Manifold allen bolts

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openroad

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When I unscrewed the manifold allen bolts, these were extremely difficult to remove and seems to have galled some with the aluminum threads. They don't really want to go back in much before binding, and I'm wary of screwing up the threads in the head. Are they a U.S. thread? I think I need to chase holes out with a tap, but want to do no harm. Mine are not plated, just black.

MIKE
 
Hey, we all have a learning curve. I did too, still do.

Actually, if you download the Walridge catalogue, towards the end with the hardware section, there is a nice chart of a whole bunch of different thread sizes. If you get a thread gauge, you can tell mostly what type of thread it is, but not always. It's handy to have a set of UNF and UNC nuts and bolts around to try different things in. Helped me.

Dave
69S
 
openroad said:
When I unscrewed the manifold allen bolts, these were extremely difficult to remove and seems to have galled some with the aluminum threads.
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It might actually be that they were replaced with BSW bolts which are identical in terms of pitch, major and minor dia but have a different thread angle. UNC is 60° and BSW is 55° - they simply don't match, however I'd expect a BSW bolt in an UNC "nut" to be rather loose but I might be mistaken on this.


Tim
 
Tintin said:
It might actually be that they were replaced with BSW bolts which are identical in terms of pitch, major and minor dia but have a different thread angle. UNC is 60° and BSW is 55° - they simply don't match, however I'd expect a BSW bolt in an UNC "nut" to be rather loose but I might be mistaken on this.
Click to expand...


Stainlessbits.com and the Norvil website both list the NM23412 (062536 '72-on) manifold allen screws as 5/16 -18 BSW!

http://stainlessbits.com/link12a.html
" 23412 SCREW BSW 5/16"x18x7/8" ALLEN
06-2536 SCREW BSW 5/16"x18 ALLEN INLET MANIFOLD"


http://www.norvilmotorcycle.co.uk/screw.htm

SCREW - CAP HEAD - 5/16" WHIT X 3/4" LONG (NM23412)
062536 SCREW - 5/16" WHIT X 1" LONG - SOCKET - FITS CARB MANIFOLD TO HEAD
 
So I guess the question is, if a UNC bolt has been run into those threads, then should it be chased with a UNC 5/16 tap since in this one instance the number of threads per inch is the same?
 
L.A.B. said:
Stainlessbits.com and the Norvil website both list the NM23412 (062536 '72-on) manifold allen screws as 5/16 -18 BSW!
Click to expand...

Funny thing is that I measured exactly this bolt yestersay evening in the process of getting an overview on all the threads Norton decided to put in the various engine parts now in my possession. I did this with verniers, a thread gauge for the TPI and a 55deg and a 60deg chisel as a gauge for the thread angle. Combine with the AN webshop, the stainless-list and Les E. succession list I managed to find out quite a few things.

One check I remember is that I put the Manifold bolts against the allen bolts from the handlebar retainer clip (being a chassis part the are UNC shouldn't they?) and it was clear that the thread angle was different - so IIRC what I measured for the manifold bolts should be BSW. However in the process I also found that the stainless list has some errors (it's a very nice tool nonetheless!) but I don't remember on which bolt that was.

A UNC bolt in a BSW nut would feel galled, so that might explain the OP's situation.


Tim
 
rvich said:
So I guess the question is, if a UNC bolt has been run into those threads, then should it be chased with a UNC 5/16 tap since in this one instance the number of threads per inch is the same?
Click to expand...

Perfect idea - as long as you remember not to use the factory-specified bolts there and tell the guy who'll buy that long forgotten old british motorsickle that you changed it .... :mrgreen:


Tim
 
Sounds to me like testing those bolts in a known nut is in order to be sure what they are. If you chase those threads with a UNC tap you better make some good notes in the back of your manual!

Russ
 
Tintin said:
L.A.B. said:
Stainlessbits.com and the Norvil website both list the NM23412 (062536 '72-on) manifold allen screws as 5/16 -18 BSW!
Click to expand...
One check I remember is that I put the Manifold bolts against the allen bolts from the handlebar retainer clip (being a chassis part the are UNC shouldn't they?) and it was clear that the thread angle was different - so IIRC what I measured for the manifold bolts should be BSW.
Click to expand...

I checked that again and I'm pretty sure is that what fits five of my six old heads is a BSW thread and not a UNC thread. One of the heads is an Atlas (the other end of the scale is an 850 head) so that should not be anything else than British anyway.

What I'm confused now is the Allen bolts from the different top yokes I also have: Only one - and following Murphy the one I used for cross checking - is UNC, the later ones are UNF and the Atlas has a BSF. I'd be tempted to believe that some *censored* ^h^h^h^beloved previous owner butchered that thing with what he had at hand.


Tim
 
I checked the old manifold allen screws from my 850 MkIII and they also appear to be Whitworth rather than UNC.
 
OK, OK, I stand corrected. I guess I butchered my manifold then, but the UNC Allens I put in it went in just fine, it may have been the PO had already done that, or I did that back when I didn't know the difference between BSW and UNC in the 70's.

Does that mean all the bolts on the engine are BSW? Even the timing cover bolts, the oil block bolt, the cheese headed screws in the crank?

Dave
69S
 
DogT said:
Does that mean all the bolts on the engine are BSW? Even the timing cover bolts, the oil block bolt, the cheese headed screws in the crank?
Click to expand...

The TC bolts are UNC - at least I couldn't screw in a 1/4" BSW in two cases yesterday. The oil block bolt is BSW, everything around and inside the crank is CEI - as the early cylinder block studs are - but I'm pretty sure that I measured BSF for the three head steady bolts.


Tim
 
DogT said:
OK, OK, I stand corrected. I guess I butchered my manifold then, but the UNC Allens I put in it went in just fine, it may have been the PO had already done that, or I did that back when I didn't know the difference between BSW and UNC in the 70's.
Click to expand...

Well, nothing's certain. And it can be difficult to tell UNC from Whitworth at times, especially as some fastener threads do not appear to have been manufactured all that accurately!


DogT said:
Does that mean all the bolts on the engine are BSW? Even the timing cover bolts, the oil block bolt, the cheese headed screws in the crank?
Click to expand...


It's more likely a pre-71 model Commando would have a higher proportion of British Standard (not necessarily "Whitworth") fasteners originally. For instance, the '69 model barrel base studs should be BSW x BSC (with BSC nuts) later they were changed to UNC x UNF.
 
It's '74 model, I'm the original owner and I don't remember ever changing the bolts out. I suppose it's possible. Some aluminum seems to have transferred to the threads on a couple bolts when I unscrewed them, one more than the others, and now it won't hardly go back in 1/3 of the way before it sticks. I'd like to chase it out, and was set to get tap and die set, but now am in a holding pattern, I guess. I'll try a UNC nut to see if glides on, or binds up.

MIKE
 
I've run the allen bolt thru a UNC nut, it goes on but does feel not as tight as a known UNC bolt. It's got a bit of give fore and aft. I can run a UNC 5/6 X 18 die over the allen bolts, but can't get a tap started into the head. I think it's not a UNC thread, but by now one hole is on the verge of being messed up. The other three are serviceable, the other one the bolt gets 1/2 inch into it then binds/stops. Maybe I should tap it to UNC to save time and money.
What do you think?


MIKE
 
openroad said:
Maybe I should tap it to UNC to save time and money.
Click to expand...

As I said: Do it - you just need to remember that you did should you reorder these bolts.


Tim
 
I would likely also tap it with a UNC. Same pitch, Major and minor dia's. Just the thread angle is different. And you're on the good side as the material comes out, it'll work nicely.
I check bolts with my optical comparator down in QC. Tells the tale pretty quickly.
I've seen a lot of British threads that were pretty sad. Seems the machinist was told to use the cutter long past the time to freshen it...
The pitch has generally been fine but the thread form has not always been the best.
 
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