2001 Land Rover Discovery II - Discarded Discovery: Part 1Posted in Project Vehicles on March 17, 2014 Comment (0)
We love a good deal and aren’t afraid of hard work, so when a 2001 Land Rover Discovery II was dangled in front of us for a mere $500 we jumped at the chance. When we took possession of this “Discarded Discovery” it had every indication of a blown head gasket, which is a common problem for the Bosch 4.0L V-8 installed in these vehicles. In fact, most won’t make it past 90,000 miles without failing. The average dealer quote for repair is close to $3,000, so the previous owner cut his losses and gave us a deal we couldn’t refuse.
Our goal was to get the Disco back on the road (and trail) by completing the repairs ourselves. After all, the labor charges are the biggest cost in having the repairs done by a professional mechanic. With parts and our free labor, we figured we could tackle the task for a minimal cost and still have a running Disco for under $2,000.
These particular Land Rover motors are plagued with failures, and the most common seems to be the head gaskets with the head bolts being large contributing factors. We planned to replace the problematic factory head bolts with ARP head studs in hope of possibly alleviating this problem but stumbled into some unfamiliar territory dealing with the proper torque spec.
Land Rover Head Bolt/Stud Torque Specs
With Land Rover engines, head bolt torque spec is always a tricky bugger. The OE specs call for the TTY (torque to yield) bolts, which use a beginning torque spec of 15 lb-ft, then call for tightening in two steps of 90 degrees each. What happens is that the bolts eventually reach a point where they begin to stretch. This stretching turns the bolts into a sort of spring and this spring force (or clamping force) is not measurable. Variations in material composition, tiny variations in number of degrees, and any inaccuracy with the initial torqueing can add variables to the final clamping force. What you are left with is a question: What is the final torque of each bolt? How this is satisfactory is beyond us, but how can we argue with Land Rover’s years of R&D; it should work just fine, yet it doesn’t.
Now, clamping an aluminum head to an aluminum block is tough -- all the materials involved expand at different coefficients. The bolts (steel), the head gasket (some composite materials), and the heads/block (aluminum) all expand and contract at different rates to different amounts. Thusly, Land Rover went to a stretch bolt in order to add a tolerance to variables that could, theoretically, increase the life of the clamp, but it doesn’t. If you get more than 90,000 miles out of your Discovery II motor without having to replace the head gaskets you’re on borrowed time. This doesn’t seem to apply to later years, just ’99-’02.
Why is 60 lb-ft of torque okay when using ARP studs? Well, there are three reasons. First, the material does not stretch like a TTY bolt. This means there is an actual final measurable torque to be had. ARP recommends 100 lb-ft of torque for this Land Rover application, which is simply too high for the materials involved (at least it was for this particular Disco). Second, the top threads where the nut screws onto the stud are finer threads than the original bolts. Each turn creates less clamping force, therefore, a 1 lb-ft difference requires more turn. This also means once you get to 60 lb-ft, you have actually turned the nut farther than you would have to have turned the bolt, and you have just as much (if not more) contact surface with the block threads. Third, the torqueing of a bolt fights the friction of the threaded surface. With a stud, there is less friction, which translates to less required torque, especially when using the ARP Ultra-Torque Fastener Assembly Lubricant. For this project, 60 lb-ft was the sweet spot.
Check back next month for Part II of this article to read about completion of the head gasket repair and some of the other cool fixes we’ve applied to our second-hand Disco. We’ll continue to improve and build our Discarded Discovery in upcoming issues, adding a lift, wheels, and tires, as well as bumpers, body armor, and more to best prepare it for the trail. Check back often to see what we do to the Disco and which trails we’ll tackle.
Head Stud Tips
If you elect to use head studs in place of head bolts for this engine application, there are a number of important factors to consider and steps to follow for proper installation.
1. Do not exceed 60 lb-ft of torque. ARP specs for the kit state 100 lb-ft, but this will strip threads.
2. Studs cannot be installed before the heads as there is not enough space. Not a problem -- drop the head on the guide dowels and insert the studs. A handy Allen keyhole sits at the top of each stud.
3. Block threads should be clean and dry: No lubricant, no oil, no grease should remain once chased and cleaned.
4. A thread chaser should be used to prepare every thread. Do not use a tap, as it will remove much needed material from the threaded holes. We used a thread chaser with a bit of grease applied. The grease helped lubricate the holes, as well as pick up any loose debris. After chasing the threads, clean the threads thoroughly. Get that grease out of there.
5. Use brake cleaner to clean the holes, not carb cleaner, which leaves an oily residue.
6. Remember, we are using studs. Once in place, they no longer need to turn within the block. All lubrication should be applied to the upper threads, where the nut turns.
7. Studs should be installed hand tight. Do not over tighten. If you require a torque spec, go with 5 lbs, then back them out one-eighth turn.
8. Make absolutely sure there is no leftover grease, oil, water, or debris left in the threaded holes. This will make it impossible to bottom out the studs, which require the depth to work properly. If you find that one stud sticks out farther than the rest, stop, remove it, re-chase the hole, and try again.
9. This is a tricky upgrade at best. The torque specs supplied are wrong, there is no other reference for these specs, the ARP studs are as hard as nails (they will gall aluminum with ease), and they do not stretch like the TTY bolts.
10. Use ARP Ultra-Torque Fastener Assembly Lubricant. It’s good.
11. Apply lube to upper threads, washers, and nuts. Remember to apply lube to the mating surface of the nut, where it touches the aluminum head. This area will gall like crazy without lube.