Stripped threads in casing for drain plug

[sime66]

I hope I'm not making a meal of this, but the more I think about it, the more important it seems that I sort this out properly; although it isn’t leaking whilst standing parked-up, it could come out at any time whilst riding and cause untold damage, so I’ve been looking into tapping an M10 thread, which is another little engineering job that I’ve never tackled before, but I really need to get right if I go ahead with it. I’ve done a bit of reading today, and watched a couple of how-to videos on YouTube:
· I see there are three types of tap, and I think I need a plug type, rather than a taper?
· Whether I tap it with the casings split (but in the frame, which seems most sensible), or with the casings together, there seems very little room between the inside of the casing and the gears, so I’m not sure about how to be sure I’m not fouling the gears when cutting the thread. I can measure the M8 bolt, but the first bit of the tap doesn't cut a thread and seems to need to pass through.
· I can’t see that it is sensible to do it with the casings together anyway because I don’t want to leave any swarf in the freshly cleaned out engine either, or am I being overcautious?
· I see various thread pitches, I don’t now what the pitch on the M8 for the standard drain plug is, so I’m not sure whether I need a 1.5mm or a 1.25mm, or whether it doesn’t matter as long as tap and bolt are the same pitch. i imagine a finer pitch will seal better?

I’ve only really got Ebay to look at available stuff, although I won’t necessarily buy it there when I get to do it, but here’s links to the sort of thing that I think I need:

www.ebay.co.uk/itm/321348859957
This looks like it might need cutting down to length, or would it be OK to just get a short bolt of the right pitch and cut it to length?

www.ebay.co.uk/itm/160930913406
I’m not sure if you just use the one you need, or use the taper first then the plug?

www.ebay.co.uk/itm/190639639164

Am I looking at the right bits? I really would appreciate any pointers to get me going in the right direction with this. I think I’d be foolish to ignore the stripped plug threads in the casing, but I really don’t want to make things worse by doing it wrong.

[mickymidas]

I had the same problem ...the way I tackled it was , split the casings , so you can see the drain hole , then filled the hole with some chemical metal stuff. When this has gone off properly ,drill & re-tap the hole to original thread so you can use a standard drain plug bolt .
Thread measuring tools are available from loads of places .
When I replaced the plug I used Loctite thread sealer as a extra precaution.

Hope this is a bit of help , Mick

[henri]

with the casings split mickys way is the best/easiest solution without any engineering help . i'd use jb weld rather than chemmy metal ,as thats whats reccommended by the smallie crowd when theve overdone the dremmelling on cases. never slipped that bad myself so havent used it that way,have used it an chemmy metal for other jobs an prefer it as easyier to measure/mix right an it comes in different types,to match the materialbeing bonded.
an taps,the taper (first)tap is tapered so it can cut enuff thread to pull the full pitch part of its cutters into the job without stripping the thread as it goes .without the taper you will find it hard to start a clean thread ,a plug (bottoming) tap is for 1 job ,getting a fully formed thread very nearly to the bottom of a blind hole an needs a taper 1 first .
any new thread you cut should be of the rougher pitch not fine,as its into ali or jb/chemmy you need the larger tooth size so theres enough area on the side of thread bearing on the parent metal not to strip.fines only really used where vibration is a problem,an its not the thread that seals but the fibre washer .
from memory ,but will look in morning to check,not sure theres enough metal there to tap a m10 thread ,in past ive gone to imperial sizes when re-tapping stripped metric threads an vice versa ,as there inbetween each other .piaggio does the same for stripped barrel studs in cases an uses a whitworth thread .
but if bolt has stayed in an is sealing ,it should be ok ,if still worried stop every 10 miles an look ,or a little blob of chemmy metal will stop it coming loose ,cant remember did you use thread lock on it,or wind it in ptfe tape ,either way should stop it moving ,ride it,check it an build up some trust that it aint going to break soon , h

[vespasco]

Id probably wait until it starts to drip or you get too worried to ride it, keeping an eye on it. Then when you decide to, take off the flywheel case side with engine in the frame, tap to next size up, maybe even use 3/8" (approx 9.5mm)
You could also check out your kick start return mechanism
The thread pitch would very likely be 1.25mm for all 6,7,8 and the weird 9mm vespa bolts, then 1.5mm for the 10mm bolts....
The tapered taps are generally used as a 'starter/guide' for the main, plug tap.
Theres probably a specific loctite out there that may do the trick? Depending on how loose that bolt is.
If you go for liquid metal type repair make sure its nice n clean.

Edit - Henri, i didnt see your post when i started typing my reply on my tiny phone.

[sime66]

Thanks very much, between the three of you you've given me a very clear idea of what’s needed to do a proper fix. I’ve read your posts and cross-referenced it against what I can buy, and where:

(1st Step) I had thought a blob of something to stop it coming off might do as a temporary safety measure, especially as, as you say, it is actually holding, and because I’d definitely like to ride it for a bit before I split the casings in case there is anything else that needs doing, so a decent few rides, keeping an eye on it is what I’ll do. I’ll carry some oil, a spare plug and PTFE with me for a while, so I can bung one in to get me home if needed. (Going to do my clutch and have a better ride tomorrow anyway, so will go and get some JB Weld if I can find it locally).

At present it is a brand new plug, wrapped in PTFE, screwed into the damaged hole, which has a smear of Threadlock in it too. The reason I’m being cautious is when I was reading-up about it I found a photo of a bolt with aluminium coils of stripped thread wrapped around its own threads, and it looked like what I’d done to mine. I mean that the threads are damaged/stripped, whereas I might have given the impression that they were just worn. I’d be sick as a parrot if, after all the work, I lost my oil, seized-up, and had to start again.

(2nd Step) I understand the proper way to do the tapping now, and I’ve found a 3-piece M8 set, and will also treat myself to a new set of drill bits (both from UK Drills). I’ll fill the hole with JB Weld and do a proper job, back to standard M8 drain bolt (going up to 6.8mm drill and tapping in sequence). There was an M9 tap, but it seems sensible to keep it standard and remove as little as possible. I can split the casings and lay it on its side to do the job.

I’ve also taken note that the fibre washer is the seal, not the thread. (Doh! I will understand this engineering lark eventually)

I’m probably making a meal of it, but slow and steady served me well with the engine, and I don’t want to be worrying about this if I’ve got everything else sorted.

I don’t mind splitting the casings if I have to; I would have been surprised if I’d managed to avoid it. (You said I’d get the bug, Henri)


Thanks again; I've been thinking about that for a couple of days, and you've sorted me out in a couple of hours

[bryno]

On a mates smallframe I just tapped to an M8 and found a nice 'flange' bolt to fit and a red fibre washer out my bolt box, not a proper fix of course, but looks just fine

[sime66]

I saw flanged M8 bolts, which seemed like a good idea, but none short enough without cutting – I have measured a proper drain bolt and it’s 8mm of thread. I can use a proper drain bolt if I tap to M8, or I thought an M8x10mm with a washer to shorten the thread length a tad, and to seat the fibre washer, just as a spare to carry - can get a bag of them for the price of a drain plug bolt, so good spares. I’ve also got a 250ml HDPE seal-nozzle bottle to carry a change of oil, just in case I lose mine down the road, until I sort it.
It’s actually holding OK after a good bang round the lanes early today, and it is the clutch adjustment that’s now proving the trickiest top-niggle, so I had to stop messing about when traffic started up this morning, but more of that one later……
(I'll just say that my new back brake shoes work lovely, and our dustman used some very colourful language!)

[bryno]

I'd not worry about the exact size TBH, there is no real danager of a slightly longer bolt making contact with anything inside..

[henri]

sorry i promised to go look at px cases today an then got caught up in welding the missus's scoot ,but seems you have sussed it already without me , m8 is def best way to go ,but with ptfe an threadlock an not leaking sounds like it will hold long enuff for you to get some runs in .h

[sime66]

No worries H, we sort of agreed yesterday that M8 was a better plan.

Bryno,
I see from the photos that it sits in a recess under 2nd gear, not the 1st, so there is a bit more room than I thought. I’ll be splitting the casings when I do it anyway, so when I do it I’ll post a measurement for anyone who reads this later. I reckon I’ve got this pretty much got this sussed now, but am about to post a bit of a question about my clutch, which I reckon I’m going to end up stripping and resoaking, but I’m going to ask the audience first……….

(There's still only these couple of teething problems, so I'm well happy with it)

[bsr65]

the standard drain plug is 10mm long, I would use a 12mm long button cap allen screw and you will catch the last undamaged thread.

[sime66]

That possibly explains why my new (standard 10mm length?) drain plug is holding OK for now; after the offending, shorter (8mm measured) one did it's damage.
OK, after I did the damage
Thanks chaps, I reckon we've got this one covered for now.

[sime66]

Given the distinct possibility that I’ll have the clutch/gears sorted soon, and will be doing longer rides, and generally be back to hooliganising for a few hundred miles before my new-build oil change, I’ve been thinking about a little cage over the drain nut.
I’m thinking about this little wire to stop it turning, or at least stop it falling out altogether.
I've bought some J B Weld for the proper repair later, but I haven’t used it before, so I’m wondering if it would be suitable for a little blob either end to hold this in place, and whether this bit of wire seems like a good idea, or one to go straight in the bin? (The idea being that it isn’t the blob I’ll need to remove; just the wire).
My drain isn’t leaking, but I know most of the threads in the casing are gone, and I’d just like to be sure I’m not going to lose all my oil without warning.
Repairing the threads is a job that I will do, but will put off until I have the casings split if I can.
What do we reckon? (the wire with blobs, not the bolt).

[henri]

that will do it nicely so long as wire sits on bolt flats tight, for race/rally prep you drill through the bolt head an wirelock for safety , but drilling a bolt head is a tricky job and you'd need to remove it to do.as its in an not leaking its best left alone ,in case removing it hurts more thread,
with jb weld cleanliness of casing is crucial for it to work an stick/bond well, even if youve sanded small spots back to give it a rough surface you still have to solvent clean it .as ali is slightly porous an will absorb oil/petrol over time especially when warm like cases . either use cellulose thinners ,which at a tenner a pot is expensive when you only want a teaspoon full, or local chemist will sell you a small bottle of acetone ,its nail varnish remover,but ya need the pure stuff as varnish remover usually has stuff added like oils/perfume.
they might give you a funny look or ask what ya want it for ,as it is used by naughty boys/druggies for bad things ,i always say for cleaning a fiberglass repair or printed circuit board of flux residue,tho you'd think in brighton a guy buying nail varnish remover would not raise any eyebrows ,but them chemists are a conservative bunch who prob dont get out much.
so once again its a "clean it til its ready,then clean it again" moment ,follow the de-structions on the box to the letter an that plug wont be going anywhere ya dont want it too. ok, H

[vespasco]

Yeh why not?!
Go for it
Good idea
If it gives you a few more 100 miles/ until the next oil change then im sure it will help.
Its not doing any harm

[sime66]

Yuk!
That stuff is horrible to work with. I thought it went like a putty and I’d be able do two quick blobs; it sticks to everything and I made a right mess of it.
Too horrible for photos, I’ve got it away from the bolt head and I’ll clean it up later.
I was in two minds because it won’t be long before the oil change anyway, but that plan is aborted.
Yuk…………………….mutter…………………….

[henri]

yep,it is a bit runny the jb weld ,but it does do its stuff , an its 1 less thing to worry you an stop ya riding your scoot "just in case" , youve done the hard work so have earned some worry free rides/miles eh, h