Jump to content

Recommended Posts

My engine on my 48 Chrysler is a 251 and I want to try and see if I can use a fuel pump off a '47 with the same engine.  However as the pictures show the contact arm that rides on the camshaft is different.  Firstly the arm on my '48 fuel pump has a bend in it.  The '47 is straight.  But I've studied the two  and taken lots of measurements and I'm pretty sure the only difference is the angle of the wear area, as it touches the cam.  However the '47 is slightly shorter, about a 1/16".  The picture of the wear mark is from my '48 fuel pump.  So since they ride on the cam about the same place once you subtract a 1/16"  you can see that if I install the '47 in my engine there won't be much steel past the wearing area. 

Should I assume that the wearing point is bottom dead centre of the cam so to say?  

I'm curious about what direction the cam is turning?  If it's turning counterclockwise then that might be a bit comforting because the rotation will be going away on the arm.  If it's turning clockwise it will be turning towards the arm. To make my point if I was to put a really thick gasket on the fuel pump and the cam was turning clockwise, I would be worried that the arm might slide up a bit and get destroyed.  Thinking that scenario through the weak point would probably be the aluminium body of the fuel pump. I don't really want to take that risk of breaking anything to be honest.  

As for the angle of the wearing point on the  two different arms in relationship to the cam, I can't really see what difference it might make as long as it is making contact at the dead bottom of the camshaft.

You might be wondering why I want to try this and that is a nightmare of a story.  Long and short of it is I don't have my '48 fuel pump and I have no idea when I will see it again.  So I'm hoping this will be an alternative solution, short of going online and buying a new one which will probably be made in China and who knows what shape or length of arm it will have. 

20191205_102959.jpg

20191205_114940.jpg

Link to post
Share on other sites

If the correct part is available just buy one ... I do understand your logic - honest,  but after 60 years of amateur wrenching I have learned that if the factory changed the part there are other not so obvious changes and you will just break something else. There are a lot of Mopar vendors out there and my guess is a lot of nos fuel pumps - not chinese repro stuff. The last time I needed a starter for a Mopar 6 I bought one at a small town NAPA - still in the box and still wrapped. I imagine fuel pumps fall into that category. Mechanical parts for those Mopar straight 6's aren"t scarce - they didn't break often.

 

Just my two cents

  • Like 2
Link to post
Share on other sites
On 12/13/2019 at 6:46 PM, vermontboy said:

If the correct part is available just buy one ... I do understand your logic - honest,  but after 60 years of amateur wrenching I have learned that if the factory changed the part there are other not so obvious changes and you will just break something else. There are a lot of Mopar vendors out there and my guess is a lot of nos fuel pumps - not chinese repro stuff. The last time I needed a starter for a Mopar 6 I bought one at a small town NAPA - still in the box and still wrapped. I imagine fuel pumps fall into that category. Mechanical parts for those Mopar straight 6's aren"t scarce - they didn't break often.

 

Just my two cents

Here in Canada genuine parts are more scarce.  Not only that, but I've found that on several occasions local parts stores show a listing for exactly what I want, but when it arrives it's not correct.  I think it's probably that the people classifying the parts don't really know what that particular part is. Perhaps they have a "close enough " attitude.  Perhaps there is a "search engine" influence as well.  I'm sure we've all searched for a car part and by the time we get to the second page of google we're looking at clothing stores selling socks or whatever.  When you tell the parts counter guy that the part is identified incorrectly, it doesn't get corrected.  The guy at the counter getting minimum wages just doesn't care and just can't be bothered to let anybody know.  I miss the days when parts counters had parts books on the counter all covered in grease and dog eared.  Not only is the p/n correct but it's sitting on the shelf in isle 3.

Link to post
Share on other sites

I' not sure about the ethanol situation in Canada, but if your modern fuel has ethanol blended in then you should rebuild any NOS pump with modern pieces to avoid any issues with using ethanol fuel.

Same goes for all of your rubber fuel lines.

Swap them all out so you don't develop a dangerous leak somewhere and risk having a fire.

Link to post
Share on other sites

They are indeed very similar. The one with the slightly bent arm at the tip, will it have a longer pump stroke? Maybe meaning more fuel volume will be pumped. Not pressure. Just volume? Perhaps the bent tip version was for a straight 8 engine. Or a larger engine like a 265, which consumes more fuel?  More fuel is pumped per stroke with this one?  Just guesses here. 

 

Perhaps the bent tip is for a cam with a different profile on the fuel pump lobe?  

 

I’d certainly try it. I’d confirm fuel pressure with a gauge too 

Link to post
Share on other sites
7 minutes ago, zepher said:

I' not sure about the ethanol situation in Canada, but if your modern fuel has ethanol blended in then you should rebuild any NOS pump with modern pieces to avoid any issues with using ethanol fuel.

Same goes for all of your rubber fuel lines.

Swap them all out so you don't develop a dangerous leak somewhere and risk having a fire.

Yes, I believe the ethanol was probably the reason the diaphragm deteriorated originally.  I've replaced the rubber fuel line section just before the fuel pump as well.  Although I haven't had the car up in the air to have a close look,  I think the rest of the fuel line is all metal.  Since I've had the car I've only used 94 octane gas.

Link to post
Share on other sites
1 minute ago, keithb7 said:

They are indeed very similar. The one with the slightly bent arm at the tip, will it have a longer pump stroke? Maybe meaning more fuel volume will be pumped. Not pressure. Just volume? Perhaps the bent tip version was for a straight 8 engine. Or a larger engine like a 265, which consumes more fuel?  More fuel is pumped per stroke with this one?  Just guesses here. 

 

Perhaps the bent tip is for a cam with a different profile on the fuel pump lobe?  

 

I’d certainly try it. I’d confirm fuel pressure with a gauge too 

I've been curious about that as well.  I think my service manual says what the flow should be, but I can't remember what it is right now.  If the pump that was on the car did have more volume than what it is supposed to be, what effect would that have on the running of the car?

Link to post
Share on other sites

The float will dictate how much fuel goes into the bowl. If the fuel pressure remains the same, the float should open normally. I tend to think the bowl will fill up quicker due to more volume, and close again as it should.  No?

Edited by keithb7 (see edit history)
Link to post
Share on other sites
4 minutes ago, keithb7 said:

The float will dictate how much fuel goes into the bowl. If the fuel pressure remains the same, the float should open normally. I tend to think the bowl will fill up quicker due to more volume, and close again as it should.  No?

I'm no expert with the inner working of the valves in a fuel pump but what you say makes sense.

Link to post
Share on other sites

Inside the fuel pump, the inlet and outlet valves open and close when fuel pressure overcomes a mechanical spring that keeps those valves normally closed. Fuel pressure (hydraulic pressure) is what overcomes the springs, not fuel volume. 

 

Regarding the float inlet needle valve and seat: The needle remains seated by mechanical pressure forced upon it by the float. The float drops, when fuel level lowers in the bowl. Then the needle opens and fuel flows in. Say at about 3-4 psi. If a fuel pump makes more hydraulic pressure than the float needle valve and seat's mechanical pressure that is designed to keep it closed, the fuel pressure can force the needle off the seat. Causing too much fuel to enter in the bowl. Depending on fuel pressure, possibly flooding the engine, or at least creating a rich Air/Fuel mixture.

Link to post
Share on other sites
4 minutes ago, keithb7 said:

Inside the fuel pump, the inlet and outlet valves open and close when fuel pressure overcomes a mechanical spring that keeps those valves normally closed. Fuel pressure (hydraulic pressure) is what overcomes the springs, not fuel volume. 

 

Regarding the float inlet needle valve and seat: The needle remains seated by mechanical pressure forced upon it by the float. The float drops, when fuel level lowers in the bowl. Then the needle opens and fuel flows in. Say at about 3-4 psi. If a fuel pump makes more hydraulic pressure than the float needle valve and seat's mechanical pressure that is designed to keep it closed, the fuel pressure can force the needle off the seat. Causing too much fuel to enter in the bowl. Depending on fuel pressure, possibly flooding the engine, or at least creating a rich Air/Fuel mixture.

That's interesting what you said at the end.  Because even though I have rebuilt my carb, it still is rich on start up. (Big soot stain on the ground) So what you say could mean I have the wrong pump on and I might be better off with a pump similar to the '47 in the picture above.

Link to post
Share on other sites
1 minute ago, timecapsule said:

That's interesting what you said at the end.  Because even though I have rebuilt my carb, it still is rich on start up. (Big soot stain on the ground) So what you say could mean I have the wrong pump on and I might be better off with a pump similar to the '47 in the picture above.

 

Your soot issues sounds more like a choke issue if it's only on startup.

If it is running rich continuously and you can't adjust it down using the needle(s) then you should look at your jet sizes.

But I would still put a fuel pressure gauge on your fuel line to make sure you don't have too much pressure, especially if you're using a substitute fuel pump.

Too much fuel can not only foul plugs but it can leak past the rings and cause fuel dilution in your oil.

That means the oil's ability to limit engine wear will be drastically reduced.

Link to post
Share on other sites

It is supposed to be rich at start up. I am not too worried about the soot stain I also get from cold, rich, start ups. The choke is there to cause a rich air/fuel mixture at start up. Extra fuel is needed as the atomized fuel tends to stick to cold engine parts and condense again, into teeny droplets. Then that fuel never makes it into the cylinders. Once the engine warms up,  the choke opens. Removing the rich A/F mixture. Then the nicely atomized fuel does not stick to the fully warmed up engine parts. By engine parts I mean, intake manifold,  valve ports, cylinder head, cylinder walls pistons. After warm up, you should not see black puffs of smoke from the exhaust, indicating a rich Air/Fuel mixture. Additionally, a rich A/F mixture leads to cylinder washing. Meaning extra wet fuel, slips past the piston rings and ends up in your crankcase. This eventually drops the viscosity of the engine oil. If not addressed, leading to low oil pressure, and failure of vital parts within your engine. 

 

Me? I'd install the pump. Check a few things over, including the fuel pressure that it creates. Test run it. All seems well, I'd run it. Watch your crank case oil level to see it's not creeping up. Indicating an internal leak in the fuel pump, dumping gas into your crankcase.

Edited by keithb7 (see edit history)
Link to post
Share on other sites

I didn't mean to take this discussion of topic by bringing in my richness on start up.

It does clear up in about 3 minutes after start up depending on the day and then it's fine the rest of the day for start up.   Only on a cold engine. 

I've recently adjusted my automatic electric choke ( manifold mounted)  and it was off quite a bit.  However I did this after my fuel pump disappeared so I'm curious to see if it will make a difference once I get a fuel pump back on the car.

Link to post
Share on other sites

Rock Auto shows 2 pumps available for a '48 Chrysler.

At $56.00 and change I would get one from them and not look back.

Has a glass bowl filter on the top, which I think is a good thing.

I got a pump from them for my '40 Buick LTD, several years ago and it still runs fine.

 

Mike in Colorado

Edited by FLYER15015 (see edit history)
Link to post
Share on other sites
7 minutes ago, FLYER15015 said:

Rock Auto shows 2 pumps available for a '48 Chrysler.

At $56.00 and change I would get one from them and not look back.

Has a glass bowl filter on the top, which I think is a good thing.

I got a pump from them for my '40 Buick LTD, several years ago and it still runs fine.

 

Mike in Colorado

Yes I noticed their listings, but when you click on each fuel pump it says it fits C-34, C-36, C-37 but not the C-38

Link to post
Share on other sites
1 hour ago, D Yaros said:

Can the arms on the 2 fuel pumps be switched?

 

I would assume that they can be switched since they are both Carters and since the bodies look the same I would assume the pivot points are in the same place.  However I don't have my fuel pump now.  Only the one off the '47

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...