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 Post subject: YD25 engine rebuild
PostPosted: Wed Apr 20, 2011 10:38 pm 
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Hi guys, a mate of mine has recently bought a 2005 Navara dirt cheap with a knocking bottom end. The guy he bought it from put it to a local garage when it started knocking and decided not to fix it when he saw what they found when they took the sump off!

Anyway to cut a long story short number 4 big end shell is in bits, the crank is heavily scored and the con rod is cracked. All the other shells are knackered but they've not damaged the other 3 journals on the crank.

We've taken the engine out tonight and mounted it on a stand ready to strip.

We've sourced a reground crank with new big end shells and main bearing shells to suit. It's been ground to 0.25 I believe. Also on it's way is a head gasket and a connecting rod. I will be ordering ARP con rod bolts/studs as well.

I'm wondering if there is anything else I will need to order to do the job? Bearing in mind we're trying to keep the cost down as much as possible. Clutch is in good nick and there are no oil leaks from crank seals etc so we'll probably just reuse them. We've decided to reuse the timing chain and we're going to strip and clean the oil pump while it's apart. The engine has been serviced religiously so the rings should be good and the top end should be fine.

Oh and when the time comes we will need torque settings for the head, main bearings, big ends, flywheel etc etc...

Any help or advice will be much appreciated. :thumbright:

Cheers, Peter.


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 Post subject: Re: YD25 engine rebuild
PostPosted: Thu Apr 21, 2011 7:52 am 
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Forgot to say, if theres anything we should watch for when stripping the engine, common problems, also timing marks, are they easy enough to see/line up? Just thought i'd be better to ask the experts on here before we dive in head first! Will get some pics up shortly.

Cheers, Peter.


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 Post subject: Re: YD25 engine rebuild
PostPosted: Thu Apr 21, 2011 4:39 pm 
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How long would you expect a reground crank to last? The crank is coming from a well known engine specialist who have been building engines for years. Shurely if they were that bad they would be fitting brand new cranks and not bothering to regrind them?

What I'm trying to say is a reground crank is an original crankshaft, probably had the same scoring marks as our one has and they have refaced the journals... how would a reground crank be substantially weaker as a standard crank?

I'm not disputing the fact cranks do snap but how/why?

Cheers, Peter.


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 Post subject: Re: YD25 engine rebuild
PostPosted: Thu Apr 21, 2011 5:27 pm 
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Into 3rd gear and pulling like a train!
Into 3rd gear and pulling like a train!

Joined: Thu Oct 22, 2009 8:46 pm
Posts: 85
Location: Blackwood, South Wales
I was just the same as you when I re-built my engine as I have always re-ground my cranks, but I got in touch with Dave at Billcar who set me straight, I wont go in to it again, but if you do a search you will find loads of info on the forum on why this is not a good idea

Here is a post I made a while back that shows what happens to a re-ground http://www.nissan-navara.net/viewtopic.php?f=3&t=12048&hilit=reground+crank

If you do choose to put a re-ground crank in, then thats up to you, but make sure you know what you are getting in to first.

Dan


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 Post subject: Re: YD25 engine rebuild
PostPosted: Thu Apr 21, 2011 8:51 pm 
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5th gear and there's no stopping me!
5th gear and there's no stopping me!

Joined: Thu Oct 21, 2010 11:21 am
Posts: 400
Location: Ystradgynlais, South Wales, UK
In all fairness, 0.5mm on a crank-pin is a large ammount, and one which will definately reduce the effectivenes of the rolled fillet. This is where a stress riser will occur, and a crack propogates.

I wouldnt suggest a grind at 0.5mm, but if you can get away with 0.25mm I wouldnt be so worried.

If you can get it Nitrided, then this would be a great benefit.


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 Post subject: Re: YD25 engine rebuild
PostPosted: Thu Apr 21, 2011 9:43 pm 
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Fully run in and going strong!
Fully run in and going strong!
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Joined: Wed Feb 11, 2009 12:16 am
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Location: Winkfield Berkshire
Although ground cranks have proved to be a 'no-no' on here and other forums I agree with stanton :thumbleft:
As you've already got the crank and bits, getting it Nitrided would 'toughen it up' and give you more resilient journals against this possible failure.
JMO
Woz

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Woz


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 Post subject: Re: YD25 engine rebuild
PostPosted: Fri Apr 22, 2011 3:18 pm 
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Joined: Thu Jan 25, 2007 8:37 pm
Posts: 1468
Location: Farnborough Hampshire
D22 cranks are induction hardened, this hardening only pentrates a very small way, a grind of .25 will pretty well remove all of it.
Sorry
Chris

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 Post subject: Re: YD25 engine rebuild
PostPosted: Sat Apr 23, 2011 9:29 am 
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5th gear and there's no stopping me!
5th gear and there's no stopping me!

Joined: Thu Oct 21, 2010 11:21 am
Posts: 400
Location: Ystradgynlais, South Wales, UK
I'd confidently say ALL OEM crankshafts are induction hardened, and as we all know many many other engines are fine with regrinds.

If you look at the pic you can see the crack has started from the edge of the journal...this is where maximum surface tension is experienced, hence the use of a tolled fillet; to put the surface into compression, so as to increase the force required to reach the tension failure point.
If you remove or reduce this; which 0.5mm will, then you significantly increase the chance of failure.

IMO 0.25mm wouldn't be so bad, but this is just my opinion.


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