[roby02]

Doing a rebuild on the ZD30
Discovered that the bottom block bolts must be stretch bolts as they are stretching
not letting me get them to torque settings
can these be bought anywhere ie repco ect or do i have to go direct to Nissan
Thanks

 

[Franky73]

Sorry mate. Maybe I'm just being a numpty, but what do you mean by bottom block bolts. Main bearing bolts, sump bolts? Which ones mate?
Catcha

 

[roby02]

yeah main bearings
book refers to it as lower block :headwall:

 

[Franky73]

Are you using a trust worthy torque wrench. I have reused main bearing bolts many times without an issue. They aren't like head bolts that are subjected to very high temps. Unless of course you are rebuilding due to it siezing.

When you say they won't let you get them up to touque, is it just because you don't want to tighten any more?

 

[roby02]

No they wouldn't torque down pulled bolts back out and they are stretched
also found another issue with only 20nm on main bolts crank wouldn't turn so its at the machine shop that bored the block to figure out why and to also replace all the lower block bolts

 

[roby02]

just waiting now for them to ring saying its all ready they are also installing the pistons for me at same time

 

[Franky73]

Did you get the right bearing shells for the mains. This all sound very odd. Can't really see how block bore machining could cause this. Anyway, keep us informed.

 

[nullack]

You sure someone didnt do something silly like lubricate the bolts and then torque them to the dry value? i.e. Yielding the bolts by stuff up? Im not seeing in the ESM these bolts are one use only mate

 

[nullack]

Here ya go mate, the ESM

 

[roby02]

Thanks guys
The bolts are the same as head bolts one use only
Did some research and there is a formula for reusing stretch bolts but its not advised to
Ill post a pic of how much at least one bolt stretched.
As for crank not turning im thinking that as the bolts were stretching instead of torqueing up
That the bottom block was getting distorted pulling crank out of align ( doesn't need to be much )
As the thrust bearings were slightly scored

 

[nullack]

Curious that the ESM only has the torque spanner on those bolts

If it were both one use and torque important, it would have the big X icon and the torque icon on it.

Whats the source that's saying its one use?

 

[suzaan]

Only use torque to yield once - Other wise they will be torque to fail.

 

[nullack]

Yeah Im not getting what Roby02 is saying on a few things. Yielding is when permanent deformation, so called plastic deformation, occurs where the elastic limits of the material have been exceeded. The part will elongate. Torque to yield bolts are engineered to yield to specified amounts and to still have enough strength/toughness/fatigue cycling to be suitable for the task. If you go again and re-yield it, the part will elongate beyond designed limits and be far less strong/tough/able to handle cyclic fatigue. There is no magic formula for fixing this. The bolt has to be remelted and remade to "fix" it for reuse.