8ba oil pump flutter

[oldford2]

Just finished rebuilding an 8ba and have it up on the test stand.



Runs great and idles down smoothly. Now my concern: I put a mechanical pressure gauge to measure oil pressure and it flutters wildly between 40-70#. I checked the gauge by putting it on our 46 and it showed a steady 50 cold. So I dropped the pan and removed the pump. Took it apart but don't know what to look for. Are all the parts there? Just a ball and spring? The spring is 1 and 3/4" long. Any ideas? Thanks John

[Vic Piano]

Lookin' good John. I don't have an oil pump available to look at; maybe you can fine an exploded view of one in a parts catalog on maybe on Mac Van Pelts web site. I can't believe you don't have a pair of Brockman Mellow-Tone steel packed mufflers on your test stand...LOL

[G.M.]

John it sounds like the bypass valve in the pump has a weak spring. I have found the springs in the latter pumps and in the front of the engine to cause fluttering and low pressure. I made a sleeve that fits snug on the pump with a gauge and adjustable restriction on the output, remove the drive gear and run the pump with a 1/2" electric drill. You can make a shim out of 1/8" brass pipe for on the spring adjusting the thickness of the shim to get 55 lbs of pressure. I would never put a pump in new or used without testing it. G.M.

[Ross F-1]

There were some posts on the HAMB a few years back about Melling's chinese-made pumps having poorly machined seats in the relief valve. I bought a Melling about 4 months back and it was Made in USA, maybe they got the message?

[Walt Dupont--Me.]

John, the pic you sent me of the pump and check valve. I've had alot of 8BA pumps apart and never seen a ball check valve. They all have a kind of flat about the size of a dime with a tapper on the edge to seat on and a 1/4in. rod made on the back of the valve that goes into the spring. I still would like to know where you got that pump and does it have the std. lengh gears or the longer gear for a high voluum pump. Walt

[52merc]

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as walt says never seen a 8ba oil pump with a ball,yes the spring is a little weak so most guys put a couple of small washers on the rod that walt talks about

[oldford2]

Walt,
Well you might be right. This engine was low mileage and stock bore with just a fingernail ridge. This oil pump was on it. As shown in my picture there was just a spring and a ball. G.M. thought I might have a weak spring. So I called my favorite vendor, Joblot, And talked to a real person who always helps me. I wanted to see if they had a spring. He called up an exploded view of the 8ba pump which also shows a relief valve plunger and a relief valve plug. These may be the parts you are talking about. He is going to scan the drawing and send it along with my order (plunger $2.50 and plug $2.00). 15 minutes on the phone and he got a $4.50 order. This is why I deal with Joblot. With all the talk about vendors lately, these folks are the greatest. I will follow up this post with the drawing and parts when I get them (usually overnight).
John

[G.M.]

John Job Lot has been a good reliable vendor over the 33 years I purchased parts from them. You sent me a PM about my oil pump tester and the shim, I think I may have others confused also so I posted here. I use a 1/8" brass pipe and cut pieces like thick washers out of it. These could be 1/8" to 3/16" thick and placed on the top of the spring to increase oil pressure. You adjust the washer thickness to adjust the oil pressure. Some will say just stretch the spring but that don't last very long. The PVC sleeve I made has 2 inside diameters a few thousands small than the OD's of the pump. The larger OD of the pump is where the mounting foot bolts to the block. The smaller OD of the pump is about 3"s up from the larger OD. The PVC stretch's very easy and can be tapped on and off. I bored the center stop out of a PVC coupling and glued that in the center of the short bored out pipe. This is to have enough wall thickness to drill and tap a 1/8" pipe nipple in the center. Don't run the tap in to deep because you don't want the end of the nipple hanging inside of the pipe because it won't allow the PVC sleeve to slip over the pump OD. put a "T" on the 1/8" nipple with a pressure gauge in the "T, out the end of the "T" put a valve, barb fitting and clear hose. The valve can be eliminated and just bend the hose and watch the gauge to get 55 lbs steady flow. You also need to take the pump drive gear off and dive the pump with a 1/2" drill. Pump rotation is CW the same as drilling a hole. Put the pickup screen in a drain pan with a quart of oil with the new hose returning the pumped oil back in the drain pan. I had pictures but can't find them. I have a lot of construction going on and haven't been to the shop often. I'll try and get by there and take a few pictures.
G.M.

[Barlea]

The tiny line that usually feeds a mechanical gauge has a damping effect on the needle. It's possible that if your gauge is plumbed directly into the engine that it is reading the non-damped fluctuations that are normal from a gear pump. ..B.

[G.M.]

I forgot that. Grainger and McMaster Carr have dampers. Damper is a fitting with a small hole. I tapped the gauge and made a small threaded screw with about a .030 hole in several gauges. G.M.

[oldford2]

Well, this is a mystery. As posted above, my pump just has a spring and ball in the relief chamber. Several posters here said they have never seen a ball in there. Here is a view of the assembly showing the parts at each end of the spring. So I guess someone "monkeyed" with this pump in the past. I should get the 2 parts from Joblot today. Thanks for all the input so far. John

[52merc]

james at joblot is a great guy to talk to about v8 parts hes helped me a lot of times

[flatford8]

Do you support those mufflers on your stand?Gonna break your
Manifolds?