OIF Engine Oil Capacity

[NM Bonny]

So, I recently bought a '71 Bonneville T120R and like the rigidity and comparative lightness of the all-welded, large-backbone frame (the height feels about right, as I'm 6'2"). I've converted the mesh filter to a cartridge setup with a CNC-machined aluminum plate, and replaced the rubber feed and scavenger hoses with aluminum pipe; same with that ugly crankcase breather hose.

But one thing about the model's new frame that I don't like is the oil capacity is evidently about a half quart (1 pint) less than the '70 model. Seems like the additional half quart would aid cooling during the summer.

One easy solution that occurs to me would be to weld a small auto drain bung onto the forward upper side of the big tube just before it terminates at the steering head, as indicated in the photo (a late model Subaru Outback bung and plug would fit just fine in that smallish space). If painted black, it would be unobtrusive snuggled just ahead of the tank above the holes for wiring, and with a funnel wouldn't be difficult to use at all. You'd just use a socket to R&R the plug to avoid scratching the paint with a spanner.

The existing cap has an O-ring, so shouldn't leak, and I can't imagine it would make any difference to the scavenger circuit to disgorge its flow under, versus over the surface of the oil in the reservoir (if anything, the teensy added resistance would infinitesimally increase pressure to the valve train). Also, the sloshing forward of the oil in the big top tube shouldn't be a concern, as any excess just runs down the 5/16" pipe from the underside/front of the top tube, which connects to the breather circuit, whereupon it drains back into the primary chain chamber and from there through the holes communicating with the engine sump.

The new filling procedure would be: (1) fill the reservoir up to the threads on the OEM filler and install cap; (2) refill sump as usual; and (3) add another half quart (1 pint) or even a little more in the new filler and install the plug.

I haven't yet seen mention of this, but wonder if anyone has done this modification...?

 

[Rudie]

'71 Bonneville T120R
one thing about the model's new frame that I don't like is the oil capacity is evidently about a half quart (1 pint) less than the '70 model. Seems like the additional half quart would aid cooling during the summer.

Depends on the ambient.

The frame tube/oil reservoir has a large surface area; UK - where the ambient rarely even approaches 30 degrees Centigrade - oif owners who have checked report oil temperatures nowhere near the desirable 100 degrees Centigrade, even after many high speed miles.

One easy solution that occurs to me
haven't yet seen mention of this, but wonder if anyone has done this modification...?

Norman Hyde bolt-on oif oil cooler kit, offers additional oil capacity and, with an easily obtainable thermostat, would work over a wide range of ambient temperatures. However, the engineer who designed the triples' oil cooling for BSA/Triumph tested Norman's cooler (at Norman's request), concluded it was not required; nevertheless, Norman went ahead with marketing it "because oif owners would pay for it" ... If you wish to read the engineer's experience, he is "Richard Beard" on Triples On Line and "Tridentman" on BritBike.

 

[NM Bonny]

Depends on the ambient.

The frame tube/oil reservoir has a large surface area; UK - where the ambient rarely even approaches 30 degrees Centigrade - oif owners who have checked report oil temperatures nowhere near the desirable 100 degrees Centigrade, even after many high speed miles.


Norman Hyde bolt-on oif oil cooler kit, offers additional oil capacity and, with an easily obtainable thermostat, would work over a wide range of ambient temperatures. However, the engineer who designed the triples' oil cooling for BSA/Triumph tested Norman's cooler (at Norman's request), concluded it was not required; nevertheless, Norman went ahead with marketing it "because oif owners would pay for it" ... If you wish to read the engineer's experience, he is "Richard Beard" on Triples On Line and "Tridentman" on BritBike.

Rudie,

Thanks for the info. One hundred degrees Fahrenheit is not uncommon in Albuquerque during the summer; it was 90 or more for a large percentage of the season this year--and I expect the trend will continue with record temps recorded regularly in the U.S. and everywhere else.

At any rate, given that long frame member's heat sink properties (which I didn't consider), I've got no worries. So, if lower capacity were a concern in terms of increased contamination rate--the only other factor I can think of--then all I'd have to do is reduce the oil-and-filter change interval.

Thanks again for the thoughtful reply.

 

[solomon]

ar the desirable 100 degrees Centigrade

Why's that temp most desirable?

 

[Rudie]

the desirable 100 degrees Centigrade

Why's that temp most desirable?

Even without condensation, burning petrol produces water, water in the engine lubricating oil is bad, 100 degrees Centigrade, any water boils off.

 

[Rudie]

if lower capacity were a concern in terms of increased contamination rate

When the triples - designed with a proper micropore filter in the engine - were introduced during 1968, both Triumph and BSA advised multigrade engine oil and changes at 4000 miles. For the 70 model year, BSA also advised both for its twins, although they had not had a proper micropore filter added; Triumph advised the same multigrade oil for its twins but did not increase the oil change interval from 1500 miles. As you have added a proper engine oil filter, the contamination rate is unlikely to increase?

 

[solomon]

When the triples - designed with a proper micropore filter in the engine - were introduced during 1968, both Triumph and BSA advised multigrade engine oil and changes at 4000 miles. For the 70 model year, BSA also advised both for its twins, although they had not had a proper micropore filter added; Triumph advised the same multigrade oil for its twins but did not increase the oil change interval from 1500 miles. As you have added a proper engine oil filter, the contamination rate is unlikely to increase?

I know most 70s twin owners, me included, change oil 1,000 to 1,500 miles.
Going on above, if twins have a proper paper-type filter fitted, logic might say a twin could have oil changes at 4,000 miles?

 

[Rudie]

I know most 70s twin owners, me included, change oil 1,000 to 1,500 miles.
Going on above, if twins have a proper paper-type filter fitted, logic might say a twin could have oil changes at 4,000 miles?

Also consider time - bike covering more than 3000~4000 miles per year, owner might be wise to consider oil changes at that sort of interval; however, I suspect many "classic" vehicles - 70s twins included - cover less than a thousand miles per year; would it be wise to change the engine oil only every three, four or more years?

Also, rather than relying on "logic", have a sample of oil tested at regular intervals, monitor increases and decreases in certain elements to determine when oil should be changed based on usage?

 

[NM Bonny]

Rudie and Solomon: Thank you for weighing in - good thoughts.

I have always changed the oil in air-cooled engines more frequently that 3,000 largely due to greater fluctuations in temp. I think the largest interval I used was 2,000 (can't recall whether this was a motorcycle or air-sucker VW). On my '51 Harley FL, I change the oil (and external spin-on filter) at 1,500 with a valve adjustment. It is superficially a very similar engine to the '71 Bonny: pushrod twin with solid lifters, chain primary (the '51 FL is modified with '66 heads, solid rather than hydraulic lifters, and belt primary).

I get that 1,500 is likely overkill but it's so inexpensive and only a leisurely hour or two of work with valve adjustment that I don't mind. Plus I am one of those weirdos who likes tinkering, and with the 'paint shaker' as I call the '51 FL, it's a good idea to check the tightness of fasteners more often than 3,000 miles. So a shorter service interval gives me a reminder to do that. Can't be a bad idea on the '71 Bonny, though it'll vibrate considerably less, I suspect...?

Oh, Rudie: I have typically run Castrol GTX 20W/50 in motorcycles, and will probably do that with this 'new' bike, too.

Can't wait to ride her, as I'll bet she'll handle well through the S-curve in the canyon coming up to the house. The rigid tail 'paint shaker' is like riding a horse--point her in the general direction and hang on...

Here are a work-in-progress photo of the Bonny (paint, rear shocks, wiring stuff done but lots more to go), and a shot of the 'paint shaker.'