300 TDi Engine Overhaul

[militantpacifist]

I know the title sounds a bit misplaced since most people here talk about their V8s.

A dumb question on engine overhaul, which I am about to do. Say in a situation where the problem is caused by broken piston ring, and the lining is still ok, should i just change the piston ring and done with it, or should i get a new lining too?

I know if I were to refer the standard overhaul practise, since it takes hell a lot of effort to dismantle the engine, might as well change the lining too, but I just wanna know whether or not changing the piston ring without changing the lining is OK. What are the considerations?

mp

 

[ShaunP]

300 tdi engines do not have removeable liners. If the cylinder is scored / worn more than what a hone can clean up you will have to rebore it. Over size pistons are available up to 40 thou oversize. If just fitting rings it must be deglazed or the rings will never bed in a diesel. It is also extreamly important to remove the head bolts in the correct order on a TDI or the head will warp. TDI heads have the valves about 1mm lower than the face and this must be maintained or the valves will hit the pistons (combustion camber is in the piston not the head). The head gaskets are also available in 3 thicknesses, the pistons are actually above the block face at tdc, so you must calculate the correct gasket to use or the pistons hit the head. These engines are not hard to build but there are some traps for young players and you can do some real damage if you are not carefull.

 

[militantpacifist]

Thanks Shaun! Now I'll need to check with the mechanic whether he's aware about all the things you've said.

Any tips on selecting a good mechanic for this job? What will you look at in a mechanic to give you the assurance that he'll do a good job for my Disco?

mp

 

[ShaunP]

Mate I couldn't comment on mechanics in KL, but there must be someone who knows these engines. Normally the only problem they have is timing belt failure and the damage this causes which is normally just bent pusch rods.

If your engine just needs rings and a deglaze you will most probably fit the same size head gasket that is on it now. The gaskets come in 3 sizes and these are denoted by 1, 2 or 3 holes punched in the right hand side at the rear. If you change the pistons or face the block it may need a different size gasket. The reason why there are different sizes is not just to stop the piston hitting the head but also to ensure you get max compression.

Now you need to be carefully with the head, they are made of heat treated high tensile alloy and are easily damaged when being recondioned. Firstly you need to undo the bolts in the correct order to avoid distorting the head. When refitting the head you torque it with a torque wrech and each bolt is tightened useing an angle gauge in 2 stages of 60deg at a time to a total of 120deg. Don't let anyone apply local heat to the head to remove seats or giudes, the head must be heated in an oven slowly if seats or guides need replacing or if it needs straightening. When the head is faced the valves must be seated so that they are 1mm +- 0.1mm below the face to ensure max compression without crashing the valves. So to if after seating the valves they are lower than this the head must be faced. A new bare head casting is about $1500 Australian.

Now the biggest problem with a 300TDI is timing belt failure due to misalignment of gears. Make sure the engine has the correct retro fit modification kit fitted. The main problem here is that the injection pump is not aligned with the cam and crank so the belt walks off the gears and rubbs on the cover till it breaks. There is a retro fitt bracket that may need to be fitted and I shim the pump to get them perfect. When setting up the belt you are supposed to tension the belt and turn the engine 2 rpm and then retime and retension the belt. What I do is start the engine( with the timing cover off) and give it a rev, then reset the timing and retension the belt, this seats the belt well. Do not over tension the belt or it will fail quickly. Lastly make sure that the crank shaft belt drive gear and harmonic balancer are glued on the crankshaft using Loctite or they can come loose and damage the crank keyway.

Apart from this they are just a normal 4 cylinder engine and normal practises apply to the rebuild. I have done a few and never had a problem. Hope this helps.

 

[militantpacifist]

Shaun,

just to update u, I have had the engine overhauled recently, and just got it back two days ago! Now, I have more questions to ask since I wanna make sure that the mechanic has actually done a good job, as what he claims he is.

Firstly, I'd say the overhaul job was pretty comprehensive, we changed the piston rings (discovered that one of the pistons, have a few unseated rings), all the bearings from con rod to main bearings, timing belt, and serviced the turbo charge. FYI, the mechanic skimmed off the cylinder head, even when I actually warned him not too, but he told me it's for the better, so, he's the mechanic, he knows better I presume.

Now, the aftermath of his job, we took the car for a test drive, it looks, feels ok to me. It's just that I observe the gear shifts at around 2500-3000 rpm at the moment. And, when I performed the engine oil dip stick test, there's still oil spurting or rather spattering out from the dip stick tube. The mechanic told me it's ok, normal, whilst my friends said it should not be the case.

But, there's no excessive smoke from the engine oil fuel cap.

Now, there's a twist on the dip stick test. I referred the situation to a mechanic in Landrover Malaysia, TDI engine specialist, and he told me the dip stick test is carried out when the engine is cold. So, this morning. I started the engine, and performed the test, and thank god, there's no oil coming out from the dipstick tube. The mechanic told me, that it's normal for oil to be spattering out from the tube when the engine is warmed up, as long as it's not excessive.

And one more thing, I do observe there's still a little spot of oil (engine oil) on my drive way. I haven't checked from the underneath, but my guess is, it must have come from the flywheel housing drain hole. I referred this to the above mechanic, and he told me, it should go away in a week's time, if it's still there, then I'll need to refer it back to the workshop.

Can u please clarify further on my current situation, what it means. Should I be satisfied with the overhaul job?

mp
Kuala Lumpur Malaysia

FYI, in case u forget, mine is 300TDI, auto.

 

[ShaunP]

Skimming the head is ok as long as you seat the valves to maintain the 1mm clearance of valve head below head surface. As for the oil spatter these engines spray lotts of oil around inside, they use oil squirting nozzles to spray oil up into the cylinders/piston crowns to cool the pistons. As for the rear main leak the seal should bed almost straight away, thats not to say some oil could be hanging around from the rebuild, clean it off and see what happens. My advice would be to run the engine in and see how it goes.