Oil Pressure problems

[lhbradley]

Don, I have several queries, but I'll use a separate thread for each.

Engine (late model) was rebuilt over the winter. with all new bearings, valves, rings, etc.

When I ran the engine this spring, oil pressure was low (mechanical gauge). And the gauge would fluctuate madly at some engine RPMs. I played with the adjustment, and was able to get it up somewhat, but still not happy with it. Tried to dress the seat up with the pipe nipple trick, but I could not get the ball out. The pring looked OK - seemed to have good "spring" to it.Things are a bit better now. Using 10W30 oil. Cold, the pressure is 55 psi. When really warmed up, running at 1600 RPM (typical cruise revs), I get 20 -25 psi, with the needle vibrataing a lot. At idle, down to around 15-20 psi.

However, changing the pressure adjustment doesn't have much effect, no matter how much I move it. The pressure appears to be proportional to engine RPM, and not really being regulated.

Thoughts?

[Don Moyer]

Your oil pressure is technically adequate for 1600 RPM, and the pressure will vary with RPM. The relatively small spread between the oil pressure at idle RPM and your cruising RPM is a good sign that the pump and major bearing clearances are in good condition.

You might be able to adjust your entire regulating range a bit higher with our oil pressure regulating valve (http://www.moyermarine.com/cgi-bin/shopper.cgi?preadd=action&key=OOIL_06_122).

Best regards,

Don

[lhbradley]

Don, you may recall that I had to pull the engine again to replace the idler gear bushing, which was badly worn after only fifty hours. We replaced the spindle as well, and found that the new spindle has a much larger oil feed hole at the bushing end than did the original. I also replaced the oil pressure adjuster with the one you sell, and it does indeed work better than the old one.

But I'm still not happy with the pressure when the engine is hot. It is nearly impossible to adjust when hot, as I can't get at the lock nut except by putting my arm across the manifold and the exhaust outlet. I'm reluctant to leave the lock nut loose while running the engine to heat it up.

I set it up when cold to 55 or 60 PSI at a fast idle. But after an hour or more of running, the pressure at 1500 to 1600 RPM is 20 to 25 PSI. At a real slow idle (500 RPM), it drops to 5 PSI or so.

I switched to 10W40 oil (as suggested by Robert Hess on his A4 web site, and that has improved things a bit.

I don't understand what could be causing low oil pressure. All the bearings are new. Russ, my mechanic, said the oil pump looked good when he rebuilt it. Am I just worrying too much?

[Don Moyer]

Larry,

I would suggest that you turn your regulating valve in at least one more turn (while the engine is cold) in an effort to get the pressure up closer to 30 or 35 psi at your normal cruising RPM. This adjustment should also get you a bit more pressure at idle. As a general rule of thumb, as long as you maintain a minimum of 10 psi per 1000 RPM you should be OK.

Regards,

Don Moyer

[tartan30cirrus]

I have heard on the Sailnet A4 site of people using a stiffer spring to get more of an effect on regulating OP. What do you think of this practice? What would be the proper size spring to replace the normal one?

Cheers,
Clint
Happy A4er this year, but still can't get the OP above 20-25 at warmed up cruise setting (although the mechanical gauge says 30-35....go figure)

[Don Moyer]

Clint,

Using a heavier spring is certainly worth a try. I wouldn't have any actual specs to pass on, but it's not a critical matter, you could simply take the spring in to a local automotive supply house and select one a bit more robust.

Don