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300tdi head problems part 2


SeriousIIa
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Hi,

Last week I made a post about the problem with the cilinderhead of my 300TDI disco Head problems part 1 . Since then I had the head fixed. And everything good the go. Then got a call from the head specialist who said that piston 1 and 3 had hit the head....

So this is probably the reason why the pushrods were bend. Not that the valves too low, but that the pistons were to high. According to the specialist this was probably caused by worn bearings on the crankshaft/conrod's. :(

So are these difficult to replace? I know that with a series this is easy doable if you take the sump off. But how about a 300TDI disco??? Also easy? Or more difficult?

Another block is costwise not an option :( So looking for a solutions which cures my current one.

Cheers Bowy

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I can't actually see how a worn big-end could make the piston hit the head. There would have to be a hell of a lot of wear in the shell for it to then be thrown up the extra distance to strike the head. In such cases I would expect the engine to knock very noticeably - especially under load. If the big end shells are badly worn or have been worn for a long time - then there's the possibility of journal ovality, which means machining or a new crank. The big end caps are removed from under the vehicle and any wear in the shells will be evident. The worse the wear - the more likely you will need work on the crankshaft as well usually.

Les.

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I can't actually see how a worn big-end could make the piston hit the head. There would have to be a hell of a lot of wear in the shell for it to then be thrown up the extra distance to strike the head. In such cases I would expect the engine to knock very noticeably - especially under load. If the big end shells are badly worn or have been worn for a long time - then there's the possibility of journal ovality, which means machining or a new crank. The big end caps are removed from under the vehicle and any wear in the shells will be evident. The worse the wear - the more likely you will need work on the crankshaft as well usually.

Les.

Hi Les,

The block wasn't knocking excessively so it sounds strange to me too. But do you know how else this problem of the pistons hitting the head could occur?

Tomorrow we're going to find out. Were taking the sump off to check the bearing and replace them when neccasary.

Fingers crossed

Cheers Bowy

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Hi Bowy ,

sounds a bit odd that only 1 & 3 have hit , Like Les said you would hear the bigend brgs (pronounced knock). Are all the pistons coming up to the same hieght at top of stroke? if not you either have worn out bigend brgs or bent conrods.If the rods turn out to be bent , and this can happen with a cracked water jacket in the head , :( , you will have to have the engine out as the piston and rod come out from below. I have seen pistons hit cyl heads through big end wear so it may well be as you have been told......I have just been thro all this with a cracked 300Tdi head = bent rod = new head + conrod etc.

hth

cheers

Steveb

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Hi Bowy ,

sounds a bit odd that only 1 & 3 have hit , Like Les said you would hear the bigend brgs (pronounced knock). Are all the pistons coming up to the same hieght at top of stroke? if not you either have worn out bigend brgs or bent conrods.If the rods turn out to be bent , and this can happen with a cracked water jacket in the head , :( , you will have to have the engine out as the piston and rod come out from below. I have seen pistons hit cyl heads through big end wear so it may well be as you have been told......I have just been thro all this with a cracked 300Tdi head = bent rod = new head + conrod etc.

hth

cheers

Steveb

Hi Steve,

Is a bend conrod easy to spot? Or is it just a slight bent? Why does the engine have to come out for this? (I have a 4 post bridge at hand so that department is sorted)

Cheers Bowy

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no they don't cos the crank is in the way, pistions/rods are removed/fitted from the top, after cylinder head removal.

But when the head is already off. isn't it possible to get them out by now when the engine is in the car? Should make life easier..... But first check the bearings and hope that's the problem.

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A bent conrod would make the effective total length of the piston/rod/assembly even shorter, so less likely to hit the head. I've never stripped a 300TDi engine, but if you can remove the big end caps from under the engine - the conrod/piston assembly is then pushed out through the top once the head is removed. Haynes manual says that the big end caps can be removed with the engine in situ after removing the oil pump strainer. If that's right, then you can in effect strip the entire engine down to almost just the bare block with just the crankshaft still in it without having to take the engine out of the vehicle.

Les.

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Yep, engine out , crank out , was only one bent rod tho, the crack in the inlet port let enough water in to hydraulic that cyl & bend the rod.....first time I've come across that happening

learn something new most days :lol:

Cheers

Steveb

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Solved the problem today.

Replaced the big end bearings (which seemed neccassery, because the upper halve was almost 0.2 worn) .

Then we put everything together again to find out the rocker shaft was broken between cilinder 1 and 2. So got a replaced from a friend. And mounted this one.

Then adjusting everything and fingers crossed.

Started right away and ran very smooth. Then after a 15 min testrun the oil pressure light came on when stationary. This had never happened before so probably not because a worn pump.

So we guessed the filter was probably partially blocked (because of all the work we did to the eninge, and carp we found in the carter....) and changed this for a fresh one. Then the light went out right away.

So everything sorted now and we went to a playday.

Then busted the diff :( Some parts went out right true the cover. So now we've got something to weld tomorrow and replace the diff. And then hopen it will be a bit longer on the road before it breaks down again.

Cheers Bowy

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A sign of a bent rod is low compression on that cylinder. A 300tdi rod will easily bend if the head gasket goes and lets coolant into the cylinder. We bent a rod badly just by turning the engine on the starter motor! But I am surprised you couldn't get the rod out of the bore at the top; this one looks like a banana but was removed from the top as usual.

So, a word of warning: if you suspect a head gasket failure, take the glows out before turning the engine over... And then look for water coming out of the glow plug holes. At least this way you won't end up with a bent rod.

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Did you use the correct head gasket?, they are available in three different thicknesses.

Rgds

Rotor

Jep.

But now the last time probably one that was one size to thick. But that was what we had lying around. So didn't bother getting another one. And it runs great with enough power!

Cheers Bowy

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