My Rescue 74 620 L16 4-spd Project Build

[Cardinal Grammeter]

There used to be 2 radiator shops in my town and I knew them both.  Closed.  2-3 more in next towns.  Closed.

 

One left, Moyers, and they said $400-500 to do a recore.

 

NO WAY RAY!

 

I suspect the recore will be extra expensive since the headers are different sizes.  I guess they wanted a wider top tank as a reserve.   (I'm trying to remember if cores come with the headers - years ago I saw one and I think the headers were included)

 

If I could buy the core, I'd do it myself - it is a trivial job to solder in the tanks and mounting brackets.

 

I've been looking at radiator threads and while many radiators have been substituted - no mention of 1) what hoses to use, 2) how did the bolts line up to core support & shroud.  No talk of the crazy hose that "wraps around" the alternator.

[Cardinal Grammeter]

I need a specific recommendation for a new radiator from Advance/Carquest/etc.

 

My main requirement is I'm not going to drill any holes anywhere in the body/core support to install some other radiator.

 

I don't care what hoses I uses as long as they are molded and look OE.

 

My first question is what must be done to fit the 75-79 L20B radiator in the 74 L18?  Yes the core supports are changed, but what are the details.

 

Part of the information is what about the shroud?

 

*     *     *

 

I'm off to search the 5,326 different radiator threads.  There is a specific one for the 74 which I would hope all 74 discussions would appear, but that is not the case unfortunately.

[datzenmike]

I imaging that the EPA has made rad repair shops difficult to make money. (lead) New cars are all aluminum crimp on tanks.

 

Some of the 620s did come with three core rad. Look on the underside of your top tank and you can see where it would go.

[Cardinal Grammeter]

I looked for room for 3-core, but on mine, the top tank and header would do 3, but the bottom tank and header is maxed out at 2.

 

I just learned today how to measure cores (you do NOT include the headers) - just the min-volume that has the tubes and fins.  And then you have to measure the dimensions of the "groove" in the header into which the tank fits.  Usually you do this when you remove the tanks, however, you can see the "outside" of the "V" from the core side of the header - that way you can get these dimensions w/o taking the tank apart.

 

From my measurements, the 74 is 18" wide while the 75-79 is 18-11/16 wide.  I'm hoping that the L20 radiator bracket could be drilled to match the 74 core support holes.  The added height to the 75-79 should not be a problem.

 

I don't know what shroud I would need.  There is a different shroud for each of the (3) engines.  I'm guessing if you fit a 75-79 radiator, you'd still use the 74 shroud?

 

I was also thinking of doing my own recore since I found a place that would sell me a core.  I don't think it would be that difficult except for properly locating the mounting brackets.  I wouldn't be surprised that they adjust a fixture to hold the brackets before they are removed from the radiator.  Then this fixture serves as a jig for reassembly.  Just a theory, but without it, I don't see how you could precisely locate the 4 mounting holes.

 

I'm going to go to the H.A.M.B. and see what those guys have to say about recoring yourself.

[Cardinal Grammeter]

I can buy a custom made core myself for $175 and maybe cheaper if I shop around.

 

The 75-79 (433638) radiator should fit:

 

I took some better measurements of mine and compared to the specs of the 433638:

• 74:  13.25 x 17.75 (is actually between 17.625 and 17.75)
• 75:  13.00 x 18.625

The bolt centers on the 74 are 3/4" out on the flange meaning the radiator could be 1" wider and there would be just enough flange for the OE bolt holes.

 

Which is just the case.

 

The top hose is on the other side but I think if you use a 75 top hose, it will work.

 

This should be a NO BRAINER and yet, no one is claiming this!  So that means there is a problem  :excl:

 

There is supposed to be a Ready Rad Application Book that has ALL the radiator dimensions, possibly even the bolt holes and hose locations.  I may also be able to order a 433638 locally just to look at with no obligation to buy.

[datzenmike]

The '75 and up with the L20B have a different rad support than the earlier 620s. It bumps forward to fit a larger rad. An L20B rad may fit the earlier trucks.

[Cardinal Grammeter]

BLOCK DRAIN PLUGS:

 

I think I located one, above the starter.  Are there more?

 

 

RUSTY MUDDY COOLANT:

 

I had some in a drain pan and it sat overnight.  The rust settled to the bottom of the pan - the water was clear. 

 

So one way to get rid of the rust would be to put in a jug, let it settle for 1-2 days and then siphon off the clear coolant w/o disturbing the settled rust.  (Of course if you have the time to wait.) 

[Cardinal Grammeter]

STATUS:  Some Progress.

 

FLUSH COOLING SYSTEM:

 

Used 1/2 bottle of CLR for about 30 minutes.  Incredible rusty froth under radiator cap.  Not too much came out - some dirty water but fairly clear.  Had to run screwdriver into block drain hole to get good flow.  I suspect there is a deep layer of rust cake in the bottom of the block.  Procrastinating the purchase of the 433638 L20B radiator and new water pump.

 

CARB ISSUE APPEAR TO BE A WORN PRIMARY THROTTLE PLATE:

 

The linkage return spring force goes into the accel pump lever, through the link/push rod, to the throttle linkage.  The link is "tilted" so that it produces a thrust load on the throttle shaft that causes the throttle plate to wear on that side.when it is open. 

 

Why the linkage "stuck:"  When the throttle is open, the shaft slide outward due to the wear.  Now here is the killer:  when the throttle is closed, the shaft has to slide inward against the spring/link load.   And this does not happen - the shaft has to slide back over a very small change in throttle position - it appears as a binding in the linkage.

 

Replaced plate from parts carb and  idle is dramatically stable now.

 

ASSHATS JACKED MY TORSION BARS

 

Not only did they raise the suspension 1" on one side, but they did 1.5" on the other side.  I had a 4 inch "H" distance on the lower control arm.  Just looking at the truck, you could see the front was actually higher than the rear.  Got it to OE height and handles much better.  I think I will lower it 1/2" next.  Ultimately maybe 1" lower - will have to see how how close the bumper is.
 

[Cardinal Grammeter]

STATUS:  One step forward, two steps back:

 

After all that work on the cowl, it was raining today and when I got in, there was a rivulet of water coming from behind the heater box.  I know I should have taken a hose to the cowl when I thought I had it finished, but that would have made a big mess where I was working.

 

And then some Same Old:

• Dealing with rusty, creaking, upper inner rear control arm bushing.  Available, but price is a major issue.
• Still vacillating over popping for a new L20B radiator since although mine had a tube that cracked and leaked, the radiator is holding pressure well.  And then there is the noisy water pump bearing...
• Carb throttle plate changed but still idle, choke and fast-idle issues - is not stable.
• Deciding whether to put a heavy 1/2" conveyor belt mat in the bed.