Help with bolts

[ted655]

I guess I need a primer on bolt threads.
MM-fine or coarse, SAE-fine or coarse These I get. I thought my AQD40A would be metric, but on the head of an alternator bolt it has UNF stamped on it. I tried cleaning the threads with a M12-1.5 die. Close, but shaved the dia. down a bit.
I can buy a bolt, BUT I need to tap the block hole to clean the rust out. I don't want to wreak it, then I'm in big trouble.
What the heck IS a UNF & what tap/dies do I use? Thanks.

 

[whywhyzed]

Re: Help with bolts

Un....

 

[achris]

Re: Help with bolts

Sounds like you have a 1/2"-20tpi bolt. 1/2" is 12.7mm and 20tpi is 1.27mm thread pitch, which explains the close fit. Any tool shop should sell a UNF t&d set.

Chris.........

 

[JCF350]

Re: Help with bolts

The metrics really have no "coarse" or "fine" so you have to pay attention to the thread pitch on these, they are listed as the distance between the threads.

UNC (coarse) and UNF (fine) is more garbage from the SAE and ignores other thread pitches. They are listed as threads per inch.

 

[ted655]

Re: Help with bolts

I'm sorry, I know you are all trying to help. These posts are confusing to me. Like the blind men describing an elephant, you all have grabbed a different part.
I own 2 tap & die sets, 1 SAE & a metric. Both have coarse & fine,(1,5M-1.75M, you say potato, I say potato).===="Any tool shop should sell a UNF t&d set."====. So... I need a UNF tap set? ===="Unified National Fine - it's a fine SAE thread"=====. If UNF IS SAE fine, then why do U need a 3rd. tap set?
=="UNC (coarse) and UNF (fine) is more garbage from the SAE and ignores other thread pitches. They are listed as threads per inch."=====. Garbage? What does that mean to me? I have whatever Volvo built. I'm sorry if it's garbage. I'm just a USA boy, raised on SAE NC & NF, learning to convert or deal with MM. Now I find a UNF bolt in a Sweadish engine.
I'm REAL dense, UNF is SAE NF?OR UNF is SAE fine BUT not SAE NF & I need a 3rd set of taps & dies????? And Sweadish engines aren't metric OR USA SAE, but are sSAE UNF?
You see the confusion if I put all these posts together?
thanks, I just need to clean up a rusty hole on an old '84 Volvo diesel I/O.

 

[MikDee]

Re: Help with bolts

It has me confused as well Ted? Aside from my memory of the old British motorcycles like Triumph, & Norton, with an even different oddball thread (don't remember what it was called?) but, is this UNF thread really an SAE fine?

 

[whywhyzed]

Re: Help with bolts

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[rodbolt]

Re: Help with bolts

SAE, Sociaty of Automoyive Engineering, they set the standards for the bolt and the hardness.,UNF is simply that,a fine thread. however there are specs on the thread root rdius that we wont go into, UNC is a course thered, here again there are specs for various standards.
bolt,1/4x20 would be a thread with a 1/4" major diameter with a thread pitch of 20 threads per inch,1/4x28 would be a fine thread with a mjor od of 1/4" and 28 threads per inch.
metric sizes are similar, a 10mmx1.0 mm bolt will have a major OD of 10mm ,now is where it gets different. metric thread standards are still a 60* thread angle but now we are going to mease the thread from crest to crest in mm.
so a 10mmx1.0 mm would have a 10mm major dia and the thread pitch will be 1.0mm from thread crest to thread crest.
most any automotive shop,parts store and most tap and die sets have a thread pitch gauge in them.
its not hard to use. that and a 30 dollar set of dial clipers and you can check most ny bolt.
the thread pitch guage is a feeler guage looking thingy with teeth like a tiny comb.
me, I have wrung off,drilled and tapped about any thread size you can think of below about 3/4" including some of the old english Whitworth stuff.
as I was a machinist for years I forgot to much about threads and cutting them. however there is some good stuff on the net.

 

[ted655]

Re: Help with bolts

Ta Da! Thanks. So my 1/2" NF tap will clean the hole. As far as tensile strength, this bolt was stamped 88 or maybe 8.8. Now maybe someone will know why Volvo isn't metric bolted. Seems strange.
MikDee, I too had a Triumph and "the tool bag". I :"think" the bolts were BSP or something like that.

 

[rodbolt]

Re: Help with bolts

8.8 indicates its a metric bolt, the markings have to do with bolt strenth, SAE bolts are marked with dash lines on the head. stainless has its own hardness standards.
out of memory I cant be more specific.
but thats why its IMPERATIVE to correctly Identify the thread being serviced otherwise uing the improper tap and die will alter the the thread at a minimum to rendering the thread usless or breakage of the tap or die or all 3 at once.
almost everything manufactured outside the US now is metric,however not all. its why a set of calipers and a thread pitch guage is mandatory.
as I have done this for about 31 years I can usully look at a bolt and tell you its size, nuts are a bit harder but not impossible. the thread root depth on SAE stuff(UNF;UNC) is a lot deeper than on metric stuff.

 

[Don S]

Re: Help with bolts

Now maybe someone will know why Volvo isn't metric bolted. Seems strange.

Volvo used a metric bolt there, obviously some previous owner used a larger (1/2") bolt in. This would require drilling out the alternator also, as a 1/2" bolt would not go thru the holes of the bracket or the alternator.
Don't forget, that engine went out of production in 1985, lots can happen to a marine engine in 23 years when many different DIYers start working on them.

 

[ted655]

Re: Help with bolts

The alternator has no bracket there, it has a thick boss through which the bolt slides, on into the block. The bottom (tension) bolt has the usual long slot bracket.
It can't be metric & have the UNF on the head. Metric bolts have "M- what ever" stamped on them. (all I've seen anyway) Plus a metric die did not fit.
.
I'm not arguing about after market repairs BUT, in this case I think this engine is all original. The alternator was French, never off the engine. The fuel filter was Spanish, never replaced (It has Racor primarys that have been changed often). VERY low hours on this boat. It was a "grandma dock queen", rarely moved. Another thing, if a bigger bolt was used, why a "BUFO 88 UNF" I'd think a SAE, hash marked US bolt would have been grabbed and used. Overall appearance of engine is total OEM, bolt had a tad of OEM paint on it.
/
As for pitch gauge, it's too late. I tried using the M12-1.5 die FIRST. No accurate threads are left to check, not even dia., as the threads were "shaved" a bit.
BUT, I sure can't screw the block up. A bolt I can buy.
UNF is my clue & it is 1/2" bolt, or very close, as the 12M was a bit smaller going over the threads.

 

[rodbolt]

Re: Help with bolts

common thread sizes for the 12mm are 12x1.0,12mmx1.25 and 12mmx1.5.
myself, I would carefully measure the block threads, the bolt is cheap, screw up the threads in the block and the repir cn be aggrevating.
but the 8.8 will indicate its a metric thread.
://euler9.tripod.com/bolt-database/22.html
here is a link to a source, ya have to add the http back to it.
many many sources of thread information for both US and metric as well as british standard threads are avalible.
dont buy into the crap that metric is more accurate,its just more widely used and therefore to sell US stuff overseas or to import to the US the US corperations cut costs buy purchasing whats avalible.
I machined to many parts to both metric and inch standards for both oil field perforating and logging and aerospace to be fooled.

 

[JCF350]

Re: Help with bolts

actually, The SAE doesn't have their own threads- they just rate the tensile strength and give the strength grade system to a bolt.
All SAE graded bolts I've ever twisted had a UNC or UNF thread.

Some places stock their bolts as SAE thread (fine) or USS thread (coarse). di
A lot of places don't have a clue when I ask for a fastener by diameter, pitch and length

 

[whywhyzed]

Re: Help with bolts

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[JCF350]

Re: Help with bolts

I too had a Triumph and "the tool bag". I :"think" the bolts were BSP or something like that.

BSF - British Standard and I forget what the F stands for.

BSF and Whitworth are the same sizes just a different scale but with different thread pitch. In these systems all the bolt heads for given diameter are the same size ie: a 3/8 bolt will have one size wrench labeled as 3/8 even though the hex on the fastener will measure considerably larger. I bought just about the last BSF/Whitworth wrenches and sockets Snap on had back in 1976 took 6 months for them to round everything up from across the globe (I have learned that they started making them again or at least made another production run)

 

[achris]

Re: Help with bolts

British standard sizes... Here's where it gets interesting..

BSF British standard fine (55 degree). BSW - British standard Whitworth (also 55 degree). And as has already been mentioned the spanners were labeled for the bolt size, not the size across the flats (which it where we get the term 'AF' from, across flats). But, during WWII the British realised that the amount of metal being used in the heads of the bolts was excessive (if you have ever seem a pre WWII BSW or BSF bolt you'll know what I'm talking about, the heads were very big), so they reduced the head size to save metal. That's all well and good but now a true BSW spanner doesn't fit the size bolt it's marked for!

BSP is a pipe thread, a tapered one at that... BSP - British standard pipe. BSPP - British standard parallel pipe.

Shall we start on BA sizes, ANC and ANF too?

Chris................

 

[Dshow]

Re: Help with bolts

I don't mean to highjack this thread, but I like Ted's quote at the end of his messages... So much so, I sent a copy to my wife... Her comment was, "That may be so, but they usually don't have a problem until a man starts F!@#'n with them"

 

[ted655]

Re: Help with bolts

===="Shall we start on BA sizes, ANC and ANF too? "=====
Hell NO! I already have a headache.
.
I went (75 mi. round trip) to "the bolt guy". He took the bolt, looked at it, said it was a 7/16 fine thread. Tomorrow I'll go see. Asked about the discrepency of markings, he said that the new global economy has destroyed most rules. He has seen metrics with hash marks, UNF with metric hardness numbers. "Quit looking at the heads", "That s%^t is ALL out the window".
SO... I have a 7/16 fine tap. I guess 'll see if he is correct. There are always Helicoils. I can't go up in size because the boss on the alternator rides on the shank of the bolt to pivot for belt tension.
.
My wife agrees with your wife. They are wrong of coarse!

 

[achris]

Re: Help with bolts

7/16" UNF has 20 threads per inch.

Have a look at this table, it may help you....

http://www.engineershandbook.com/Tables/uncunfthreadsperinch.htm

It's not a commercial link (I couldn't see anywhere they were trying to sell me anything) so the mods shouldn't get angry at me (again)

Chris............