Advice Appreciated for 340 w/ Low Oil Pressure

Hi all,

Background:
I have a '66 Skylark that I bought late last year that has 44k miles and the original 340 4v which might be a survivor (never rebuilt). I drove the car sparingly last fall before the weather turned but was plagued with getting the carb and ignition tuned and I was also concerned about having no idea what the oil pressure was like (no gauge). The bad news is that I have since put a manual OTC oil pressure gauge on the car and it is getting about 25psi at fast idle and ranges to maybe 35psi if you rev it lightly. The car runs well other than a miss that I can't track down (but I haven't spent too much time on this after replacing the entire ignition) but the power is not what I would consider great. She doesn't burn oil that I can tell but there is a bit of a rattle at start up that could be coming from the valve train at startup but quickly goes away (maybe the lifters take a while to get oil).

Question:
I would like to pull the engine and give everything a once-over before replacing the oil pump, but I am a bit nervous and would appreciate any advice from other folks that might have been in the same boat. I am hesitant about doing a full rebuild due to cost and worry about finding a machine shop that will do a good job on an old Buick. I might be okay with burying a grand or two in the engine max but then I have to start wondering if it would be better to invest in a nailhead or a 455 (still expensive but broader aftermarket support).

Has anybody done this and have any lessons they learned (possibly the hard way)?

Thanks,
Ray

 

Ray, your best bet is probably to just drive it for awhile. 44k is minimal mileage and the standard rule of thumb for a Buick is 10psi per 1000 rpm so it sounds like you are right there with it. (Bypass will open around 45 psi stock)

Jim

 

Well, crap, that is a lot cheaper than what I had started contemplating. I am tempted to at least update the stock pump with a new replacement stocker like what TA has and maybe try out their booster plate and regulator ideas if it means another few psi per 1k RPM- opinions? Maybe I am overreacting from my years of having a chevy.

 

Hey Ray, your miss can be as simple as a bad plug, bad wire or a bad cap and rotor, all easy and cheap things to replace if need be. Tuning can get you going better as well, check out Larry the Wizard's power timing thread in the 455 street strip section in the stickies at the top.

A couple really good carb rebuilders here as well. GL




Derek

 

Put fresh oil and filter on it and check oil pressure in gear hot. That will tell you much

 

Since you're a chevy guy you need some info specific to Buicks and how they are different. First and foremost they run tighter bearing clearances, about half what you would see in a chevy. The reason this is important, is if a Buick engine is built like a chevy it will hemorrhage oil past the bearings and the resultant band-aids end up destroying the oil pump drive. I shoot for a .001" clearance.

With tight bearings the stock oil pump is quite adequate. However close attention must be paid to pump gear end clearance. I set that to "barely drag when cold" and never had any problems with pump output, although I also use a booster plate, port the openings, enlarge the pickup tube and galley, and use a stiffer bypass spring. TA has oil pump shims.

However for your case I'd start with a stiffer bypass spring or adjustable bypass. Don't get carried away, stick to the 10psi/1000rpm guidelines.

Loose bearings will show up as low oil pressure at idle. A properly assembled engine will hold 10psi or better. If you aren't getting that the easiest solution is to increase oil viscosity. If you are running 10w40 try 20w50. I've run 50wt racing oil in some engines with this problem and the only issue was cranking speed in cold weather.

Jim

 

Never run thick oil just to boost your pressure gauge reading. You will starve the bearings for oil. You are just dead heading the pressure gauge, not putting oil to the bearings.
Also the thicker oil puts more drag/stress on the timing chain, dist gear, and front cam bearing making all of them wear much faster.

 

Normally I'd agree with you Steve, but if the bearing clearances are excessive it can be an effective band-aid. Not the right fix and can cause other issues of course. But it can stretch out the time to the next rebuild.

Jim

 

Also, cheapo oil filters will cause a rattle on start-up because the oil drains back & the filter has to fill up 1st. before oil gets to the bearings. Could be as simple as that for the dreaded cold start dry rattle of BEARINGS with NO OIL.