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Vibratey little motors


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I'm noticing some little traits of the L block.


I know it's inherant for the carb to come loose periodically. I actually had the bolts for my alternator come loose as well. Just something I need to add to a periodic check list, make sure the bolts on the motor stay tight.


I'm curious if anyone's found a decent solution for this. I've been using lock washers everywhere I can, hopefully that'll solve it. Now that I know what's happening, I at least know to keep an eye on it.

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For the carb.  I did this to a 12MM wrench.


Not only is the wrench bent, but one jaw is ground down.

To put the carb on the manifold, put the most difficult to reach flat washer, lock washer, and nut on first.  just start it.  Put the next most difficult washers on next, and leave them loose also.  Put the rest of the nuts, washers, and do not forget the throttle cable bracket.

Use the bent wrench to tighten the most difficult to reach nut first,   Then tighten the nut diagonally across the carb base.  Then the nut on the long side of the cab base, and finally diagonally across to the last nut.  Recheck the first nut you tightned, and follow the pattern above rechecking the nuts.


An option on the lower alternator mount, but this is hard to do with the engine in the truck.  Drill out the holes for the lower bracket, and rethread the holes for  3/8 National course thread.  Then get two Allen socket cap screws to hold the lower alternator bracket to the block. 

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I too had my 521 alt. bolts shear off back in the '70s.The 521 and probably all L16/18s only use two mounting bolts. This makes only two fixed points that can turn on the same axis. All other L20Bs and up use a third mounting bolt and this locks the mount in a third dimension. Use some kind of thread locker on the bolts..

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Yea I am back to 2 bolts on the alt mount, I had to make a custom mount because the alt was to big for the stock mount, so I had to lean the alt so far to the side to clear the hose above it, well that caused another issue, it started hitting the top of the idler arm which would bust the bolts holding the alt on the mount, front one always busted first, and it was a major pain to get it out of the hole after it sheared off.

So I lowered the mount position, I checked the bolts yesterday, they were still tight, that is the longest it has stayed in place so far, I guess if I made another bracket out of a bigger plate I could use all 3 mount bolts.




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I likely have another issue that hurts me, I need to move the mount away from the block, the result is re-clocking the alternator, this moves the base of the pivot point out away from the block, at the same time it pivots the top adjustment point towards the block, the result is that one inch of adjustment at the top makes a bigger difference at the pulley itself, than before when a lot of movement at the top didn't move the pulley out much, it just moved more down towards the idler arm than out.

I need to make another mount for four reasons, the first reason is to put at least 1 inch legs on it, to get the bottom out even farther, as this will make it easier to adjust the belt with less movement, the second reason is to use all 3 mount bolts, the third reason is to move it away from the oil pump so the front mount point will have more meat/metal, as that joint has actually broke on me once, and the fourth reason is that you can see there are washers shimming the alternator forward, I need to have it without shims, or at least thinner shims. 



I do not have studs sticking out of the block to put lock nuts on, so I use bolts, in the photo above you can see there are thick washers under the mount, and thin washers on the outside of the mount, but it doesn't look like there are lock washers, I have used lock washers in the past, but the bolts still fell out, will installing studs and using lock nuts make any difference, isn't that just a bolt?

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Lock nuts are not recommended imo on the block. The heat will cook the rubber making it pretty much not a lock nut anymore. What I'm doing is using a hefty lock washer with thread locker. Hopefully this'll be enough, I'll post up with an update in a few weeks with an update.

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I put lock washers on the bottom alternator bolts and never had a problem again on my L.  Lock washers on the carb studs, never had those rattle loose either.  That's if you use the mount that is drilled and tapped for bolts to go into it.  For the other style, use a KA alternator mount bolt.  Goes through all the way with a nut on the backside.  Trouble-free.

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I actually never had the L20b mount come loose either from the bolts coming loose, but I had to tilt the big IR alt to the side so far to clear the hose above it with the stock mount, that it would hit the top of the idler arm and shear that front bolt off, so then I made my custom mount, that is when I started loosing the mount bolts.


L16 and L18 engines only have the two bolt holes for the alternator and this is the problem. L20Bs have three. I've never had an L20B come loose.

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Lock nuts are usually nylon aren't they? The block wouldn't get any hotter than the oil splashed inside it. Say 250F maybe. That's 175F below it's melting point.

They are nylon yes. I call em rubber just outta habbit. Yes, the engine does run above the melting point, but there's a caviot. When the nylon gets hot for long periods of time, it gets hard and shrinks making it pretty much worthless. I work on bikes a lot and, unfortunately, have experienced this. I know bikes run a bit warmer than cars, but it'll still happen eventually.


This is just what I've experienced.

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I had tons of isses with my 521 alt mount L16 small bolt. I put a 510 mount in wiith a enlarged hole for the 50amper bolt. Think would always rattly loose.

Find out a bolt was busted in one and the threads were enlarged.

I got a one side cleaned up the threads and other I got the longest bolt that I could find and went back to the thinner 521 alt mount which gave me more thread as the 510 mount was thicker. Then I drilled the bolts to use safety wire. Now I have no proplem. I did have to go back and use the 35 amper alternator

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