hehe yep swoop, sometimes those engineers just have a problem coming out and just saying it, they have to make it difficult.....
I wonder why, does the manual suggest to use a 90⁰ torque at the 5 step, instead of 51 ft. It will probably give the same torque...
also mentioned in the manual is to use a lubricant on the threads of the bolts and a nice caution message at the bottom of the paragraph about using an angle wrench service tool or protractor to make sure you get the 90-92 deg exact. Do not estimate the angle. So we can safely assume that they know the last torque value achieved on this last step, they just simply dont bother to just say what it is? A wild guess it would be around 51 ft-lbs? ;o) Yet another note above the caution about the angle wrench stating 51 ft-lbs can be used in step 5 as shown in the diagram figure for service.
Carlos, I expect that 90 degrees should put the final torque value very close to the 68.6 Newton meters attained in Step2.
Consider that the head gasket has already been "squashed out" significantly in the earlier Steps 1 & 2 and that means that very little (if any) additional flattening and spreading of the gasket will occur in the re-tighten process.
Usually if the bolts are deemed as "Torque To Yield" type fasteners the OEM mandates new bolts be used in head and/or gasket replacement.
I do not see Nissan making bold statements in the manual to use new bolts every time.
My position on that is to replace bolts that show any pitting or rust/corrosion or other obvious defects but reuse them if they pass inspection.
Bolts labeled as Torque To Yield get replaced without even considering them for reuse.
By the way, Steps 3, 4, & 5 are actually supposed to be done AFTER running the engine to operating temperature and then allowing it to cool. But we don't and I actually think very few people bother to do that.
Thanks, L1ftmech, this is more or less the same procedure that we use in Mitsubishi 4G64. However, in 4G64 we repeat step 4 twice (90 ⁰ and then another 90⁰).
Don't You think that 23.52 N.m + 90⁰ is a small torque?
Should we replace the head bolts every time we replace gasket?
Beware! The 90 to 92 value given in step 5 IS NOT a torque wrench value, it is an angular value of 90 degrees to 92 degrees of arc using an angle measuring wrench or a common protractor.
The basic sequence for the tightening of the head bolts is as follows.
Oil the threads of the bolt and the underside of the cap of the bolt. Tighten bolts in sequence specified in manual.
Step 1, Tighten all head bolts to 19.6 to 23.52 Newton meters.
Step 2, Tighten all head bolts to 68.6 Newton meters.
Step 3, Loosen all head bolts completely.
Step 4, Tighten all head bolts to 19.6 to 23.52 Newton meters.
Step 5, Tighten all head bolts 90 to 92 degrees of arc from the position set in Step 4
This was paraphrased from the Nissan shop manual for K-21, K-25 engines.
Jplayer, could you give more details about this 5 steps of loosen and retorque?
connecting rod nuts:31.4-37.3N.m (3.2-3.81kg-m)
crankshaft main caps:83.4-93.2 N.m (8.51-9.51 kgf-m)
headbolts: 68.6 N.m (7.0kgf-m) with a max of 90 - 92 after breakin if performing a retightening
word of caution though
there is a special sequence to torquing down the head which requires you to torque to certain specs, loosen and retorque in stages. There are 5 steps to this process to insure you get a good even seal on the head and to help prevent warping.
You really should use the tightening sequence instructions in the service manual to save yourself some headaches.
main 65 ft. lbs.
rod 24
head 68