How broken is my L20b?

Engine, Transmission and related drivetrain.
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Beev
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How broken is my L20b?

Post by Beev » 29 May 2019 12:59

Hi Everyone,

I wanted to get some opinions and thought the internet might be a good place to find those! Last year I purchased this complete L20b engine:

http://the510realm.com/viewtopic.php?f= ... el#p266792

Once in my hands it has had a bit of a rough go. First the original oil pickup gasket was missing the oil passage hole. This resulted in the engine being run for a minute without oil pressure, it was primed first and no metal shavings showed up in the oil after to cross my fingers it is ok. I was able to resolve that and proceeded to start it but the wiring on the distributor was out 180 degrees and the car made 2 trips and had multiple installations of the manifold as I chased what I thought was a vacuum leak. The place I had to take the car for inspection eventually figured out the 180 degree thing and the car ran much better (shocking I know).

From then it has always had this lag off idle and trouble warming up, I chased the timing, had another fuel injection chip tuned and nothing in fact the problem has continued to get worse. I eventually found a oring seal for one of the FI failed and was dumping excess fuel into the manifold and this was cause some problems but ultimately didn’t fix the main issues.

I finally decided to actually measure the vacuum and ordered a gauge. I was fairly confident there wasn’t going to be a leak and my assumption was the engine is good. However I found that the gauge bounces all over the place at idle and higher RPM. Sometimes it swings in a natural range other times not. This is sometimes compounded I am sure by the FI system as it is trying to figure out what is going on. At low RPM around 925 it is -12 +/-3 inHg, at 700 it bounces the full 0 to -30 range. Another time I tested where I didn’t have RPM showing but was idle (in this case I would guess ~1000-1200 rpm) right after the wet compression test it bounces between -15 and -20.

I think these readings at the very least means my valve guides are worn.

I also did a static dry and wet compression test the results were as follows (Cylinder #, dry psi, wet psi)

1, 190, 270
2, 185, 250
3, 175, 230
4, 210, 260

For all cylinders the compression climbed in regular intervals to their maximum pressure.
Videos of each cylinder test, vacuum gauge, pictures of new spark plugs (less than 50km, 1 is on the right), and a video of smoke from the cylinder head blowby is here:

https://photos.app.goo.gl/jZ61WyXbw5hBUM227

So my questions:
1. Am I correct about the valve guides?
2. Is there something else wrong with my engine?
a. There was a large change on the wet compression test
b. Cylinder 2 and 3 are lower next to each other but still within 15%
3. Is there any other testing I need to do in the current state?

I am hoping I can just get away with redoing the head but if the entire engine is basically shot I don’t want to waste my time and money.

Thanks for your help,

Bevan

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RMS
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Re: How broken is my L20b?

Post by RMS » 29 May 2019 16:31

with the separated runners on your su manifold, getting a clean no bounce vacuum reading will not happen.

when you did your compression test was the battery on a charger, all plugs removed and the throttle wide open ?

for your wet test what did you introduce to the cylinder ?

did you touch the butterfly adjustment screws and what did you use to measure the velocity?

do you want a carb and stock intake ?
two_68_510s wrote:I guess our donkeys are quicker then your sled dogs!

Beev
Posts: 23
Joined: 11 Apr 2018 13:49

Re: How broken is my L20b?

Post by Beev » 29 May 2019 17:13

Hey Robyn! Long time no chat.

Is there a better place I could measure the Vacuum off of?

Not on a charger, battery was new last year, all plugs removed, WOT, engine was hot, did dry test then wet as you can see no pattern to relate to a weakening charge

10W-30 motor oil, 10CC per cylinder

I touched them last year used Empi Universal Pro-Sync Carburetor Synchronizer Tool. Haven't looked at them this year.

I think I gave you a stock carb last year! I still have some of the pieces of a stock intake. I am a little hesitant however to pull anything off yet as I want to determine if there is a signal I can pick up on now to find out what needs to be done. I am a little sick and tired of pulling the intake on and off still from last year. Plus I don't have a lot of experience with Carbs stock or otherwise. I am sure I could figure it out if needed.

datzenmike
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Re: How broken is my L20b?

Post by datzenmike » 29 May 2019 17:49

10cc would account for the huge increase in compression. wow. Usually they go up under 10 PSI.

If the engine had been running OR first start with assembly lube I wouldn't worry.

An engine will not run with the ignition wires 180 out. It's impossible. When #1 cylinder is on the compression stroke #3 plug would get the spark. The distributor can be 180 out but all that's needed is to move the plug wires around on the cap and it will run exactly the same as a properly timed distributor. On a four cylinder you can be 90 and 270 degrees out and again just move the wires around. If it ran better the timing was probably changed.

12 inches of vacuum is low but probably the cam you are running. Large overlap cams have lower intake vacuum, generally.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

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RMS
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Re: How broken is my L20b?

Post by RMS » 29 May 2019 18:27

Hi Bevan sorry to hear your still having problems...

Andrew had that motor running pretty good before it was pulled (witch makes me think its all in the settings).

with individual runners I dont think you can get a clean vacuum signal because your only reading one cylinder and from my understanding even with a balance tube the signal will be all over the map.

have you used a advanced timing light ? one mistake I often see is guys chasing the timing. too much idle with retarded advance.
your cold motor makes me think that's the case.

verify tdc and the timing marks. find out when the mechanical advance starts and how many deg it will produce (@ say 3500) to figure out your max base setting. (search user chickenman / advance he has a few really good write ups) once you have exhausted all efforts in timing move back to the carbs/throttle body, lower the idle and recheck your timing.
two_68_510s wrote:I guess our donkeys are quicker then your sled dogs!

Beev
Posts: 23
Joined: 11 Apr 2018 13:49

Re: How broken is my L20b?

Post by Beev » 29 May 2019 18:38

10cc is based on the instructions with my compression tester and general research around the web. It seems to vary from teaspoon (~5cc) and table spoon (15cc) so in the middle I went. If there is a better measured value I am happy to try that.

As for the procedure again I just tried to follow instructions happy to try another way. Cold is easier because the car sure doesn't like to run!

I did a poor job of explaining the 180 degrees out. Basically it was 1243, or some wrong combination like that, rather than 1342 . Likely some bad translation from me reading a website, crossing wires, and the extreme lack of sleep. It probably would have been better to just say 2 cylinders were 180 degrees our, in which case it runs very very poorly... very

The cam is apparently the turbo grind (I don't have access to the exact grind number at the moment) but with FI you don't want much overlap as my understanding is it messes with the MAP sensor and ruins your vacuum as you have indicated.

Robyn I also forgot to follow up with for vacuum bounce what would you expect it to be centered around and the +/- range for it to bounce.

Beev
Posts: 23
Joined: 11 Apr 2018 13:49

Re: How broken is my L20b?

Post by Beev » 29 May 2019 18:44

I chased timing for a while these are my settings:

900 RPM 8 degrees
1200 RPM 10 degrees unstable RPM
2300 RPM 19 degrees unstable RPM
3200 RPM 28 degrees stable RPM
4000 RPM 33 degrees stable RPM
It appears advance is all in around 3300 RPM
Advance is all mechanical
IAC blocked 630 RPM 7 degrees advance

I use a timing light that allows you to change the point of the flash so the marker is always aligned with the notch. I have also tried 2 differed distributors.

Beev
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Joined: 11 Apr 2018 13:49

Re: How broken is my L20b?

Post by Beev » 29 May 2019 19:06

Also I am taking the Vacuum measurement from the middle of the manifold (which I think is the balancing tube). Given my poor knowledge of appropriate terms I have added a picture to the shared album above... it is where the blue silicone tube is connected to.

datzenmike
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Re: How broken is my L20b?

Post by datzenmike » 29 May 2019 20:19

Reversed firing order would run on two cylinders.... barely.

It's just that 10cc of space is removed from the combustion chamber. On a stock 8.5 compression L16 putting 10cc of oil in raises the compression to 10.61. Now this is not strictly true at cranking and lower speeds speed as the intake closes well after BDC but it seems significant to me. I guess the oil would get pushed past the rings while cranking.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

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RMS
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Re: How broken is my L20b?

Post by RMS » 29 May 2019 20:23

thats good you have an advanced light, but too retarded you should have 15deg @ 800
two_68_510s wrote:I guess our donkeys are quicker then your sled dogs!

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RMS
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Re: How broken is my L20b?

Post by RMS » 29 May 2019 20:31

Chickenman ...case sensitive....
http://www.the510realm.com/viewtopic.ph ... ce#p250358

its about weber tuning but loads of good info on timing
two_68_510s wrote:I guess our donkeys are quicker then your sled dogs!

Beev
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Joined: 11 Apr 2018 13:49

Re: How broken is my L20b?

Post by Beev » 29 May 2019 20:50

I will have a read. The numbers seem all over the map for timing I remember checking a few sources but if the engine isn't out of sorts there really is no downside of trying.

Beev
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Joined: 11 Apr 2018 13:49

Re: How broken is my L20b?

Post by Beev » 30 May 2019 18:45

So I adjusted the timing as well I could to match this suggestion the car does run much better. The computer is still trying to fight something by adjusting the IAC and the person I have been in contact for with the system say it is the vacuum flutter. Can anyone please confirm with a video that the flutter happens on their dual SU setup when measured from the balancing tube?

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