R12 Missing on Cylinders 3 & 4
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  1. #1
    Fellow Frogger! Bolla's Avatar
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    Icon5 R12 Missing on Cylinders 3 & 4

    Got the order backwards - I mean missing on 1 & 2

    I want to know if there is a possible mechanical reason, or if it is most likely the ignition.

    I have been resurrecting my 75 12 sedan which I have had in storage for 8 years. I ran it for 5-10 minutes semi-regularly for about the first 4 years I had it (every few months). Then for the last 4 years, it hasn't run at all until 6 months ago when I started it up, and have been running it every few weeks since.

    This last week I have started to get ready to get it on the road - unfortunately on trying to start it, I found it to be running rough and unable to idle . I have replaced the leads and plugs as an obvious step, and given the carby a quick squirt of carby cleaner. All this has improved things slightly - it will now idle, but very rough.

    Further checking shows that it is only running on cylinder 3 & 4 - disconnecting the leads on 1 or 2 or both 1 & 2 produces no noticeable change in running, disconnecting either 3 or 4 shows a significant change. I suspect it is the distributor, but not being very familiar with the 12 engine internals, I wondered if there might be a mechanical reason for 1 & 2 not to be working?

    Next step is to change distributor cap, points (points seem clean) and rotor to see if that makes a difference, but other suggestions welcome.

    Thanks.

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    Last edited by Bolla; 1st January 2011 at 11:44 PM. Reason: Got my cylinder order wrong - 1 at flywheel according to Haynes
    Bolla

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  2. #2
    VIP Sponsor 59 Floride's Avatar
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    Yer got all the plug leads going to the right places...1342 ??
    Every day when I wake up I reach up in the darkness with my eyes shut and if I cannot feel anything that resembles a wooden lid I know it will be a good day. No lid today.

  3. #3
    Fellow Frogger! Bolla's Avatar
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    Default Plugs in the right places

    Yes all in correct sequence - I have been caught by that one before. I even tried putting them out of sequence on 3 & 4 and it made no difference.
    Bolla

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  4. #4
    COL
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    Hi Bolla

    What engine do u have in it? is it an 810 or 847. Could be broken rings, I have had this happen to a number of 847 engines on No1 cylinder thats the one closest the fly wheel. A simple compression test will prove this. Its most likely and ignition problemso i would change cap and leads and double check the plugs(even new ones have been found faulty) Lets know how u go.
    Regards Col

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  5. #5
    VIP Sponsor 59 Floride's Avatar
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    It may be worth pulling the plugs out and crank her over and stick a finger in each plug hole to test if there is good compression and suction...may be sticky valves
    Every day when I wake up I reach up in the darkness with my eyes shut and if I cannot feel anything that resembles a wooden lid I know it will be a good day. No lid today.

  6. #6
    COL
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    Bolla

    Just had another easy check for you. Pull out the plugs on 3 & 4 Cylinders and push plugs into ignition leads and sit plug on motor and crank over and see if there is a spark. Will prove ignition system is working.
    Regards Col

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  7. #7
    Fellow Frogger! Bolla's Avatar
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    Default Update

    Back from the shed - engine is the 810, not 847. There is some spark on the missing cylinders, but particularly on 1 it seems weaker?

    No obvious cracks in the distributor cap.

    I am on my own, so I didn't test the compression with the leads off, but with the plug out and engine running both cylinders are definately pumping (not sticking my fingers near the plug hole on a running engine). Will do the quick compression test tomorrow when i can get some help.

    I appreciate all the comments.

    Thanks.
    Bolla

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  8. #8
    Tadpole
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    Default Stale fuel?

    How old is the petrol in the 12...?

    Seems that unleaded stuff - premium or otherwise, goes off very quickly...can make an engine run like a dog....

    M@92

  9. #9
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    Default ????

    Try Takeing the rotor button off the distributor shaft and see if you can move the shaft from side to side, Sometimes worn dizzy bearings will cause the point gap to close up os some cylinders and not others, If you find it low on compression on these cylinders before blaming rings lift the tappet cover and see if the valves are closeing up completely, if not give the valve stem a light tap with the handle of a hammer and check again.
    Cheers Peter.

  10. #10
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by Bolla View Post
    Got the order backwards - I mean missing on 1 & 2

    I want to know if there is a possible mechanical reason, or if it is most likely the ignition.

    I have been resurrecting my 75 12 sedan which I have had in storage for 8 years. I ran it for 5-10 minutes semi-regularly for about the first 4 years I had it (every few months). Then for the last 4 years, it hasn't run at all until 6 months ago when I started it up, and have been running it every few weeks since.

    This last week I have started to get ready to get it on the road - unfortunately on trying to start it, I found it to be running rough and unable to idle . I have replaced the leads and plugs as an obvious step, and given the carby a quick squirt of carby cleaner. All this has improved things slightly - it will now idle, but very rough.

    Further checking shows that it is only running on cylinder 3 & 4 - disconnecting the leads on 1 or 2 or both 1 & 2 produces no noticeable change in running, disconnecting either 3 or 4 shows a significant change. I suspect it is the distributor, but not being very familiar with the 12 engine internals, I wondered if there might be a mechanical reason for 1 & 2 not to be working?

    Next step is to change distributor cap, points (points seem clean) and rotor to see if that makes a difference, but other suggestions welcome.

    Thanks.
    Try new plugs first.

  11. #11
    VIP Sponsor 59 Floride's Avatar
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    Default If all else fails......

    If all fails just put it on a truck and send it up to me in Brissy, I will take real good care of it for yer.
    Every day when I wake up I reach up in the darkness with my eyes shut and if I cannot feel anything that resembles a wooden lid I know it will be a good day. No lid today.

  12. #12
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    Quick suggestion.
    Is there a hose to the inlet manifold from that end that has failed or leaking? Brake booster failed? Pollution hoses?
    It may be leaning it out so the cylinders that end cannot fire.
    Cheers Jaahn

  13. #13
    Fellow Frogger! Bolla's Avatar
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    Icon10 Running on all 4 Cylinders

    I have been busy with afamily commitments, and no time to spend on the 12, but today I managed to get some time.

    Following all the good advice I removed the plugs and turned the engine over by hand with my thumb across the no 1 cylinder spark plug hole - no compression on cylinder 1. Removing the rocker showed the clear reason - a bent rod and stuck open exhaust valve. A few minutes of persuasion had the valve moving freely, and a replacement push rod fixed the rest. It is now running perfectly smoothly, and ready for me to get it back on the road.

    As best I can tell the car was last driven on the road in 1998, so it has been a long time coming.

    Thank you very much to all for your help.
    Last edited by Bolla; 7th January 2011 at 09:39 PM. Reason: spelling
    Bolla

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  14. #14
    COL
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    Hi Bolla

    Glad you got it sorted out. sounds like it was a reasonably easy fix
    Regards Col

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  15. #15
    Real cars have hydraulics DoubleChevron's Avatar
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    Gee's I wish I'd seen this sooner, every "laid up" motor we have done has ended up with bent pushrods or seized valves. Giving them a good run can free up the valves sometimes.... but not if they have bent the pushrods. The traction motor here we bent 3 pushrods on ... and we had to give each valve a good solid whack to break free

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  16. #16
    Tadpole
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    Hi Bolla, Don't you just love the reliability of R12's, knew it whould be something simple, just bought a beautiful '75 R12GL in Adelaide, been sitting for some time, quick check of fluids and drove back to Brisbane no problems, through Broken Hill thought I better be careful so I purchased a spare fanbelt, didn't need it, I've owned dozens of Renaults of all persuasions from 750's through to Clio Sport but I'm going full circle and really enjoying the R12 after buying one new back in '72, glad to be part of the forum again

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