Datsun L-Series Engine Testing and Tuning Ep.7 Compression Test and Diagnosing

[@tungscrx]

Incredible series of videos! My car is running badly right now. Cant wait to go through these videos. Very informative.

[@xPeterthepallyx]

Great quality video. Btw, open your garage when you run your engine..

[@drunktortila3632]

Great videos keep it up. Im hopefully picking up a z in the next few months so find this very informative!!

[@RestorationForBeginners]

YES. I have a suspicion that Z's are cheaper in the winter because no one wants to drive them in the snow/salt. Pick one up right nowww

[@danlombardi1797]

Awesome videos, very informative and helpful! I have a '75 280z with compression numbers varying from 130 to 215, but I suspect because the valve lash was maxed out on a the same two cylinders with low compression, and the N42 head's valve seats being brass have sunken valves... I need head work. My father-in-law will be coming to visit us for a few weeks soon and he used to be a Datsun mechanic, so with him and your videos, I should be good to go!

[@RestorationForBeginners]

+Dan Lombardi ah haha thats awesome. If he was a professional Datsun mechanic, he probably knows more than i can ever hope to learn! Let me know if he finds any errors or has suggestions to the videos :)

[@dinto_louis]

Hi, the wet reading on one of the cylinders is lower than dry reading..what could be the inference..? I have done dry & wet compression test on my VW Polo 1.2 TDI..the reading is lower in the wet test than the dry test on cylinder number 3..? Dry: 1 - 26.7 (Bar) 2 - 26.5 3 - 27.8 Wet: 1 - 27.6 2 - 26.7 3 - 26.3

[@Slyzxx76]

Man this was awesome. I'm new to this and this made it easy thanks soooo much it really helped

[@Sickstringfarm]

I finally did this test and yielded 158 on 1, then 148-150 on rest... adding oil boosted most back to 158. Might have to get bottom rebuilt or get another N 42

[@BryceandKyle]

Great video as always!

[@RestorationForBeginners]

Thanks! I got your decals too! I'm going to stick one on my tool box and stick another on the car.

[@BryceandKyle]

Nice! Enjoy them. I have a new one going out soon I'll send your way.

[@slv_car_refinisher6864]

Did it make any difference in the rpm The you delete alot of valves that go on a the intake?

[@davewm9589]

I am going to try the warm test, I have only tested them cold, generally in the 150-160 range. Do you recall if they were lower before the valve job? just wondering if the new valve seats helped your readings.

[@RestorationForBeginners]

I think the readings were generally in between 165~175 prior to the doing any work. I can't pinpoint exactly what did the trick since lots of things happened since.

[@davewm9589]

just checked mine with warmed up engine, all between 162-165. Think I will check the camshaft timing just to see if it has retarded any.

[@RestorationForBeginners]

Yeap, makes sense! Let me know if you end up making adjustments to the valve timing. I'd be interested in seeing how much, if any, that advancing the cam timing makes a difference.

[@somefitcarguy]

So question. I recently rebuilt my L28 and we did a leakdown test and the motor was solid, no leaks but the compression was low on 3 cylinders. We checked valve clearance and all was fine. Would you try adjusting the cam sprocket?

[@RestorationForBeginners]

Which three cylinders?

[@somefitcarguy]

@@RestorationForBeginnersthink it was 3,4 and 6 gotta double check again.

[@RestorationForBeginners]

Seems pretty odd to have the leakdown results come out good and compression testing come out bad on three cylinders. Check this out grassrootsmotorsports.com/forum/grm/riddle-me-this-compression-vs-leakdown/82649/page1/

[@somefitcarguy]

@@RestorationForBeginners ya I'm stumped. Something is out with the timing

[@simonmooncalf3892]

Min, It seems like your car is starting easier? Did you sort out the depressurizing of the fuel system? Great video as usual. Keep it up!

[@RestorationForBeginners]

Haha hey Simon, that's very perceptive of you. All I did was buy a battery charger and fully charge the battery to 100%. I hesitate to say that that was the only issue, but it may not have anything to do with the ignition system or the fuel pressure after all. Might just a cheap alternator that can't keep the battery charged because I don't take this thing out for extended drives right now.

[@BryceandKyle]

You should look into a Noco G750 battery maintainer. You can use the included Noco X-Connect adapter for the battery terminals so you can easily connect and disconnect the G750 for maintaining your battery while you're not using the car. I always used something like this on my motorcycle so the battery is always fresh.

[@RestorationForBeginners]

Ah yes, the battery charger I mentioned is a automatic charger/maintainer, but I don't leave it plugged in all the time since it makes a loud high-pitched noise that bugs the crap out of me.

[@BryceandKyle]

Ah, that would be annoying. Thankfully my Noco products don't do that.

[@charlesmiller5078]

So compression is right where its suppose to be....Great, But the question is still there, where is the blue smoke coming from? Is it possible you can have good compression rings and weak oil rings? Maybe the blue smoke is gone away. Maybe it takes a little while for the Valve seals to seat correctly. At this point I would not give it a second thought, numbers are to good. You had me on the edge of my chair watching those numbers come in. Looking Good. Maybe PVC isnt clearing out oil laden gases from engine. Install a Catch Can, or Plug Anti Fouler s on 5/6. They are the 14mm ones that are long, short ones will crush the plug tip, Dont ask me why I know this :)

[@RestorationForBeginners]

I have no idea, but I suspect that's the issue. I'll discuss much more in detail in the next episode on the spark plugs, but the plugs are really fouled up at cylinders 5 and 6, which was also the case before I took off the head. My guess is that the car running for an extended period with a blown head gasket between cyl 5 &6 took a toll on the piston oil rings. It's just a guess, but unless I have a crack in the block, I can't imagine what else it would be.

[@marrisonh]

I have a problem with cylinder 4. Whenever stuck in traffic the spark plug gets fouls and car looses power when driving.

[@charlesmiller5078]

I would guess valve seals, it can only be valve seals or piston rings, how many miles on the engine.

[@marrisonh]

@@charlesmiller5078 cylinder compression test measured 180 to 182 psi for all 6 cyl

[@marrisonh]

@@charlesmiller5078 engine was remanufactured by california datsun

[@TRUTH4U2NO]

You have tight valves I bet in ur 170 cyl. Adjust ur valves 10intake 12exhaust with motor hot.