Help with oil consumption and leak down test
07-18-2007, 06:44 PM
#16
Peter,
The PO did a comprehensive rebuild with receipts and machine work done by Ollies about 40K miles ago. This included new Mahle P/C. The car was used primarily for POC racing at the time. The heads were re-done by Ollies about 5K miles later but I can't be clear exactly what was done at that time. About 7K miles ago I had to do a complete teardown due to a failed intermediate shaft sprocket hub. I had Ollies evaluate all parts from the bare case to the rockers and they guided me on everything that needed to be done. They advised to leave the P/C alone based on mileage and visual inspection but I don't think any measurements were taken (this in hindsight was a mistake to not verify measurements). They inspected the heads and also said everything was within spec and did not recommend a valve job at that time. So, we just worked on the case, crank, rods, rockers, cam housings, and of course bearings, seals, and incidentals.
I believe that the car started smoking within a few thousand miles after reassembly but the timing is not certain. The onset of this condition seemed to be sudden and also seemed to become elevated suddenly as well.
The leakdown test indicated "0" after pressurizing the cylinder for 30 seconds at 10 psi. I still need to go back and test at 100psi with a different gauge although there is nothing suspect about my current gauges. Compression is +/-155psi.
I am beginning to think that maybe there is a bad oil ring or carbon chunk on the oil ring land that allows excess oil into the cylinder on the down-stroke. I guess I am hoping for something simpler like a damaged/dislodged valve guide seal though.
The car is carbed and I have dealt with some tuning issues over the past 6-9 months with lean and rich conditions. Here is a recent picture of the spark plugs as well.
Clear as mud, eh?
The PO did a comprehensive rebuild with receipts and machine work done by Ollies about 40K miles ago. This included new Mahle P/C. The car was used primarily for POC racing at the time. The heads were re-done by Ollies about 5K miles later but I can't be clear exactly what was done at that time. About 7K miles ago I had to do a complete teardown due to a failed intermediate shaft sprocket hub. I had Ollies evaluate all parts from the bare case to the rockers and they guided me on everything that needed to be done. They advised to leave the P/C alone based on mileage and visual inspection but I don't think any measurements were taken (this in hindsight was a mistake to not verify measurements). They inspected the heads and also said everything was within spec and did not recommend a valve job at that time. So, we just worked on the case, crank, rods, rockers, cam housings, and of course bearings, seals, and incidentals.
I believe that the car started smoking within a few thousand miles after reassembly but the timing is not certain. The onset of this condition seemed to be sudden and also seemed to become elevated suddenly as well.
The leakdown test indicated "0" after pressurizing the cylinder for 30 seconds at 10 psi. I still need to go back and test at 100psi with a different gauge although there is nothing suspect about my current gauges. Compression is +/-155psi.
I am beginning to think that maybe there is a bad oil ring or carbon chunk on the oil ring land that allows excess oil into the cylinder on the down-stroke. I guess I am hoping for something simpler like a damaged/dislodged valve guide seal though.
The car is carbed and I have dealt with some tuning issues over the past 6-9 months with lean and rich conditions. Here is a recent picture of the spark plugs as well.
Clear as mud, eh?
07-18-2007, 09:29 PM
#17
Just as a reference my '85 is now at 181K with no engine work and is getting 800-600 miles/qt. using 20W50. (This has been the consumption since 120K.)
In the beginning, 17K miles, oil consumption was 2qt after 3500 miles.
I started doing 3K OCI at 120K and there was some start-up smoke at that time. Before that my OCI was ~7K. All of this was dino GTX or some Val Racing.
Now no smoke at start-up.
I've been studying and testing oils now for about a year. Right now I have Valvoline 20W50 in which is a full PAO. It's more viscous than the GTX at 100C (18 vs 20 cSt) and I'm sure has much lower %Noack(less burning) and better HTST.
So far, 2200 miles, it's seems almost the same consumption. I assume valve guides. I'll be taking it out to maybe 6K miles. Usually I find consumption goes up as oil gets dirty but it may be the GTX was sheering down.
My next test is Quaker State Q 10W40 (GrpIII synth) for San Jose winter to see about better gas mileage.
After that in spring, Pennzoil Platinum 15W50 (cSt 100C is 21.4 and PAO-like %Noack). This stuff is 20% thicker at 100C than GTX and probably thinner at 40C.
ZDDP on these synth's are ~800ppm but I'm not worried. I don't race and I'm past break-in with stock cam/springs. I just recently did valve adjust and the cams looked great. So after 20K miles I'll look at them again.
In the beginning, 17K miles, oil consumption was 2qt after 3500 miles.
I started doing 3K OCI at 120K and there was some start-up smoke at that time. Before that my OCI was ~7K. All of this was dino GTX or some Val Racing.
Now no smoke at start-up.
I've been studying and testing oils now for about a year. Right now I have Valvoline 20W50 in which is a full PAO. It's more viscous than the GTX at 100C (18 vs 20 cSt) and I'm sure has much lower %Noack(less burning) and better HTST.
So far, 2200 miles, it's seems almost the same consumption. I assume valve guides. I'll be taking it out to maybe 6K miles. Usually I find consumption goes up as oil gets dirty but it may be the GTX was sheering down.
My next test is Quaker State Q 10W40 (GrpIII synth) for San Jose winter to see about better gas mileage.
After that in spring, Pennzoil Platinum 15W50 (cSt 100C is 21.4 and PAO-like %Noack). This stuff is 20% thicker at 100C than GTX and probably thinner at 40C.
ZDDP on these synth's are ~800ppm but I'm not worried. I don't race and I'm past break-in with stock cam/springs. I just recently did valve adjust and the cams looked great. So after 20K miles I'll look at them again.
Last edited by glenncof; 07-19-2007 at 12:51 AM.
07-19-2007, 12:12 PM
#21
Rennlist Member
VNTG: The reason I asked about induction is the thought that it might be contributing to your smoke. #3 actually looks like it might be fouled, the other five are pretty much typical for a slightly over-rich carb car. I also wanted leakdown numbers (I do leakdown at 80 psi) to see if you have some kind of ring problem, which a comp test probably won't show. To many guesses are possible on this one!
07-19-2007, 01:01 PM
#22
Drifting
Originally Posted by douglas bray
when is someone just going to come out and say "some valve guides on '87's are bad" that is all I got when I was shopping. when I got mine home and started driving it arround everyone asked if it was an '87 with bad valve guides....nobody here wants to talk about it. I got an '88 and don't yet have the milage history to say exactly what mine is consuming but it is in the 1,000+ mile range. I've added 6,000 miles and 3 quarts, so I'm just getting started.
The rub with valve guides is that unless you have the oil consumption history - it's difficult to detect.
07-19-2007, 02:28 PM
#23
Originally Posted by Peter Zimmermann
VNTG: The reason I asked about induction is the thought that it might be contributing to your smoke. #3 actually looks like it might be fouled, the other five are pretty much typical for a slightly over-rich carb car. I also wanted leakdown numbers (I do leakdown at 80 psi) to see if you have some kind of ring problem, which a comp test probably won't show. To many guesses are possible on this one!
Agreed that there are a few possibilities with no sure bet. Thanks for your time and expertise on this one.
I will do another leakdown at 80psi and report the findings if they reveal anything noteworthy.
David
07-19-2007, 02:58 PM
#24
Addict
the first time I fired mine up it let out a big puff of smoke and I almost walked away. It hadn't been started in two weeks. I got on the phone with a friend and calmed down a little. once I got it home it smoked once when I had my foot on the gas. I have never got another puff in six months.
I was a little strong with my assumptions above about '87's. I will take your word long before anyone of my friends or the guys in the parking lot at Performance Products.
I was a little strong with my assumptions above about '87's. I will take your word long before anyone of my friends or the guys in the parking lot at Performance Products.
