Torque Of Main Bearings?

[ikari1]

Hi

In the RAVE manual for the P38 Range Rover it says to final torque the main bearing cap bolts nearest the flywheel to 68lbft and the other 8 bolts to 53lbft. In the ARP sticky above it says to torque the ARP bolts to 90lbft. Any suggestions/recommendations on the big difference?

[kiwicar]

Hi
That is partly why you spend the money on the ARP bolts, you can torque them to a higher load without stripping the threads. Check the conditions under which that torque is recommended (ie lubricated with the correct oil/ molly past for the torque setting). Strictly speaking you should get the main bearing bores honed with the main caps torqued to the higher setting.
Best regards
Mike

[DaveEFI]

Hi

In the RAVE manual for the P38 Range Rover it says to final torque the main bearing cap bolts nearest the flywheel to 68lbft and the other 8 bolts to 53lbft. In the ARP sticky above it says to torque the ARP bolts to 90lbft. Any suggestions/recommendations on the big difference?

Interesting. My BL SD1 manual gives 70 and 55 lb.ft.

[DEVONMAN]

Hi

In the RAVE manual for the P38 Range Rover it says to final torque the main bearing cap bolts nearest the flywheel to 68lbft and the other 8 bolts to 53lbft. In the ARP sticky above it says to torque the ARP bolts to 90lbft. Any suggestions/recommendations on the big difference?

Interesting. My BL SD1 manual gives 70 and 55 lb.ft.

Also interesting and confusing,
My Land Rover book says "make sure the thread holes in the block are clean and dry"

My SD1 book says use engine oil on the bolts.

Denis

[shaunod]

I have always used 70ft/lb for the main bolts, all of them, it has always been fine. The ARP bolts are I believe advised slightly higher but unless it is on main studs I have never found a need.

[mcgill]

Well the factory workshop for my old 1968 10.5 to 1, states
Rear main<65/70 lbs rope seal
Other mains<50 to 55 lbs
"rope and cork for rear mains seal......i do love a early engine ,yes sarcasism

[DaveEFI]

Well the factory workshop for my old 1968 10.5 to 1, states
Rear main<65/70 lbs rope seal
Other mains<50 to 55 lbs
"rope and cork for rear mains seal......i do love a early engine ,yes sarcasism

And likely recommends using ScotchClad for all the threads - so a lubricated figure?

[unstable load]

Also interesting and confusing,
My Land Rover book says "make sure the thread holes in the block are clean and dry"

My SD1 book says use engine oil on the bolts.

Denis

Not at all confusing.
The holes in the block must be clean and dry to ensure they are clean and free of debris. Debris can pick up in the threads and oil in the holes can cause the bolt to go into hydraulic lock if it hits oil that is too deep, resulting in a false torque reading and a loose bolt.
Oiling the threads then ensures they are lubricated with the right amount of oil and screwed in so that there is free space for the bolts to tighten all the way down without going hydraulic on you.

[DEVONMAN]

Also interesting and confusing,
My Land Rover book says "make sure the thread holes in the block are clean and dry"

My SD1 book says use engine oil on the bolts.

Denis

Not at all confusing.
The holes in the block must be clean and dry to ensure they are clean and free of debris. Debris can pick up in the threads and oil in the holes can cause the bolt to go into hydraulic lock if it hits oil that is too deep, resulting in a false torque reading and a loose bolt.
Oiling the threads then ensures they are lubricated with the right amount of oil and screwed in so that there is free space for the bolts to tighten all the way down without going hydraulic on you.

My point was that the Land Rover book says nothing about oiling the bolts but the SD1 book does.
I probably have a naf LR book.
However, nobody has answered the initial question, Why a bigger torque for the rear two bolts.

I can think of a couple but none with confidence, such as
-Extra forces due to the flywheel.
-Larger surface area of the cap therefore more clamping force needed.
Any more anybody

Cheers Denis

[teamidris]

Bad old forum ate my answer

Try again;
I assumed the higher torque was because the rear cap had more work to do with the seals. And that it could take the extra force as there was more metal at the back of the block.

As far as we knew fine threads apply more leverage than course. So standard torques on ARP studs apply more clamping force than the standard set up. And because the course thread isn't rotating in the aluminium they can stand a higher torque on top of that?

[spend]

Length of bolt in tension between thread & clamping surface + the torque is what gives the clamping force? Large & small journal as well as the rear caps all probably have slightly diffeerent values to result in the same compressive load at the bearing.