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Crank Journal Bearing Z20Let


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#1 andywilson

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Posted 21 July 2013 - 04:03 PM

hi all

 

as some of you may know, i'm putting a z20let into my kit car.

I was doing a balancer shaft delete so removed one of the crank journal thingys and saw this:

 

Posted Image

 

 

first time I've ever seen anything like that.

anyone know a likely cause?

 

pistons looks fine, bores look fine, oil looked fairly clean, nothing suspect at all about the engine.

I've inspected all the others and they look fine

 

 

also...I think I know the answer to this... but is it possible to just replace this half of the bearing? :huh:

 

thanks, andy



#2 Nev

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Posted 22 July 2013 - 04:30 PM

Blimey. Just replacing 1/2 a shell rather than having that ripped up thing must be way better surely ?

#3 Dave E

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Posted 22 July 2013 - 08:24 PM

We found one of my shell's was the same when the engine was stripped down. The reason for my rebuild was boost passing the piston rings which meant the turbo wouldn't hold the proper pressure. This also had the side effect of overheating the oil and its that that we believe was the cause for the shell delamination.

#4 andywilson

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Posted 22 July 2013 - 08:58 PM

hmmmm, tis a strange one.

 

I agree Nev, you'd think it would be better, however having one half of a shell worn and one half new may have some adverse effects? not sure really

 

I think i'll stick half a replacement 1/2 shell in there and see how it goes. soon as it's in and running i'll do a compression test to see what the rings are like.

 

thanks chaps



#5 Nev

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Posted 22 July 2013 - 09:11 PM

@Dave, I wonder why only one shell would delaminate, surely all would blue/discolour and start failing in a similar way? I reckon it might be due to oil starvation on that journal for some reason. With that in mind Andy, it might be worth poking a wire up the oil hole and clear out any possible debris. Also, if that is the central bearing (which it does look like), it might be sideways pressure on it causing the side of the shell to be stripped, as the central bearing acts as a thrust bearing. Worth checking for lateral (end to end) play in the crank...

Edited by Nev, 22 July 2013 - 09:13 PM.


#6 Robsturrs

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Posted 08 May 2022 - 08:28 PM

Hi Andy, how did you get on with this? I have just found exactly the same, on the same bearing, while doing the balance shaft delete mod, although the damaged area is slightly smaller. Im thinking of changing just this bearing but looking at sliding the top half around as well.
Thanks, rob

#7 blackoctagon

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Posted 09 May 2022 - 09:56 AM

You might struggle to get an answer after 9 years.

What I started writing was:

"I do not have a z20let, but that looks like a bit of oil starvation.
Often in balance shaft deletes the oil flow is changed as you have taken other bearings/restrictions out of the flow path, so the oil goes for this new path of least resistance and you loose pressure where you need it.

I did see this:
https://rndmotorspor...ce-shaft-delete

Are you sure your grubscrews and girdle are all correct? "


Then I re-read it and saw this was when people were going in to actually do the delete.
So my theory is the oil was either hugely hot from the turbo and that was also a hot spot in the engine and it was a magic coincidence.
Do the non-turbo X2OXEVs that use that block design suffer this? If not then the oil heating theory might be right.

#8 Robsturrs

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Posted 09 May 2022 - 01:18 PM

What I find strange is that on two separate engines, both going through balance shaft delete modifications, so not stripped due to any knocking, both have this damage to this bearing. The other bearing I have seen had some wear but nothing like this. I assume Andy’s was just this bearing as well. I am curious as to whether the single bearing or even the just the half was swapped out, and if just the half how things panned out. On one hand I’m thinking it was like that before I saw it, if I hadn’t seen it it would still be like that, so put it back and run it with the heads up that it’s gonna need work soon but at a better time… ie not the start of summer. But on the other hand now I’ve seen it I’m struggling to unsee it

#9 blackoctagon

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Posted 10 May 2022 - 09:41 AM

Bearings will take quite a lot before they really give in if the majority of the surface is level. It's when the thing overheats and the soft metal starts to give way and the oil film thickness becomes uneven and can't support the load that you start to get accelerated wear, less film stability, more wear, less film stability etc. then the knocking starts.

It maybe means that there are many Z20LETs and X20XEVs out there with the same thing, but no one would ever tear down an engine that makes no noises so it goes unnoticed.

If it were me i'd be cleaning the sump, changing the oil and filter, bottle brushing any oil passages I could get to and swapping out the bearing to prevent the bits of dead bearing givign problems.

If you are already at a stage where you can inspect bearings and need to bolt the engine back up anyway, and clearly a capable mechanic, why are you considering not replacing a relatively cheap wear item that is worn?

#10 Robsturrs

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Posted 11 May 2022 - 05:40 PM

Im a mechanical engineer but this is my first adventure working on the internals of an engine. I bought this car not only for the fun of driving it but also to put myself out of my comfort zone like I am with the stuff I’m doing at the moment. I’d love to do a full forged engine rebuild at some point but only when the circumstances are right… engine out of the car, mounted on a proper stand, heading into winter rather than summer.

Nearly everything in my tells me to change it out however there are other things coming into play here, Life’s just a nightmare at the moment and the car should be last priority however part of that nightmare has lead to me wanting it back on the road for Tuesday next week.

Replacing just one half of the bearing doesn’t sit well with me really and I have been looking into how people change the other half without moving the crankshaft. It’s possible and I do t feel it’s too far out of my comfort zone however if I start it and anything goes wrong it could potentially blow all chances of next week, maybe even longer.

If it has to be done in most peoples opinions then I’ll have to bite the bullet and crack on, but having done 900 miles since 2020 I’m leaning towards putting it back together and enjoying it now armed with the knowledge it may need doing soon.

#11 blackoctagon

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Posted 17 May 2022 - 10:09 AM

Late to the party, and it is now your 'next Tuesday', but...

As a mechanical engineer put on your tribology hat and ask "Do I want a full width flat surface to hold a supporting oil film, or a partial one?"

My knowledge of the z20LET is limited, and I suspect that to do a full set of crank bearings in the car you need to get all the main bearing caps off and release the crank from the clutch and flywheel, so the halfway house is (assuming you're not done yet) to get in the half bearing.
If you already have the offending cap off that alone will get a wider support for the crank and that has to be better.

Hopefully by the time you've read this it will be redundant.


With a Z22se/L850 block engine you need to drop the whole bottom girdle. I cannot contemplate doing that in the car, although i'm sure some brave soul somewhere will have done it.

#12 Robsturrs

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Posted 18 May 2022 - 08:49 PM

I ended up turning a blind eye to the bearing for now, no, I’m not particularly happy about it, but if I hadn’t seen it I’d have still been blissfully unaware of any damage to the bearing. And as you say, maybe there’s hundreds of Z20LETs out there exactly the same.
I know it’s a risk but it’s one I’ve had to take, I am working on the car at work and it’s been in the workshop for nearly two weeks after what was supposed to be a few simple jobs. Im lucky to be able to do this and I don’t want to start taking the p*ss… life just gets in the way when you least want it to doesn’t it. Oh and Tuesday didn’t work out.

Hopefully when everything settles down I can have use of the workshop one weekend over winter. I will have everything ready to go and I won’t be so bogged down with other stuff. I will replace all main bearings at the same time, both tops and bottoms.
Touch wood nothing dramatic will happen between now and then, VX related or otherwise 🙂




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