3.9 rebuild - Defender Source
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  #1  
Old November 9th, 2006, 09:10 PM
meyvn2
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John M
'95 Defender 90 Tdi
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3.9 rebuild

Any insight is appreciated. I had an independent mechanic check the compression on a '94 D90 prior to purchase. The compression was down 40% in two cylinders and 20% in the other 6. What can a rebuild cost for a 3.9?
Thanks,
Mark
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  #2  
Old November 9th, 2006, 10:29 PM
robisonservice
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John Robison
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A rebuild can cost $7,000-$9,000, if it's a complete job done by a professional shop.

But you may not need a rebuild. You may just need a valve job, which would be in the mid$2,000's at many shops.

You might want to read some of my magazine article reprints on this on our web site. Look at www.robisonservice.com > service > rover >articles.
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  #3  
Old November 10th, 2006, 01:30 AM
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Roadsiderob
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Robert Dassler
1994 D90
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I personally would upgrade to a 4.0 shortblock...maybe pick up a good used one and rebuild it while you drive the truck. Internally, the 4.0 is a better engine with crossbolted main caps, bigger main & rod journals, and better rods (longer). If you can find one with moderate mileage that has been reasonably well cared for you will probably find the pistons & bores hardly worn at all. These engines tend to have stuck oil rings and respond well to lightly honing the standard bores and fitting new rings and having the heads rebuilt. Undersized rod and main bearings are now available for the 4.0L, and any competent machine shop can handle the machine work. To date, I have not located a source for oversized pistons for a 4.0 (althouth I think they are readily available for the 3.9) even though the rebuild manual claims that they are available in .5mm O/S. Last week I finished an engine rebuild on a 1996 Discovery. At 180K miles the K&N filter ripped and it ingested something. #1 plug was oil fouled, compression numbers varied wildly. Whatever #1 cylinder ingested managed to score the piston wall deeply and embedded itself into the crown of the piston. Even at that mileage, the bores all measured to spec and the cylinders still showed crosshatch. The unavailability of O/S pistons to fix the scored bore necessitated replacing the block with a good used one. I thought about having the block sleeved, but that wasn't an option at this time as no one in Albuquerque wanted to do it. I had the heads rebuilt with some light port work to the exhaust bowls, had the crank ground undersize and the rods reconditioned. The bores were lightly power honed and new standard rings fitted to the original pistons. A new camshaft, cam bearings, and timing set were also fitted. The truck runs very well. I did some other work at the same time, so I'm not sure of the exact cost breakdown....but parts & labor for the whole engine rebuild came to a little more than a new 4.0L shortblock alone would have cost. You will get into significantly more money if you want to go with oversized pistons & rings and bore the block to fit. If the block you have is that worn, it will probably be less expensive to find a decent block than to buy & fit 8 O/S piston assemblies. This stuff isn't in every junkyard, but it isn't that rare or exotic either. These engines cost more to build than a 350 Chevy for sure, but it CAN be done well for a reasonable cost.

Look at www.roverparts.com to get an idea of what parts costs can run.
www.aluminumv8.com and www.v8engines.com are 2 other resources.
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  #4  
Old November 10th, 2006, 05:05 AM
meyvn2
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John M
'95 Defender 90 Tdi
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valve job v rebuild

Thanks for your responses and the links. How do I know if the motor needs a valve job rather than a rebuild?
Mark
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  #5  
Old November 10th, 2006, 12:20 PM
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Neil McCauley
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Neil McCauley
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I don 't need one now, but BP's got 4.0's since yesterday for $1200. Thats damn cheap. http://www.landroverparts.us/LandRoverSpecial.html
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  #6  
Old November 10th, 2006, 01:44 PM
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Robert Dassler
1994 D90
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That is a really inexpensive price...the going rate for a new 4.0L shortblock lately has been about $4K.
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  #7  
Old November 11th, 2006, 12:45 PM
cr7707
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carl, joseph
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what does a compression check typically cost? Are there any other similar engine checks that arent ussually done by a novice that should be done?
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  #8  
Old November 12th, 2006, 02:09 PM
meyvn2
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John M
'95 Defender 90 Tdi
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The mechanic did a leak down test involving injecting compressed air into the motor while the piston is at TDC and then measuring the leak. The cost was is about an hour of shop time.
Mark
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  #9  
Old November 13th, 2006, 07:04 AM
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evilfij
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evilfij
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New 4.0 block and gaskets etc, skim the 3.9 heads, remove and refit, new crower cam and lifters etc. about 2200 in parts and 1000 in labor.
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  #10  
Old November 13th, 2006, 08:37 AM
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rover4x4
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Phillip
1995 SW #487/500
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talk of the 4.0, why not 4.6 isnt the swap the same? Also I wonder what is the potential with the 4.6 with the old 3.9 top end and 14CUX management as opposed to the bosch or gems stuff? Granted theres no replacement for displacement but are the benefits more significant with the 4.6 than the 4.0 keeping all the old "stuff" from the 3.9.
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  #11  
Old November 13th, 2006, 09:08 AM
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a crower cam and a 4.2 lwb chip with a new 4.6 block in a 14CUX truck gets out of its own way pretty good.
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  #12  
Old November 13th, 2006, 09:19 AM
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Phillip
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hmm.. what about a 4.2 chip in the 3.9? This chip you speak of where is it? Would it be the same and just swaping the 3.9 ecu out for the 4.2. my boss has an LWB what would happen if i put that computer in my truck?
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