emission test for MOT - Peugeot 306 xrd

I'm fond of my car, and I just spent £520 to get it through its mot. I am really annoyed that the mot test may have caused damage to my car. If anyone has any advice on what to do about this, I would be very grateful.

did they change the cambelt? if so it may need checking and either they have done it wrong/and/or the injection pump timing may be wrong.

generally if the engine and pump etc. are in good working order then the mot test revving up will not do any damage, if however there are faults then it is possible to over-rev the engine and damage things.

mrcheerful

Some do indeed. they're supposed to rev it up for 1 second at a time, effectively as soon as the revs reach max, foot off. I've seen some of them with their foot to the floor whole they talk (shout) to their mates.

It's a stupid test anyway, IMHO. Diesels are designed to pull heavy weights from low revs, not scream at the redline. When did you used to see old trucks belching out black smoke before the emissions test came in? Trundling up steep hills in low gears, no?

I've always believed it would make more sense if they made it drive the rollers against some resistance.

Steve

Rule of thumb in a lorry is not to change down unless it looks like it'll drop below 1200 RPM.

The message from "shazzbat" contains these words:

In what way would the engine revving against a load differ from the engine revving to the same speed against the governor?

It wouldn't be revving against the governor, it would be straining to get any revs, and it would be taking a long time to get there.

Steve

I took mine to Masterfit and they buggered up the brakes for me. It was unauthorised work carried out and this was later admitted by the head office. The problem is proving what you say. A lot of people will take a complete shed to a garage and then as we live in a compensation culture they will say various things. In my case Trading Standards got involved and it was found that the oil level was overfilled, air filter & fuel filter & spark plugs not changed but charged for, then some YTS person broke the brakes which have now been put right fter 3 further visits. They released the car with defective brakes after issuing the MOT certificate! The other costs I am having to recover from them as the car was marked up before it went into the garage and examined after it left. The main difficulty is proving your car was OK, I think you sign a disclaimer when you take a diesel car to some garages to state you're responsible for the car being in a good condition.

If you were to stand in a court how would you answer the following question, "can you prove your engine didn't sound the way you describe before leaving it at the garage?"

Sadly, I doubt you can - but I believe you as I know how some garages do mess with cars and break them without telling customers. Sometimes it is to create extra work as the fast fitting type outlets pressurise the mechanics into being sales staff.

It would take an age to hit the governor and is a more realistic test of the emissions.

Clue, it's accelerating.

Cambelt may have jumped a tooth. If that's the case, you are very lucky it didn't actually break. They'll need to remove the belt covers and have a look.

The message from Conor contains these words:

Yes, very clever. How do you think that affects the engine in a way that's relevant to the engine's likelyhood to self destruct?

It would be helpful to know what the =A3520 was spent on before any suggestions can be given, although it is possible that the timing belt was changed and the timing now slightly out, giving the 'old-taxi' sound that you describe.

The engine does have to be floored during the diesel smoke test, but this is after numerous pre-checks have been carried out. If any doubt as to the condition of the engine / pump / timing belt, then the smoke test will be abandoned.

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You can't go 'too far' with a diesel. They all have rev limiters. And that limit is very much lower than petrol engines - despite the engine being very much stronger.

That would be by allowing components to slop about using the inevitable free play which they wouldn't have if the engine was under load.

The message from "PC Paul" contains these words:

I'm not sure that makes sense. During the power stroke the piston will still be pushing down on the conrod and crankshaft, during the induction stroke it'll still be pulling up. During compression there won't be any difference as the amount of air available will be the same so the downward force will be the same, and during the exhaust stroke the conrod will be under compression as usual.

The only difference really is that there's less load during the power stroke, though still some, and the main bearings will be experiencing less sideways force.

Big end bearings rattle when an engine gets old. Or when it runs unloaded. Thats where the play is that really gets hit hard by high revving when unloaded.

Under load there is always a resistive force in the same (rotational) direction, so they don't bang about side to side and hence wear a lot more slowly.

The message from "PC Paul" contains these words:

The resistive force on big end bearings isn't always in the same direction at all. It's one way on a power stroke, the other way on induction.

It'll be the same , they're still applying the same force to accelerate the flywheel.

Correct.

And under load the crank is always held to one side so it slides up one side of the big end shells and down the other. Try and imagine the forces at work all the way round.

Without a load it's free to jump from one side to the other, causing it to impact on the other side rather than smoothly slide round to it. Which will wear the big ends much much quicker.

well only if you've got no oil in there, in which case you're buggered anyway & it's not under no load , it's accelerating.