C2: '66 BB fuel pump outlet thread size & elbow

[Steven S.]

[Michael H.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

The original 137425 90* fitting for 65-66 big block is shown as having a 1/4" pipe thread on the male end. Pipe thread sizes are roughly 1/2 of the actual diameter.
The fitting and outlet thread size for most early small block pumps is 1/8" pipe.

[Steven S.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

Thanks, that confirms my theory. I think I found a source for another fitting, it has been a bit more difficult than one would think. I will report back with my results.

Steve

[Michael H.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

Thanks, that confirms my theory. I think I found a source for another fitting, it has been a bit more difficult than one would think. I will report back with my results.

Steve

Steve,

It may be a fitting that's available at an auto parts. The sizes are 5/8"-18 for the female end and 1/4" pipe for the male end.
A currently available fitting will most likely have a slightly different (larger) wrench size than an original but the other dimensions will be the same.

[Steven S.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

That is the one I have currently, but the Carter pump uses the 5/8-18 for the outlet size.

Steve

[Michael H.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

That is the one I have currently, but the Carter pump uses the 5/8-18 for the outlet size.

Steve

Sounds like you have a 67 and later pump with machine thread instead of the correct 65-66 pump with 1/4" pipe thread for the outlet. Look in the hole, see if there is a seat for a flair.

To test, see if the fitting on the end of the fuel line screws into the pump without the 90* fitting. If it does, it's definitely a 67 pump, not 65-66.
For 67, the fuel line made a 90* bend at the bottom and attached directly to the pump, eliminating the need for the 90* fitting.

[Steven S.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

Sounds like you have a 67 and later pump with machine thread instead of the correct 65-66 pump with 1/4" pipe thread for the outlet. Look in the hole, see if there is a seat for a flair.

To test, see if the fitting on the end of the fuel line screws into the pump without the 90* fitting. If it does, it's definitely a 67 pump, not 65-66.
For 67, the fuel line made a 90* bend at the bottom and attached directly to the pump, eliminating the need for the 90* fitting.

You are absolutely correct, aparently there is NO replacement pump for 65-66 that uses the correct 1/4 NPT outlet, all available replacement units are the '67 style. I didn't realize it at first, I was thinking the outlet was 3/8 NPT, which at first glance is very close to the 5/8-18 that is used on the fuel line. The problem is there are adapters to go from pipe to the inverted flare style fitting, but not the other way around, which is what is needed. What I did was take a 3/8 NPT to 1/4 NPT reducer and turned the 3/8 NPT end down and re-threaded it to 5/8-18, and will use a seal between it and the pump, which after looking over LI Corvettes catalog it appears they sell the replacement style pump coupled with what appears to be the same type of adapter (but they don't appear to sell the adapter seperately).

Thanks for the input, it helps to have another brain to point out what in some situations should be the obvious.


Steve

[Michael H.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

You are absolutely correct, aparently there is NO replacement pump for 65-66 that uses the correct 1/4 NPT outlet,

I'm surprised no one is making a 65-66 pump out of a 67 pump. I've heard the 67 pumps are being rebuilt/restored by someone and they come with a new bottom plate.
It wouldn't be at all difficult to make a bottom plate with a new outlet fitting made for 65-66.

[Steven S.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

They are rebuilding/restoring correct pumps for 65 and 66, what I meant to say is no one is making new pumps with the correct outlet fitting. If I would have realized the difference in the outlets I might have thought differently when I chose to go with a replacement pump, but at the time I couldn't see spending the extra money for the restored pump as my car isn't at the level that it would be justifiable.

Steve

[Michael H.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

They are rebuilding/restoring correct pumps for 65 and 66, what I meant to say is no one is making new pumps with the correct outlet fitting. If I would have realized the difference in the outlets I might have thought differently when I chose to go with a replacement pump, but at the time I couldn't see spending the extra money for the restored pump as my car isn't at the level that it would be justifiable.

Steve

I haven't seen a rebuilt 67 pump but I understand the top housing is an original but the entire bottom stamped plate has been reproduced.
If they reproduced the plate and fitting for 67, I suppose it would be just a matter of time before someone makes a bottom plate/fitting for 65-66. The 65-66 plate/fitting could be installed on a currently available AC 67 pump..

Hint.... if you (or anyone) needs a temporary fuel line for a 65-66 with a 67 pump, the fuel line from a 67-69 L88 will fit perfectly with no other modifications. The upper section of the line is exactly the same as 65-66 big block but it has the 90* bend and machine thread nut at the fuel pump end.

[Clem Z.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

those brass 90 degree fittings will kill the fuel flow and cause a pressure drop that is why they went to the bent fuel line on the L-88

[Michael H.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

those brass 90 degree fittings will kill the fuel flow and cause a pressure drop that is why they went to the bent fuel line on the L-88

The new design fuel line without the extra 90* fitting was used on all 67 and later big blocks. It's true that the fitting used for 65-66 may have caused some restriction but the other reasons for the change were cost reduction and ease of assembly.

I think that same 90* fitting was also used on all 65-66 passenger cars so by eliminating it completely for all 67's, GM saved a lot of money.

[Clem Z.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

The new design fuel line without the extra 90* fitting was used on all 67 and later big blocks. It's true that the fitting used for 65-66 may have caused some restriction but the other reasons for the change were cost reduction and ease of assembly.

I think that same 90* fitting was also used on all 65-66 passenger cars so by eliminating it completely for all 67's, GM saved a lot of money.

cost first better flow second. sharp 90 degree bends in the oil system on a SBC will drop the pressure about 5 # for every one and that is why race engines feed the the main oil gallery from the top front of the block to eliminate all those 90 degree bends in the stock oiling system.

[Joe L.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

Michael and clem------


I think the biggest reason for the elimination of the brass fitting is that GM was phasing out the use of all NPT fittings for FUEL systems during the mid 60's. As far as I know, there was no use of an NPT fitting on a Corvette fuel system after 1966 and very limited use during the 1966 model year.

I suspect that safety considerations were at the root of it.

[Michael H.]

Re: C2: '66 BB fuel pump outlet thread size & elbow

Michael and clem------


I think the biggest reason for the elimination of the brass fitting is that GM was phasing out the use of all NPT fittings for FUEL systems during the mid 60's. As far as I know, there was no use of an NPT fitting on a Corvette fuel system after 1966 and very limited use during the 1966 model year.

I suspect that safety considerations were at the root of it.

I never thought about that but it's probably correct. Also, when 90* NPT fittings are used, it becomes time consuming on the assy line aligning the fitting properly so the vertical part of the fuel line is in the correct position.

Seems like fittings with NPT always reach proper torque about 15* past it's correct installed position and one more turn is not possible.