[RESOLVED] Rough Idling & Compression loss

[tsunari]

Ok, here's the story. I just recently put my engine back together (Valve job, BSE kit, 4-layer Mits head gasket, ARP head studs torqued to 90 ft*lbs, belts, etc . . .) I drove her for ~ 500 miles and was planning on checking the torque on the head tomorrow morning. This afternoon I did a compression test and everything looked great! All cylinders had 175-180 PSI

So I checked my intake for leaks and ended up finding a couple of vacuum leaks, so I fixed those and got ready to head out for a test drive. Did a couple of pulls and everything SEEMED ok . . . until I headed home. I did one last pull and the engine started to feel weird, so I backed off. I let it down to idle and the engine died. Looked under the hood expecting to see an intake hose blown off and found my intake pipe -> compressor housing wasn't clamped down

Clamped down the intake, double-checked EVERYTHING and tried to start it up. It was idling ROUGH, but sporadically. Every now and then it would smooth out and idle just fine.

I got her home and checked the compression. Here's the comparison before and after the problem:

1 - 175 | 150
2 - 175 | 120
3 - 170 | 165
4 - 185 | 140

Any ideas? I was thinking MAYBE the head does need to be re-torqued. At this point I'm frustrated and really can not think straight

 

[chaye]

did you do anything to the bottom end?
retorque the head to see what happens, after that do another comp test. If its still the same add a teaspoon of oil in the combustionchamber, if the pressure rises your rings may be shot

good luck

 

[tsunari]

Only thing I did to the bottom end was remove the balance shafts. I considered putting a new set of rings in, but decided against it.

Well I'll retorque the head in the morning and also check the timing. I've read several threads where if the belt jumps a tooth or two, the car will run like crap, but does anyone know if it affects the compression? (Because valves will not be fully closed on the compression stroke?)

Also . . . how many teeth can be skipped before valves start getting bent?

Originally posted by chaye
did you do anything to the bottom end?
retorque the head to see what happens, after that do another comp test. If its still the same add a teaspoon of oil in the combustionchamber, if the pressure rises your rings may be shot

good luck

 

[tsunari]

Ok, took the valve cover off and checked the torque on the head studs and all were still @ 90+ ft*lbs, so I'm hoping that might rule out the blown head gasket idea.

So I guess . . . check the timing belt now?

 

[chaye]

i know by a fact that if you skip about 16 teeth your engine is gone (personal experience, my timing belt took a crap on my while i was going 85 on 3rd gear) It may be that they are not fully close, let us know if the timing marks all align

add a teasspoon of oil and then do a comp test (add oil where the spark plug goes in then screw in the compgauge)

 

[tsunari]

On a side-note, my EGT probe broke when this happened and met my exhaust turbine blades . . .

Here's the link:
http://www.dsmtuners.com/forums/showthread.php?s=&postid=942003#post942003

 

[tsunari]

Just checked my timing and here's what it looks like:

Looks to me like everything is lined up properly . . . or am I mising something?

**EDIT**
I just took a straight edge to the cam timing marks . . . when I would line the marks up from left to right or right to left, I could only get 3 of the marks to line up perfectly straight. The fourth mark on the outside of either cam would be off by a tooth.

Sound like a skipped tooth?

Cam Gears:

 

[tsunari]

Crank Sprocket

 

[tsunari]

Oil Pump Sprocket

 

[tsunari]

** UPDATE **

+Checked the timing belt and it's fine - did NOT skip any teeth.

+Did a leak down test and got the following:

#1 - 55% loss
#2 - 5% loss
#3 - 65% loss
#4 - 75% loss

+Did a dry compression test on a cold engine:

#1 - 120 psi
#2 - 120 psi
#3 - 165 psi
#4 - 125 psi

+Added a tsp of oil:

#1 - 170 psi
#2 - 160 psi
#3 - 190 psi
#4 - 200 psi

*SIDE NOTES*
--While doing the leakdown test, I had a significant amount of air coming through the oil filler hole and the dipstick hole.
--No air was coming out of the exhaust
--No air was coming out of the intake

--Called ARP and they told me that I had OVERTORQUED my head (90 ft*lbs with ARP moly lube is WAY too much)
--Using ARP moly lube, the nuts should be torqued down to 65 ft*lbs (which is 75% of the yield strength for the stud), but definitely no more than 81 ft*lbs.

So . . . only thing I can think is wrong is I stretched the studs and now have a blown head gasket or perhaps my rings are toast? Someone have any ideas?

 

[tsunari]

Ok . . . did a couple more leak-down tests. This time a dry one, then a wet one. On the assumption that if it's rings, the oil should seal em up and I should get a significant improvement. Here's what I got . . .

+Cold & Dry Leakdown:

#1 - 77% loss
#2 - 12% loss
#3 - 23% loss
#4 - 54% loss

+Cold & Wet Leakdown: (Capful of oil)

#1 - 69% loss (8% improvement)
#2 - 9% loss (3% improvement)
#3 - 15% loss (8% improvement)
#4 - 40% loss (14% improvement)


So what do you guys think . . . still pointing to rings?

 

[1fast97gsx]

sorry to bring this post back but what did you end up doing? How did torquing the studs down that far end up? I torqued mine to about 90 ft lbs as well with the lube and my compression numbers are pretty decent, but I'm wondering if I hurt anything.

My numbers were 167, 162, 163, 168 today. Seems pretty consistant although I was expecting closer since it is a freshly rebuilt engine with only 100 miles on it.... I have the metal headgasket and arps torqued to 90 ft lbs with 8.5:1 pistons.

 

[tsunari]

Oh hey! Glad you did bring this one back up . . . I had meant to come back and post my findings.

Well, I took the head off and cleaned everything up. Put it back on with new studs and a composite gasket this time. I now have 180+ compression across the board. After doing quite a bit more research, I found out that the finishing surface on the head and block needs to be pretty damned smooth in order to use an MLS gasket. Last time I had head work done, the guy milled the head and ####ed my finish up. So unless I can find someone competent enough to do it correctly (and has the proper equipment), this head will see nothing but composite gaskets.

So . . . to wrap everything up, I believe my problem was a combination of improperly torquing the head studs AND using the MLS head gasket when the surface finish on my head wasn't smooth enough.

Just remember, when installing NEW ARP studs, torque them down in steps to 65 ft*lbs (using the ARP moly lube) then loosen them up in the proper sequence (check your FSM or chilton's manual). Do this 3-5 times and once finished, do one last final torque to 65 and you should be good to go. I'm going to get my 'old' studs Magna-Fluxed to see make sure they didn't stretch or twist. If all is good, I'll be putting them up for sale on here most likely.

Hope this answered your question and anyone elses