69' Triumph t120 Bonneville repair.

[riverbob9101]

Hey guys, my dad has a 1969 triumph t120 Bonneville that I'm working on currently. I wanted to get some advice on oils though.

For motor oil it recommends a variety that are all SAE 20 to SAE 40 such as energol SAE 20, 30, 40. For this I was looking at mobile1 4t racing 10w-40 because it has a good reputataion, 1200 ppm ZDDP, and was recommended by an oil chemist that I spoke too. I want to get some more opinions though and would like to hear if there is anything else I should look out for when getting oils for such an old bike.

For gear oil it recommends EP 90 oil from a few different brands such as castrol hypoy EP90. I haven't done any research into this yet and wanted to get opinions on what might be some good options, and what to look out for. I have found that Kroon oil carries a "classic gear EP90" in addition to a "classic monograde 30" and "vintage monograde 30". Does anyone know whether any of these are any good? In a brief search I didn't find much of anything. Is it worth getting "classic" oils for the bike? I feel like getting an appropriate modern oil should provide superior protection.

Thanks,
River

 

[Silk]

I'd run a straight 40, and a 75/90 gear oil. I don't know if they had shifted the breather into the primary case by 1969, if it has, then engine oil in there, it will keep it's own level. If it has the timed breather on the inlet cam, I'd go for ATF in the primary.

 

[BigCahuna]

If it were mine, I would run Rotella 15/40 in the motor. And if you need gear oil, any extreme pressure 90wt wt oil will do. Does your Triumph have an actual oil filter, or just the screen that you clean? Remember oil made today is worlds better then what was made almost 50 years ago, so you won't have any problems with that. But I would still change it out at 2500 miles. Most likely you'll have problems sorting out the Lucas " Prince of darkness" electrical system. But they used to sell conversion kits to help straighten out that mess.,,

 

[Robenstein]

Originally Posted By: Silk
I'd run a straight 40, and a 75/90 gear oil. I don't know if they had shifted the breather into the primary case by 1969, if it has, then engine oil in there, it will keep it's own level. If it has the timed breather on the inlet cam, I'd go for ATF in the primary.


Here most of the straight 40 stuff is SA or SB rated, which means it is REALLY lacking in additive packages for detergency and wear. As someone else mentioned, Rotella 15/40 would be good. The Triumphs need relatively short OCI's so using a synthetic is a bit of overkill I think. He has a good bike there and desirable being a pre oil in frame model. As someone else mentioned, get in touch with guys that own and run these and get the updates done to the electrics to prevent the issues there.

 

[KernelK]

Why not run a 20w-50 like what was originally specified by Triumph?

 

[riverbob9101]

The triumph just has filter screens, not a proper oil filter. I took a look at the rotella that was suggested, but it says it is a diesel engine oil, is it ok to use that with a normal petrol engine? I am also asking around on a triumph specific forum, but thought I might try here as well. Any opinions on the mobile 1 oil I mentioned? Robenstein mentioned that triumph have short oil change intervals, but with the improvement of modern oils and if I switched to synthetic wouldn't that increase the interval?

 

[BigCahuna]

I wouldn't push it that long do to the fact there is no oil filter. Diesel oil is also rated for gas motor usage. Plus it might take a while just to get 2500 miles on it.,,

 

[barryh]

I used to run 20W50 in a Bonneville. The oil pump in those things is not exactly a wonder of engineering so I'd be wary of anything thinner. After market oil pump upgrades were very popular back in the day.

 

[Robenstein]

If you do want a 50 weight oil, Mystik sells a 15w50 Diesel/Gas engine oil that is semi synthetic. Many Harley riders seem to like it. Valvoline conventional motorcycle 20w50 would also be good.

As for OCI's if I recall they were around the 1,000 to 1,500 mile mark for those old twins. With only a screen and a sludge trap, best to keep it conservative. These engines were not long lived being generally of late 1930's design.

 

[Bzab32]

In my triumph (1970 T120) I run a 20W-50 conventional and 75W-90 gear oil. I would change the oil every 500-750 miles (thats what i says in the 1970 workshop manual i have) and gear oil every 1000-1500 unless there was a filter added. The oiling system is prone to water contamination and without a filter it really doesnt last too long. I personally wouldnt run anything thinner unless the weather permits, I know in Wisconsin once it gets around freezing in not driving it. The main thing is to change it often and when you ride it to get it nice and hot.

 

[KernelK]

Just for the record, my factory workshop manual for 650cc unit construction twins specifies engine oil changes at 1500 miles, transmission oil changes at 6000 miles, and primary chaincase oil changes at 1000 miles. I think I changed my oil every 1000 miles. The 500-750 mile interval is probably appropriate for motors running velocity stacks, and many in those days did.

 

[Bzab32]

Originally Posted By: KernelK
Just for the record, my factory workshop manual for 650cc unit construction twins specifies engine oil changes at 1500 miles, transmission oil changes at 6000 miles, and primary chaincase oil changes at 1000 miles. I think I changed my oil every 1000 miles. The 500-750 mile interval is probably appropriate for motors running velocity stacks, and many in those days did.


Sorry you're right I was thinking of something else I read. I was trying to flush mine out as it was sitting in my father-in-laws garage for 25 years and got that interval stuck in my head. Doing anything else to the bike? Is it a restoration or is it in good condition?

 

[riverbob9101]

It was my dads bike back when he used to ride. He says it ran when he put it in the garage but he left gas in it. I've already done extensive cleaning of fuel tank and carburetors. I have new fuel hose and two inline fuel filters to add when its ready. Otherwise I'm just changing fluids and battery and cleaning it up. I'm reluctant to run the 50 weight oil since the manual only suggests a variety from 10 weight to 40 weight, but no 50. I've also found a place that sells castrol classic 90EP that is supposed to be the same formula as back when this bike was made, so I'm thinking of using that just to avoid any risks. My manual says 1,000 miles for the primary chain case, 1,500 for motor oil, and 6,000 for gear oil. Bzab mentioned adding an oil filter, where exactly would that go? Thanks, for mentioning the water contamination, I'll keep my eye out for that once I start using it.

 

[KernelK]

How many miles are on this Bonneville?

 

[Bzab32]

They sell kits for the oil filters on a lot of the brit bike parts sites. It goes on the oil return line by where it goes into the oil tank, so if it gets plugged it doesnt starve the engine of oil. I would also recommend changing out the forks as it is super easy and it probably didnt get changed. I just use 30W oil. I would highly recommend the 20w-50 oil (i use castrol 20w-50 conventional) and you have to remember the technology changed a lot since the 60's and 70's. As multi weights became more avilible the recommended viscosity changed to 20w-50 (1971 yes OIF bikes so slightly different oiling system same engine) in the manuals.

 

[Truckedup]

OP, was the engine ever disassembled completely ..And if so what was done? I work on vintage Triumphs and have several Triumph race bikes. The crankshaft has what the Brit's call a "sludge trap", better called a centrifugal filter.Dirt and carbon collect in there and over time will restrict or even plug oil flow to the connecting rod bearings..If you care about the engine and has no history of the trap being cleaned , now is the time to split the cases and do it.
The correct oil is 20/50...If the engine has a breather on the top left rear then the wet clutch runs in engine oil...Use a Jasco rated oil....

 

[Langanobob]

I have a 1966 Bonneville that I've had for a lot of years. I used to run Castrol GTX 20W-50 but now I use Rotella T 15W-40. As has been mentioned, oils have improved a lot since 1969. I personally stay away from any old school gear oil or motor oil formulations, based on my experience over decades with this bike, there is no reason that I know of not to use a modern oils with modern additives in an old Triumph.

About oil filters, I once tried connecting one of those aftermarket filter kits on the return line. It restricted the return flow and oil started coming out of the engine everywhere it could find a place to come out of. This was years ago and I don't recall exactly where the leaks were but I ended up removing the filter and staying with the original design. Just change the oil often.

These are actually good bikes, fun to ride and you can have a lot of fun while going slow, unlike many newer sport bikes where you have to go fast to get the adrenaline going. I have ridden mine across the USA with no issues other than a worn out chain which was just a maintenance item. I got an aftermarket Boyer ignition and an aftermarket voltage regulator, they were both a huge improvement. Anywhere you see the name Lucas on your bike, try to find something else to replace it with.

Lots of fun!