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My 620 build thread.

J's 620

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This will be my build thread, follow along if you’d like. I’m only doing what others have done before me. 
 It’s a 76 620, California truck, I’ve added a Weber 38, a Saturn alternator, aluminum 510 radiator with an electric fan, and just put on a stock looking fuel pump that was for a different year truck. I can’t remember what year it was from, I’d have to look. 
 Right now I’m doing a head gasket. Here’s what I pulled off. 


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Lots of crud and build up on the valves, the pistons were covered with a layer of crud as well, cylinders 1 and 4 have some pits like a foreign object was bouncing around in there. They cleaned up easy enough, I’ll have to snag a pic when I get back home.

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6 hours ago, J's 620 said:

There was an oil film in my coolant, but no coolant in the oil. Plus oil leaking off the back of the head like a mofo. I just didn’t want the condition to get worse.


Probably valve cover gasket. Put the old gasket back on, bet it still leaks.

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6 hours ago, datzenmike said:


Probably valve cover gasket. Put the old gasket back on, bet it still leaks.

This could Have been a contributor in the past, I did do a valve lash adjustment about 4years ago at  least and then another check 2 years ago maybe? So that’s a new gasket. There is a lot of build up on the back of the block from this leak so I really can’t tell where the leak comes from. 
 It could even be the oil pan Gasket leaking as well these days. 

I was up in Payette Idaho  helping a friend with some work about 3 years ago now, and my clutch burned out, I had it replaced by a near by shop, they did good work, it’s an LUK clutch, Cones automotive I think is what they were called, they also did the rear main seal for me, and it wasn’t the source of the leak I was seeing from it. They claimed it was coming from the head so at that point I considered it.

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My plan right now is to pull that front cover, clean it up, and replace the timing set. After watching Hainz’s videos a few times, I’ll get to work. 
 I got a timing set from rock auto, it’s an ITM brand and seems pretty good. It has the 8 holes or something in the cam sprocket. The current sprocket  has 4 larger “windows” if you will. Maybe it’s 3, I just don’t  want to go out in the garage and verify. 

Tomorrow I’m taking the entire head to a machine shop. Here’s the plan with that part:  

   •Send the rocker arms and cam to Delta cams, regrind to a “272” grind.

 •44mm intake valves 

 •new guides and hardened seats

 •a good polish job with a port match to the gasket right at the mating surface of the manifolds and head only, and just a blend of that in about an inch, I do not want the entire port reshaped. 

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  • 1 month later...

Lately I’ve been cleaning, painting, and polishing parts. My next step is to replace the timing set, put the cover back on and all accessories, replace the oil pan gasket, and get it ready for the cylinder head to go back on. More pics to come. 

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3 hours ago, banzai510(hainz) said:

Delta Cams were never right the ones I got.  I NEVER USED THEM.

 Interesting, can you elaborate a little? What wasn’t quite right about a delta cam? 
 I’m having mine reground to a 272.

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Well I hope mine has a little lift and duration over stock.

On 8/24/2020 at 12:30 PM, banzai510(hainz) said:

The Lift they claim was off.. I think they listed 450/460 but when I calculated it wasn't more height than stock .

More or less the lobes were flatten out to get the duration out of the lobe.


I paid like 30$ a cam and gave them more cores. This was like 20yrs ago already

 I thought that flattening out the lobes is what any cam manufacturer does?

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They usually cut the back side of the line to get the lift back up and you buy taller lash pads.

then if the lash pads are too tall one gets taller retainers so the lash pad has support on the bottom so they don’t flop out.

there is a place in Australia that has counter sunk lash pads where one can use the stock retainers.All the lash pads I seen are flat which raises the pad up loosing some support.

to measure cam lift take the top of the line and measure and then subtract it from the 90 deg measurement.then x by 1.48 or most do 1.5 and that’s the claimed valve lift.of coarse minus the valve lash

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