C15 oil grade

[rhyatt]

my apologies if covered already.

My C15 BSA handbook advises monograde 30/40 depending upon summer /winter.

in the light of oil developments, is it worth/useful for me to consider a 20/50 multigrade.
the C15 crank has its timing side bush etc and I wonder if this benefits from the monograde 40(stays thick enough when hot)
 or the 20/50 may be helpful to it when hot

I am sure that BSA suggested 40 for a very good reason at the time , but oil has moved on since.
thank you

[limeyrob]

The BSA recommendation is still good.

[DAVE BRADY]

Hi,

I think that 20/50 is the oil for plain bearings.  It behaves like a 20 when cold and can more easily circulate through to the bushes and shells for better protection on start up and then behaves like a 50 when warm to continue to lubricate as required.
It is not necessarily about how thick it is but how well it flows through to lubricate and cool the engine.

Dave.

[rhyatt]

thank you all

[limeyrob]

Beware, the base on a 20-50 is a 20 that has additives so it behaves "like a 50 would at high temp" but its not a 50 and those additives get chopped up. A straight 40 is not relying on an additives for viscosity so its a true 40 at temp.  My tuned A65 could turn a 20-50 into a 20 in about 1000 miles so I went to straight oils.

[DAVE BRADY]

Hi,

Do plain bushes and big ends chop the additives as well as ball and roller bearings?

Dave.

[limeyrob]

My rather non-expert answer is "yes".  The rolling bearings are a lot less sensitive at our speeds.  If I take the A65 it was pushing 50 hp which would be 100hp from the 1300, a huge amount then but quite common on family cars now.  But modern car plain bearings are large with high flow oil systems and full flow filtration.
What they don't have is a 1 1/2 plain bush on one end of the crank.  I won't criticize that bush, my A10 is still running fine at nearly 70 years, but it does hammer the oil.

[DAVE BRADY]

Hi,

70 years is quite impressive. How many miles has covered in that time and have you stripped to clean the sludge trap?

Dave.

[limeyrob]

Its fairly new to me but I have rebuilt it and cleaned the sludge trap. I had the A65 for over 30 years from new and yes, the sludge trap did block and seize the engine at under 20,000 miles.  After that I went to straight oils and fitted a full flow cartridge filter on the return. I did suspect that the detergent oils were just moving the dirt to the sludge trap.  I've fitted a cartridge filter to my A10.

[DAVE BRADY]

Hi,

Not quite C15 but.
The detergent oil helps to keep the engine clean by carrying it to the filter.  Non-detergent oils allow the sludge trap to collect the sludge.  If you put a detergent oil in a used engine you. may mobilise the sludge with potential disaster.
Although they both have end fed cranks, two engines, an a10 and an A65, lasted over 120,000 miles each before fatigue called for new big end shells.  On stripping the engines there was barely enough sludge to cover a 10p piece.
Detergent 20/50, full flow filter and regular oil changes.

Dave.

[limeyrob]

I never stripped the A65 after I fitted the cartridge filter but I suspect the sludge trap was clean and I'm hoping for the same on the A10.

[idie]

Years ago when the world was young, I was at the Earls Court motorcycle show. I was talking to the Duckhams rep about using their oil in my Panther 600. He said don't as ball and roller bearing chop up the long chain molecules in the oil and reduce it over time to it's  base oil. So use monogram. Which I have done ever since.

[DAVE BRADY]

Hi,

I would tend to agree re ball and roller bearings also I think that gears do the same thing but gear oils molecules are able to reform.
However, my long lifer engines have the std. roller main on the crank and the combined needle roller/ball race thrust on the timing side.
Whist it was available and cheap in Asda I used Duckhams 20/50.

Dave.

[limeyrob]

Years ago when the world was young, I was at the Earls Court motorcycle show. I was talking to the Duckhams rep about using their oil in my Panther 600. He said don't as ball and roller bearing chop up the long chain molecules in the oil and reduce it over time to it's  base oil. So use monogram. Which I have done ever since.

Thanks for settling that!  it explains a lot.  As you can see from I above, I backed the wrong horse!!