[Teddy]

Hi guys and gals,
I just discovered the secrets of a long lasting mystery that Royal Enfield keeps hidden from us.
For all of us who like it precise about tightening all fasteners on our beloved rig. By looking into my service manual of my Yamaha 70HP boat engine I discovered the torque value of the M8 x 1.25 drain bolt for the boat engine gearbox. My Yamaha engine and the drain bolt at the front of the RE engine both carry M8x1.25mm threads. Yamaha specifies 9 Nm on torque. 

I personally do not recommend to use copper washers under the drain bolts since they, during compression become case hardened and can embedd into the softer aluminum of the engine casing. My BMW I used to have all specified alu washers. On the large M14x5 mm drain bolt I use a alu washer (from China - not expensive for 20 pieces) and for the front drain M8x1.25 I use a fibre washer (as my Yamaha boat engine does too).
Cheers

[grey pegasus]

It is advisable to chosse a lower torque as the cast aluminum of the RE engine is of a lower quality compared to what other manufacturers use. The torque values you specified presuppose that the counterpart is made from a sturdy material and do not consider that at an RE it is not.
I never had problems with the oild drain threads as I use dowty washers and safety wiring to prevent the screws from coming loose.  Tighten the screws a little bit more than finger tight, attach the safety wiring (correctly !) and that's it.

[ozpacman]

I've never seen so many drain plugs and fasteners stripped since people became obsessed with using torque wrenches for everything. They're plugs. They don't actually hold anything. Nip them up by hand and you won't have a problem.   

[grey pegasus]

I've never seen so many drain plugs and fasteners stripped since people became obsessed with using torque wrenches for everything. They're plugs. They don't actually hold anything. Nip them up by hand and you won't have a problem.

That is not quite the case. Some time ago, the oil drain plug of my Yamaha SR 500  (like the RE 500 a single cylinder) came loose by engine vibrations and I lost it during a ride without getting it aware.  The indication that something was wrong was a loud bang and the engine stopped working due to the lack of oil and some internal damage.
Therefore, there is a good reason for tightening the drain plugs with a specific torque or having other measures preventing the drain plugs from coming loose.
 

[gizzo]

That is not quite the case. Some time ago, the oil drain plug of my Yamaha SR 500  (like the RE 500 a single cylinder) came loose by engine vibrations and I lost it during a ride without getting it aware.  The indication that something was wrong was a loud bang and the engine stopped working due to the lack of oil and some internal damage.
Therefore, there is a good reason for tightening the drain plugs with a specific torque or having other measures preventing the drain plugs from coming loose.

You sure you didn't leave it loose by mistake? 

[Adrian II]

I'm with ozpacman on this. Still, it sometimes works in your favor, as I was donated a set of Electra-X crankcases where their owner had reached for his torque wrench and THIS happened. I advised him to throw it away.



In this example the casting could be reclaimed without welding, as the threaded hole for the banjo bolt went went deep, I got away with trimming the alloy back to the base of the crack.

A.

[grey pegasus]

There is nothing wrong with tightening screws with a torque wrench if done correctly.

It depends on the material of the screw and the material of the counterpart into which the screw is screwed. Most of the time, the torques are given in tables for steel, whereby one must of course distinguish between the information for the different grades (5.4, 8.8, 10.6, 12.8 etc.). Different numbers apply to stainless steel - and of course all the more to aluminum alloys, and you also have to distinguish between coarse and fine threads. So if you tighten screws in aluminum with torque values ​​for steel, you shouldn't be surprised what happens. At Royal Enfield, because of the poor quality of the cast aluminum, I would also reduce the special values ​​for aluminum again. So the problem is not generally in the use of a torque wrench, but in the wrong use in combination with inferior material from the motor housing. The problem is not the torque wrench, but what is in front of it.

By the way: Some screws on the C5 are labeled 8.8, but I have already torn off one with a torque that is specified for screws with the designation 5.4. Obviously, Royal Enfield doesn't take it too seriously when it comes to screw quality either, which fits in well with the overall picture.

About my lost oil drain plug: The motorcycle was in a specialist workshop for an engine overhaul, where the oil was also changed. Two days later I lost the oil drain plug. The use of a torque wrench (in this specialist workshop!) Would have prevented another engine overhaul.

[grey pegasus]

For all that are interesting in correct safety wiring you may have a look in Section  7. SAFETYING  of the  Advisory Circular AC 43.13.

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43.13-1B_w-chg1.pdf

All information inside this publication is very interesting for people busy in repair and maintenance environments, even Royal Enfields do not fly under normal conditions.

[Teddy]

Hi grey pegasus,
working as design mechanical engineer in the field of machines and components for 30 plus years I have a nifty little program on hand that works out the percentage of yield strength of the bolt used against the torque applied. It gives you an indication of the stresses in the alu cast threads of the housing. I tend to agree with you that the aluminum housings of a Yamaha engine might be better strength wise than the ones from RE.
I came up with the following:
Our M8x1.25 drain bolt at the front of the housing reaches at 9Nm (thread lubricated from the old oil, assuming 8.8 quality) 32% of yield strength.
In comparison the M6x1 bolts holding the oil filter cover RE says 6Nm (again thread lubricated, and assuming 8.8 quality) reached 50% yield strength.
The stresses of the oil filter cover threads in the alu of the housing are higher than the ones from the larger M8 bolt.
This morning I removed the M8 front bolt, placed a fibre washer under it and torqued it up to exact 9Nm. I a couple of weeks I will have to replace the oil of the engine and will let you know if the M8 thread in the housing is still there where it belongs.

[Richard230]

On both of my BMW's the drain plug torque specification is 42Nm. That level of tightness kind of creeps me out and I usually use less. Plus, I bet that torque specification is for a dry plug and when do you get to insert a drain plug into a crankcase thread that is not already well lubed - or will be as soon as you clean it off and then try to screw in the plug? No matter how fast you are, any remaining drop of oil in the sump will jump right onto those threads before you can insert your clean and dry plug. 

[Mad4Bullets]

Early on, I stripped out one of the two female threaded holes in the crankcase for mounting the mesh oil strainer cap, and did so quite handily with a properly calibrated torque wrench, with the best of intentions.  One of the more depressing events in my otherwise blissful C5 ownership. I've since installed threaded inserts in both holes, and now I hand-tighten by feel only. As for the other two oil drain plugs, I always anneal the copper gaskets and hand-tighten both plugs by feel as well. I've developed a feel for it, which is honestly far more satisfying than that sinking feeling you get when your threads unexpectedly give way - even when using a torque wrench. To each their own I say.

[grey pegasus]

Hi Teddy,
I am an engineer in development and repair branch myself and made a lot of improvements to my Classic 500 after I got it new from a RE dealer.
My thought was to buy a new bike to ride and not to have to spent a lot of time with repairing and modifications, but the opposite happened. You may find some topics elsewhere in this forum showing my modifications. 
It looked like a never ending project to get my Classic 500 to an acceptable quality level as the factory quality was too bad for a 2017 bike and the quality was very variable. So I decided to end this adventure and sold my bike for a price higher than I had to pay at the dealer when it was new.  I think, I got off without losses. All the time I spent in this project was not paid, of course, but this was for fun.
Thanks for your offer sharing your knowledge with me in future, but I am out of business now with a different view of Royal Enfields.

[fressko]

Torque wrench is how I managed to strip the threads on my old Honda.
Since then I only use it for major torque such as rear axle bolt.
What i do is finger tight then up to 1 tenth of a turn. Striping the oil drain threads is a PITA.

[GBT]

Torque wrench is how I managed to strip the threads on my old Honda.
Since then I only use it for major torque such as rear axle bolt.
What i do is finger tight then up to 1 tenth of a turn. Striping the oil drain threads is a PITA.

I agree. When I started spannering nearly sixty years ago I had never heard of a torque wrench, and so I learned to tighten nuts and bolts by feel. I stripped one or two of course, but I was young and still had a lot to learn. Although I have a torque wrench now, I really don't trust it, especially with small thread sizes. It clicks when the torque setting is reached, and at that point I always think it's just gone and stripped the thread. It's just the way it works, so I prefer not to use it.
When I changed the engine oil in my C5 recently I noticed that the large drain plug (M14 x 1.25) only has roughly four threads in engagement, even though there appear to be nine or ten threads in the crankcase. The M8 drain plug at the front has eight or nine threads in engagement.
So which one is more likely to strip? If I were to use a torque wrench, the M14 thread would have a higher torque setting than the M8 thread, and my guess is that the M14 thread in the crankcase would strip quite easily, given the questionable quality of the crankcase material. So I may search for an M14 x 1.25 magnetic drain plug with more threads on it, just for peace of mind.
Meanwhile, I did what you did and finger-tightened the two drain plugs and then nipped them up a touch. Not very technical, but these aren't F-35 jet fighters. I suppose it would be possible to drill the heads of the drain plugs and lock wire them if they were likely to unscrew themselves in service. I have heard of it happening, but guess that it was vibration-related. At the speeds I ride at, it shouldn't be an issue. I don't plan to enter my bike in the TT races.
If every road in the country was littered with Royal Enfield drain plugs I think we would have heard about it by now.

[Stevie Mac]

Changed the oil in my C5 recently removed M14X1.25, threads came out with the plug .  As above noticed the plug itself has very few threads & the crankcase is threaded though its entire length.  Unfortunatley at the time I had no option but to try & replace the plug.  Fortunatley it caught the last few threads & has remained intact since.  Have purchased a thread repair kit (helicoil) but was wondering if anyone can suggest an alternative or longer drain plug.  I mean there is plenty of good thread left in the crankcase, a bit reluctant to start drilling & tapping if an alternative exists.