Light Aircraft Association

I have an unflown Nipper with a 1834 VW. The small amount of paperwork that I have relating to the engine indicate that it was built by the owner before last from a Mexican crankcase which Barry Smith machined for the larger cylinders and supplied bearings, gaskets etc.
The engine has two oil pressure relief valves. I understand that the one nearest the propeller with a long spring prevents over pressure to the oil cooler . The rear one with a short spring is the oil pressure relief valve proper.
The engine had not run for about a year following the death of the previous owner. When we started it the oil pressure was only about 20 psi at 1500 rpm ,dropping to 5 psi when warm. Investigation revealed that there was only a spring in the rear relief valve. I ordered a new piston at a refreshingly cheap non aviation price and fitted it. The oil pressure is now about 40 psi after start , but rises within about 30 seconds to 90 psi when my courage fails me and I stop it.
I have just fitted two new springs and pistons and the indications are the same.
My next move is to try another pressure gauge, but I'm not hopeful since the indications changed from low to high with the fitting of the missing piston.
Has anyone any ideas ?

Hi JHT (?) - Remember that this is a car engine and they tend to produce high oil pressures (I raced a Cooper S many years ago and that would show 100psi cranking it on the starter motor!).

I've just looked in my GtPlanes VW Engine assembly book and it gives the following info:

Oil Pressure cold - 90 psi
Min at cruise (2500rpm) 28 psi
Max - at cruise 70 psi
Average oil pressure at cruise 40 psi

So it looks like you don't have a lot to worry about

Hi,

I don't know if this helps but I have just rebuilt a VW 1834 (re-ground crank, new oil pump etc) and on its first run I remember the oil pressure initially rising to about 90 psi but then starting to reduce within 2 or 3 minutes. I am not familiar with VWs and I have no idea whether my engine is typical of others but, for what it is worth, in some early ground running I logged the following figures using Morris' SAE 30 'Running In' oil.

1000 rpm, 125ºC CHT, 45 psi, 45ºC oil temp
1500 rpm, 140ºC CHT, 32 psi, 58ºC
2000 rpm, 150ºC CHT, 39 psi, 74ºC
2500 rpm, 150ºC CHT, 41 psi, 82ºC
2900 rpm, 175ºC CHT, 42 psi, 87ºC

As someone who likes to run car engines in by degrees (albeit not mollycoddling them), it grieved me to take this engine up to 2900 rpm so soon but I needed the fuel flow figures. The oil temperature is higher than I would like and I am hoping that this will come down as things bed in and also when she is flying with a better flow of cooling air.

Best of luck with your engine (I just hope mine hangs together!).

John.

This is not intended as a criticism but why running in oil ? I would use the oil I intended to use throughout life but carry out a change (including the filter) after about 5 hours just to confirm that all is OK. If I had built up an engine from scratch I would fit an oil priming pump to ensure that lubrication is dispersed through all galleries and bearings before initial start up. In my navy days all ships boat inboard engines had a small stirrup pump (a bit smaller than a bicycle pump - pull to pump) to prime the system as these engines would be not run for a couple of months.
It is very refreshing to see that the VW is still going strong.

The 1835 cc VW engine on my VP-1 shows an oil pressure a little over 40 psi on start up falling to 39 psi during cruise.
The second pressure control is not, in fact, a relief for the oil cooler. Its function on a car is to close a bypass of the oil cooler when the oil pressure gets low, corresponding to hot oil, so that the cooler comes into full operation. In fact, my engine has no cooler (the oil cooler ports are permanently bypassed) and the oil always seems to remain on the cold side, hardly ever exceeding 60 deg. The oil I use is Millers classic 20w/50.

Noel.

Fair point, Bill. My philosophy was this - because of the initial ground running that I would inevitably have to do and because a good oil such as Millers would have lots of anti-wear and anti-scuff agents, there was a chance that I would glaze the bores rather than bed in the rings during the initial few hours. Although the aircraft has yet to fly, I have already drained the running-in oil and replaced it with a good 20/50 ready for flight. I shall, of course, drain it again after 5 hours or so to see what comes out. As for priming the system and filling the galleries, I swung the engine with the plugs out for 100 or more revs for almost all of which I had pressure on the gauge. I'm reasonably satisfied that the oil had reached all parts before it started for the first time. Things like the cam and followers were coated during the build with an anti-scuff grease. Fingers crossed that all is well!

John.

Hi Joe where are you based , I also fly a nipper up in Bedfordshire and try to contact as many people as possible . Have you posted on the Nipper site ? We all need to stick together !
RiP [email protected]