stripped threads gearbox oil drain plug

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GandT
On the street
Posts: 11
Joined: Fri Nov 13, 2020 3:02 pm
Country: Ireland
Suzuki 2-Strokes: 74 GT250

stripped threads gearbox oil drain plug

Post by GandT »

Hi

I decided to change the gearbox oil for the first time - in my recently acquired 1974 GT250.
Well I am very sorry I did.

1 - The drain plug nearest the rear came out OK, but it had teflon tape on it and so did most of the threads in the case came out too, as I noticed when I examined the drained oil.
Has anyone repaired stripped sump drain threads on a GT250 or similar ???

If yes - could you point me to where to acquire the parts (I live in Ireland) and what technique you used, for I do not want to remove engine and certainly wish to avoid having to strip engine.

2 - The other drain plug bolt would not budge -so I decided not to force it, worried it too is damaged. Does anyone know how much oil would remain in the engine, if only the rearmost drain bolt is removed and the one nearest cutch is not removed ?
The strange thing is although most of the oil was drained - oil came out of the level screw hole when I removed it?? - seems daft with so little in gearbox ??

Thanks
G&T
Thanks
74 GT250 L
74 RD250 A
93 Honda C70 cub
02 Honda CB400SS (jap mkt)
dollydog
Yeah Man, the Interstate
Posts: 630
Joined: Fri Aug 11, 2017 7:09 am
Country: england
Suzuki 2-Strokes: several gt250 ramairs

Re: stripped threads gearbox oil drain plug

Post by dollydog »

don't know about the stripped threads, but would a helicoil go in? as for the oil coming out of the level plug, that's right and there's probably about 600cc of oil in the clutch cover [ask me how i know] if you want to empty the gearbox completely, put a pan under the clutch casing and take it off :D
cheers, dd.
p.s. if you drill the drainplug hole, when you've finished, put the new drainplug in and fill the gearbox with old oil, then take the drainplug out again. this will [hopefuly] flush any aluminium drillings that are in there. bit long winded, messy and fiddly, but worth doing. of course you'll have to take the clutch casing off again. one thing though: once it's all empty, refit the drainplug with a new copper washer. refit the clutch cover and MEASURE 1300cc of 20/50 out and pour it in. don't trust the oil level plug for the correct amount :D
p.p.s. yes, i've used common or garden 20/50 oil for the last 40 odd years and never had a problem. just change it every 4000 miles or so, it's plenty good enough for the gt250 :wink:
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.
karl pa
To the on ramp
Posts: 490
Joined: Sat Sep 05, 2015 3:14 pm
Country: us
Suzuki 2-Strokes: GT
Location: southeast pa

Re: stripped threads gearbox oil drain plug

Post by karl pa »

dollydog wrote: Sun Mar 28, 2021 12:26 pm but would a helicoil go in?
Had stripped threads on my GT500 drain plug. Local Suzuki shop put in helicoil, no problems since, been about 7 or 8 years now.
76 GT185
77 GT250
77 GT380
76 GT500
73 GT550
73 GT750
74 GT750
71 T250 scrambler
75 T500 cafe
dollydog
Yeah Man, the Interstate
Posts: 630
Joined: Fri Aug 11, 2017 7:09 am
Country: england
Suzuki 2-Strokes: several gt250 ramairs

Re: stripped threads gearbox oil drain plug

Post by dollydog »

i'm 99.9% sure the drain plug holes are the same size and thread as the spark plug holes. m14 x 1.25. i bought a spark plug helicoil set years ago and it's given me great service. the only thing i had to do was turn the shank of the drill down to 10mm, as it wouldn't fit in my electric drill. real easy job though :D
cheers, dd.
p.s. i've just checked and a gt250 drain plug screws straight into a spark plug hole :up:

what i bought:
https://www.ebay.co.uk/itm/Brand-New-15 ... SwRihgL9no
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.
dollydog
Yeah Man, the Interstate
Posts: 630
Joined: Fri Aug 11, 2017 7:09 am
Country: england
Suzuki 2-Strokes: several gt250 ramairs

Re: stripped threads gearbox oil drain plug

Post by dollydog »

should have added this to my last post, just in case. if you've never used helicoils before, make sure the top of the helicoil sits just BELOW the top of the threaded hole when you screw it in, otherwise the copper washer won't seal properly :D
cheers, dd.
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.
GandT
On the street
Posts: 11
Joined: Fri Nov 13, 2020 3:02 pm
Country: Ireland
Suzuki 2-Strokes: 74 GT250

Re: stripped threads gearbox oil drain plug

Post by GandT »

Thanks everyone for your input. Seems helicoil is the most practical solution.
I have seen couple of examples on Youtube etc. since posting - messy but doable.
I did eventually using a sharp knock to the Tbar wrench manage to remove the clutch drain plug too and that is a big relief.
At least now I can add the correct quantity of oil as suggested.
Thanks again :)
G&T
Thanks
74 GT250 L
74 RD250 A
93 Honda C70 cub
02 Honda CB400SS (jap mkt)
TOwenR
On the street
Posts: 17
Joined: Tue Sep 18, 2018 1:03 am
Country: USA- Connecticut
Suzuki 2-Strokes: GT 550 K, L, A and GT 750 L

Re: stripped threads gearbox oil drain plug

Post by TOwenR »

I would have first tried to chase the thread with the correct size rigid tap, which might have straightened out and repaired any cross stripped threads. Then I'd have wrapped the drain plug threads with teflon tape before re-installment. If this didn't work and there was still a leak, then I'd go with a helicoil. Just make sure you get the tang out. {piece of the insert that breaks off} I would imagine you wouldn't want that thing floating around inside your gearbox.

In any case, I would think that it would be a smart move to take off the clutch cover in order to make sure that there are no pieces of metal left over from either chasing the original threads, or drilling, tapping, and installing a helicoil.
karl pa
To the on ramp
Posts: 490
Joined: Sat Sep 05, 2015 3:14 pm
Country: us
Suzuki 2-Strokes: GT
Location: southeast pa

Re: stripped threads gearbox oil drain plug

Post by karl pa »

TOwenR wrote: Mon Jul 05, 2021 11:09 am I would have first tried to chase the thread with the correct size rigid tap, which might have straightened out and repaired any cross stripped threads. Then I'd have wrapped the drain plug threads with teflon tape before re-installment. If this didn't work and there was still a leak, then I'd go with a helicoil. Just make sure you get the tang out. {piece of the insert that breaks off} I would imagine you wouldn't want that thing floating around inside your gearbox.

In any case, I would think that it would be a smart move to take off the clutch cover in order to make sure that there are no pieces of metal left over from either chasing the original threads, or drilling, tapping, and installing a helicoil.
The last thing you want is the plug to come out when on a ride! When mine stripped, there was no way I was going to do anything but replace the threads with a helicoil or thread insert!
As for shavings, you coat the tap with grease to catch as much shavings as you can, you can flush transmission with diesel or oil to get remainder.
76 GT185
77 GT250
77 GT380
76 GT500
73 GT550
73 GT750
74 GT750
71 T250 scrambler
75 T500 cafe
TOwenR
On the street
Posts: 17
Joined: Tue Sep 18, 2018 1:03 am
Country: USA- Connecticut
Suzuki 2-Strokes: GT 550 K, L, A and GT 750 L

Re: stripped threads gearbox oil drain plug

Post by TOwenR »

karl pa wrote: Mon Jul 05, 2021 1:43 pm
TOwenR wrote: Mon Jul 05, 2021 11:09 am I would have first tried to chase the thread with the correct size rigid tap, which might have straightened out and repaired any cross stripped threads. Then I'd have wrapped the drain plug threads with teflon tape before re-installment. If this didn't work and there was still a leak, then I'd go with a helicoil. Just make sure you get the tang out. {piece of the insert that breaks off} I would imagine you wouldn't want that thing floating around inside your gearbox.

In any case, I would think that it would be a smart move to take off the clutch cover in order to make sure that there are no pieces of metal left over from either chasing the original threads, or drilling, tapping, and installing a helicoil.
The last thing you want is the plug to come out when on a ride! When mine stripped, there was no way I was going to do anything but replace the threads with a helicoil or thread insert!
As for shavings, you coat the tap with grease to catch as much shavings as you can, you can flush transmission with diesel or oil to get remainder.

I suppose application of a loctite compound could insure that the drain plug will not loosen and that there wont be any leak. And who is to say that just because there's a helicoil insert that the drain plug wont loosen? {especialy if it was installed by someone with no prior experience in their usage}

Having 25 years of a broad range of aerospace, marine, department of defense machining experience, using all manner of lathes, mills, surface grinders, honing, wire and sinker EDM, etc... I've certainly come across many a chef with their own recipe on how best to season the soup.
karl pa
To the on ramp
Posts: 490
Joined: Sat Sep 05, 2015 3:14 pm
Country: us
Suzuki 2-Strokes: GT
Location: southeast pa

Re: stripped threads gearbox oil drain plug

Post by karl pa »

:wth:
76 GT185
77 GT250
77 GT380
76 GT500
73 GT550
73 GT750
74 GT750
71 T250 scrambler
75 T500 cafe
TOwenR
On the street
Posts: 17
Joined: Tue Sep 18, 2018 1:03 am
Country: USA- Connecticut
Suzuki 2-Strokes: GT 550 K, L, A and GT 750 L

Re: stripped threads gearbox oil drain plug

Post by TOwenR »

karl pa wrote: Mon Jul 05, 2021 5:46 pm My experience is once threads strip,teflon tape will not work, teflon tape is for sealing threads not fixing stripped threads. I tried it many times and can tell you I would not attempt it on something as important as the drain plug
My experience is that the existing thread might best be chased with the rigid tap of its original size, and then inspected to see if it is acceptable in that state.

When you install a helicoil thread repair insert, you are first drilling to a minor diameter of the tap that is called for, then using the tap, then installing the insert, followed by knocking out the tang. Ideally this work should be performed with as perpendicular and stable a toolholder as available.

Myself, I'd first try the suitable rigid tap and then inspect the thread. And I would most definitely remove that clutch/gearbox cover to make sure that any chips are removed.


But...if you want to use handtools and lie under a bike at whatever angle you can to get at the drain hole, drill, tap, install a thread repair insert, pour some diesel into the gearbox, drain it, and hope for the best, then by all means do it your way.
karl pa
To the on ramp
Posts: 490
Joined: Sat Sep 05, 2015 3:14 pm
Country: us
Suzuki 2-Strokes: GT
Location: southeast pa

Re: stripped threads gearbox oil drain plug

Post by karl pa »

When drilling,most chips are pulled out of the hole, when tapping, most chips are pushed inward, that is why you coat the tap with grease. I didn't feel comfortable doing the job so I had the dealer do it.
On the 500 and I believe the 250, if you remove the clutch cover, you still have no access to the transmission cavity. Your only options are to try and flush out, or split the cases!
I am not trying to be confrontational with you, but again I must state the importance of the drain plug, If it comes out while you are riding, the oil is going under the rear tire and can be deadly.
76 GT185
77 GT250
77 GT380
76 GT500
73 GT550
73 GT750
74 GT750
71 T250 scrambler
75 T500 cafe
TOwenR
On the street
Posts: 17
Joined: Tue Sep 18, 2018 1:03 am
Country: USA- Connecticut
Suzuki 2-Strokes: GT 550 K, L, A and GT 750 L

Re: stripped threads gearbox oil drain plug

Post by TOwenR »

karl pa wrote: Tue Jul 06, 2021 4:12 am When drilling,most chips are pulled out of the hole, when tapping, most chips are pushed inward, that is why you coat the tap with grease. I didn't feel comfortable doing the job so I had the dealer do it.
On the 500 and I believe the 250, if you remove the clutch cover, you still have no access to the transmission cavity. Your only options are to try and flush out, or split the cases!
I am not trying to be confrontational with you, but again I must state the importance of the drain plug, If it comes out while you are riding, the oil is going under the rear tire and can be deadly.
You're the expert.
{or left it to one}
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