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Scrapson

Bent valve?

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I had been driving normally not flooring it or anything and got an intersection and it died it started back up but refused to idle and now the idle is rough and high. It sounds like a bent valve but I’m not sure. I don’t know where to find valves for it and to get the valve out I have to take the head off so any tips of taking the head off with less pain than it is or suggestions for what might’ve happened because I have not a clue what happened it just did. It’s a 79 datsun 620 2.0liter never have had this or similar happen. I swear I’m here at least once a month

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You can't possibly know or suspect a bent valve, they don't just happen driving around. There are probably dozens of easily fixable causes for the symptoms you describe.

 

Take the top off the air filter when the engine is warm. Is the choke plate partly closed? If the wire fell off the choke heater it might come partly on and not only run poorly by set the fast idle on. The choke plate should be fully vertical.

 

 

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Maybe remove the spark plugs to see if one or more are fouled?  Start with the easy stuff first and assume total chaos last?  Maybe your first step should be to buy a shop manual.  The diagnostic sections are very helpful and its a good investment for some day when you WILL need to remove the head.    

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Pull the valve cover and look for loose lash pads. Then rotate the engine and look/feel for loose valves. If you find one that is REALLY loose, it may be bent. If you don't find anything odd, adjust the valves while you're in there and button it back up.

 

If you do need a valve, an engine machine shop can get one for you. (Surprised more people don't know about machine shops...)

 

But yeah, valves don't just bend. A lot of shit has to happen before a valve gets bent.

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I pulled the valve cover and it all looked and felt pretty fine. I think it could be in the carb I’ll check but I should probably do the head gasket because it sprays oil and I don’t know where from. 

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if it was running you wouldn't be doing a head gasket.

How about fix whats wrong 1st .

 

where you get the idea a valve went bad? Im trying to figure out your trouble shooting skills. taking a head off is going to be a lot of work for a novice with a emission geard L20.

 

you check the lash pads under the valves? Not missing.

 

you see if gas is squirting in the main barrel of the carb, maybe pour a tiny bit in and see if starts. If not gas its needle valve on carb, fuel pump

bolts tight on carb and intake

fuel filter.

check the distrutor cap and coil wires for looseness. coil wire tight ect……..

 

I think this is a simple fix most likley

Edited by banzai510(hainz)
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It just happened after driving for an hour but then it stopped running it cranked right over then started diseling which was probably linked to the carb prior because after tuning the carb prior it was fine but I’ll drive it out to have someone look over the carb since I don’t know how that well. It is a Weber 32/36 and I have a large vacuum leak on the intake manifold where the old emissions stuff went. 

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6 minutes ago, Scrapson said:

It just happened after driving for an hour but then it stopped running it cranked right over then started diseling which was probably linked to the carb prior because after tuning the carb prior it was fine but I’ll drive it out to have someone look over the carb since I don’t know how that well. It is a Weber 32/36 and I have a large vacuum leak on the intake manifold where the old emissions stuff went. 

not to be offensive or anything but it doesn't seem to me that you know anything about an engine very well. Get some pics of the plugs and post them here. check your plug & wires, get a spark tester, check your cap and rotor button for corrosion, look for a bad or open vacuum line, check your fuel filter, air filter, etc etc. there's a half a million reasons a car could stop running properly. one of the very last of which is a bent valve.

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as for the spraying oil, that sounds more like a valve cover gasket, timing cover gasket, or pan gasket to me. I'd check those first before doing a headgasket. that's a fairly large undertaking.

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First thing you need to do is plug the vacuum leak on the intake manifold.

Edited by wayno
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1 minute ago, wayno said:

First thing you need to do is plug the vacuum leak on the intake manifold.

that was the first thing that came to my mind. I had a manifold vacuum leak on an A15 a few weeks ago. the hose was old and dry rotted and just popped off. stuck it back on and went back to runnin smooth.

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To add to the oil leak comment... there is only a single small diameter hole that feeds oil to the head..... its between cylinders 2 and 3.... 

So dont go down the replace the head gasket route to quickly....  gdat210 stated the most likely location for leaks...

Maybe start with a good cleaning of the motor then you'll be able to see where the leak is better.... careful of the electrical stuff like the distributor.... dont need to cause more trouble..  

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36 minutes ago, gdat210 said:

not to be offensive or anything but it doesn't seem to me that you know anything about an engine very well. Get some pics of the plugs and post them here. check your plug & wires, get a spark tester, check your cap and rotor button for corrosion, look for a bad or open vacuum line, check your fuel filter, air filter, etc etc. there's a half a million reasons a car could stop running properly. one of the very last of which is a bent valve.

I did check for spark that was the first thing I did after checking the fuel filter I also tested the fuel pump which seemed to be pushing enough fuel through to the carb. my last theory which I don't think it would be is the clutch not engaging which could lead to a rough idle from starting in gear with the clutch in. I checked the majority of the vacuum lines also they looked fine and the air filter is still good. I am going to replace all the spark plugs they appeared to be mismatched from the previous owner. it is a new cap and rotor but I will check it the wires are in good shape. The vacuum leak is off of the intake manifold I will take a picture when I get home but it is from the old EGR setup which I removed about a month or so ago. I checked the timing chain for tension and it should be replaced at some point. I will plug the leak area and check more. thank you for all the suggestions I hope it is nothing too gnarly to fix I will double check all my lines and carb but one thing I forgot to mention is there is not that much fuel in the filter after I checked it and it started running odd instead of half full like it normally is when I shut it off it is almost empty I will replace it if there is a clog in it or something.

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1 hour ago, Scrapson said:

I did check for spark that was the first thing I did after checking the fuel filter I also tested the fuel pump which seemed to be pushing enough fuel through to the carb. my last theory which I don't think it would be is the clutch not engaging which could lead to a rough idle from starting in gear with the clutch in. I checked the majority of the vacuum lines also they looked fine and the air filter is still good. I am going to replace all the spark plugs they appeared to be mismatched from the previous owner. it is a new cap and rotor but I will check it the wires are in good shape. The vacuum leak is off of the intake manifold I will take a picture when I get home but it is from the old EGR setup which I removed about a month or so ago. I checked the timing chain for tension and it should be replaced at some point. I will plug the leak area and check more. thank you for all the suggestions I hope it is nothing too gnarly to fix I will double check all my lines and carb but one thing I forgot to mention is there is not that much fuel in the filter after I checked it and it started running odd instead of half full like it normally is when I shut it off it is almost empty I will replace it if there is a clog in it or something.

I'd definitely swap that fuel filter out first. if it was the clutch it would run fine in neutral. try fixing that manifold leak first and see what happens. you may be surprised.

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long as the fuel filter is new it fine half full.

 

if ypu put a weber on there this should be EZer to figure out. just make sure the bolts are snug.  Sometimes people put the carb adapter on the carb wrong and causes a gap.

 

 

if you see gas squirt in the carb and you have spark it should fire if one has compression. Compression needs to make sure the valves are gapped correctly.

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So blown headgasket I compression checked it the cylinder 2 was lower than the rest by a moderate amount. So I’m pulling the head off replacing the gasket also the timing chain tensioner is broken. 

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6 hours ago, Scrapson said:

I did check for spark that was the first thing I did after checking the fuel filter I also tested the fuel pump which seemed to be pushing enough fuel through to the carb. my last theory which I don't think it would be is the clutch not engaging which could lead to a rough idle from starting in gear with the clutch in. I checked the majority of the vacuum lines also they looked fine and the air filter is still good. I am going to replace all the spark plugs they appeared to be mismatched from the previous owner. it is a new cap and rotor but I will check it the wires are in good shape. The vacuum leak is off of the intake manifold I will take a picture when I get home but it is from the old EGR setup which I removed about a month or so ago. I checked the timing chain for tension and it should be replaced at some point. I will plug the leak area and check more. thank you for all the suggestions I hope it is nothing too gnarly to fix I will double check all my lines and carb but one thing I forgot to mention is there is not that much fuel in the filter after I checked it and it started running odd instead of half full like it normally is when I shut it off it is almost empty I will replace it if there is a clog in it or something.

 

39 minutes ago, Scrapson said:

So blown headgasket I compression checked it the cylinder 2 was lower than the rest by a moderate amount. So I’m pulling the head off replacing the gasket also the timing chain tensioner is broken. 

 

Forget the clutch it has nothing to do with your idle or running.

 

Plugs should be BP6ES only use NGK!!!!!

 

32/36 conversions are well known for adapter bolts coming loose or the adapter cracking from over tightening causing a vacuum leak. If you have a vacuum leak, FIX IT first. I think you may have two separate problems.

 

Full or 1/2 full fuel filter means nothing.

 

There is no check for timing chain tension. There is a check for timing chain stretch which will cause the cam to be too advanced. If found to be stretched, Nissan has provided a way to adjust it out. 

 

Compression readings.

What does moderately low mean???? What are all the cylinder compression numbers???

 

Compression testing should be done on a warm engine and the numbers recorded. Odd readings should be repeated to be sure. When compete, squirt a tablespoon of oil in the plug hole and do them again and record the numbers.  They should all come up slightly but if a very low cylinder comes way up then the rings are likely the cause.

 

A low cylinder can also be a badly sealing or a burnt valve.  So I wouldn't race to pull the head off until I was sure and ready to replace it or do a valve job.

 

It's hard for a gasket to blow without hitting another cylinder or the water jacket. It it blows between cylinders both will read lower. If into the cooling system water can be sucked in causing a steamy exhaust and at the same time compression gets onto the cooling system over pressurizing it and pushing coolant out the rad cap. If you are constantly replacing lost coolant, this can be the cause.

 

 

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Low compression on that cylinder check the valve lash on intake and exhaust. When lobes are up see if rocker is TIGHTt. Overtime the valve will sink making the valve not fully close making you loose compression 

Edited by banzai510(hainz)
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I don’t have the compression I should’ve written them down but the chain needs to be replaced and I found my oil leak so that’s a plus but I gotta pull the timing chain cover to replace that gasket because it’s wet there which is my assuming leak. Also any tips to get the broke valve cover bolts out? Also it refuses to stay running which is my other thought of lost compression but I don’t know much about engines I just know some simple things. Also why the hell is it dieseling and I have no pressure in my cooling system I’ve replaced the cap 3 times to fix it and this just happened yesterday aswell I didn’t mention it. 

Edited by Scrapson

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If you cannot build any pressure in your cooling system either you have a leak somewhere which you should be able to find because of coolant on the ground or you have a blown head gasket.

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27 minutes ago, Scrapson said:

I don’t have the compression I should’ve written them down but the chain needs to be replaced and I found my oil leak so that’s a plus but I gotta pull the timing chain cover to replace that gasket because it’s wet there which is my assuming leak. Also any tips to get the broke valve cover bolts out? Also it refuses to stay running which is my other thought of lost compression but I don’t know much about engines I just know some simple things. Also why the hell is it dieseling and I have no pressure in my cooling system I’ve replaced the cap 3 times to fix it and this just happened yesterday aswell I didn’t mention it. 

a head gasket will often pressurize your coolant system and blow it out the radiator. id lean much closer to a bad ring or burnt valve. post compression numbers and try the oil trick datzenmike mentioned. youre missing a lot of information, try to slow down and read what people are recommending.

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A little knowledge is very dangerous.

 

 

 

Well do the test again again. Then do again with a few squirts of oil in each cylinder. Record the results.

 

How are you coming to the conclusion that the chain needs replacing????

 

Dieseling is probably the weber carb that's on it. The stock Hitachi has an idle cut or anti dieseling solenoid to stop dieseling and the weber probably doesn't. Just hold the brake on, put in 4th gear, let up the clutch like your going to drive away and as the engine lugs down turn the engine off and it stalls right away. Wait till fully stopped and let the clutch up all the way. Three or four tries and you'll do it so well no one will even notice.

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I fixed the lower radiator hose leak it doesn’t leak from there anymore but I will do a compression check tomorrow after work which won’t be till 8 west coast time. I’ll try the oil trick as well but I had the local mechanic swing by to take a gander and the valves are loose as shit on cylinder 3 and 4 like incredibly loose also the chain is slapping on the cylinder head I’ll post pictures in the morning when I wake up before school. I figured it might be the carb that causes the dieseling but I fixed it by adjust the air fuel mixture screw I think it was and it hasn’t done it since till now. 

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Nissan could not stop the dieseling until they put a cutoff valve in the carb, you have a Weber which has no cutoff valve, so you need to learn to leave it in gear, put your foot on the brake, turn the key off and let out the clutch at the same time, no more dieseling.

These trucks are not new vehicles that cost a shitload of money, they are simple low cost vehicles that one can work on on the side of the road to get home to make a proper repair, these vehicles talk to you and most the time give a warning that something is wrong, it's not ever going to be a modern vehicle unless you put a modern engine/wiring harness in it.

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That part I understand as soon as it bogged and died I figured something was wrong so I stopped at a friends house got it running ish and made it home to pull the valve cover off. I’m going to have a mechanic come by and see what he has to say about it again since I pulled it apart a little more.it seems odd that it would just happen randomly like I was hotrodding or anything stupid just going 55 on a highway. The rocker or whatever it is under the cam that sits about the valves is loose as hell so we shall see. 

Edited by Scrapson
I can’t english

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