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Procedure to set tappets in DiscoII TD5 motor

John Groome

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Hi All

I am new to this forum and I have a question to ask. I have found that the tappets are not set correctly on my TD5 Disco motor. ( this was discovered when it began to run rough - "missing" on one cylinder). A friend, who is a diesel mechanic, had a look and found that the inlet valve was not closing properly on one of the cylinders. He proceeded to slacken off all the tappets by 1/2 a turn and the engine ran fine and has been ever since. We looked all over for the correct procedure to set the tappets and have not found anything. He believes that the tappets are all too tight and should be correctly set.

Can anyone help?


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I seem to recall that the tappets on a Td5 are hydraulic ... so I don't know what he was trying to set as I don't have one to look at but I didn't think they were adjustable....

The only service adjustable "tappets" are the ones that drive the injector plungers and the procedure for setting these is completely different to a conventional valve tappet but is shown in the book - if it is these he has been faffing with then they should be reset according to the book, I can't remember it offhand.

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I do not believe the inlet tappets are hydraulic as the rockers run directly on the overhead cam. I think the exhaust tappets may be hydraulic.

The fact of the matter is that by slackening the tappets the problem goes away. I was also not convinced at first but it seems to be so.

The Landrover agents here in South Africa are pretty useless. They charge you an arm and a leg and still stuff it up, so it is pointless asking them.

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If you don't believe there are no valve tappets to adjust then why don't you read the book? If you don't have it I or someone else can post the relevant diagrams.

Having hydraulic tappets one some of the valves and classic nut and bolt adjustable tappets on the rest of the valves (no matter which) is a bit preposterous, technically speaking.

What BogMonster told you is entirely true. What your "mechanic" did is undo the injector adjusters half a turn which does nothing. In fact it reduces the pressure in the injector a little bitty tiny amount which has nothing to do with the missfire you had. It's just a coincidence. Or there's the known issue of "oil in the loom" and the "mechanic" moved/unplugged the connector there so the issue got sorted for the moment.

Or maybe he did something else as well as "adjusting the tappets".

I wonder how did he "found" an inlet valve is not closing properly? :huh:

Don't know about the LR in SA but, as far as your story tells me, if entirely true and if you didn't misunderstand something, your "mechanic" is more than pretty useless.

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OK I have now read the book. Both inlet and exhaust valve use hydraulic lash adjusters so I am afraid cipx2 is probably correct, your man probably adjusted the tappets which control the high pressure plunger on the injectors. At a glance the injector plungers look similar to valves (a sticky-up bit of metal with a strong coil spring wrapped around it) so I could probably just about forgive him this mistake :unsure:

It is possible that these were either wrongly set up from a previous job, or one had worked loose, though I have never seen such a thing. I would suggest the best thing to do is get hold of a RAVE workshop manual, get the injector adjusting screws set up properly according to that, and see what happens then. They are NOT set up the same way as a conventional valve tappet so whoever does it needs to read the book first or they will cock it up as it is completely different to the way you would guess they are done. Basically you turn the engine over by hand until the injector you are working on is at maximum depression (the lobe is pushing the plunger right down) then adjust the screw clockwise till it bottoms out the plunger, back it off one turn and tighten the locknut.

Coincidentally my first thought when you said "misfire" was also the injector wiring harness, so while you are in there get that changed as well as it will take about 2 minutes extra and will rule it out - if it hasn't been done already then sure as eggs are little chickens it will need doing at some point.

Bluddy Land Rover dealer eh, who'd use one? :ph34r::lol::ph34r:

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these people are spot on the valves are hydraulic and the tapets you are adjusting are for the injectors see the ligk below on how to check and change the injector loom 2/3 of the way down the page you will see the cam shafts and the the injectors and the tapets that you are adjusting


also found thie link showing how to refit a td5 head and at the bottom of the page its shows how to set up the injectors its just as discribed above but its got som pictures to make things a bit easyer to understand


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Good links Martin :)

Re-reading the original post, it will appear as if the tappets are all "too tight" if he was expecting a clearance like a valve tappet would be on other engines i.e. a few thou when the thing is at rest. They are supposed to be tight because of the way you adjust them.

I forgot to say, John, welcome to LR4x4 and hope you find it useful :)

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Thanks guys for you insight on this issue. There have been some more developments on this now, so here is the story.

The engine has started running rough again and it would seem that it is coincidence that the problem went away with the "twiddeling" of the tappet settings. They have been set back to what they were.

I had a Landy shop run the diagnostics on the engine and the result was "Topside switch failed pre injection". The guy at the Landy shop said that it could be one of 3 things:

1. Faulty Injector.

2. Fuel pressure problem.

3. ECU problem.

The fuel pressure regulator is leaking so this may be the fuel pressure problem.

Any ideas anyone?

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I would suggest:

- check for oil in the injector harness (better replace it anyway as already suggested) and also check for oil traces in the ECU connector

- replace the fuel pressure regulator AND the filter and o-ring behind it

- see how it goes after you replace the above

- if no luck then probably the ECU is fried

I don't think a faulty injector would give that error but don't rule it out.

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"Topside switch failed" errors usually mean a new ECU in my experience but I'd try the harness first on the basis it is 10% of the price...

You can plug a pressure gauge into where the fuel temperature sender goes and that will tell if its a fuel pressure problem or not, should be 58psi/4bar.

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I am thinking the fuel pressure could be right but the fuel flow could be low due to a filthy filter (the one behind the regulator) so he needs to check the pressure with the engine running and under load (depends when the engine was missing though).

To check the filter he needs to remove the pressure regulator and since it's already leaking better replace it with a new one - hence my suggestion.

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Hi Guys

Thank you for all your help.

Any ideas on price of the ECU? The prices of Landrover parts here in SA are unbelievably high, so in idea of the price would be helpful.

This Disco has been a money pit from the day I bought it. In the 2 1/2 years that I have had it, the following major things have been done:

1. Clutch overhaul. (2 weeks after buying it)

2. Engine harness replacement.

3. New fuel pump and hoses.

4. Gearbox overhaul. (2nd clutch overhaul)

In this time I have done 60000km in the vehicle.

I bought it from Landrover 2nd hand with a Landrover warrantee. Fortunately the warrentee covered most of the above, but not without some fighting.

We have 2 Landrovers, a Defender 2.5TDI and the DiscoII. My wife often says we should trade the 2 of them in on a Toyota or something less troublesome.

Rant off.

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  • 2 weeks later...

The final outcome of this story is that the problem was not the tappets or the ECU, but the injector harness.

We replaced the fuel pressure regulator and the injector harness. The injector harness plug was full of oil and the O-rings were perished. She now runs like a thoroughbred. :D

We also discovered that Landrover had lied to me. They had told me that they had replaced the engine wiring harness as there was an upgrade chip installed and it had damaged it. This chip was supposedly installed by the previous owner. Landrover wanted to rush me R25000.00 to do this as they claimed it was not covered by the warrantee. I told them that, as I did not have the chip installed and they sold it to me with the chip, it was their problem. The eventually agreed and kept the car for some time while they did the replacement. With this problem I have now had, we checked the wiring harness and found the place where the chip had been installed. They had removed it and covered the damage over with tape. :angry:

Anyway all is well now.

Thank you all for your suggestions and advice.

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