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newb questions


tnip

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first of all i have a '71 521 w/ L16 and weber 32/36 carb.

 

1. i was told by the PO that the #2 and #3 cylinders have low comp. apparently about half of what they should be. while #1 and #4 have good compression. the truck does not smoke at all. as far as i know with it not smoking this could be caused by a bad valve seat. am i right? EDIT: my dad said that he thinks that i just need to loosen up the head bolts and re-tighten them in proper order and to proper torque, but wouldn't it smoke if that was the only problem? is there something else (like rings or head gasket) i need to look into or what do you guys think?

 

2. while giving it a tune up i noticed that the dizzy was not actually screwed down and so i fixed that and then rebuilt the carb and while i was messing around with the adjustments to get it to run smoother i had to have the dizzy very advanced, more than the stock adjustability of the dizzy. does this indicate the timing chain needs to be replaced, or just re-aligned or what?

 

3. does anyone have a stock lower alternator bracket i could purchase. the alternator in my truck is not original and the lower bracket is some fabricated (poorly) thing that prevents me from aligning the belt the right way and on top of that the alternator is not charging the battery. so i'd like to just get a stock alternator in there. kind of get everything back to stock and then go from there.

 

4. the PO installed an electric inline fuel pump just after the tank and just after buying it i found out the stock pump worked fine and it would start and run fine (altho it was setup to run super rich). after rebuilding the carb and tuning it properly i now have to use the elec. pump to start it but after that i can turn it off and it runs just fine. what does this indicate? i would like to be able to only run the mechanical fuel pump, what could i do to change this?

 

thank you very much to anyone that has any information or answers to my questions.

 

-thomas :confused:

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1:The motor could just be worn. There is a possibility that the head gasket is blown between the two middle cylinders and would cause both to be low. If you should change the gasket, check that the head isn't warped. I've had a warped head on my old 521 and it caused a gasket failure.

 

2: The dizzy is driven off a gear on the crankshaft and is independant of the timing chain. If you are at the limit of adjustability you could remove the oil pump and advance the oil pump/distributor drive spindle one tooth to put it in range.

 

3: I think a 620 L20B alt (40 amp) and bracket will fit fine and is a nice up grade. The best one to get is the one with the internal IC regulator ('77 and up?). I had a 720 60 amp on my L20B and it worked fine ('80 and up). You would have to figure out the wiring to eliminate the fender mounted regulator.

 

4: Check the line from the tank for kinks or restriction as this may make it difficult for the mechanical pump to suck gass from the tank. Pushing gas is always easier for any pump ind could be why you need the electric one. If the lines check out ok maybe replace the mechanical pump.

 

This is by no means all the answers to your questions. I might also suggest setting valve lash too.

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1. so basically i should just go ahead and pull the head and check the gasket. how would i go about checking to make sure the head is not warped so as to prevent gasket failure? take it to a machine shop?

 

2. what would make the engine need this much advancement?

 

3. this alternator has an internal regulator but i'm guessing something is not right with it because it's not charging the battery.

 

4. all the lines are fine, it's just odd that it would start and run with the mechanical pump when it was running super rich and needed a rebuild and tune up... and now the mechanical acts like it's not strong enough to start it?

 

i should do the valves today, give me something to do this afternoon.

 

thanks mike

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tighten the intake bolts upper and lower

adjust the valve lash. on the 2 3 just to make sure the valve are closing all the way. If worn ring you would have alot of blowby(stinky smell from the valve cover outlet.

 

On the dist to much advance to get it to run maybe means the dist is off a tooth.. But it would be at the end of the slot where the 10mm bolt goes thru.

 

the fuel pump remove the output line and start the rig if gas comes out I would say its OK.

 

if you have a internal regulator did you remove the extnal reg(dissconnect the plug?)

http://datsun510.com/photopost/showphoto.php?photo=124&size=big&papass=&sort=1

this is for a 510 but give you a idea of what to do.

 

The alternator bracket. If a bigger alternator is used on the 521 it will hit the idler arm thingy. the 521s use a sheet metal stamped type alternator bracket to the block and use a 35 amp alt. The later l20 ones I seen also used the same alternator so cant confirm other peoples what they have seen.I assume cause of the idler arm get in the way. The later bigger alternator use a bigger bolt also that goes thru them as the earlier 35amper use the thinner bolts. So you need to know what your looking for. (50ampers I use the 3/8 bolt, I have the 510 alt brackets machined out)

 

The upper alt bracket u put it on one side of the alternator or the other side so it doesnt put a load on the bracket cause it will crack at the lower slot adjustment. or add washers to the front cover(radiator has to come off to get the bolt all the way out)

 

Hope this helps but this is all a ez fix. well maybe the head gasket part. Better now in Summer than winter

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1. so basically i should just go ahead and pull the head and check the gasket. how would i go about checking to make sure the head is not warped so as to prevent gasket failure? take it to a machine shop?

 

4. all the lines are fine, it's just odd that it would start and run with the mechanical pump when it was running super rich and needed a rebuild and tune up... and now the mechanical acts like it's not strong enough to start it?

 

i should do the valves today, give me something to do this afternoon.

 

thanks mike

 

1:If the gasket is blown, you will see the gap between cylinders 2 and 3 when you take it off. You can check for warpage yourself. Clean the head surface and borrow a precision straight edge or long ruler. Place diagonally across the head surface in an X pattern and measure with a feeler gauge. Warp must not exceed 0.003" over 6" or 0.005" over the total length of the head. If it does, have it milled at a competent shop, as replacing the gasket only will see it fail again in a few weeks.

 

4: There should be enough gas in the carb to start any motor even if the pump has been removed. Is the fuel level in the carb at the right height?

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