s15 SR 100psi on all cylinders, jump a tooth on the crank sprocket?

[SR2oD3T]

long story short, went to drifting event 2 weeks ago and drifted pretty hard. car spung out couple of times and engine stall. realizing a little lack of power, weak start up, but still pulls when turbo kicks in. drove home fine just feeling a 30% power lose. did compression test, 100psi on all four. (was done when engine is cool and forgot to WOT, but i shouldn't be that low). did some research and i m pretty sure the timing was jump that causes losing compression on all 4 cylinder and have same reading.

did some research, #1 cylinder at TDC by looking at the crank pulley, both in and ex cam line up with the dots on the sprockets and the silver mark on the chain.

question:
i m thinking it might jump a tooth in the crank sprocket. even tho the cam sprockets all lines up, i have no way to find out if the crank is line up with the chain unless i drop the oil pan, take off the oil bump and all those right?

from research, the two silver spots on the chain is just for initial installation. once the engine turns, it takes up to 60 turns at the crank before it lines up with the dots on both cam sprockets.

going out for dinner now and i think i can't escape from taking all those things apart. just wanna get more opinion from u guys see if i m going the right direction.

btw, its a s15 sr20det.


thanks
KELvin

[fliprayzin240sx]

Its not possible to jump teeth at the crank, well not impossible but pretty far fetched. There's a finger that sticks out from the oil pump cover that secures the chain from popping off the crank. If that piece broke off, then it might be possible. But even then, you still have the tensioner keeping the chain from slacking and jumping teeth.

Drop a cap full of oil in each cylinder and re-do the compression test. If it jumps up to 150-160, its not a mechanical issue and points to your rings.

[SR2oD3T]

or maybe both the in and ex cam gear jump tooth??

[cotbu]

If you were off a tooth on the crank every time you rotated the engine over, that off link would have to jump again if you have the correct links from dot to dot. That is almost impossible from the clearance the chain has from the head on the intake side, if there was a 10mm groove cut by the chain and the oil pump guide/finger was broken then yes it could happen. When the chain jumps it's would be noticeable during manual rotation, and loud during running operation, and if the tensioner was doing it's job the valve would contact the pistons in no time at all.Why? The cams would eventually rotate out of time.
Set the engine to TDC and #1 cam lobes pointing out, count the links from dot to dot. 11 links

So let's hope that the impossible didn't happen.
Re-do your compression test, properly. And add a cap full of oil after you do the test properly then test each cylinder again.

Now if you choose to pull the pans, might as well schedule machine service, just in case, you only need a re-hone and new rings, worst case overbore and new pistons and rings.

[brndck]

+1 for you did NOT jump timing.
do a leakdown test.

[ZX88]

regardless sounds like a rebuild at 100psi across the board.

[SR2oD3T]

i ending up didn't pull the oil pump but i rotated the crank like 40 times and got the mark line up. crank pully second mark from the left. both silver chain lines up with the in and ex cam sprockets. so i ending up putting everything back and re do compression test.
before i re do the compression test, i did one with my other KA motor which shows 150psi so the gauge should be pretty accurate.
engine cold after sitting over night, WOT, fuel pump fuse out, i still get around 110psi. #3 seems to be a little strong and gives 125-130psi.
put some oil in it and it gives around 120psi ish.
check the timing with timing light seems to be normal.

the motor still runs kinda normal, idles fine, pretty strong and high rpm.
i m stuck now. i might start looking for a shop to rebuild the whole thing. any recommendation at bay area?!?

more background:
car was running stock boost all the time, i have still have SMIC. i m having a feeling that the engine runs really rich cus not only it smell gasoline, i also got a lot of back fire. only have a SAFC from the pre owner. don't really wanna mess with the setting.

any input?!

thanks.
KELvin

[SR2oD3T]

http://img.photobucket.com/albums/v517/punkelvin/IMG_0819.jpg (http://smg.photobucket.com/user/punkelvin/media/IMG_0819.jpg.html)

http://img.photobucket.com/albums/v517/punkelvin/IMG_0818.jpg (http://smg.photobucket.com/user/punkelvin/media/IMG_0818.jpg.html)

[mr.nismo.]

Your asking for problems with just an SMIC and SAFC


Sent from my iPhone using Tapatalk

[fliprayzin240sx]

Mech timing looks good...if adding oil didnt bump the compression significantly, then its something else. Did you inspect all the rocker arms and make sure nothing is funky up there? Atleast can kinda rule out the rings, but like said already, now time for a leak down test to see where its leaking. Could be valves or HG. The valvetrain isnt noisy when it was running right?

[SR2oD3T]

the rocker arms and valve looks normal as i turn the crank like 60+ times. i wouldnt say the engine is quiet, it does have some like "dot" sound when u accelerate or rev it up. but once it revs up, i dont hear anything. cant tell if thats chain or valve.

however, it has been like this since i got the car. and i never check the compression till 2 days ago cus it was running pretty strong and smooth until i realized some lose of power.

will get a leak down test done and see if there's something going on in the head or valve. thanks.

KELvin

[racepar1]

First off, if the engine is as stock as you say, take the SAFC off and smash it with a hammer. There is absolutely no reason to run that on a stock engine. It is completely possible that it is what caused your compression drop.

As for diagnosing the mechanical compression issue, do a leak-down test. If adding oil only bumped up the compression 10lbs then your rings are fine. The next possibility is that you burned valves. Do the leak-down test and listen for air leaking through the intake and exhaust manifolds. If that is not occuring the last possibility is that you lifted the head and are leaking compression between cylinders. In that case you should be able to hear the compression leaking to the next cylinders when you're doing the compression test or the leak-down test.

[Kingtal0n]

Wait, wait wait wait. You run the car hard, really hard, and it runs fine.

Then, eventually you notice it losing power, and running rich.


You probably sprung a boost leak my friend.

[SR2oD3T]

i m going to get a leak down tester cus there's too many possiblity for low compression. dont wanna diagnose base on guessing.

dont think it will be a boost leak as the low compression number clearly tells me my engine is not running 100%. rings seems to be fine as compression doesnt jump much after putting a little oil. i m leaning more toward the head, some valve related issue.

i'll put an update after i do the leak down test this couple days. will most likely send it to the shop and rebuild the head with upgrade valve, springs and all those. and also remove the SAFC. regardless, i'll update this post with the final problem and solution.

KELvin

[Kingtal0n]

you really think that every cylinder has valve(s) that have been damaged in the same exact way? If so, somebody put domed pistons in backwards while you were sleeping. Or every single lobe on your camshaft has been ground worn the same exact way.



Consistent compression is consistent. If anything it is just carbon buildup, slow cranking, tired motor.

[SR2oD3T]

update:

yesterday was my day off and got my hands on the leak down test. unfortunately, air leaking noise from oil cap and dip stick. its not LOUD, but its very obvious. nothing much i can heard from intake or exhaust unless i the crank away from TDC just to test it out how it sounds like. car still drives fine, boost strong, but valve cover is leaking bad now probably the pressure build up. not gonna leave it like this for the track event in 2 months.

i already got in touch with a sr20 specialist shop for a full rebuild. he told me its pretty normal for higher miles SR with wear out rings, or sometimes in a hot track day and/or drifting, having oil starving. or it might be like this low compression since i purchase it from pre owner just that i never checked.

will very soon send to the shop and tear apart. will have a full rebuild with upgrade. wanna get my normal 160psi back and reliable power for drifting.