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Spun bearings. causes and prevention? (L20b)


Dawa

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i wasnt asking the easy solution for how not to oil starve an engine, you silly guy. that was borderline insulting, although i know you meant well. 6 cars & a bike and ive never had an oil problem, it wasnt me that spun that bearing :)

 

i was asking josh817 what the simple solution for the problem he id'ed

 

lol i know but what was mentioned above is just the way the engine is designed unless your going to cast an l series block with modified oil passages there isnt much that can be done. i know there are spray bars for the cam but ive never heard of any oiling mods for the lower end

 

i know im guilty of letting my engine oil run a little low from time to time in the subi but thats cause it leaks like a stuck pig

 

jesse c hit the nail on the head what is there works just fine when you rebuild be sure its clean and all will be good

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The L series has MASSIVE bearings and the crank and rods are well supported. I've driven them with the mains and rods worn through the bearing lining to the copper? under neath. Just keep lots of oil 20W in them when they are old and check often. Anyone with a rod through the block cannot sat there was no warning.

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6 cars & a bike and ive never had an oil problem, it wasnt me that spun that bearing :)

 

 

then why you second guessin yourself with the thread?

 

anyways, since i just did the rod bearings in the Z24 i might have some insight on preventing the bearing from physically spinning in the rod or cap.

 

ive always put red locktite behind the bearings and then let the engine sit over night. never had a bearing spin in one i setup like this. but with machine work being done, it should be in tolerance and not need anything but just to be put together.

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so whats the easy solution

Most of the racers avoid using the 1500. Some sanctioning bodies throw you in a different class or a different set of SCCA/FIA rules if you go with a bigger displacement. For those who insist on more displacement, you have to cross drill the cranks and do some other things.... Comes out to like an extra $600 worth of machine work. I would have to ask my father the nitty gritty details.

 

Mind you though, those motors are more comparable to our J13's than our L motors.

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It's physically impossible to spin a good rod or main bearing. By the time the bearing is ground or pounded down to razor thin so that it can jump up over or slide behind the other or if dry enough to friction weld to the crank, it's a moot point if you have loctite on the backs of them.

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In fact loctite on the backs of bearings might be a very bad idea. If the bearing isn't perfectly placed, then it may stick in the wrong place and bind when you bolt the caps on later. Or worse, when the bearing DOES move when tightening the cap bolts, the dried loctite can end up in the oil passage and going through the bearing, or pilled up behind the bearing, causing deformation.

 

However, I've seen it done by professional builders. But then again the same professional builders slather orange RTV (or any other sealant) like peanut butter on brand-new gaskets. Old habits die hard.

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then why you second guessin yourself with the thread?

 

i want to apologize for the last few posts because i was getting defensensitive

because everyone was mentioning common sense solutions that anyone with half a brain should know

(keep the engine oiled, assembly it properly, etc.)

 

i started the thread because i assumed that the recent sufferers of spun bearings on their L20s were keeping

up with their oil and that it MUST be something else besides common maintenance that was causing this problem.

 

turns out people just arent taking care of their engines facepalm.jpg

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i know there are spray bars for the cam but ive never heard of any oiling mods for the lower end

 

One mod to get more oil to the bottom end is to drill the main feed holes in the block, but only the #2 and #4 main feed holes. Drill them to 1/4" and drill the main bearing oil hole also. Since the rods are fed through the #2 and #4 mains, the others are left alone. Also, make sure you get a bearing set that has full grooves, not just grooves in the upper bearing half. If you can't find them, you can use two bearing sets. I have even machined the groove in before (like on a KA24).

 

In fact loctite on the backs of bearings might be a very bad idea.

 

Right, but for more reasons than the reason you described. Heat transfer from the bearing is crucial and the way the bearing sheds it's heat is back into the block. Next time you tear down a motor, look at the back of the bearing and notice the cross hatch and discoloring in the back of the bearing. These are good, as it means the bearing is seated in the block tight enough to etch these markings in the back of the bearing. One test to see if they have lost their tension is to feel how tight they fit by just installing them and removing them. If they don't want to hold in place, then they have sprung and should be replaced. Note- you can bend them backwards slightly and very carefully to regain some of this tension.

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The same can be said about rod bearings, but one important factor key to rod bearing health is detonation. Some detonation can be heard (pinging) but other detonation cannot. Either way, detonation pounds a rod bearing and it can actually be in measurable amounts. It can be so bad that it pounds the tension right out of a bearing.

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So the main causes are these?

* Running out of oil

* Improper installation

* Extended detonation (for Rod bearings)

 

 

The FSM says to measure this, I wonder how many guys do it. I know a lot of guys put new bearings in without checking the installed clearance so they probably don't do this either.

24984.jpg

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So the main causes are these?

* Running out of oil

* Improper installation

* Extended detonation (for Rod bearings)

 

 

In order of likelihood of bearing damage, I would say

 

*Continuing to run heavy loads on very worn bearing and not checking the oil level enough.

This probably covers almost all bearing failure problems. Most 30-40 year old motors are... very worn. They probably have worn rings and lots of clearance and use oil and so it needs checking even more often.

 

*Extended detonation.

Can happen even on a new L series motor if the timing is run too close to the edge then one day it's hotter or a cheaper (lower octane) gas is used. Older motors tend to be not maintained as well and simple problems are not fixed and so it runs hot or overheats from a bad rad that never gets fixed.

 

Improper installation.

Unlikely from the factory which leaves.... Would be most likely the home mechanic that doesn't have the proper tools or 'doesn't need to check' bearing clearances on his rebuild.

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Or the shadetree mechanic that does this (look VERY closely)

 

#3 (center) Main (cap is to the left):

 

bearing1.JPG

 

 

#5 Main:

 

bearing5.JPG

 

#5 Main with cap off:

 

bearing6.JPG

 

 

 

That was exactly as I disassembled it. And yes, it ran. And had good oil pressure. But as it wore and wore the timing got worse and worse (would change 10-20 degrees between going uphill and downhill... gee, I wonder why?) I took it apart and found the above.

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About 6 years ago I had a chance to get free parts off a 4-door 610 that was going to the crusher. I'd just blown the head gasket on the L16 in my 510, so a free L20 looked like the perfect thing. The 610 looked decent leading me to think the engine might be good enough to just stick in the 510 and try it. I about killed myself pulling the L20 and 4-speed in a pasture is 95F heat, but I got it home. It occurred to me it would only take a few minutes to pull the pan and look at the bearings before dropping it in the 510. Maybe slip in some new bearings if the old ones looked bad. Took off rod bearing caps 1, 2, & 3, and none of the bearings or journals looked especially bad. The face of the bearings had some dark areas, looked sort of dirty, but no copper showing and everything was smooth. I almost put the pan back on, but thought to be thorough I'd look at #4 rod bearing too. Put the socket on the rod cap nut and I felt the big end of the rod move sideways with a clunk. I knew before I finished taking the cap off It was a spun bearing! Part of the reason I jumped to the conclusion the engine might be good is the oil level was up and didn't look very dirty. But most mechanics will tell you it is common AFTER the engine is run out of oil and starts pounding, then the owner adds oil in hope it will cure the problem. And always lie to the mechanic about running it out of oil cause they don't want to look stupid.

 

But the really dumb thing I did was not realizing 610 parts are not so easy to find and someone might want these. I should have grabbed every part off that car EXCEPT the engine. I think the only thing I did get was the pedal set cause I was pretty sure they would work in a 510. Oh well, I'll know better next time.

 

Len

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I didn't even know that was possible.... I know the mains have different widths, didn't know the thrust bearing would fit the rear main.... >______>

 

Anyway, pretty relevant here. Yesterday I was coming back home. Mechanical oil pressure gauge on my L20B. I knew the front oil pan gasket or the front seal was dripping but didn't know the rate of oil loss. Never drips when parked. started her up, running 20w-50, always get 55psi when cold even at idle. So I'm going up the hill, gauge is hovering at 40psi, even though my RPM is increasing. Check the oil level and I'm reading just a nudge under the low mark.

 

So to give you a sense of things, just under or right at the low mark is when your oil pressure gets sketchy. If you have a stock 521, and maybe your oil pressure warning light were out, you would have never caught it. Even a Z electric gauge, a slug of a gauge, wouldn't show those signs right away. Anyway, the low mark, to the high mark, is about 1-1.5 quarts. Don't think I did any damage since I had decent pressure. I mean, 40psi and poking up a slight hill, I don't see any worries. Especially if you like to make her chug, staying in a gear at idle RPM while your pressure is 30psi momentarily.

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L to H is one quart difference.

 

This is where Datsun A-series is superor, it can run two quarts low with no problems. 2-1/2 quarts low is where it becomes sketchy.

I've never understood this. Surely either the oil pickup foot is in oil or it's out - ie it's sucking oil, or air into the pump - not some of both?

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As the oil level get low, the oil pickup sucks some air, and oil, both at the same time. This puts air bubbles, or pockets of air in the oil filter, oil galleys, and eventually pushes air through the bearings, for a short period of time.

The oil pump getting air is most likely when you first start the engine. The oil is cold, and takes a long time to run back down into the oil pan, from the top of the engine. Over head cam engines would be more likely to have a problem with oil staying on top of the engine, simply because there is more oil needed on top of the engine. If the camshaft is in the crankcase, it is getting oil thrown on it by the crankshaft, and oil coming out of the connecting rod bearings. A camshaft in the head is isolated from all that oil splash and needs extra oil pumped to the top of the engine. Another factor is oil expands and contracts a lot between hot and cold. that is why you check the fluid level in an automatic transmission hot.

 

Most mechanical oil pressure gauges are plumbed with too small of tubing, or pipe. If your oil pressure does not rise and fall with the engine RPM, your gauge is not reading your actual oil pressure, it is showing you an average of that your oil pressure was about 10 to 20 seconds ago. If your mechanical oil pressure gauge is not plumbed with AT LEAST 1/4 tubing, is is pretty much just a decoration on the dashboard that really does not give you any useful information.

 

The last Datsun 521 I had as a daily driver has a mechanical oil pressure gauge, plumbed with 1/4 tube. When the oil level got low, when I first started driving a not yet fully warmed up engine, the oil pressure would drop briefly as air bubbles moved through the engine oil system. As the engine got warm, the oil pressure would no longer fluctuate. That is when I knew I had to add some oil to the engine.

 

 

So, how do you keep from spinning bearings, keep the right amount of oil in your engine. If you have an oil pressure gauge, that may give you a clue on the oil level getting low, but it is no guarantee.

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