compression numbers?

[tic55]

hey guys, i have a 99 M3 with the ces cutring combo. its got the spacer and ces says its supposed to put the car around 9-1 compression. ive been working on the car a lot doing a custom turbo build. i got everything done and went to start up and the car is running rough and it wont stay running for more then a few seconds. i took the cams off when i did this job and im starting to think it was a mistake. i checked compression as ive been doing some research and most problems this comes down to the cam install and timing wasnt done right and bent valves occurred. going from front to back 1-6... 1 being the front cylinder then the next one being two, next one being 3 all the way back. 1 ( up at the front ) had about 75psi, then 2 had 75, 3 had 92, 4 had 72, 5 had 75 and oil was on the plug washer when i pulled it... and 6 had 80.. after i got home and did some looking on the numbers i didnt know you where supposed to pull the fuse relay and open the throttle body to let it pull in the air? i did not do either of those and intake piping was hooked up... could some one possibly tell me what they think on these numbers?

[someguy2800]

If the guage is accurate those numbers are way too low

[tic55]

what would be suitable numbers for 9-1? and ive seen some threads where people open the butterfly and go from 90 to 150? and dissconnect the fuel pump, so ima try that somepoint and see what the numbers are, but on average i feel like people dont do those things and are getting good numbers? idk....

[Mklock]

Im at 160 on a 9.0:1 compression ratio. No varience between, (new engine)

I followed the foot on the floor, luke warm engine method.

[jclausen]

A more accurate test is a leak down test

[NOTORIOUS VR]

my 8.8:1 would show 175-180 on all cylinders warm

[Greenday694]

I agree those numbers are extremely low. But on the bright side , because you actually have compression in all 6 cylinders pretty much rules out bent valves.
Your cam timing can still be off. That can cause low compression numbers, and rough idle.

Sent from my VS995 using Tapatalk

[tic55]

so are we all or who ever sees this going to agree and say that bent valves are not likely? thats obviously the biggest concern. i would like to try rule that out first and quickly as possible as i just got the head sat back down on it. second i will entertain the idea of doing the throttle open method... there is a lot of controversy on it so ig i will just test it myself. i will look into the leak down test, rings a bell but i dont know what it is. but i will look into it.. i also found a nice guide on how to set the timing correctly so i think this weekend i will pull the cams off and reset the timing completely. this is the guide i found link and i will keep doing research till i am comfortable but if you guys know off a good thread to read or a good guide to follow pleas post it up, it would be much appreciated.!

[NOTORIOUS VR]

keep in mind, gauges can be wayyyy off/broken (I've seen some almost 100 psi off) - if you can test a known good motor with your gauge so you are not chasing your tail it could save you a lot of time/headaches

[pbonsalb]

I’d retime the cams. I don’t think you need to remove them. Verify TDC. I go forward — direction of engine rotation — to TDC. Backwards could make it a little bit off. There is some play around TDC. I also try to mimic the engine mounting angle when looking at the TDC mark on the crank damper. Look at it from one side or the other and you could line it up a little off. If you have a stock flywheel you can go off the hole but I have not had TDC locking pin holes in my flywheels since 2008.

[philly98540]

Maybe good idea to do a proper compression test with the throttle plate wide open and fuel pump fuse out.

[tic55]

the gauge i bought was a harbor freight one for 35 bucks... i bought it the same day i did the test, i know that doesnt mean that the gauge is perfect but is less likely to be off. but with that being said i might as well test good engine just to make sure. i will do the test again with throttle open and fuse out, and im not gunna lie when i did the job i was not prepared for it obviously. and when i first set the car to tdc i was standing on the side of the car and then i rotated it to clean the piston tops and when i set it back to tdc again i did it standing at the front of the car and i thought i had it a little more one way then the other. so im sure my timing is off but that just means im probably super close to touching a valve if i didnt already.... but! i did rotate the engine by hand 2 full revolutions before ever starting the car and it went smooth all the way around with no issues at all. and on initial start up there wasnt any loud or weird noises it sounded normal, just rough and wouldnt stay running, but there wasnt any ticks or clicks or clanks or anything like that... ill probably stick a bore scope down and check it out this weekend as well. and i was told the car had a stage 2 competition clutch kit, so im going to assume it is not a stock flywheel. i did buy the vanos and cam lock kit that cam with the pin to put in the flywheel so i guess i will give it a try at least i appreciate all the insight and help guys! i will give an update probably thursday or friday.

[spyderg0d]

You have to have the throttle all the way open and the fuel relay pulled. Throttle closed will dramatically lower numbers. The fuel spilled in from the relay not being pulled makes cylinder wash andblow numbers as well.. Those numbers seem about right for those 2 not happening. Id do it again the right way first though. Id also redo the timing if you werent dead certain it was accurate.

[tic55]

i will redo the compression test as stated before i do anything else and post up my numbers again. can kinda confirm this idea of having it open or close, but i do see it, i have a few feet of intake piping and a little turbo its trying to pull the air from. soo i will give at go before i do anything else. im assuming i still need to retime the car though... at least look at the position of the cams at tdc... so on... i have thursday off work so i plan on getting up early and getting started on it. ive spent to much time and money on this car in the last month for it to just be sitting there....

[tic55]

so i redid the test today with the throttle open and the fuel pump relay out. it did not make a different, in fact it was the exact same numbers. so having it open and fuel pump out does not make a difference but i did put the car at tdc and my cams are literally upside down. we have the two dots at the back of the cam to show the " top " of the cam? its in that guide i posted up... but my cams are literally upside down... so in a sense i am 180 degrees out on my timing.... which i mean half and half.. half of 160 is 80psi... but i dont think it works like that? maybe i just got to be the luckiest guy in the world? can anyone verify if its possible to legit have the cams installed 180 out and the car start up and run roughly without hitting any valves or anything? i am going to take it all apart later and use a bore scope to check things out.. but thatll be either sunday, or within the next few weeks...

[pbonsalb]

The headgasket spacer may have helped, and you ran only at idle rpm.

[Randy Forbes]

Back to Step One; when you start the timing procedure, #1 piston @ TDC, the cam lobes on #1 should be as close as they can to pointing at each other.



The #1 cam lobes can just barely be made out in this picture.

[philly98540]

To check valves, you can put compressed air in each cylinder one at a time with cam lobes up or at least not actuating any valves on the cylinder being tested. The piston needs to be at tdc or bdc or else the engine will rotate. With your cams being 180 out, maybe best to fix that first, but maybe could do as is. Only need like 40 psi but whatever. You will hear air rush out intake or exhaust if valves are bent. Some leakage is ok. Use a compressor testor hose and quick couple to your air line.

use a wooden dowel inserted into spark plug hole to ensure tdc or bdc at each cylinder.

[E30s50dude]

You could just pull the cams were they're at right now. Use a long 3/8 extension and have it rest on the top of the piston so you know cly #1 is at TDC then re install the cams as normal with both front lobes facing each other at a 45* angle with dots on the back of the cam facing up. BTW I would still leave FP fuse or relay out while doing comp test just so you don't wash the oil off the cylinder walls.

[tic55]

so today i learned that there are two top dead center.. the exhaust stoke and compression stroke at tdc... i was on the exhaust stroke when i pulled the cover, i rotated it again and for the most part the cams lined up... my intake one is off a little so i am going to take the sprockets and vanos off and redo it all at some point... theres a lot of frame rust on the car. two sub frame bolts are broken and rusted all the way out. i ordered rtab bushing as i was missing them but i have their reinforcment plates and subframe bushing kit. i already have it all apart just gotta clean and cut some metal out and weld in the new plates... sometime in the next two or three weeks ill get that done and some time inbetween or shortly after i will re-time the car... THANK YOU!!! all for the help and support... im sure ill be back when re-timing it doesnt fix the issue lol.

[spyderg0d]

Engine doesnt care. The cams are what define whether its an intake or compression stroke. The ecu is supposed to figure it out which is intake or compression stroke via the cam sensor. If your timing was off at any revolution of the crank, then your timing was never right to begin with. Which is probably the actual problem.

[someguy2800]

You don't need to take the vanos off to reset the cam timing. You just have to loosen the 4 bolts on the front of the exhaust cam and then you can rotate both cams freely. Rotate both of them till the block fit and tighten the exhaust sprocket bolts again and your done.

Unless the cams were way way off though that will not be enough to make an otherwise good motor compression test at 90 psi.

[ba114]

If your compression looks like this, throw the motor in the bin

[h82crash]

so today i learned that there are two top dead center.. the exhaust stoke and compression stroke at tdc...

That was my first thought when you said cams were 180 out. If you rotated to true TDC and the cams were in the proper orientation, you should be good with cam timing. But if it is indeed the source of your low compression, you need to get it right.

[pbonsalb]

2 revolutions crankshaft for 1 revolution camshaft. You were halfway there. The crank pulley showed TDC but if you had checked the piston, it would not have been there. This can happen if you have the motor apart and are not paying attention. Hopefully there is no damage.