'63 Fuel Injection Wobble Pump History

[G B.]

I'd like to pin down a timeline for the rise and fall of the notorious '63 FI wobble pump design. Here's the only information I have so far.

The Volume 5, Number 6 issue of Corvette News contains an article beginning on page 16 entitled "Corvette's Fuel Injection System Undergoes Refinements for Extra Efficiency". It describes some new features of the '63 7017375 FI unit. One change is called a "new high pressure fuel pump". This pump has five small cylinders "positioned axially around the pump drive shaft. And the driveshaft turns a wobble plate, producing a reciprocating action that operates the five spring-loaded pistons for fuel supply. During cranking, this new pump has a higher output for better starting." I don't know the date this issue was printed, but it probably wasn't distributed until after the '63 models were introduced in early October(?).

Several GM photos of Pilot Line '63 Corvette FI engines show they were equipped with wobble pumps. This indicates wobble pumps were available for even the pre-production (sand-cast) 7375 FI units. From this I assume they would have also been available for the beginning of regular production on the assembly line.

The new Avedisian/Keith Z06 book has some fascinating documents in it. The first indication of '63 FI performance problems is in a GM letter dated 12/26/62. The letter is from R.M. Clift to Z. Arkus-Duntov. In it, Clift describes the numerous broken drive cables and clogged nozzles he witnessed while testing five '63 Z06 Corvettes and one Grand Sport at Sebring about ten days prior. The letter didn't specify the root cause of these problems, although it did say the in-line fuel filters contained "a large quantity of fiberglass and other trash". The letter also mentioned trying a "new greaseless pump, but pump appeared to have grease coming out beside gasket when tightened". (I don't know what is meant by a "greaseless pump".)

The next mention of FI performance problems is a 2/13/63 Technical Test Report written by R.O. Crider. It describes more clogged nozzle problems that occurred during further Sebring tests conducted in January, 1963: "Fuel injection nozzles continued to plug, even while using the gear pump. Apparently the contamination comes from the fiberglass fuel tank."

Evidently these testing problems resulted in a Chevrolet Product Campaign (or warranty replacement/recall) described in a 4/12/63 Chevrolet Central Office memo. Campaign Number 63-6 was assigned for the "Fuel Injection Fuel Pump (Major)". This particular recall was to cover '63 Corvettes with serial numbers "S100001 - S106228".

From the above I concluded that wobble pumps were originally installed on all 7375 injected Corvettes through VIN #6228. After VIN #6228, wobble pumps were replaced with gear pumps either prior to initial assembly line installation or through the April, 1963 Corvette recall.

Please give me your comments on this timeline, especially if you disagree.

Thanks,

Jerry

[Mike M.]

Re: '63 Fuel Injection Wobble Pump History

great detective work jerry. I read tony A's book right after carries '17 and didn't pick up on your observations. I can attest to 36 gal tanks contaminating FI systems, even tho my old NO3 63 ZO^ was built in late July of 63. regards and happy holidays. mike

[Alan D.]

Re: '63 Fuel Injection Wobble Pump History

Jerry, Sometime in the early 1970's I picked up a "63" unit which had the wobble pump, it's serial number was 3548.
Not sure if the FI serial number will help, just wanted to keep track of subject as others chime in, great subject.

[Michael J.]

Re: '63 Fuel Injection Wobble Pump History

Yes, those fiberglass tanks are something you really have to pay attention to with the gas you use. I took a fuel filter off one of my '64s, it had small bits of resin and rattled like a castanet when I shook it. Some in the fuel pump too.

[John D.]

Re: '63 Fuel Injection Wobble Pump History

Jerry, Sometime in the early 1970's I picked up a "63" unit which had the wobble pump, it's serial number was 3548.
Not sure if the FI serial number will help, just wanted to keep track of subject as others chime in, great subject.

Alan, Someone installed the wobble pump on the late '63 you bought. No way did it come from RP with that pump.

Before I tell you all a story I want to thank Jerry Bramlett for the wonderful write up on the pump. Good work friend.
If you are considering using a wobble pump let me tell you this. There aren't any parts for that pump available. Only thing we have is the pump seal. Even the pump shaft is different than the gear pump as I believe its longer.
One ofGail Parsons projects before he passed was to have a few parts made for those pumps. Gail told me he had about 5 or so pumps and wanted to save them. Jerry may have more accurate info on that statement.
Frank Sciabica was the head engineer for Rochester Products fuel injections in the old days. Here's what he told me several times as I asked him to repeat the info.
GM was losing engines because of the wobble pumps. Look in your '63 Corvette shop manual in the fuel injection section. Engine Fuel 6M-49/51.
See Fig. 112-Fuel Pump exploded view. Notice #. Inlet piston. There are 5 of them. Then see Item #10. Inlet valve. I hope I have the right part as I haven't taken a wobble pump apart in years. The inlet valve is made of a ceramic material.
The ceramic would break and then get into the fuel unit. Clog up the anti-siphon valve in the fuel meter, Clog up the check valve in the fuel spider (which was originally called fuel distributor) and then good by connecting rods or possible a blown engine. Frank said Chevy was not amused at this problem and ordered RP to recall the pumps and go back to the gear pumps. And so they did.
I have the recall notice buried here and I imagine Jerry has it now.
The Wobble pump has it's own spider so you got a new spider and a new hi-pressure pump,etc with the recall.
One thing I have noticed over the years that I never mentioned to Jerry. Every early unit that I have had here that should have had a wobble pump had an early gear pump on it. Early style pump that has different configuration than the 5630006 correct pump.

Look in Fig 113. See the piston, then the ceramic (if that's what the material is) under the piston, then the spring, etc. You are not supposed to mix up the pistons either.
Problem is people ignored the recall and there's too many of those pumps out there. I don't know how the judging would go on that pump. If there's a recall notice involved. But if my '63 the LWC would requite that pump I would take the point hit.
The wobble pump has it's own drive cable assembly also. And as mentioned a different spider.
By the way if you didn't know this the '63 shop manual fuel injection section was written using the early sandcast unit. It's a great reference for what parts the early unit had.
. Something funny in Fig 84 is the presence of a flag on top of the plenum lid. It was done by an artist but he didn't have a clue as he drew the flag backwards. The sand cast units did not have a flag. John

[G B.]

Re: '63 Fuel Injection Wobble Pump History

Thanks for posting, John. I know you're the NCRS Technical Advisor for FI and members ask you about judging details. Perhaps you can work out a compromise position for judging that allows both gear pumps and wobble pumps to be acceptable on early '63 Corvettes.

Gail Parsons never followed through on his plan to have repair parts made for wobble pumps. His estate did include four wobble pumps, but two of them were incomplete. There were no loose parts.

Last night I studied Technical Service Bulletin #880 dated 4/17/63. It's the five page explanation of the recall that was addressed to "ALL CHEVROLET SERVICE PERSONNEL". The bulletin is a little confusing. It clearly says that injected vehicles built "prior to serial number 106228 should be updated" with "Major Kit 7017374". That kit included a new gear pump, main diaphragm, nozzles, spider, and some installation gaskets / seals. However, it went on to say that VINs 106229 through 109846 should be updated with "Minor Kit 7017353". The Minor Kit just contained a few FI gaskets and seals. The next paragraph says: "If unit incorporates a gear pump as shown in Figure 1, it will be necessary to install Minor Kit 7017353 only. If unit incorporates a wobble type high pressure pump as in Figure 2, install Major Kit 7017374." To me that implies some wobble pumps may have been installed on VINs higher than 106228.

[Mike M.]

Re: '63 Fuel Injection Wobble Pump History

jerry and John:regarding the judging of 63 FI's equipped with a wobble pump, at a NCRS regional within the last year, we mechanical judges were presented a vet with a wobble pump. as it was an early 63 Vin, we had no problem with scoring full credit to the pump. unfortunately I can't recall the vin # of said 63 corvette. mike

[Duke W.]

Re: '63 Fuel Injection Wobble Pump History

Alan, Someone installed the wobble pump on the late '63 you bought. No way did it come from RP with that pump.


Frank Sciabica was the head engineer for Rochester Products fuel injections in the old days. Here's what he told me several times as I asked him to repeat the info.

Did he ever tell you why the wobble pump was designed to replace the gear pump in the first place? Seems to me that the wobble pump is a much more complicated design and, therefore, more expensive to manufacture.

As a rule, GM would not redesign something that performed satisfactorily, so did the gear pump have some problems? Keep increasing the speed of a gear pump and it will eventually cavitate. The speed before cavitation sets in can usually be extended with tooth design refinement, but the wobble pump design would be inherently much more resistant to cavitation.

Duke

[John D.]

Re: '63 Fuel Injection Wobble Pump History

Duke, I never heard from Frank or anyone why the wobble pump was used instead of the gear pump.
Jerry. Thanks for the information on the bulletins. I talked to Gails machinists today and he agreed with you. Gail had told me he was going to have pump parts made but that was it.

I have a wobble pump on the shelf that will need restoring gang. Anyone wanting it I will swap for a gear pump. John
T

[John D.]

Re: '63 Fuel Injection Wobble Pump History

Jerry, I do not typically get involved with the judging process. That's up to the team leaders. I also am not allowed to voice my opions at a show nor are the judges permitted to ask me FI questions while the judging is going on.
If you don't believe this ask the little guy from Augusta.

[Joseph S.]

Re: '63 Fuel Injection Wobble Pump History

Guys, As Mike stated earlier, we did see a wobble pump earlier this year in Altoona. Considering how early the car was, we did assign full credit as it was proper . We typically do not make a deduction for gear drive pumps on cars that should have a wobble pump since it is a safety concern. If I remember correctly, we told the owner that he may want to remove that wobble pump and replace it with a gear drive pump.

[G B.]

Re: '63 Fuel Injection Wobble Pump History

... I never heard from Frank or anyone why the wobble pump was used instead of the gear pump. ...

Oh, wait... see line five of the first post in this thread: "During cranking, this new pump has a higher output for better starting."

[John F.]

Re: '63 Fuel Injection Wobble Pump History

Hey guys, I'm in the processing of correcting and fine tuning the things that were marked incorrect from Altoona. It was my car that was judged and I lost 24 Points out of 60 under FI Unit, Drive Cable, Base Plate, Bolts, Gaskets and seals.

Notes on judging sheet in pencil indicate the following:

Config of Plenum
Unit too late for wobble
No Plenum Washers
Screws on air adapter
non typ heat shield
base plate 2nd design
Air meter washers SB black
Enrichment diagram is SR

The three big ones that lost me the majority of the 24 points (from my memory) were were the recessed nozzle blocks on the plenum, the wobble pump and the 2nd design adapter plate.... which actually I had the third design with the two snowflakes, not the 2nd design... the one with a snowflake in the middle of the two front plenum feet AND one to the left or adjacent of the water intake on the front = third design. The judging manual (6th edition) discusses 3 different adapter plates with a single snowflake each which is incorrect. This may have been updated in the latest manual to reflect the late 63/64 design with two snowflakes. The part I'm struggling with is the recessed nozzle block plenum on the first 100 units of 1963, again per the 6th edition judging manual. Mike and Joe you may not have taken points for the wobble pump which is cool then the majority of the 24 points would have come from the plenum and adapter plate? That unit came from Gail Parsons and was #311. I have the original tag. I'd be curious if anyone has a 63 plenum with recessed nozzle blocks, what serial number it is.

[Michael G.]

Re: '63 Fuel Injection Wobble Pump History

John,

We have more fuel injection expertise in this thread than existed in all of the United States in 1963....so, between John and Jerry you sure have the right guys here to answer that question about recessed nozzle blocks. I'm sure they must have some idea what number that was the last FI unit to have them.