How to change glow plugs & measure compression

[tolsen]

I noticed when reading the excellent thread titled "Glow Plug/heater Circuit A Malfunction- Po380, with removal instructions" 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.

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 may break. 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 on 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.

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:

The long compression probe at bottom of photo is perfectly straight. Not banana shaped as depicted.

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 125 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. Spray penetration oil down the bores before refitting new plugs. You may need to gently tap them down into the bores to get the threads to engage. Don't use a big hammer. Tighten to 15 - 20 Nm torque.

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.

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

 

Compression testing

Oviously 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 fitted 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 sensors 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

Edited November 1, 2017 by tolsen
Sorted out image links following Photobucket fiasco.

[Cacarella]

Nice work! I've earmarked this thread for future reference!

[Graham]

Great write up - Just read the earlier one too by Gandalf

On our MB diesel, I have changed the glow plugs 3 times in 300k km. Usually just one or two (of 5) failed, but changed them all. When changing MB glow plugs, it is recommended that a pre-chamber reamer be used to clean carbon deposits out of the pre-chamber. Anyone know if this is something that should be done on the smart?

I read somewhere here about testing glowplugs with a clamp-on meter - Seems like a good idea, but be sure to get one that measures DC Amps. The cheap ones at Princess Auto do not, but I did get one at CT for about $59.00 when tracking down leakage currents on one of our other cars. Sears in USA have nice ones.

[tolsen]

A reamer is another expensive kit to your toolbox.

I've found there is not always a need to ream provided you keep running the old plug up and down well wetted in penetration oil until it turns freely by hand.  There will be difficulties applying right torque if new glow plug does not turn freely in the bore.  End result may be the plug leaks causing threaded part of plug to be sized in soot and increasing chance of plug snapping off when later removed.  You must therefore ream if you cannot screw new plug in by hand and positevely feel when plug bottoms out.

Note that thread size is M10 x 1.0 and not M10 x 1.25 as indicated in the NGK catalogue from where above diagram was copied.

The 5.0X mm bore housing the 40 mm tip is what is reamed if you find there is a need for it. The annulus between bore and tip gets filled with rock hard soot.

It is important that you feel the stop point when fitting the new plugs. Mine went in easily turning extension bar by hand like a screw driver. Some mechanics perform a soap leakage test after fitting plugs to confirm seal is holding. As for glow plug testing, there is no better test than visually examining the tip to confirm tip is getting red hot first.

Edited November 1, 2017 by tolsen

[Graham]

A reamer is another expensive kit to your toolbox.I've found there is no need to ream provided you take extra care when removing the old glow plugs. You can always keep running the old plug up and down well wetted in penetration oil until it moves more freely.

Tolsen,As you said further down, the reaming is to clean out the carbon build up around the heating element. Not for the threads.For my 300D, I made a reamer out of an old glow plug. I drilled out the element of the plug and inserted a small cutter of the right diameter. Just screw it and out a couple of times and reaming is done. Don't know what they cost for a smart, but not much for a benz. If you don't do this, at least on a mercedes, the carbon build up reduces the affect of the plugs and may cause them to burn out prematurely. It would be interesting to know if the smart/MB shop procedure says to ream or not.This link relates to the old benzes, but principal is likely the same for a smart?

As for glow plug testing, there is no better test than visually examining the tip to confirm tip is getting red hot first.

Someone had suggested using a clamp on meter so you would not have to remove a glowplug to test which one was not burned out. Seemed like a good idea to me!

[tolsen]

Threaded area on glow plugs fitting the OM660 engine is too short for a fixed reamer being guided on the threads. You will need a reamer that is guided by reamer housing like the small one shown in below photo:

The tool is Sealey SX0406 costing about GBP 60 in the UK. Small reamer measures 6mm Reamer x 10mm Thread x 103mm from Thread top to Reamer tip. This one is stated to be suitable for Smart OM660 diesel engines.

I can still not see the point reaming if plugs go in freely by hand. The annulus will fill up with carbon any way after some time. Good idea making a reamer guide out of a bored out old plug. I might do that soon. The only problem is that reamers are fairly expensive. Perhaps a long drill bit with a positive stop will do the same job. Stop will safeguard against drill dropping into cylinder.

The special rather expensive clamp on DC ammeters are very handy but I doubt whether you will be able to clamp it over any of the glow plug leads unless you open up the harness.

Edited November 1, 2017 by tolsen

[Alex]

Two notes:Tolsen doesn't mention anti-seize compound upon installing the new plugs, probably because it is too obvious to anyone capable of doing the hard part. It is a must unless you are planning on getting rid of the car soon, and even then you will burn in hell for passing on an avoidable problem like that.If, as Tolsen states, a plug can lose the heat on the most important tip, just taking an ampere draw reading won't confirm a plug working at peak efficiency. Also for the hassle of doing the one failed plug, you might as well change all three. Once you have assembled the tools needed and gained access for one, it is not that much more work or expense to do them all.

[tolsen]

I did not mention use of anti seize compound due to concerns of over tightening. The recommended torques are for dry fitting. Perhaps it is better to angle turn 30 degrees from first contact as recommended as an alternative to torque by Beru.

Denso has issued a warning about lubrication:

DO NOT USE A THREAD LUBRICANT! If a thread

lubricant such as grease is coated on the tread, the

resistance between the Glow Plug and the cylinderhead

will be less -> resulting in over tightening.

Must admit that I did use thread lubricant myself - I have always used thread lubricant and won't change my habits.

There is some good info on Beru's web site. See page 15 of document in this link which I hope works.

Beru recommends hot wiring into the glow plugs and leaving each on for 4-5 minutes - this heats up the glow plug and burns it free.

Beru also states you can remove combustion residue in the bore using a reamer but does not state that you must. I think the important thing is that the new plugs go in reasonably freely as otherwise it is impossible to angle turn and you may not know if the plug has seated. Reaming will obviously ensure those problems won't arise so reaming would therefore seem to be the way to go.

Another tip: Coat reamer with grease first. Ensures most hard carbon deposit is collected by reamer.

[smart142]

Excellent post and great tips!! I used a copper anti seize when I did mine and torqued to 10 NM. My auto supply store (which sold me the Beru glow plugs) didn't have the Beru thread lubricant.

[Graham]

Two notes:Tolsen doesn't mention anti-seize compound upon installing the new plugs, probably because it is too obvious to anyone capable of doing the hard part. It is a must unless you are planning on getting rid of the car soon, and even then you will burn in hell for passing on an avoidable problem like that.If, as Tolsen states, a plug can lose the heat on the most important tip, just taking an ampere draw reading won't confirm a plug working at peak efficiency. Also for the hassle of doing the one failed plug, you might as well change all three. Once you have assembled the tools needed and gained access for one, it is not that much more work or expense to do them all.

Anti-seize as you say is important. Some spark plugs already have it on, but don't know about glow plugs. Copper based is good for conductivity, but probably not good for use with aluminum. Any recommendations? (oops - written before I read Tolden's post)On our 5cyl diesel, when starting deteriorates, first thing is to check the glowplug resistances. There is a junction box from where this can easily be done. Perhaps there is such a location on the smart? I agree that it is probably impossible (on the smart) to get the clamp on meter around a single conductor feeding a glow plug (I got that idea from the earlier glow plug discussion!). Agree that it makes sense to change all three at same time. One thing that is different on the smart, is that the glow plugs appear to protrude right into the cylinder head. Perhaps carbon build up around the element is therefore less important. On the earlier MB diesels, there is a pre-chamber and it is that that gets carboned up and therefore needs reaming. Nevertheless, I must ask our dealer mechanics what they do on the smart. Edited October 21, 2010 by Graham

[Graham]

There is some good info on Beru's web site. See page 15 of document in this link which I hope works.

Good Link - Especially the Tips for the Shop on P14/15/16 - Cover most of our discussion.

[tolsen]

Mark 1 reamer:

Made from my old Beru no 3 glow plug, a 5.5 HSS 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.

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 vise using 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.

Edited November 1, 2017 by tolsen

[Alex]

Very nice! If the length of the drill (from the under-side of the collar nut) is correct there will be no danger of contacting and damaging a piston should it happen to be at TDC. No idea what that length is, though.Holes drilled in the piston top. Think that might lower compression a bit? It seems that Tolsen has extensive technical ability, a superb shop and perhaps just a little too much time on his hands. Awesome work done and great info provided. Thanks, I always like your posts.

[Graham]

Made from my old Beru no 3 glow plug, a 5.5 HSS 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.

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 vise using 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.

Good job! When I made the one for my 300D where the plugs are much shorter, I found a Dremel type cutter . Cut part of the end of the glow plug off and epoxied the cutter in place. As it was screwed in, it cleaned the hole in the pre-chamber. But with the longer smart plugs, yours is much better in that it has a guide. Is there a collar on the drill to prevent it from going too far in?

REgarding Alex's comment about having time on your hands, I wondered what people DO in Banchory Looked it up - seems like a lovely village and not too far from Aberdeen.

Edited October 22, 2010 by Graham

[MikeT]

It's a very scenic valley, stunningly beautiful. Lots to do. Stone circles everywhere, pubs, the Queen's summer place, cycling, hiking, you name it....

[tolsen]

Is there a collar on the drill to prevent it from going too far in?

I wondered what people DO in Banchory Looked it up - seems like a lovely village and not too far from Aberdeen.

The drill, when inserted into the guide is about 3 mm longer than the parallel part of the 40 mm glow plug tip so no risk of making swiss cheese out of pistons.

I have just tried the reamer on my Smart and it worked perfectly. Greased the flutes and collected lots of black hardened soot.

Could screw in the plugs using my fingers whilst before I had to use my hands. I do recommend silver soldering the nut onto the drill bit. A fluxed rod does not cost alot. Silver soldering can be done using a good gas torch - no need for oxy acetylene.

Banchory is a nice place to live. Pieceful and quiet. There are 5 pubs of which 4 are selling real ale. Mike T mentioned cycling and stone circles. There is a stone circle nearby inside a boneyard. Some time ago 3 of us went cycling dressed in helmets and yellow tops. We stopped to check out the stone circle. The minister came out of the kirk asking us to leave because he thought we were druids!

Lots to see in Banchory. Steam rally. Steam railway. Leaping salmon. Watch tower at Banchory-Ternan Churchyard. They used to guard the boneyard at night at a time when grave robbing was a serious possibility.

[tolsen]

Mark 2 Cable Tray Cover Release tool:

Plate thickness 0.5 - 0.7 mm. Air cap in fold 1.5 - 2 mm. 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. Insterting a small flat bladed screw driver into these holes did not work as the plastic just cracked. Use 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.

Edited November 1, 2017 by tolsen

[Graham]

Mark 2 Cable Tray Cover Release tool:

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

SOLAS??? Hadn't thought of bringing our smart up to those standards

[tolsen]

SOLAS??? Hadn't thought of bringing our smart up to those standards

Nearly any safety equipment, whether a torch, whistle, knife or hatchet require a lanyard to comply with SOLAS. Makes good sense for small tools as well and if you won't use the hole for a lanyard you can always use it for pinning the tool onto your shadow board.

[houseofdiesel]

Just a quick question, Smart glow plugs are indeed 12V? Some other brands of diesel have gone with 6V...testing with 12 is not good.

[tolsen]

houseofdiesel said:

Just a quick question, Smart glow plugs are indeed 12V? Some other brands of diesel have gone with 6V...testing with 12 is not good.

Operating voltage for glow plugs can be as low as 3.3 V. I think the Smart glow plugs are rated at 11.5 V. The important thing when testing without heat sink is not to leave them on for too long.

Edit:

I found some info on Beru's website.

"GN glow plugs, for vehicles with operating voltage up to 14.5 V."

Beru GN015 is specified for the Smart Cdi.

Contradicting info found as well:

"BERU recommends: Before installing the glow plug, grease its shaft and thread with BERU special glow plug grease."

 

Beru glow plug grease GKF01, part number 0890 300 034. "GKF" is abbreviated from German "Glühkerzenfett" meaning glow plug grease.

Denso is not for grease: "DO NOT USE A THREAD LUBRICANT! If a thread lubricant such as grease is coated on the threads, the resistance between the Glow Plug and cylinderhead will be less -> resulting in over tightening."

Edited November 1, 2017 by tolsen

[gordo.bernard]

Is there any need to be concerned about where the rock hard buildup is falling, or even more so, the minute metal particles that may be created when "cleaning" the threaded portion?Should the tools be made from 316 stainless (most salt water resistant) in order to be SOLAS compliant?

Edited October 28, 2010 by gordo.bernard

[Alex]

Should the tools be made from 316 stainless (most salt water resistant) in order to be SOLAS compliant?

Hastalloy!!! Beats 316 hands down, at only 10X cost. We are not too concerned about salt water corrosion, that's child's play. We need something that won't go brittle under neutron bombardment, can withstand a pure fluorine environment under elevated temperature and exhibits resistance to pitting and stress cracks. Actually, most stainless grades are terrible metals except for corrosion resistance, weak, brittle and soft at the same time, prone to cracking, hard to machine, hard to weld, lousy thread characteristics (galls and spalls like crazy), heavy, just crap. Except for corrosion resistance! I've done a lot of work with stainless, and I hate it until it's all finished bright and polished. Then it looks good.

[Alex]

Sorry to go off topic, but he started it, and I had a hard day!

[Speedie]

Bahh Hastalloy is for amateurs! Real tools should be made of titanium with carbon fibre handles and kevlar tethers (just in case you really need it bulletproof!).And don't forget that you can anodize the titanium really cool rainbow colours!Actually I was going to ask if the puller was a homebuilt items - was wondering if it could be made so they can attach to a slide hammer for a bit of persuasion - I was wondering how sticky the glow plugs get in there (seem to recall Duck's were stuck).Cheers,Cameron