head coming off again

[Peter Connan]

Check whether the score marks align with either the gudgeon pins, or with the ring gaps.

[Andre Steyn]

Andre.jpg (62.5 KiB) Viewed 2123 times

[Andre Steyn]

Patrol%202.jpg (92.3 KiB) Viewed 2123 times

Nissan%20Patrol.jpg (79.01 KiB) Viewed 2123 times

[Andre Steyn]

So can anyone see anything really odd on those pics?

[Michael]

Andre, this is not good news!

These seize marks usually only appear in two ways. Overheating is the first option but I don't think that is the case or was there an instance where the engine over heated?

The other possibility is pistons to sleeve clearance that is to small. Thus when the piston expands it fits to tightly in the sleeves and seizes. The only way to determine this is for the engineers to measure the block and pistons when they are out.

Another possibility is the piston coolers, but I think I read in one of the posts that you did check them and the were fine.

[Andre Steyn]

There was one or 2 instances where the heat gauge went up from normal but I never allowed it to go into a dangerzone, it moved up to just past the image for water on the gauge. If the piston to sleeve clearance is incorrect I'll put the mistake at the engineers door. Could it be injectors? The other thing I'm worried about is the sleeve protrusion and the deck hight, also the pistons we used! Cost me R7500 for the sleeve kit! What would you recommend? New sleeves and pistons or just a good hone and new pistons?

[Andre Steyn]

The other option is to up the bore size and use oversize pistons then resleeving isn't needed or am I wrong?

[Michael]

I'm not an expert in any way, but here is my 2 cents

I cannot think that Injectors can do this as they only inject into the precoms and not directly onto the pistons. But we all have seen what faulty injectors have done to ricster's Patrol so not sure. But very unlikely as all 6 sleeves have the same issue.

I also don't think sleeve protrusion and the deck height will make score marks on the sleeves, if there were any problems there you would have surely picked it up on the EGT? Worst case for an incorrect sleeve protrusion is a blown head gasket, incorrect piston deck height will just effect the compression. What was your piston above block protrusion?

If the sleeves were not bores/honed to the correct size I don't think you have to re-sleeve. they will just have to hone or bore until they get to the correct size. The down side is that your pistons now might have seize marks on them which will mean that they must be replaced.

What brand Pistons did you use?

Maybe Frans can give his opinion.

[ricster]

Hmmmm.... difficult to see clearly on the pics, but I'm wondering if there isn't a broken ring. I remember easily breaking a compression ring when I fitted it to the piston. I couldn't believe how brittle it was.

Step one I think, get those pistons out and try assess where the marks came from. Check piston walls etc. Here is something a little lateral..... Was the intake manifold, intercooler, turbo and connecting pipes perfectly clean? I'm thinking that some small "stones" or metal chunks got blown into the cylinders and wedged between the sleeve and the piston.

If the sleeves are too small I think fitting the standard pistons and rings would be very difficult, but may be wrong here ( I've never had that experience ) so there must be something scratching the sleeves, and that can only be dirt or gudgeon pin circlip that wasn't seated properly in the piston head housing. There isn't anything else that can scratch.

On the first pic, is that metal shavings on the piston top???

On the first pic, zooming into the bottom left quarter, I can see what looks like a piston ring ( silver in colour) then moving clockwise it ends suddenly and there is what looks like a large gap. I'm thinking broken rings. Did you dump oil on top of the pistons before fitting them and before fitting the head? I'm thinking that dry rings on dry sleeves on first start up may have started the destruction of the rings, if that is the cause of the marks.

[Andre Steyn]

Hmmm deck hight I cannot remember,also there is 0,sleeve protrusion which will have to be sorted somehow. I checked now, we could only find autopower pistons at the time we did the rebuild, according to google they are good for the price and can handle high boost and compression. The pistons will be out today so maybe I'm lucky and they can be reused.