Visual differences between 3.9 & 4.0 - Defender Source
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  #1  
Old November 15th, 2006, 06:03 PM
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Visual differences between 3.9 & 4.0

Does anyone know how to visually tell the difference between a 3.9 and a 4.0 with the block still installed in the engine compartment? I'm guessing block stampings but I couldn't find anything in the archives. Any help would be appreciated.


neil
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  #2  
Old November 15th, 2006, 07:09 PM
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4.0 is cross bolted
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Old November 15th, 2006, 07:10 PM
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Quote:
Originally Posted by Roadsiderob
4.0 is cross bolted
Dosen't the oil pan have to be dropped to tell if its cross bolted?

Neil
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Old November 15th, 2006, 07:28 PM
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No, you can see the heads of the bolts themselves on the side of the block.... I just forget which side of it. (I have a 3.9). They are just above the oil pan.

Also, a 3.9 has an extra set of head bolts that can be seen just below the header bolts, these are not present on a 4.0 engine.

Lastly, a 4.0 throttle body can be unbolted from the intake plenum. A 3.9 throttle body is a permanent part of the plenum.
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Old November 15th, 2006, 07:55 PM
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Quote:
Originally Posted by Hans
No, you can see the heads of the bolts themselves on the side of the block.... I just forget which side of it. (I have a 3.9). They are just above the oil pan.

Also, a 3.9 has an extra set of head bolts that can be seen just below the header bolts, these are not present on a 4.0 engine.

Lastly, a 4.0 throttle body can be unbolted from the intake plenum. A 3.9 throttle body is a permanent part of the plenum.

Oh thanks but are you saying that your 3.9 is cross bolted? If thats true than both 3.9 & 4.0 are crossbolted? I wonder why its only bolted on one side? You would think it would be bolted on both sides for better strength. Thanks for answering the questions.

Neil
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Old November 16th, 2006, 12:30 AM
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3.5s, 3.9s, and 4.2s are not cross bolted, 4.0s & 4.6s are. There is a row of 5 bolts above the pan rail on both sides of the block.
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Old November 16th, 2006, 02:30 AM
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Ahhh, sorry for the confusion on that bit. What I meant is that I have a 3.9, so it has no cross-bolts, and therefore I can't remember which side they would be on for you to check. For some reason I had thought they only had the bolts on one side, but I was confused with a totally different engine.
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Old November 16th, 2006, 12:49 PM
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Man I just found out the replacement motor on my 90 is actually a 3.9 and not a 4.0. Damn and all this time and I never noticed those 5 bolts. Thanks Rob and Hans.


Neil
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Old November 16th, 2006, 06:14 PM
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I just came back from Huntington Service Center in San Marino. I talked to both Keith (british pacific) and took a look at the 4.0 block that I just bought. There is no crossbolts on the 4.0. Pete and Keith both said that the 4.0 does not have crossbolts on the sides and never did. They've been selling/installing these motors for years and they swear only the 4.6 has crossbolts....not the 4.0's. Thanks.



Neil
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Old November 16th, 2006, 09:22 PM
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In the Land Rover Service Training document "Introduction to Land Rover Engines" they have a list of design changes. Under 4.0 and 4.6 GEMS Design Changes they say . . .

Cylinder block with cross bolted main bearing caps
Crankshaft with larger journals and better balance
Pistons with lighter weight and tighter tolerance

. . . .

So there's your answer, from Land Rover

As regards the cross bolting - the bolts go across the main bearing saddles, so the bolt heads are present on both sides of the engine.

Follow-up Post:

Here's a picture from the factory overhaul manual that shows the cross bolt setup
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Old November 17th, 2006, 11:24 AM
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Look for #7 in the pics.

Also if it is still installed in the engine and it was installed in place of a 3.9 you have to run a spacer at the end of the crank which should be visible inside the lower pulley. The little plate where the crank sensor mounts is different too.

Ron
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Old November 17th, 2006, 11:53 AM
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I uncovered the block from the plastic and your right I see the crossbolting. The block they showed me yesterday must be an early version of the 4.0. Pete did mentioned that the early 4.0's did not have crossbolting. I'm not sure at this point. Sorry for the confusion. I don't know why Keith from BP and Pete keep insisting that the 4.0 did not have cross bolting. They did my block swap a few years back and I just believed what he told me. Sorry about that.


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