[6pack] Help needed, TR250 engine rebuild oil pressure problems

[Larry Young]

I have a TR250 that I have had since new.  It was showing the same 
problems for some time before I finally did something about it. I 
assumed the bearings were worn out, so at 110,000 miles I tore it down 
for a rebuild.  It was in excellent shape considering the mileage (with 
no overdrive).  The bearing journals showed a small amount of wear, but 
were well within the wear limits and the cylinders were showing marginal 
taper. This is a mostly stock motor, so we went 0.020 over (or maybe 
0.030) on the cylinders and installed new bearings, but did not grind 
the crank or install cam bearings. With the small amount of wear 
elsewhere, I thought cam bearings could wait until the next time around. 
We put a new oil pump in it, because the TR250 pump is said to be 
marginal.  After the rebuild, it was still showing some of these 
symptoms but to a lesser degree.  I got new relief valve springs, both 
stock and "heavy duty".  The relief valve on these engines does not seem 
to be up to the task, because with 20-50 oil, it pegs the pressure gauge 
at startup, but then settles down to about 40 - 45 psi at 2,500 rpm (on 
a 100 degree day) with the heavy duty springs.  The pressure is about 5 
psi less than with the stock spring. I believe the manual calls for 
something like 40 to 60 psi at 2,000. It still shows the very low 
pressure at 800 rpm idle.  The relief valve is probably not open at 
idle.  I believe this is just a basic engine design issue. Perhaps since 
this engine grew from a much smaller one, the oiling system did not keep 
pace.  Cam bearings may help the problem, but installation is nontrivial 
since the block must be line bored. As long as you are getting good flow 
to the rockers at running speed, I would not worry too much about rocker 
lubrication at idle.  I do not use an external line to the rockers, 
because that would further reduce the oil pressure and oil flow to the 
bearings, which is much more critical than the rockers.  The best 
solution would be a higher volume pump.  The later TR6 pumps are 
supposed to be better, but I couldn't tell any major difference.  Is 
there a higher volume pump available?  A larger capacity relief valve 
would also be an improvement.

Ed Barnard  mentioned a cracked block issue.  I believe mine was crack 
tested, but will have to check with the machine shop.

Larry Young

On 9/14/2013 7:55 PM, Andrew Packard wrote:
> Hello Triumph problem solvers.
>
> I nearly have my TR250 ready for Triumphest/VTR after an engine rebuild.  I'm
> trying to solve a problem now with maintaining consistent oil pressure.  When
> I first ran the car after the rebuild, the 20 minutes at 2000 rpm start, I had
> Castrol 5W30 and ZDDP additive.  After the engine really got up to
> temperature, I had trouble with maintaining oil pressure, dropping way down
> close to zero at idle.  A mechanic friend of mine checked it out with me and
> with the rocker cover off, we saw little flow at the rockers at idle.  I had
> an external oiling line on my shelf so I added that and saw very good flow at
> start up when oil pressure was about 65 and settled down to just under 50 as
> it started to get warm, but continued to drop to the same near zero level once
> it was at temperature.
>
> Today I changed the oil to 20W50 Castrol with Lucas ZDDP break-in additive.
> Same symptoms.  I drove the car about four miles near my house and at
> temperature, I was running at 20-25 psi when driving, dropping to near zero at
> stop signs.  When I arrived home, I removed the quite hot valve cover oil fill
> cap and started the car.  Very little oil was dancing around, if any, at idle.
> I revved the car a bit and saw sufficient oil flowing and splattering in
> there.
>
> Now I don't know what to do.  I have the braided oil pressure line from TSI.
> I don't think my gauge is bad with oil flow symptoms consistent with the
> pressure readings.  Could the oil pressure regulator be an issue?  Mine is
> relatively new from BPNW.  I do have a second one I could swap in.  The oil
> pump was new with the rebuild.
>
> Any advice or guidance is appreciated.
>
> Andy Packard
> CD6746L
> President - Triumph Travelers
> Autocross Chair - 2013 Triumphest/VTR
>
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