HI Don,
No matter what oil you use, a ridge will develop at the top of the
cylinder over time. That's because the rings don't travel all the way
to the top. The point of maximum wear is at the top of the ring travel
because that's where the top compression ring is when the max cylinder
pressure from firing occurs. It's the pressure of the expanding gases
in the cylinder that forces the compression rings against the cylinder
walls to seal the cylinder during the firing stroke. The pressure is
greatest at or near the top of the rings' travel and decreases as the
piston travels downwards. So there's more friction at the top of the
ring's travel. The ridge is actually an unworn area of the cylinder at
the top. The rings may break against the metal ridge on a an extremely
worn engine (I've had it happen) but the varnish isn't in the ring's
travel area.
Cheers,
CR
Don Malling wrote:
> Hi CR,
>
> I checked my owners manual and you are quite right. It does recommend
> the same oil in the Engine and transmission. It doesn't specify a
> difference between OD and non-OD transmissions. I understood John
> Esposito to say that his recommendation to use non-detergent 30W applies
> only to OD transmissions.
>
> I also noticed that the MG manual recommends 10W/40. I found that
> especially interesting because I have understood from several sources
> that 10W/40 was not a wise choice at all. Under high heat conditions it
> leaves hardened deposits. For that reason, I don't think it is
> recommended for turbos and I don't think it's recommended for air cooled
> engines.
>
> I understand that it leaves hardened deposits at the end of the piston
> travel and as the rod bearings wear the piston travel increases and the
> rings hit the deposits. The rings can crack and lodge the piston in the
> cylinder and blow the engine.
>
> After using Kendall 10W/40 in a 2.3L Ford for years it started to knock
> and about 2 weeks later a piston seized in the cylinder, snapped the
> rod and pushed it through the block. It failed exactly as predicted in
> the literature.
>
> Whether it was caused by the 10W/40, I can't say for sure. But it was
> enough for me. I wouldn't use 10W/40 in anything.
>
> I would view any recommendation to use 10W/40 with a bit a skepticism.
> Perhaps when the manual was written they were not yet aware of the
> problems with long term use of certain lubricants.
>
> :-)
>
> Don Malling
>
>
>
> Charles & Peggy Robinson wrote:
>
>> He's full of beans. I've been running Castrol GTX 20W-50 oil in
>> both my MGB engines and OD trannies for over 15 years, no problems. I
>> do not understand why people want to ignore the owner's manual which
>> clearly states that you should run the same dino oil in the tranny as
>> you use in the engine.
>>
>> Cheers,
>>
>> CR
>>
>> Don Malling wrote:
>>
>>> According to John Esposito www.quantumechanics.com, only 30W
>>> non-detergent motor oil should be used in an OD transmission. John
>>> said that deteregent motor oil will foam in the transmission and will
>>> not work well with the OD. I can't remember the details of why the
>>> foaming was not good for the OD.
>>>
>>> Don Malling
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