    Thinking back I must have made my spark plug ones some 35 years ago when a cylinder leakage tool was a great big over engineered box thingy costing a lot back then.
    so did i, later i ended up with two, snap on and krypton, both were a small fortune, its quite incredible how cheap they can be now, i looked again and found one for £13

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