MY2014, QR25DE, 206kmiles - compression test values

[V6er]

Yello, ladies(?) and gents!

It has been awhile...
Anyway - so, tonight did compression test. 1-2-3-4, got 150-135-135-150. with harbor freight compression tester tool.
FSM says that normal compression would be 200 and minimal 175, with deviance no more than 14 between cylinders.
I think I saw pretty much the same values like ~4yrs ago. Except now I have P0303 (misfire in 3rd cylinder). and vibrations up to, approx, 1700rpm.
put it new spark plugs(4yrs ago installed denso 3490, they did ~80kmiles, now 2 and 4 had gaps 0.055 instead of 0.044). swapped coils 3-1. still the same.

Right now I think it might be injector... probably time for aceton coctail .

But what are your typical values? And what do you think about valve adjustment? I think I saw it somewhere in FSM about checking those ~60kmiles, but now can't find it... may be I was just dreaming

[VStar650CL]

Standard is 205, minimum is 177, maximum differential is 14, but did you test it correctly? Test should be done with all plugs pulled and the gas pedal bricked, you'll get low cranking speed (and hence artificially low readings) if you don't do that.

If you think the rings may be bad, do a wet test. Squirt about a teaspoon of 20W50 in the hole and repeat the test, if you get a major rise in the reading then the rings are wiped out.

You can also tell a lot from how bouncy the needle is. Healthy cylinders will just pump up and down. A fluttery needle on one cylinder usually means a bad valve, on adjacent cylinders usually means a head gasket.

Note that on QR25's the walls between cylinders are very thin, so it's fairly common to have a compression blowout between adjacent cylinders without any involvement of the oil or cooling jackets. You can test for that by pressurizing one of the low cylinders at the bottom of its compression stroke, then seeing if air comes seeping out of the plug hole on the other one.

There's no adjustment for valve lash on a QR without pulling the camshafts, they use shims and not screw adjusters.

[V6er]

all plugs were out, fuel pump and fuel injector fuses out, fuel pressure released. but forgot about pedal - thank you (read about it in FSM, but forgot to do that

my main concern right now is not really compression, but 3rd cylinder misfire. because need to move from points A to B - and second car right now is not in working order

thanks for answers. going for round too in measuring

[VStar650CL]

If the problem is an injector then you should probably see some difference in the spark plugs. If an injector is leaky then you'll generally get a blackened plug, plus the piston crown may have some bare spots from the excess fuel blowing the carbon loose. If it's sticky then you'll generally have a white (or at least lighter) electrode from that cylinder running lean. Both will usually cause a slightly-stinky exhaust.

[VStar650CL]

Oh, PS - I know you swapped coils, but you should try swapping a spark plug too. It wouldn't be the first time a plug had a hidden issue like an internal crack in the ceramic.

[V6er]

I just replaced all spark plugs for new.
anyway:
1) did redo compression test this morning with pedal-to-the-metal. 150-150-135-150...
2) Will take a picture of old spark plugs.
3) will try to use borescope in cylinders.
4) at some point later will measure valve-camshaft clearences to see what is going on there.

also buddy of mine suggested getting leak-meter... to see if I have to take off head to lap(is this the word?) valves or not. Probably will not be doing full-blown seat replacement etc.

[VStar650CL]

Well, that's more in line with a miss on #3 only, and pretty much leaves out a blowout between cylinders. Unless you have a broken lobe on the camshaft, the clearance would need to be hellaciously bad to cause a 15 psi compression loss. I doubt that's the issue. If it is a leaky valve seat, a leakdown test will show it up (and you may be able to see it with the borescope). I'd do a wet test first to see if it's a cracked ring, since that's so simple to do.

[V6er]

will try to do wet test later tonight - in 20minutes need to leave for work. and tomorrow this pile of happiness needs to be back driving :DD
leakdown test I will probably do in weekend

anyway:
1) here are old spark plugs. 1 and 3 had gap of 0.04 (slightly less than 0.044, but they were 0,044 when I installed them). 2 and 4 had gap of 0.054 (bigger than 0.044).
top is 1 and bottom is cylinder 4.
https://prnt.sc/KGSsacC4sZwE
2) pistons with borescope (sorry for quality):
1st cyl - https://prnt.sc/jz84o1VAoDfo
2nd cyl - https://prnt.sc/iIXlqtJHPO4K
3rd cyl - https://prnt.sc/UfyvnGNP8KCf (crappy pix - will have to redo it)
4th cyl - https://prnt.sc/fbHW3la-PmKJ
3) now - more interesting pix - valves.
cylinder 3:
https://prnt.sc/X0m2iR6p7eUT
https://prnt.sc/2ROyxVIG6Pu9
https://prnt.sc/IxiUlLwiFUTs
https://prnt.sc/eSA4orYbafg5
one valve sticks out with its light brownish tone. three of valves have "wetness" around the seats (probably leacking valve seals?)

for comparison - cylinder 4:
https://prnt.sc/wYVxlxefoGAH
https://prnt.sc/G7miYBQAa-m7

[VStar650CL]

Both of the exhaust valves should be that light brown color, just like 1-2-4. The exhausts run much hotter than the intake valves and will always look whitish in a healthy engine. Look for a problem with the one that's dark on #3, it probably isn't opening completely or at all. The most likely culprit would be a broken or demolished cam lobe.

[V6er]

damn...

[VStar650CL]

The good news is, that cylinder will simply be down on power because it can't breathe well. It will run rich and heat the converter up a bit, but it shouldn't cook the cat like a dead miss with no burn. You should be able to drive it without hurting anything, it will just be sluggish.

[V6er]

thanks for kind words!
will use time to prepare for taking off the head. fingers crossed

[VStar650CL]

You can inspect the cam without pulling anything but the rocker cover. Changing it if it's bad is a different story, but looking at the lobes and the valve action just takes turning the crank with the cover removed.

[VStar650CL]

Here's what you'll find under the rocker cover. There are 2 identical lobes on each cam for the intake and exhaust sides of each cylinder. What Nissan calls a "lifter" is actually a depressor, they're on top of the valve springs directly under the cam. They come in different thicknesses and double as lash adjustment shims. If necessary, you can use a borescope to peek under the cam and watch the lifter as the cam turns to see if it's doing what it's supposed to.

[V6er]

don't want to hang out engine twice without serious need. either way head will need to come off. valves relapped, at minimum, valve seals... if that camshaft is messed up - another camshaft will be required... valve adjustments... may be head surfaceing...

have to start with getting subaru back on street

[VStar650CL]

Replacing cams or rebuilding QR heads in-shop is such a complicated PITA (largely because of the shimming) that absolutely nobody I'm aware of would do it, especially on a head with 200K miles. You'll be far better off getting a JY engine or a $500 reman head off eBay that already has cams and proper lash.
https://www.ebay.com/itm/185365997808

[V6er]

this is good suggestion (god knows, of course, how good are their heads) - thank you!
(especially if valve guides are bad, seats etc etc.)

though - shimming isn't scaring me. and I am not doing for profit. kinda like the car and want to keep enjoying it... though wife was browsing car advertisements already - she doesn't have enough trust in me

p.s. after putting things back yesterday - today I got P0304 in addition to P0303 :DDD will check closely mpg, because it feels that it is ~290miles/tank.