Random Misfire while cruising

[Racer X]

On 10/27/2020 at 6:30 PM, jalexquijano said:

What about the PCV valve? Could the valve be stucked and the cause of the fouling of that 4th plug? 

 No. A malfunctioning positive crankcase ventilation valve will not affect only one cylinder.

On 10/28/2020 at 3:40 PM, jalexquijano said:

Plug closing has not recur. However i recently installed a set of NGK BP5ES and after 5 minutes of warming, plug 4 came out fouled in dry black oil. I will do a test drive tonight. Saturday i am opening the valve cover. I will not spend US$500 in a set of new valve, guides, seals and seats just for the sake of eliminating all posibilities. 

Dry black isn't oil, oil would be wet. Dry is usually carbon, left behind by the unburned fuel during the misfire. The pictures of the fouled plugs support this. A rich mixture, or a weak ignition spark is typically the cause.

 

 

 

Also, you don't need to pull the cylinder head to change the stem seals (although I don't think this is your problem). A tool to compress the valve spring is required. The tool I have was made for valve spring changes on the L series heads. It is a lever that has two books the go under the camshaft on either side of the cam lobe, and an open cup that fits over the spring retainer. You simply hook it under the cam, push down on the lever, and remove the keepers with a magnet on a stick.

Sorry, I can't seem to find a picture of one.

 Also needed is a means to keep the valve from dropping into the cylinder. I made a tool for this using an old spark plug. I broke the porcelain out of it, cleaned the bore, and welded an air tool quick connect nipple to it. You also need a compressor that will supply enough air flow to keep up with the air leakage past the  piston rings.

You can buy an adapter that does this, but I'm a cheapskate, so I made the tool I described.

 

 One last note. 

 

I noticed there isn't any antisieze on the spark plug threads. It is very important to use antisieze on the threads, and torque the plugs (I set them at 13 ft lbs). If you don't, then the threads in the cylinder head will call, then pull out. Then you will be repairing the threads in the head.

This is what I use. It doesn't take much, just a thin coat, on all of the thread on the spark plug. Be tidy with it, get it on your fingers and it will suddenly be everywhere, something you don't want. I bought a can (it used to come in a steel can) over 40 years ago, and still have over half of it left, and I have changed thousands of spark plugs.

 

 

[jalexquijano]

21 minutes ago, Racer X said:

 No. A malfunctioning positive crankcase ventilation valve will not affect only one cylinder.

 

 

Dry black isn't oil, oil would be wet. Dry is usually carbon, left behind by the unburned fuel during the misfire. The pictures of the fouled plugs support this. A rich mixture, or a weak ignition spark is typically the cause.

 

 

 

 

 

Also, you don't need to pull the cylinder head to change the stem seals (although I don't think this is your problem). A tool to compress the valve spring is required. The tool I have was made for valve spring changes on the L series heads. It is a lever that has two books the go under the camshaft on either side of the cam lobe, and an open cup that fits over the spring retainer. You simply hook it under the cam, push down on the lever, and remove the keepers with a magnet on a stick.

Sorry, I can't seem to find a picture of one.

 Also needed is a means to keep the valve from dropping into the cylinder. I made a tool for this using an old spark plug. I broke the porcelain out of it, cleaned the bore, and welded an air tool quick connect nipple to it. You also need a compressor that will supply enough air flow to keep up with the air leakage past the  piston rings.

You can buy an adapter that does this, but I'm a cheapskate, so I made the tool I described.

 

 One last note. 

 

I noticed there isn't any antisieze on the spark plug threads. It is very important to use antisieze on the threads, and torque the plugs (I set them at 13 ft lbs). If you don't, then the threads in the cylinder head will call, then pull out. Then you will be repairing the threads in the head.

This is what I use. It doesn't take much, just a thin coat, on all of the thread on the spark plug. Be tidy with it, get it on your fingers and it will suddenly be everywhere, something you don't want. I bought a can (it used to come in a steel can) over 40 years ago, and still have over half of it left, and I have changed thousands of spark plugs.

 

 

So you all recommend not taking out the cylinder head refurbished by California Datsun maybe 10 years ago? Mechanics here in Panama charge anywhere from usd 200 to 250 only to take out the head and put it back in. This is exclusive of the cost the machine shop will charge to verify the head cylinder and change all the stem seals.

[Racer X]

6 minutes ago, jalexquijano said:

So you all recommend not taking out the cylinder head refurbished by California Datsun maybe 10 years ago? Mechanics here in Panama charge anywhere from usd 200 to 250 only to take out the head and put it back in. This is exclusive of the cost the machine shop will charge to verify the head cylinder and change all the stem seals.

Based on the spark plug you posted it doesn't look like the problem is oil from a bad valve stem seal, so no, removal of the cylinder head is not indicated.

 

[Racer X]

On 10/20/2020 at 12:11 PM, jalexquijano said:

Just tried a new plug. Car starts to misfire once it gets stucked in traffic.  Im about to get a new valve cover gasket, open the valve cover and adjust the valves to see if there is something wrong with that 4th cylinder.  

If you have the correct valve cover gasket, the grey fiber type, not the cork ones, it should be reusable.keep the gasket surfaces clean, and don't use any sealing compounds. I find on  mine  the gasket usually stays stuck on the cover, so I lay out clean shop towels and set the cover on them while doing valve work. I use stainless steel allen head bolts with flat washers, and a speed wrench with an allen head socket that fits the bolts. Except for setting the initial valve lash on freshly built engines I usually set the valve lash hot, so I gotta be quick. I also use a starter button to bump the engine over. The lash settings can be done moving the engine only once after setting it for number 1 cylinder if memory serves me. It usually takes me 15 to 20 minutes from taking the cam cover off to torquing the bolts on it after I'm done.

Always torque the bolts. With a good torque wrench, like MAC, or Snap Off. I do mine at 10 ft lbs.

How long have you had this car?

How many miles has it been driven in that period?

Has valve train maintenance been done on it since you have owned it?

L series engines demand a well maintained valve train. Keeping things adjusted and watching for developing issues is all part of a regular routine that must be implemented. 

 

 

i 

[Racer X]

On 10/24/2020 at 2:02 AM, siteunseen said:

https://www.google.com/search?client=ms-android-americamovil-us-revc&ei=zeyTX_PtEanO5gK726CwCw&q=head+on+valve+spring+compressor+classiczcars.com+&oq=head+on+valve+spring+compressor+classiczcars.com+&gs_lcp=ChNtb2JpbGUtZ3dzLXdpei1zZXJwEAMyBQghEKABOgQIABBHOgUIABDJAzoGCAAQFhAeOggIABAWEAoQHjoFCCEQqwI6CAghEBYQHRAeOgcIIRAKEKABUPI3WLlWYKdoaABwAXgAgAG9AYgBnQmSAQMwLjeYAQCgAQHIAQjAAQE&sclient=mobile-gws-wiz-serp#scso=_7-yTX-2qF8us5wKCg6CAAg12:3041.333251953125

 

That's the one I have. A bit fiddly, but works. I've swapped out springs with the head on many times.

[jalexquijano]

On 10/24/2020 at 9:54 AM, Mark Maras said:

 New valve seals and checking guide wear would be my next step. It's possible the #4 seal was damaged when it was installed.

How hard could it be to replace only number 4 seal? Any step by step tutorial to to this safely without taking the carbs and head out of the engine?

[Mark Maras]

 Try searching on You Tube. There are some videos there about changing valve seals on L24s and L28s without removing the head and manifolds. 

[Johnny280]

I used this video as a reference: 

worked like a charm for me (with the right tool).  

[Racer X]

On 5/3/2021 at 7:36 PM, jalexquijano said:

How hard could it be to replace only number 4 seal? 

No more difficult than changing any of other ones.

The only limitation would be the mechanical skill and aptitude of the person doing the work.

 

[jalexquijano]

On 5/5/2021 at 3:44 AM, Racer X said:

No more difficult than changing any of other ones.

The only limitation would be the mechanical skill and aptitude of the person doing the work.

 

Well since i bought all the complete valve seal set i believe its better to change them all, so ill guess the head must be removed. What kind of hassle. Mechanic here is charging US$200 for removing the head. 

[Mark Maras]

 The head doesn't have to be removed to change the valve seals. You can do it.

[Racer X]

3 hours ago, jalexquijano said:

Well since i bought all the complete valve seal set i believe its better to change them all, so ill guess the head must be removed. What kind of hassle. Mechanic here is charging US$200 for removing the head. 

The head doesn’t need to be removed to change the valve stem seals. 
 

We covered this before.