I can't speak directly to TR6 but this is a common problem with many
motorcycle and car engines. I don't think I'd bother lapping--a minor leak
won't relieve that much oil, though it might not be ideal at idle with the
oil hot. I doubt sufficient lapping is the cause of your problem. It's
possible that you've got a little piece of swarf (or perhaps dervis) under
the plunger. I've also seen plungers get stuck in their hole, both from
foreign junk in the port jamming the plunger into the full relief position
or clearance problems between the plunger and the bore--which might be the
case here. A lot of parts like this are made "sloppy" to reduce the
likelihood of jamming from grit. An extreme example is float needles on
carbs, which are never made as round plungers anymore, but are square,
with the plunger being located in the bore by the edges of the square.
Unless the shaft wear on the old plunger is heavy galling that might snag
in the bore, it probably would work fine. I'd try sticking the old part
back in, with the stiff spring.
-----Original Message-----
From: MARK J WEATHERS [mailto:markjwea@email.msn.com]
Sent: Sunday, December 29, 2002 4:36 AM
To: fot@autox.team.net
Subject: TR6 Oil Pressure Relief Valve
Amigos,
Here is a practical problem to divert us from the ongoing legal debate:
I have an oil pressure problem in my fresh TR6 engine that is limiting the
pressure to 50 psi max. I suspected the oil pump and in the process of
replacing it decided to test the pressure relief valve that unseats and
dumps oil back to the suction side. I don't know if this is a common
design but it consists of a plunger under spring pressure that seals off
the return passage from the main gallery.
The only way I could test it (engine in the car with oil pan and pump
removed) was to apply air pressure to the return port in the block, which
is the reverse of the actual relief valve flow in operation. I did this
and was able to detect slight air leakage back into the main gallery
through the bypass valve. If it leaks in this direction it will surely be
as bad or worse with actual pressure working to unseat the valve. I now
think my oil pump was okay after all (no threat of libel lawsuit, I worked
on the pump myself).
Some important background: When I built the engine I replaced the stock
plunger with a part I made in our machine shop because the original was
worn on the shaft. I reamed the housing to the new shaft size and made the
'head' thicker to effectively shim the spring. I also bought the stronger
spring from Moss but did not use it. I suspect that I have screwed this up
somehow (not the first time but I can't resist trying to 'improve' things
when I have them apart). What I don't understand is that I lapped the new
plunger into the block with coarse grinding compound and I do see a
witness mark all the way around. The lapping mark isn't as deep as I would
like as it is hard to rotate the plunger to lap it in, but I am sure the
angle and concentricity of the sealing suface is good.
My options that I can see:
1. lap it some more
2. put in a stock plunger and housing
3. Pull the motor and recut the seat $$$$
4. Plug the return port, pipe the return flow out of the side of the block
to an external relief valve and into the oil pan 5. Hope someone in FOT
has seen this before and can help me before the event next weekend!
Anybody out there have any experience with this, Kas, anyone?
Mark
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