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E: Engine Imperial or Metric - Pros and Cons

oexing

Well Known and Active Website User
VOC Member
No , I don´t have BSF spanners, have never seen the logic to look up files about bolt threads to know the type of hexagon and spanner. In metric world nobody cares about threads, you get your vernier onto the hexagon and see in same second what size of spanner you take - when you happen to deal with non-standard metric screws and in doubt about size of hexagon. On the sixties Jag there were mainly UNF so I got UNF spanners, no interest in waisting any penny in obsolete British tools. Why should I keep BSF or the like when you got in deep trouble in case of some repair on the road. You won´t find something fitting in any garage or supermarket within 500 miles here. Well - for that reason I can see the urge to have a monkey wrench on you 24 hours a day in certain countries . . . . .

Vic
 

Peter Holmes

Well Known and Active Website User
VOC Member
Yes, but those who use the inch were never limited to 1/1000" My long deceased ex father-in-law worked for De Havilland and then Rolls Royce in the aircraft industry, and I know for a fact they broke the thou down into far smaller increments, and I am sure on very accurate drawings also, don't forget Rolls Royce built the engines for Concorde, surely the Vincent of the skies, it might well be regarded as an outdated measurement today, but I would not denigrate it, some very fine work was produced using the thou.
 

Mike 40M

Well Known and Active Website User
VOC Member
Steve, you must have a very worn 13mm spanner if it fits on a 1/4W which nominally is 13.34mm.
Though I live in a metric country, I've noticed some advantages with UN or BS threads.
You don't need to use the vernier caliper to determine spanner size. You immediately can see the difference between 1/4W and 5/16W. In the metric world, you never know if it is 12 or 13. 16 or 17, 18 or 19 as they have changed standard a couple of times.
Though Norton and BSA in their infinite wisdom partly changed from Cycle threads to UN threads in the late sixties. The shield under the engine on my Victor Specials is fastened with two UNF screws and one Cycle thread bolt. Luckily our Vincents are not affected.
Another drawback with metric threads is that normal metric is rather coarse. Fine threads are difficult to find and varies a lot in pitch. Both UN and British Standard are defined in both coarse and fine.
I actually fitted Cycle thread screws on my sons Honda CBR600RR for a phone holder. It had two unthreaded holes in the fork top crown which had right diameter for tapping 5/16 BSC.
One thing I use metric sockets for on British bikes is Monobloc and Concentric main jets, where AMAL recommend 8mm.
 
Last edited:

Albervin

Well Known and Active Website User
VOC Member
A set of Metrinch sockets and spanners covers alloy Japanese, Euro and British bikes. No problems, no AF and never, ever rounding a hex screw head. We all know metric screws and bolts are way cheaper than imperial. We all know metric bearings are as cheap as chips. BUT I want a bike to ride as was designed by PEI and built by PCV. I have a Puch, Maico and BMW and they are very fine and well built machines with some occasionally very strange metric fasteners.
 

Keith Martin

Well Known and Active Website User
VOC Member
I am not smarter than the two Phils so we just try and put the bikes back together as they designed them.
I have a large collection of Snap On British wrenches and sockets and enjoy using them daily. Snap On has made many different ones that fit British fasteners for the aircraft industry over the years. The fit and feel of Snap On tools to me are the best in the industry. The thought of using a metric wrench on a Vincent sends shivers down my spine.
One of the worse things is seeing a restored bike here in the USA with all stainless steel USS coarse thread hardware they bought at the local hardware store. You know the extra large diameter washers with nylock nuts and the bolts have at least 8 threads protruding past the nuts because they only come standard lengths.
Sorry but I could not sleep at night knowing I tapped original Vincent cases to except metric hardware.
 

ericg

Well Known and Active Website User
VOC Member
I am not smarter than the two Phils so we just try and put the bikes back together as they designed them.
I have a large collection of Snap On British wrenches and sockets and enjoy using them daily. Snap On has made many different ones that fit British fasteners for the aircraft industry over the years. The fit and feel of Snap On tools to me are the best in the industry. The thought of using a metric wrench on a Vincent sends shivers down my spine.
One of the worse things is seeing a restored bike here in the USA with all stainless steel USS coarse thread hardware they bought at the local hardware store. You know the extra large diameter washers with nylock nuts and the bolts have at least 8 threads protruding past the nuts because they only come standard lengths.
Sorry but I could not sleep at night knowing I tapped original Vincent cases to except metric hardware.
Amen!
 

Peter Holmes

Well Known and Active Website User
VOC Member
Vic, Not quite on subject, but with all the many improvements that you have made to the Vincent motorcycle, have you ever considered it necessary to improve the locking of the C20 clutch nut other than the bent tang on the C45 spring or Loctite, I am thinking here of a proper engineering solution.
 

greg brillus

Well Known and Active Website User
VOC Member
Peter this problem is exactly the same as a loose output sprocket nut.........If the C 3 is moving on the input shaft splines then the C 20 nut will continue to periodically loosen itself..........I have just been through this exercise on a bike here and had to replace the C 3 with a new one........The C 20 nut should be done up quite tight as well, just as the output sprocket or ESA nuts should be done just the same.
 

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