D40 yd25 piston removal

[Kobus Combrinck]

Good evening guys. New to posting on the forum. I have a Navara d40 yd25 2008 model with endless issues.

I have watching and reading comments on the forum and there seems to be a lot of guys out there with notable knowledge.

I have a question. I need to replace my nr 3 piston(if counted from the front of engine). The motor was redone completely about 1000km ago, new pistons rings, head engineered, new.bearings etc. The mechanic definitely stuffed this one up.

The valves seemed to have been touching the pistons every so slightly, and to make a long story short the engine overheated and blew the head gasket. (3 notches). The nr 3 piston(counted from the front of the engine) needs replacing as it is missing a small piece right at the edge which I am not comfortable with. Can I loosen the conrond at the bottom and push it out the top to replace as the head is already off. Or would the best be to remove the engine, change piston and put it back.

Just seems to be a lot of work for 1 piston but want to do it right.

Thanks all comments and help is highly appreciated

 

[Old.Tony]

If the head's off and the sump is off, that's one way to do it without removing the block (and would likely be my choice if I were to do it myself).

If the valves have touched the piston, have you worked out why? Is it timing, or is the head gasket too thin, or the valve shims too large? It's the answer that's needed to prevent it happening next time.

 

[Kobus Combrinck]

I think the head has been machined a couple of times and when the mechanic assembled the engine did not take this into consideration.

I did a pressure test after installing my own manufactured gasket(2.5mm thick) and the pressure was consistent although below recommended spec, reading was at 290 PSI and I think tolerance at the lower end is somewhere at 380.

I will do a test on with a dial gauge on the pistons tomorrow as I already removed the head to calculate head gasket thickness and see if it is in spec and order one

here are some pictures of the nr 3 piston and the piece that is missing

 

[Kobus Combrinck]

I did forget this part. the timing was out with 2 links on the chain running from the crank to the middle of the engine. the 3 top pulleys lined up with the links that are colored but obviously the bottom linked being out would have contributed to the problem

 

[Old.Tony]

That wouldn't have helped at all!

 

[Damian m]

If the timing was out you got away with minor damage there, I would be inclined to remove all the pistons and visually inspect them for damage, but also I would want to get the whole motor balanced again with the replacement parts.

 

[Kobus Combrinck]

If the timing was out you got away with minor damage there, I would be inclined to remove all the pistons and visually inspect them for damage, but also I would want to get the whole motor balanced again with the replacement parts.

will it be possible to pull all the pistons out without removing the engine. so will I have access to loosen all the big ends and push the piston upwards from beneath the bakkie if I remove the small sump. picture attached

I am alone in tackling the job and pulling the engine will be my last resort due to the labor involved, and I think one person will not be able to do it but I have been proven wrong in the past

 

[BarneyB]

I haven't worked inside a YD25.....yet....so I don't know the specifics of disassembly/re-assembly for this engine
But....part of my occupation involves overhauling very large marine diesel engines, compressors, pumps etc.

Is there another section to the sump, or a casting, that can be removed to access the whole crank? It would be a ****-move by Nissan to design an obstructed block...?

I've never seen an engine (of conventional layout) that you could NOT lift con-rod & piston out after removing the big-end bolts from underneath.
I can't see why/how you couldn't do it on a YD25...?

Use different lengths of timber and a small engineers hammer to tap parts apart or together. Use plenty of engine oil between anything that slides apart under load.
Be careful when you're re-installing. Use a decent ring compressor or make something that works. And treat the bore/liner and the big-end bearing surface like glass. It's easy to scratch the big-end journal during assembly. If the rod bolts have only done a few kms you could prolly re-use them, but consider new ones if they've stretched/fatigued.
Check the big-end bearing shells on #3. The engines I work on have different thicknesses available. Maybe the wrong shells were mixed up?

The way I would look at the whole job....
If the bakkie is half-rooted anyway and you use it for smashing around the farm / mine / worksite / whatever, then I'd just fix #3 with your DIY gasket, fix the timing and see how it goes. There might be slight damage to other components, but if it runs OK then job done.

But if it's a nice bakkie with low mileage and good condition - that the wife drives - then you probably should buy or borrow an engine crane & haul the engine out. Check all the cylinders and valves thoroughly etc etc.
Was there a stated warranty period offered by the overhaul workshop?

 

[Damian m]

Pulling the motor out will give you a lot more room to do the work required, in chassis rebuilds are always difficult and always take way more time.
Just really depends on how well equipped your shed is, or how willing your friends are to lend the correct tools for the job

 

[BarneyB]

Pulling the motor out will give you a lot more room to do the work required, in chassis rebuilds are always difficult and always take way more time.
Just really depends on how well equipped your shed is, or how willing your friends are to lend the correct tools for the job

Totally agree.
If you suspect that the whole motor needs a tear down & inspect, then just commit to removing it. More work initially, but much better overall.
Obviously depends the tools & shed available.

 

[Kobus Combrinck]

Ok so I have taken the head of and measured the piston protrusion with a dail gaudge. It is at the limit of the head gasket with 6 notches. Whilst checking everything I noticed something.

On the head the valves are actually protruding past the flat surface. Not much but when it comes to clearance it is a hell off a lot. Measures 0.5mm .

My question or thought process no is that the head has been skimmed or engineered to many times and this is the reason for the valves touching the positions. If I calculate the piston protrusion take the gasket into consideration after it is torqued and the valve sticking out there is no gap left.

I need to now make a decision. Pull the pistons and Machine them down to create clearance, buy a new head which in this country is almost the price of buying a small car or change the complete engine which is even worse, as replacement engine is more than 50% the value of the vehicle and taking into account I just spent close to R40 000 on overhauling the engine...

Any suggestions on what route I should take

 

[Old.Tony]

While this isn't the exact one we bought (2009 model), it's close. Notice that it says it comes with gaskets and new head bolts (vital). Ours was advertised as coming with camshafts and valves all adjusted, just like this one, and indeed it was. The mechanic told us that it was a perfect fit, and only required one extra gasket which they sourced for me.

https://www.ebay.com.au/itm/2648142...vniL9S7TVQ%3D%3D|clp:2334524|tkp:BFBMtP-SvvRf

 

[Old.Tony]

^ Note: that's an option you could consider. Ours has given us no grief at all, but I'm quite a moderate (if not outright gentle) driver. I cannot say how it would perform for someone with a penchant for higher RPM, although we've done some towing with ours and it performs very well.

 

[Kobus Combrinck]

I looked at it. Actually not bad if all the gaskets are part of the deal. I have send them a message as they say they do not ship to South Africa. Hopefully they can make an exception.