I'll share a short story that will also answer your question. Several years
ago I was coming back from Import Carlisle. About a 5 hour trip. I run
20W-50 oil. When I stopped at the Turnpike Toll gate between PA and Ohio I
happened to glance at my oil pressure. It was about 5 pounds, maybe less.
Came up when I revved the engine and at 70 MPH it was maybe 40 pounds.
Needless to say I needed to do something. The next weekend I dropped the pan
and found the rod bearings pretty worn and in spots you could see the
copper. I replaced them but I went one step further and also rebuilt the
oil pump. This had never been done on my engine. It's a 1966 TR4A that I've
owned since 1969. 1 rebuild on the engine, original crank, standard size
bearings. The most important part of the oil pump rebuild is to get the
clearance between the bottom plate and the rotors as close to spec as you
can. In my case the bottom plate had a lot of wear and was badly scored. I
used emory paper on a piece of glass and worked the bottom plate until the
scores were gone and the plate was flat. It takes a lot of work to hone that
plate. Oil on the emory helps too. Start with coarse and work the scores out
then go to a fine to get it as smooth as you can. Be sure the rotor to rotor
and rotor to case clearances are at spec too. That was in 2001 and since
then I've had excellent oil pressure at hot idle (40 or better) and 65 at
hot running speeds. Still an original crank too with a guess of close to
100,000 miles on the crank.
It worked for me.
JVV
----- Original Message -----
From: "Randall" <tr3driver@ca.rr.com>
To: <triumphs@autox.team.net>
Sent: Friday, November 12, 2010 12:41 PM
Subject: Re: [TR] Engine Rebuild -- Sorta
>> Book says to replace the rod bearings at 50k. Without taking them off
>> to peek, I'm wondering how necessary this really is?
>
> Seems to be good preventative maintenance to me. Like most PM, it's not
> really necessary, but it helps reduce problems farther down the line. For
> example, it might help avoid having to regrind the crank the next time the
> engine gets "freshened".
>
> Just changing the rod bearings is a pretty minor operation, actually. I
> did
> mine in an afternoon, before TRfest (and they really needed it, were worn
> clear into the brass backing).
>
> However, if you want to avoid it, I would suggest keeping track of the oil
> pressure. If your hot idle pressure is the same as it was right after the
> rebuild, then there is no appreciable wear on the bearings. But if it has
> been slowly creeping downward ... (mine was down to only 10-20 psi with
> 20W50 oil).
>
> One thing I learned the hard way; if you use the lock tabs on the rod
> bolts,
> it is essential to replace them every time. I've been using Loctite
> instead.
>
> -- Randall
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