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Thread: Smart 450 Cdi - How to change glow plugs & measure compression

  1. #1
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    Smart 450 Cdi - How to change glow plugs & measure compression

    I noticed on the Canadian ClubSmartCar forum that some members found it a bit fiddly changing glow plugs so I thought I would have a go at it.

    Main problem is getting access. The job will be a whole lot easier by removing the cable tray that supports cables for glow plugs, intake pressure sensor and rail pressure sensor.

    Ensure engine is warm as much easier unscrewing glow plugs on a warm engine. You can also hot wire into the glow plug you are about to remove. Beru recommends leaving each on for 4-5 minutes - this heats up the glow plug and burns it free.

    Unclip fuel lines, remove the torx screws that hold fuel lines at RHS of engine.

    Unclip cable tray cover. A special tool is required or cover will brake. See note on tools further down.

    Unclip vacuum pipe for brakes and move forward of its support.

    Cut tie wrap holding cables on RHS. Disconnect connectors for intake pressure sensor and rail pressure sensor. Earth lead may need to be disconnected as well (reconnect earth lead before turning engine in starter).

    Cable tray and cable tray cover.

    Lift cables out of cable tray and place forward of tray.

    Unclip cable tray using a small flat bladed screw driver. Release each of the 4 catches from above. Remove cable tray.

    Removing glow plug terminals. Pull vertically up using a special tool, see further down.

    A long 10 mm 3/8" socket and extension is required to remove glow plugs. A 10 mm 1/2" socket won't fit. Make sure engine is warm. Soak threads in diesel or penetration oil. Unscrew very carefully using a T-bar as shown. Note that glow plug will snap off if applied torque exceeds 35 Nm.

    Slacken initially just a few degrees then tighten a few degrees. Unscrew in an oscillating motion similar to tapping theads. No brute force. Pull glow plug out using a special tool, see further down.

    Special tools:


    1) Small flat bladed screw driver for unclipping catches on cable tray (not a special tool but added for completeness as shown in photo).
    2) Cranked plate tool. Used for unclipping cable tray cover. Made from 0.6 mm stainless steel plate. Approximately 12 mm wide.
    3) Tool for removing glow plug terminals and pulling glow plugs. Made from 5 x 13 mm flat bar. Jaws are 8.7 mm wide and bent slightly outwards forming a V shape.
    4) Compression testing probes. The black ones did not work. Impossible to fit quick fit connector due to very tight for space. Interference with inlet manifold. The long probe is made from my no 2 glow plug, a 111 mm long piece of bronze and an M8 stainless steel nut.


    All 3 glow plugs have been succesfully removed. I ran an M10 x 1.0 tap down the theads but found they were all clean. New plugs are NGK bought on ebay for GBP 7.95 each.

    Clean bores with compressed air or turn engine on starter. Visually inspect bores. Spray penetration oil down the bores before refitting new plugs. You may need to ream out the bores for the new glow plugs to fit. (DIY reamer information is coming soon). Alternatively run an old plug up and down a few times until it turns reasonably freely. You should be able to hand turn the new plug by holding the extension bar as a screw driver. Tightening torque varies from make to make. NGK recommends 15 - 20 Nm. Beru recommends 12 - 15 Nm. Both are dry torques without lubrication. Torque with lubrication will be less. It is safer to angle turn 30 degrees. Also a lot cheaper as torque wrenches capable of low torques are rather expensive. Using extension bar as a screw driver, screw in glow plug until seat contact is felt, then angle turn 30 degrees.


    Testing glow plugs
    I use a heavy duty battery charger capable of providing 30 amps. Tip should go red first. If not so just discard. Amps drawn should be between 15 and 25A. Don't leave it on for too long as it may overheat - a couple of seconds is sufficient for this test.

    Above plug goes read hot away from the tip so fubarred.

    Compression testing
    Obviously you need a compression tester suitable for diesel engines. My Silverline tester would not fit due to the size of the quick fit connector. Probe fitted no problem but very tight getting connector on.
    Solution: A couple of hours in the shed making a new long and slim probe.


    New DIY probe screwed into bore for glow plug and ready to connect gauge.

    Important: You must inhibit engine from injecting fuel or you will find you are measuring firing pressure instead of compression. I disconnected fuel rail pressure and intake manifold pressure senors but engine was still injecting. Disconnected rail pressure control valve (regulator) and I was ready for testing. Those that do not have access to diagnostics equipment should not disconnect above sensors as check engine light will turn on when you start engine. Run starter directly from solenoid instead by hot wiring.

    Turn engine on starter until pressure no longer increases on gauge, takes about 5 - 6 seconds.

    Took above photo before making new probe. Had great difficulty getting connector on and off.

    Make a note of the readings. Repeat if there are anomalies. Add a spoon full of oil to those cylinder(s) that appear low. No rise in pressure after adding oil normally means there are leaking valves.

    My readings:
    No 1 - 24.5 bar
    No 2 - 25.0 bar
    No 3 - 25.0 bar

    All good readings. Much better than I had expected. The engine has clocked 143K in 8.5 years.

    Cheers,
    TK
    Last edited by tolsen; 01-11-2017 at 01:03 PM. Reason: Sorted out image links following Photobucket fiasco.
    Drives a Smart Cdi - 65 to 85 MPG

  2. #2
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    Has it felt much different with the new glow plugs?

    That's a very even compression reading after 143k! Do you know the compression figures for when the engine was new?
    _________________________________________________


  3. #3
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    Quote Originally Posted by JMM View Post
    Has it felt much different with the new glow plugs?

    That's a very even compression reading after 143k! Do you know the compression figures for when the engine was new?
    No difference whatsoever. I decided changing them as a preventative measure. Only one was bad but the other 2 could go any time now. By the way, have you not heard we are getting a severly cold winter?
    I have no as new spec for compression pressures. I think compression ratio is specified as 18.5 : 1 or something but it is not that straightforward to estimate compression pressure from compression ratio.
    Last edited by tolsen; 21-10-2010 at 08:26 AM.
    Drives a Smart Cdi - 65 to 85 MPG

  4. #4
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    That's bad that it's going to be a cold winter. I've still got my thermostat and plug to fit. Seemed quite a big job and so I put it off during the Summer but now the weather is changing I really need to get on and do it. The plug looks very easy to fit and I could easily do it without lowering the engine. The thermostat looks a pain though. I can't see either bolt and managed to get a socket around one but not the other. Really want to try and replace it without lowering the engine as it seems like a lot more work and the FQ101 way of doing it only gives 1/2"-1" of extra room which doesn't seem worth it.

    It will be interesting to see if the compression ratio has changed much. I was really impressed with the diesel engine and it's great how long it lasts compared to the petrol versions. It's a shame more weren't sold as 450's.
    _________________________________________________


  5. #5
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    DIY Reamer


    Made from my old Beru no 3 glow plug, a 5.5 HSS Lidl drill bit and a 10 mm between flats collar nut. Ideally I should have used an 8 mm collar nut but could not find one.
    Diameter of tip of glow plug is 5 mm so a 5.5 mm reamer is adequate. Internal diameter of the Beru glow plug housing is 5.5 mm except at the crimp area where the tip enters housing. This means you can make a reamer like the above without a metal working laithe.

    Grease the flutes to collect carbon deposit from bores. The carbon will stick to the grease.

    How to make one:

    1) Sacrifice and old glow plug. Cut off the top bit about 1 mm from housing.
    2) Heat glow plug housing until it gets red hot.
    3) Fit in a vice with soft jaws and knock out the internal core from above.
    4) Drill out crimp area of housing using a 5.5 mm drill bit. Drill will be guided by the 5.5 mm bore.
    5) Get an 8 mm between the flats collar nut. Drill out to 5.5 mm bore.
    6) Silver solder nut to end of a 5.5 mm drill bit.
    7) You may need to shorten glow plug housing a wee for the reamer to reach all the way into the bore.


    Mark 2 Cable Tray Cover Release tool:


    Plate thickness 0.5 - 0.7 mm. Air gap in fold 1.5 - 2 mm. Corners and working edge need be rounded to avoid cutting into plastic cover. Above tool is made out of 304 stainless steel.

    The hole is for connecting a lanyard so you won't loose it. This means the tool will also comply with SOLAS 1974.

    Operation:
    The catches are below the rectangular holes in cable tray cover. Inserting a small flat bladed screw driver into these holes did not work as the plastic just cracked. Using the folded area of above tool to pry out the catches one after the other from below works a dream. It is best starting from the right. Lift cover whilst releasing each catch.


    Smart lanyard for release tool.
    Last edited by tolsen; 01-11-2017 at 12:48 PM. Reason: Sorted out image links following Photobucket fiasco.
    Drives a Smart Cdi - 65 to 85 MPG

  6. #6
    Well written and thorough, good photos as well
    Thank you for adding this useful post
    Www.BigPerformance.Co.Uk

    020 328 REMAP (02032873627)
    07702948467
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    Key codingTAN codes. SCN codes. Body shop. Trimming. Crash repairs

  7. #7
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    Replace glow plug

    Hello,
    Why is it so long (more than 200 full circle up) to remove original glow plug and so fast to place new one (about 40 full turn down)???
    I replace originals with Beru GN015 and seems to be exactly the same!?!

    Also, it is not necessary to replace glow plugs to remove all the cable tray, there is enough space.

    remaining question: now, when I turn the key on 1, preheat light doesn't turn off after few seconds???
    Is it normal???

    Thanks for your reply!
    PhilLu

  8. #8
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    The glow plugs will be stuck in their bores with hard soot. That is why Beru and other manufactures recommend always to remove glow plugs on a warm engine and attempt to burn out the soot by hot wiring them. Obviously burning soot by hot wiring will only work if the plugs themselves are not burnt out. Anyway, due to the soot build up you may have to keep turning your glow plugs for quite a while to get them out.

    It is important that you ream the bores before fitting your new glow plugs. You will then find you only need a few turns and that you will also feel when they bottom out so much less chance of causing damage to the new glow plugs.

    Removing cable tray makes the whole operation a lot easier and less chance of causing damage. I doubt you will be able to ream the bores or measure cylinder compression with cable tray in position.
    Drives a Smart Cdi - 65 to 85 MPG

  9. #9
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    Thanks Tolsen!
    By reaming, is it dangerous to produce soot pieces folling into the cylinder damaging engine?

    Also, now, why preheat light doesn't turn off after few seconds when I turn key on 1?
    Is there another problem???

  10. #10
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    Grease in the flutes of the reamer will collect most of the soot pieces. It is unavoidable that some soot will enter combustion chamber. This will soon be blown out when engine is started.

    Preglow indicator light will also indicate faults in preglow system. Perhaps a glow plug or two got damaged during fitting, there are cable faults or your glow plug controller is faulty? There may sometimes be a fault code so read your engine control unit first.
    You can measure continuity to each glow plug from the forward square connector to glow plug controller. Each glow plug should have a resistance of approximately 0.6 Ohm. Note that the rear connector is for you electric heater.
    Drives a Smart Cdi - 65 to 85 MPG

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