Service Bulletin: Triumph 650 & 750 Sump Filter Plug O-Ring
When most folks think of vintage British motorcycles there are many things that come to mind from the infamous Lucas electrics, Amal carburetors, the deep glorious sound of glass packed silencers and so on...
The first thing that usually pops into ones mind whether they’ve owned a British bike or not is there reputation of leaking oil.
Oh yes the oil stains that are left on the drive way from a vintage Triumph, BSA or Norton marking its territory.
The funny thing is they all leak oil..
I mean, it’s the nature of the beast. Wouldn't you agree?
For those folks out there that have put together (or what they thought) was going to be an oil tight Triumph engine, perhaps this little tip might help you solve some of your oil leaking problems.
Allow us to present to you an original Triumph service bulletin dated May 5th, 1973.
This service bulletin gets into minor detail regarding the 70-9336 / E9336 crankcase oil filter drain plug.
This crank case drain plug was fitted to all unit construction Triumph 650 and 750 unit twins from 1963-1982. In all fairness there where 2 different types of plugs used during the 1963-1982 period that we will cover below...
Most models used an annealed copper washer to prevent oil leaks but sometimes the copper washer is simply not enough to seal the oil in the crankcase, therefore you must use an o-ring as described in this service bulletin.
The O-ring
The o-ring as described happens to be the same o-ring that is used on Triumph twin models for the bottom of the pushrod tubes.
| Part Type | Part Number | Material | Measurements (approx) |
| O-Ring | 70-7310 / E7310 | Viton | 1 3/16" (OD) - 1 1/16" (ID) - .093" |
The reason why the factory took use of the 70-7310 / E7310 o-ring is the fact that it fits but it is a "viton" o-ring. Viton material o-rings are excellent for applications where heat, oil and pressure play a major role.
The plug
The sump filter plug that was installed on all Triumph 650 and 750 twins from 1963-1982 came in 2 types of conditions. Although this Triumph service bulletin only lists the later 70-9336 / E9336 plug using an o-ring on the early plug 70-5312 / E5312 will not do any harm.
Pictured above is a Triumph sump filter plug (70-9336 / E9336) with the 70-7310 o-ring
| Part Type | Part Number | Year | Model |
| Sump Plug Filter (Early) | 70-5312 / E5312 | 1963-1968 | T120 / TR6 |
| Sump Filter Plug (Late) | 70-9336 / E9336 | 1969-1982 | T120 / T140 / TR6 / TR7 |
*Both the early and late plugs do not have a recess to accept an o-ring however it works. Make sure when you install the plug to not over torque the plug as it can deform the o-ring. I personally think Triumph was applying a Band-Aid to a problem that should have been redesigned from the start.
Replacing the copper washer
To switch over from the copper washer select your 70-7310 / E7310 o-ring and insert it over your oil filter plug.
Fasten the oil filter plug into the case and you are done...
That easy..
Need a plug or an o-ring? or both?
Should you need to replace your oil sump filter or install a new o-ring to put a stop to your oil leaking problems perhaps you should see some of links below that we have compiled for you.
| Parts Link | Part Type | Part Number |
| Link | Sump Filter (Early) | 70-5315 / E5315 |
| Link | Sump Filter (Late) | 70-9336 / E9336 |
| Link | O-Ring | 70-7310 / E7310 |
Thanks for reading
I hope this blog post serves you well.
As always should you have any questions please feel free to drop us comment in the section below.
Click here for more blog and technical information like the one you just read...
Ride safe!
Classic British Spares
@Jerry Roy – that is 100% correct. The sump plugs do not have the recces groove. For those who do own or have access to a lathe cutting a groove in the sump plug is recommend. As Jerry said, keep an eye when fastening and applying pressure to the plug as the o-ring will want to squeeze out. When the o-ring starts to deform or squeeze that’s when you need to stop.
Jerry Roy
A word of caution those who use this method. Since there is no circular recess cut into the sealing face of the plug, if you tighten the plug to much, you extrude the o-ring. So if you don’t have a lathe, and are not able to cut a groove in the shoulder of the plug, you should not tighten the plug too far. Watch the o-ring when you tighten it up, and when you have compressed it half way, stop. Don’t worry about it coming loose. the spring effect of th o-ring, and the friction between it and the sealing surfaces keeps the plug from loosening. Back in the day, when the Triumph pre unit rocker covers, with the factory cork gaskets would come loose and land in the barrow pit when you where trying for top speed, the trick was to go to the dealer, buy new covers, put O-rings on them, and tighten them hand tight. We never lost any more.
YMMV