[TR] TR4 road draft tube plug

Brad Kahler bkahler1 at gmail.com
Mon Sep 7 16:56:37 MDT 2015

>From all of the documentation that I've been able to read there seems to be
three variations of the emissions equipment.  The earliest is like the
TR3/early TR4 with a vented breather cap and road draft tube.  Then at
engine number CT14234E through end of TR4 production the cars had air
filters with vent openings coming from a flame trap from the valve cover
along with a "sealed" valve cover cap and no road draft tube.  TR4As had a
gulp valve with a vented (1/8" metered opening in the cap) valve cover cap
and no road draft tube.  This information was found in Service Bulletin

Your TR4 sounds correct having a sealed cap.  The TR4A valve cover caps
were definitely vented.  The TR4A caps have a nice little vent mechanism
attached to the top of the cap.  I'm not convinced that I have blow by.  I
will do a leak down test to verify but I won't have time to do that for a
week or two.

My particular engine is original block for the car but has been rebuilt.  I
don't think it should have had a road draft tube because it's well past the
CT14234E number.  It should have had the closed circuit system like yours
originally had.

I've attached the service bulletin but I don't know if PDF attachments are


On Mon, Sep 7, 2015 at 2:52 PM, Geo Hahn <ahwahneetr at gmail.com> wrote:

> On Mon, Sep 7, 2015 at 10:08 AM, Brad Kahler <bkahler1 at gmail.com> wrote:
> ...Also, is your valve cover cap vented (i.e. TR4A style) or non-vented?
> Those terms (or something) confuse me.
> My late TR4 does not have a vented cap - it seals tight.  I presume that
> TR4As are similar.  Early TR4s and all TR3s had a cap that vents to the
> atmosphere.
> If you are fighting blow-by (and I think you are) it would seem that a
> vented cap might help -- and since your engine apparently has a road draft
> tube fitted as original then I believe a vented cap would have also been on
> it.
> Geo
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