factory nuts and bolt strength

850commando · Apr 9, 2015

what would the original fasteners provided to hold the engine together have been rated for ultimate,tensile and yield strength? comparable to grade 5 or grade 8, more than or less than?

acotrel · Apr 9, 2015

Are you talking about conrod bolts, head studs or the bolts that hold the engine in the engine plates ? Those Unbrako cap screws have Ultimate Tensile Strength of about 90 Tons per square inch, The rod bolts would probably be about 10 TSI less. I believe head studs would be about 60 TSI and the engine bolts about 50 TSI.

gjr · Apr 10, 2015

I would use grade 5 for the through bolts in the engine plates. The factory bolts don't seem as hard as grade 8 (which can be brittle) and they are harder than grade 2. The bolts, studs, and nuts used in assembling the engine are Whitworth (26 tpi).

Greg

Rohan · Apr 10, 2015

gjr said:
The bolts, studs, and nuts used in assembling the engine are Whitworth (26 tpi).

The bolts, studs and nuts used in assembling the engine are Cycle Thread 26 tpi = Whitworth doesn't come into it.

Cycle Thread and Whitworth are 2 completely different thread/fastener systems.

gjr · Apr 11, 2015

[quote="Rohan"The bolts, studs and nuts used in assembling the engine are Cycle Thread 26 tpi = Whitworth doesn't come into it.
Cycle Thread and Whitworth are 2 completely different thread/fastener systems.[/quote]

I'll have to try to remember that.

Leave it the English to make something as straight forward as a bolt complicated. Hmm, I suppose I should start looking for a set of Cycle wrenches.

Back to the original question - grade 5 fine thread

Greg

pierodn · Apr 11, 2015

Please,
I need to rethread the cylinder barrels for fix the head studs.
What is the correct thread for standard stud?
Thank you.
Piero

dave M · Apr 11, 2015

GJR, fortunately cycle thread nuts and bolts can be tightened using Whitworth Spanners.

Rohan · Apr 11, 2015

dave M said:
GJR, fortunately cycle thread nuts and bolts can be tightened using Whitworth Spanners.

Quite so. And even BS spanners (British Standard).
Some even come with BS stamped on them.

They'd even have had different size bolt heads, once-upon-a-time...
There's that BS stuff again....

And as anyone knows that has tried to jam coarse ole Whitworth threads into fine threaded Cycle Thread places,
that durned Whitworth stuff is VERY different to Cycle Thread stuff.

850commando · Apr 11, 2015

i need to crack the crank case open. most of the original fasteners have lost any zinc or cad plate and look like crap. I plan to replace all fasteners that i can with UNC/UNF. the local machine shop will make up new studs if wanted with thread forms more to our liking. I like the ARP stuff the CNW is selling but, don't want stainless steel.

therefore my original question. for some of the nuts, arp 12 point are available in high strength steel, so those would be the preferred replacements.

other stuff will just end up as grade 8 if i can't get a definitive answer

CanukNortonNut · Apr 11, 2015

850dunstall said:
i need to crack the crank case open. most of the original fasteners have lost any zinc or cad plate and look like crap. I plan to replace all fasteners that i can with UNC/UNF. the local machine shop will make up new studs if wanted with thread forms more to our liking. I like the ARP stuff the CNW is selling but, don't want stainless steel.

therefore my original question. for some of the nuts, arp 12 point are available in high strength steel, so those would be the preferred replacements.

other stuff will just end up as grade 8 if i can't get a definitive answer

I am using CNW stainless steel 12 point stuff and it works. Nothing has come loose yet. Call Matt he can give you his comments on the ARP bolt/nut kit.
Cheers,
Tom
CNN

Rohan · Apr 11, 2015

850dunstall said:
i need to crack the crank case open. most of the original fasteners have lost any zinc or cad plate and look like crap. I plan to replace all fasteners that i can with UNC/UNF.

other stuff will just end up as grade 8 if i can't get a definitive answer

Aco gave the definitive answer - and so most stuff outside the engine is not super strong.
Stick with UNF outside the engine, thats what it came with anyway.
Going stronger isn't going to hurt...

Inside the engine is mostly cycle thread. (unless its UNF, and stamped with the overlapping circles)
Changing to anything else isn't necessarily going to be an improvement.
Especially for future owners. Or you, when you forget....