Motor mounting

Went for a ride the other day and when I returned home I saw oil leaking from the bike. Upon further inspection it was determined that the oil was leaking from the inner primary gasket. It was easy to find the cause as the lower cradle/engine mounting bolt was snapped off and the middle bolt was loose. While dismantling the primary I also found that the chaincase steady stud was broken. Oh, and did I mention that my brand new right side silencer broke also? Enough with the crying and on with the repairs.

I ordered all brand new hardware and gaskets from Morris Place on Tuesday and received them today (Thursday). That is a quick delivery. I’m going to install everything tomorrow. The question I have is, should I use loctite on the threads? I’m thinking yes and blue. Any other tips or ideas? I’m going to take my silencer to my welder to see what he can do about welding it up. It broke perfectly at weld. We’ll see. After I get everything else put back together I would like to know if I’ll mess anything up with riding with just the headers with no silencers. I have read that you can burn up your exhaust valves if your headers are too short or too large of a diameter. Something about cold air hitting the valves ruining them. I didn’t completely understand it but it seems valid. Thoughts?

Thanks for all the help.

Which bolts are you asking about re loctite?

If it’s the 3 that secure th e primary to the crank case then yes.

But IMHO ALL other engine / cradle bolts, and nuts, that are accessible, should not be loctited, you should instead periodically check them for tightness and keep ‘em nipped up.

Loctite is glue. And glued on nuts can feel tight when they are not. Then things move around and that how studs can break and things generally go down hill…

Re the pipes, your bike will sound horrible if you run it on the headers only, you’ll also negatively effect performance and screw up the jetting.

I had the same on my RH silencer. I bought a replacement from RGM, which doesn't have that weld point. It was <£100. I don't like the fitting arrangement for the silencers. The headers must move more than the rubber silencer mounts will allow. But not many failures reported. I was tempted to leave the silencer to header clamp off, but thought it would leak, so put it on.

Fast Eddie said:

Which bolts are you asking about re loctite?

If it’s the 3 that secure th e primary to the crank case then yes.

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However, it's an 850 Mk3 so they are four studs (item 20) that also pass through the stator outrigger plate (18).

The Mk3 lower engine cradle bolt is (or should be) larger 3/8" diameter.

Mart UK said:

I had the same on my RH silencer. I bought a replacement from RGM, which doesn't have that weld point. It was <£100. I don't like the fitting arrangement for the silencers. The headers must move more than the rubber silencer mounts will allow. But not many failures reported. I was tempted to leave the silencer to header clamp off, but thought it would leak, so put it on.

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I don't use silencer clamps
Stopped using them years ago with no problems at all

Fast Eddie said:

But IMHO ALL other engine / cradle bolts, and nuts, that are accessible, should not be loctited, you should instead periodically check them for tightness and keep ‘em nipped up.

Loctite is glue. And glued on nuts can feel tight when they are not. Then things move around and that how studs can break and things generally go down hill…

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Interesting. How do owners rate those self-locking nuts fitted by the factory, e.g., 063024, which goes with both 3/8 bolts at the engine to cradle joint ?
Lock nuts of this type are supposed to be resistant to vibration and torque. Do they work as intended, or not?
If they require to be nipped up, I guess they will wear out. What is the life expectancy of those nuts, in terms of miles and age?

NV experimented with various nut locking methods, but if your statement is true, none seems to work properly.

How about replacing both washers #000010 (ID 3/8, 2 off per bolt) with heavy duty Belleville spring washers? Has anybody tried that, and what's your verdict?

- Knut

Nuts do not only need nipping up because they’re coming undone though Knut.

A fasteners job is to provide clamping force to two (or more) surfaces.

If anything on or between any of those surfaces (or the surfaces themselves) compresses, the fastener is no longer clamping correctly, ie it is loose.

Thick paint, powder coat, gasket joints, etc can all compress and thus render fasteners loose.

Personally, i love love love Nord-locks. Spensive tho. I think you can use them a couple times then the locking groves get rounded down

Mart UK said:

I had the same on my RH silencer. I bought a replacement from RGM, which doesn't have that weld point. It was <£100. I don't like the fitting arrangement for the silencers. The headers must move more than the rubber silencer mounts will allow. But not many failures reported. I was tempted to leave the silencer to header clamp off, but thought it would leak, so put it on.

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If you get an exhaust leak, you will often get a back-fire as you back-off. It can be very irritating. The exhaust system affects your jetting, if there is not enough back pressure, or too much extraction, you can start burning valves and pistons. My exhaust system is two into one and goes under the motor. So the two header pipes are equal length, and the tail pipe is the same length as a header pipe. The tail pipe has the ID to cope with the sum of the areas of the two header pipes. So the whole system can resonate without back pressure. For a road bike, the exhaust would be too loud. But it is very effective.

Hmmm this is an interesting one, i have previously (on not a Norton) tuned the pipes on a dyno by cutting the header pipes back or lengthening until i hit the sweet spot on the curve. Also i have run plenty of Harley's with straight through shorty pipes no, burnt valves or pistons. Many people suggest that back pressure is required to help extract the gases. Has anyone done some experimenting with exhaust length and silencers on a dyno, of course we know that Steve Maney and others would have done this for their systems but what about us average shed builders. We spend crazy dollars on engine and gearbox builds but the exhaust system often gets over looked. I am getting to the final stages of my 71 build and this is definitely on my mind. Any feedback would be appreciated.

Guessing here: Is your cradle power coated? If so and it was not properly masked (PITA) when coated, you better check those three nuts often as well as the two gearbox bolts. All the broken stuff you talked about tells me loose engine. I used to powder coat my cradles (in-house) but now I paint them. There is so much masking required and the re-masking and painting the bare spots that it's not worth the effort for something barely seen.

Before replacing I be looking at what caused the bolts to break in the first place, bad vibrations happening somewhere, I am still using all my original engine bolts and nut but I do replace spring washers when I remove them, but I now run with hard mounts now with the Featherbed frame but still with my original engine bolts and nuts with matching spring washers.
As for running straight through header pipes your bike will preform better with a decent set of tuned mufflers, they preform better with a bit of back pressure and you don't annoy the neighbours.

Ashley

ashman said:

Before replacing I be looking at what caused the bolts to break in the first place,

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Looking through Larry's rebuild thread I think they could be stainless mounting bolts instead of the originals that I believe were high-tensile.

One of the reasons I don't like SS bolts, worked with steel all my working life so do know a bit about nuts and bolts and where to use the right ones for the jobs.

L.A.B. said:

Looking through Larry's rebuild thread I think they could be stainless mounting bolts instead of the originals that I believe were high-tensile.

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You are correct about the stainless. I will be replacing all the stainless with the correct high-tensile bolts with new nuts and washers.

ashman said:

One of the reasons I don't like SS bolts, worked with steel all my working life so do know a bit about nuts and bolts and where to use the right ones for the jobs.

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But there's stainless and stainless (just like there's steel and steel).
As an example the stainless hardware from ARP is high strength - good stuff.
Some of the discussion around stainless seem to ignore that there's mild steel (240MPa) and there's 4140 (steel) (1100MPa).
Never heard of anyone saying "don't use steel" simply because they've fitted a low strength bolt that let them down.
Do your homework on what you're buying/installing.
Cheers

Stainless steel comes in many forms and grades.

ashman said:

Stainless steel comes in many forms and grades.

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Obviously I used the wrong grade of stainless. You live, you learn. Just wish it didn’t cost so much to learn!

Larry
with regard to welding the muffler bracket, make sure the welder uses a TIG with a stainless steel rod. The stainless will mix a little with the chrome of the muffler and being stainless it will not rust. I have seen many repairs with stainless welds on chrome steel that look as if original.
ando

Fast Eddie said:

Nuts do not only need nipping up because they’re coming undone though Knut.

A fasteners job is to provide clamping force to two (or more) surfaces.

If anything on or between any of those surfaces (or the surfaces themselves) compresses, the fastener is no longer clamping correctly, ie it is loose.

Thick paint, powder coat, gasket joints, etc can all compress and thus render fasteners loose.

Click to expand...

True, but is this scenario really applicable to the cranckcase/cradle connections of the Commando? I am assuming cradle has a thin layer of paint only. The crankcase joint should have a very thin smear of non-setting sealing compound. I understand the possibility of the compound flowing initially, but this flow will stop as pressure evens out (the compound does have compressive properties). The bolts are preloaded, right? So there is equilibrium between tensile force of the bolt(s) and compressive force(s) of the cradle lugs plus lugs at the crancase including the sealing compound layer. I can't see a reason for preload failure other than either nuts coming undone, or bolt material deforming by plasticity.

It's a fact that many so-called stainless bolts are cheap products made of AISI 304, which has limited staining properties actually. Looking at the stress strain curve at elevated temperatures (the bolts will heat up as crancase temperature rises - 75-85 deg C is to be expected - the stiffness gradient quickly approaches nil (0) as preload is increased beyond 400 MPa. Now, if the same preload is applied as for high-tensile bolts, say 60% of a bolt which yields at 800 MPa, the outcome will be a large plastic deformation and a diminishing preload. Repeated load cycles will result in a lasting elongation of the bolt. What happens when the preload is nil (0) is open to speculation. I guess the entire powerpack will twist and this could ultimately result in bolt rupture and damage to the crankcase lugs.

Reverting to my initial question, do owners nip up their engine studs and bolts regularly when high-tensile bolts are fitted? In my opinion, it shouldn't be necessary. If you do, do you replace the nyloc nuts regularly?

- Knut