MK 111 engine to cradle bolts .

ludwig said:
In critical applications where vibration is involved (drive shafts, wheel lugs..) always a finer thread.
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I take your point in increasing resistance to loosening under vibration compared to a coarse thread bolt. This is due to their lower helix angle, which makes them less prone to backing off when subjected to dynamic loads (more work energy required).
Pitch of UNF 3/8 is 1.058 mm and the pitch of an M10 bolt should be no greater. I don't know how susceptible self-lock nuts are to loosening their position? To increase resistance of the nut backing off, one could provide a conical bolt head and seat connection, similar to wheel bolts.

- Knut
 
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SteveBorland said:
Any links to where such bolts can be sourced? I've had no luck so far...
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Buy overlong M10 bolts where the unthreaded section is the length of a Cradle bolt, cut it to length and cut a 1.0mm pitch thread.

www.ebay.co.uk

Metric Split Die Threading Tool Thread Cutter 38mm Tungsten Steel M6 - M18 | eBay UK

Total width of the die 38mm so suitable for 38mm die holders (this is a lot larger than the majority so suitable if a bit more leverage is need). Manufactured from tungsten steel for strength and durability.
www.ebay.co.uk
 
SteveBorland said:
Any links to where such bolts can be sourced? I've had no luck so far...
Click to expand...
Purchase longer 10mm bolts (i got some off ebay 180mm long, making sure they are 8.8 grade ) Using these bolts you can then shorten them to 125- 130mm and cut a 10 mm thread (either leave it 1.5mm pitch or go finer 1.25mm or 1mm) You could turn them down and cut a 3/8 UNF thread and make it look original. Leave the plain shank 97mm long, 95mm minimum. You will have to ream the top rear most hole in the case as the 10mm bolt won't go through the hollow dowel.
Long bolts are a great source of high tensile steel, useful for all sorts of stuff, but you have to know what grade material the bolt is made from.
Metric makes that a bit easier than imperial.
 
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SteveBorland said:
Any links to where such bolts can be sourced? I've had no luck so far...
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I used to buy excellent quality bolts, nuts, washers & spacers, including satin chrome, from Custom Fasteners in Newtown, Wales.
They seem to have been bought out by a motorsports group.
I've emailed them to see if they still sell fasteners.
I'll let you know.
Cheers
 
baz said:
A finer pitch gives and maintains a greater clamping force than a coarser thread
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Yes, for the same torque, there is a slight increase in clamping force for the fine pitch vs. coarser pitch. Typical values for M10 threads (dry) preloaded at 50 Nm are 21 kN for M10 x1.5 mm and 23 kN for M10x1.0 mm . That's 10% and not insignificant.
As for maintaining the clamping force, the picture is far from clear. Measured over a fixed engagement length, the theoretical contact area is almost identical (348 mm2 vs. 360 mm2 for 1.5 vs. 1.0 mm pitch, 10 mm engagement assumed). However, load distribution is more a matter of number of threads, and here the coarse thread wins hands down (259 mm2 vs. 173 mm2 for 5 loadbearing threads, that's a ratio of 1.5). In a bolt/nut connection, the loadbearing is exponential (first thead carries way more load than the last thread).

- Knut
 
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I may remember wrong, but I think @mdt-son started the 10mm bolt thing a while back.

Didn't understand the point then, don't now. If the idea is to get a tighter fit between the bolts and cradle holes and bolts and through holes in the engine, on the surface it makes sense. However, getting those holes all in the exact location for a tight slip fit seems hard to me. If only one bolt were being changed to act as a location "dowel" it would make more sense to me, but I wouldn't bother.

It's already a struggle in many cases to get the bolts out - can't imagine if they were tighter in the holes!

Also, having to have metric tools to work vintage British motorcycles would put me off. I was forced a while back to buy all the tools needed to work on an ARP equipped bike - what a PITA and expense that was.

So, please enlighten me on the point.
 
marshg246 said:
I may remember wrong, but I think @mdt-son started the 10mm bolt thing a while back.

Didn't understand the point then, don't now. If the idea is to get a tighter fit between the bolts and cradle holes and bolts and through holes in the engine, on the surface it makes sense. However, getting those holes all in the exact location for a tight slip fit seems hard to me. If only one bolt were being changed to act as a location "dowel" it would make more sense to me, but I wouldn't bother.

It's already a struggle in many cases to get the bolts out - can't imagine if they were tighter in the holes!

Also, having to have metric tools to work vintage British motorcycles would put me off. I was forced a while back to buy all the tools needed to work on an ARP equipped bike - what a PITA and expense that was.

So, please enlighten me on the point.
Click to expand...
Greg
Have a look at a Mk3 inner primary case where the g/box mainshaft goes through the oil seal, I have seen loads of these with evidence that the shaft has been rubbing the side of the hole in the alloy. This means the engine & g/box are not held in place properly and effectively are just moving about in the cradle. The engine, cradle, and g/box are all clearance holes. Its no wonder the shaft rubs the case. Using 10mm bolts/studs helps counteract this unwanted movement. Going one better is to get fitted studs/bolts for the g/box to cradle.
Corrosion is usually the cause for engine bolts to be stuck, the front mount is especially prone to this. Grease the bolts/studs on fitting and they are no problem to remove.
 
marshg246 said:
However, getting those holes all in the exact location for a tight slip fit seems hard to me.
Click to expand...

CAD and CNC machining.

marshg246 said:
Also, having to have metric tools to work vintage British motorcycles would put me off.
Click to expand...
Metric dimensions for M10 bolt heads and nuts are larger than the corresponding 3/8" UNF dimensions. Thus, no problem milling the head and nut smaller for imperial tools, should one wish.

For instance,
3/8" UNF nuts according to ASME B18.2.2: A/F 14.05 --- 14.32 mm & A/C 15.57 --- 16.33 mm
M10 nuts according to DIN 934: A/F 15.70 ---16.00 mm & A/C 17.80 --- 18.48 mm

- Knut
 
The RGM bolts look like a better engineering solution to me. Fitting metric bolts to Brit bikes is wrong as it means having to use two different sets of spanners, & is a pet hate of mine. I will only use metric if I'm fitting a part from a modern bike, such as a brake caliper. Also, reaming engine mounting holes out to 10mm & fitting metric bolts won't leave you any better off, as commercially available bolts will usually be between 0.002" & 0.004" down on nominal.
 
Matchless said:
The RGM bolts look like a better engineering solution to me. Fitting metric bolts to Brit bikes is wrong as it means having to use two different sets of spanners, & is a pet hate of mine. I will only use metric if I'm fitting a part from a modern bike, such as a brake caliper. Also, reaming engine mounting holes out to 10mm & fitting metric bolts won't leave you any better off, as commercially available bolts will usually be between 0.002" & 0.004" down on nominal.
Click to expand...
You must hate your commando as you already use two different sets of spanners Whitworth and A/F
Using an expanding reamer, can size holes exactly. Only needed on the top rear most hole (coz of the hollow dowel) A 10mm drill will do.
What ever bolts you use, the plain (unthreaded portion) section needs to span the cradle so needs to be 95-97mm long. Having a load bearing bolt take a shear load on its thread is wrong. The thread will wear into the cradle.
The RGM bolts are no better than the std ones with the threaded section too long and a sloppy fit in the holes.
 
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