Augusta Oil Pressure

[JohnMillham]

Having recently rebuilt my Augusta engine (new rods, Mini Coopper shells, Triumph Herald pistons, Nissan valves, new oilpump gears, new timing chain tensioner,etc, I was rather miffed to find that the oil pressure was much lower than before. However, I also changed the bolts which hold down the rocker shaft - and that, it turns out, is where the oil was leaking. I now find that the six 6 mm threaded holes for the bolts are not all as deep as one another. I measured a couple of them, but not all of them and ended up with at least two of the bolts not pulling the rocker shaft down properly. The front holding down bridge has a hole below it for oiling the shaft and there was a poor seal there.
  I found out on my way to the Oxfordshire meeting last evening, when two of the bolts sheared at the root of the thread. This made the tappets rather noisy and one of the valve "caps" escaped, but luckily didn't go far. I replaced the bolts today and  - lo and behold, my oil pressure is now at least as good as it was before the engine rebuild. I have also adjusted the tappets to 0.06" and 0.08" in stead of all at 0.06", as I think it was probably unwise to have the exhaust clearances so tight. I have just returned from a test drive and it seems to be fine. So now for the driving tests on Sunday.
 Regards, John 

[Running Board]

Hello John,

Good to hear that you've got the Gussie running again.  I'm amazed at the valve clearances you're using though: our two Augustas run on a fraction of your clearances!  No wonder you're losing valve stem caps!  Perhaps you want it to sound like a Lambda.......Oops!! 

Seriously though, I take it that you're running 0.006" inlet and 0.008" exhaust?  I tend to prefer a tight 0.010" for both but I can't see any problem with reducing this somewhat. 

Regarding oil pressure, have you tried measuring the pressure at the Autoklean to see what is actually at the main bearings?  I have a second gauge permanently plumbed in as such on the Astura and get 42 psi here all day, even though the standard gauge (tapped off the head) often registers below "Normale".  Asturas, like Augustas, lose oil pressure around the valvegear and give misleadingly low readings on the dash.  I've noticed also that the dashboard reading varies inversely with cylinder head temperature - hardly surprising - thus explaining the "worrying" readings. 

We also had a worry when we first put my Augusta on the road.  I returned from MOT with nothing registering on the gauge, unless the engine was revved to about 3000 rpm when the pointer started coming off the stop.  Cold, the pressure was good.  This turned out to be the gauge which at some point had been fitted by a gorilla using only one spanner to tighten the union.  The connection inside the gauge is only soft-soldered and he had managed to break the bond and rotate the Bourdon tube, causing the gauge to read from about 40 psi to 100+ psi!  Italy was calling, so all I did was to slacken the union and rotate the gauge connection back to roughly the right place, then tightened the union with two spanners!  I checked it subsequently using air from my spraying regulator and found that 40 to 50 psi gives mid-scale.  Must fix up another gauge though! 

Best regards,

Morris. 

[johnturner]

Good to hear that the Augusta is back on the road.  I remember all kinds of problems finding oil pressure when we rebuilt he engine in Christine's car.  Taking off the crankcase side plates with the engine running revealed oil pouring out around the main bearing housings which was solved by sticking them in with a Loctite sufficient to provide a seal but not sufficient to prevent them being removed when needed. This produced a dramatic improvement. But having sealed the crankcase, as I expect you know, oil then bleeds away around the camshaft chain tensioner.  We had a old tensioner drum white metalled and the sprocket ground and this was reasonably effective until we eventually bought a complete new unit from Cavallito. Morris is right that what shows on the gauge has very little to do with what is going through the crankshaft, and its the flow that counts as I keep telling myself.

John

[JohnMillham]

Sorry, I got the tappet clearance measurements wrong by a factor of ten! It is 6 and 8 thou' I use! I can't get used to these imperial measurements when they're written down!
The oil pressure is now excellent, as I found out the cause and cured it. I had replaced all of the six bolts holding down the rocker shaft and two of them bottomed in their holes before the shaft was tight. It let me know by breaking them on my way to the Lancia meeting in Wendlebuey last Thursday evening. I should have measured all of the holes, rather than just one or two, and not assumed they were all the same. The oil pressure stays at or above "normale" all of the time except tick over, when it's at the bottom of "normale". I shall put a proper gauge on it soon, so I will know what the actual pressure is. I did put new oil pump gears and a new timing chain tensioner in - complete with a new spring.
 The engine is now running quite well again, although a tad down on power compared to what it was. It's very smooth, ticking over extremely slowly, at 300 rpm or so, a lot slower than I can get the Lambda to achieve, but then it does run on a coil and not a mag. I haven't run at more than about 55 mph so far, as it does feel a bit tight, but that's about 3,500 rpm with the 165 x 400 tyres, so fast enough for a week or two. It will be interesting to see if it's still as economical as it was, always returning over 30 mpg.
      Regards, John