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I have been chasing a tapping tappet for a while now. I think I finally solved it, albeit with way too much time. I ended up machining a new tappet plunger on a lathe. I think the path might be of interest.
Two years ago when I was reassembling the engine I used the factory bubble test to check for leaking ball check valves, found it was not a clear cut procedure and made a new seat for one (a previous post). After I started and ran the engine the tappets quieted right down initially, but after the oil warmed up one tappet would start ticking at idle. It would disappear with an increase in rpm so it seemed it must be a leaking check valve. I tried to isolate which tappet was giving the problem with a stethoscope, but could only narrow it down to the 3rd tappet block (for cylinder 5 and 6). I then ran it with the valve cover off to observe them, and found that a lot more oil was pouring out of the top of #6 cylinder’s tappet bodies than the others. For simplicity I label the tappets #1 to 16 front to back, so #6 cylinder’s are tappets #11 and 12.
By the way, if running with the valve covers off the blowby of the exhaust gases will no longer be captured by the blowby tube running from the back valve cover to the aircleaner and will put carbon monoxide into the garage even if you have an exhaust pipe extension going outside the garage, so positive fresh air ventilation is needed.
I was using 5W-30 oil for break-in, and measured the temperature of the oil pouring out of the tappets when the ticking would start – 85F. Looking at oil viscosity charts it looked like it would take an oil thicker than straight weight 50 to keep it quiet with 160F oil temp on a car fully warmed up. I really don’t want to drag the pistons through 50 weight oil.
I did the bubble test and found nothing definitively different between the four tappets in the third block. I have since given up on the bubble test and I now clean the tappets dry, close the two holes halfway up the plunger body with my fingers, suck it down and hold with my tongue to gauge how well the ball seat seals (no rude comments please).
There are two paths for excessive leakage in the lifter, one is the check valve leaking, the other is the oil leaking through the clearance between the cam follower and the tappet plunger. That leakage of course increases as the oil warms up and gets thinner. The bubble test only tests the check valve. I rigged up a very simple and crude test apparatus out of some scrap wood to be able to provide enough leverage to generate the force the valve spring puts on the lifter when it pushes the valve up. The cam follower body was filled to overflowing with oil and the tappet plunger inserted. On the far end (not visible in the picture) I hung a bucket with about a gallon of water and measured how fast each lifter would leak down. I understand that when Packard and Cadillac adopted the same tappets as used on the 36-38 Pierces they had a purpose built tester that did the same thing, and obviously less crude than my setup.
#11 leaked down twice as fast as #9 and 10, and #12 took almost twice as long as 9 and 10, so it was the winner, #11 clearly the loser and most likely problem child. Measuring the diameters I found 9, 10, and 12 had .001 clearance, while #11 varied from .0015 to .002 clearance. To tighten that up first I tried pressing a brass sleeve onto the bottom of the plunger and carefully machined it down to .0005 clearance. It didn’t change the leakdown. Since it seems my plungers are neither the first design for ’33-35, and not the second design ’36-38 it was unlikely to find any replacements. The only option seemed to be to convert the whole mess to ’36-38 style, or make a new plunger. I am very much a novice learn-by-doing hobby machinest, so it seemed a bit daunting, however if I built a new one I wasn’t risking any damage to the original. I machined the new one from a tight tolerance steel shaft which I very tediously worked down to .0005 clearance using very fine grit sandpaper. It tested at being about 50% slower leakdown rate than the #12.
I just tested it in the engine and seems to have worked – it is quiet now with 125 oil temp at idle.
Jim
That was a great process of elimination and self made solution.
Do you think you could reproduce more very easily or would it be better to have someone measure and scan the plunger to create a CNC routine for reproducing them?
I only ask because if you were having the leakdown issue I’m sure others have, or will have, the same issue and reproducing them may be beneficial to others in the PAS.
Great job and thanks for sharing.
The way I did it for a single tappet of course was very tedious and time consuming doing it on hobbiest lathe and mill. They could be produced professionally on a CNC, but I have no idea what it would cost. I do have CAD drawings that could be used. The tappet I replaced could be also be used for a pattern, if I take off the brass skirt I added.
One issue on getting them reproduced is how many need them? I believe mine might have been produced for only part of the 1935 model year as they don’t match the designs seen in the PASB’s for either ’33-35 or the ’36-38 design. Mine have external springs and a tapered nose but basic diameter dimensions of the first design. That was one of the reasons I decided to try and make one.
The inside diameters of the tappet follower bodies seemed to be very consistent (.500) so the plungers could probably be ground to a consistent diameter and be interchangeable (.499). The originals were also surface hardened for wear resistance, my replacement isn’t but the surface area is very large with flooding oil flow lubrication, and the side loading is virtually non-existent, so within the limited miles this engine will ever see I don’t think that is an issue. The plunger I replaced did not appear to be worn, I think it was undersized from the get-go.
Jim
Actually, it could be that the external spring tappet plungers like mine are interchangeable with the original internal spring ’33 design. I don’t have a’33 tappet to compare dimensions, but the diameter of the cam follower in the block is the same .688 as reported in PASB 80-5 and the action of the check valve is the same whereas the ’36-38 design is quite different with a larger bore diameter and the check valve works upside down relative to the first design, despite also having an external spring.
Jim
Jim, I have a new old stock lifter that I think is a Seagrave issue. At
the time of the purchase I wasn’t aware that different years had
different lifter sizes. Could you or anybody else tell me what years it
would work in?
Tony, I had a post a couple years ago on this message board that showed cutaways from the two basic designs from earlier PASB’s. Just do a search using tappet. Presumably a Seagraves NOS would be the ’36-38 design that was built in large numbers during WWII as they were used in a Cadillac powered tank. Egge bought up
that inventory, or so I understand.
Jim
Thanks for the tip. I heard that Cadillac flathead lifters were OK for P.A.
use with some modification. Then I heard they were difficult to source. I’m
excited that you can fix yours.
FYI- John Cislak has made a fixture to pressurize and the three different type of Pierce hydraulic lifters. The system works well, and eliminates having to take apart a rebuilt motor several times to get the lifter tick to go away.
Ed, do you know if the earlier ’33 design tappets interchange with my ’35 design, i.e. either style plunger can drop into the same cam follower?
Jim
I can’t keep track anymore, call John, he can answer off the top of his head. There were two style Pierce units and two style Seagrave if I remember correctly, parts can interchange, but there are modifications necessary.