[BOUNCE triumphs@Autox.Team.Net: Non-member submission from [Egil Kvaleberg
<egil@kvaleberg.no>]]
Date: Thu, 4 Sep 1997 06:43:25 GMT
From: Egil Kvaleberg <egil@kvaleberg.no>
Subject: Re: Increasing TR6 oil usage after rocker oil feed modification
On 3 Sep 1997, Anne van Leeuwen wrote:
> Recently I installed an external rocker assembly oil feed line on my 1972
> TR6 engine, after which oil consumption increased considerably. Before the
> modification the engine used hardly any oil, now the level is dropping
> steadily. Also after starting a still warm engine some blue smoke comes out
> of the exhaust. I guess the oil is disappearing via the valve stems. I
> checked for leaks: no problems at the connections.
>
> Does anybody have similar experiences? I've never seen the internals of the
> engine: can somebody explain why this could happen?
The valves on your TR6 engine does not (at least in their original state)
have any particular means of sealing against oil leaks. This means that
the only thing that prevents oil from leaking down the valve stem is the
clearance between the valve stem and the valve guide. As the valve
guides get worn, this will of course significantly increase the oil leaks.
As a countermeasure against this, the TR6 engine (and indeed all other
pushrod Triumph engines AFAIK) was designed with a limiter on the oil
supply to the valves. The limiter simply consists of a "flat spot" on the
rear camshaft bearing, through which the oil supply passes. Thus limiting
the oil supply proportional to the engine RPM.
The good thing about this is that this will limit oil leaks, simply by
limiting the amount of oil being pumped to the valve and rocker area. The
downside is obviously that the rockers are prone to suffer from lack of
lubrication.
By installing an external oil feed you significantly increase the oil
feed to the valve areas, particularily in the (quite likely) case that the
rocker bearings have excessive clearances. This may, as you have noted,
significantly increase the oil consumption.
The modern fix to this dilemma is to install special Teflon valve stem
seals on the end of the valve guides, which will prevent oil leakage even
when a lot of oil is present. These can be retrofitted to the TR6, but
requires machining or changing of the valve guides.
As a final note, if the oil consumption is really excessive, as well as
hurting the environment, you run a real risk of burning the exhaust valves
since the oil will form a heat insulating layer on the exhaust valve
seats.
My advice would be to remove the external oil feed, and only consider
reinstalling it at some later date when you have had the valve and rocker
gear overhauled.
Egil
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