Sealik Posted October 15, 2011 Report Share Posted October 15, 2011 I'm wondering what is the acceptable amount of air (blow by) for a recent rebuild (LZ23)? Seems to be a lot of air coming out of the oil fill cap on the valve cover. Zero oil consumption....compression is 173 + - 3 across the board. About 3000 kms on engine. New pistons/rings Assuming the rings haven't seated yet.....or the rings (end) gaps are all lined up???? http://youtu.be/1JR1onIaxRA Quote Link to comment
datzenmike Posted October 15, 2011 Report Share Posted October 15, 2011 Doug it's more usual (at idle) to put your hand over the hole and slight vacuum will build. At idle the PCV valve keeps the inside of the crankcase below atmospheric pressure... slightly. PCV working? Screen in block plugged? Quote Link to comment
Sealik Posted October 15, 2011 Author Report Share Posted October 15, 2011 Doug it's more usual (at idle) to put your hand over the hole and slight vacuum will build. At idle the PCV valve keeps the inside of the crankcase below atmospheric pressure... slightly. PCV working? Screen in block plugged? PCV rattles and seems to be functional Screen was cleaned and refitted during rebuild. I'll go out and see if my engine sucks... :D Quote Link to comment
Kramer Posted October 15, 2011 Report Share Posted October 15, 2011 IIRC my leakdown tester's documentation stated 5%... much more than that and you better buy stock in your favorite oil company~ get up into the teens and you best get your blue cloud generator home ASAP b4 peeps start throwing rocks at it.... If you don't have one and suspect a problem you could also tee (or block the vacuum side & hook it straight to the VC~ a cork makes a great adapter) a vacuum/pressure gauge directly into the PCV line, using as large and short a hose as possible so as not to dampen the signal, run engine and observe for large/varied vac/pressure pulses, and pull plug wires to isolate.... Quote Link to comment
Sealik Posted October 15, 2011 Author Report Share Posted October 15, 2011 IIRC my leakdown tester's documentation stated 5%... much more than that and you better buy stock in your favorite oil company~ get up into the teens and you best get your blue cloud generator home ASAP b4 peeps start throwing rocks at it.... If you don't have one and suspect a problem you could also tee (or block the vacuum side & hook it straight to the VC~ a cork makes a great adapter) a vacuum/pressure gauge directly into the PCV line, using as large and short a hose as possible so as not to dampen the signal, run engine and observe for large/varied vac/pressure pulses, and pull plug wires to isolate.... Yup...already tested... :D Actual readings. Same on all 4 cylinders 2-3 per cent loss Quote Link to comment
Sealik Posted October 15, 2011 Author Report Share Posted October 15, 2011 Of note....the engine has a miss, and cannot locate it. Bad when cold....better when warm. My theory is.....there is a leak at the IM and head, between intake (1 and 2) runners. Vacuum gauge is low and fluctuating when cold...smooths out when warm at 19lbs. Probably has nothing to do with the air (blow by)...but worth mentioning Quote Link to comment
datzenmike Posted October 15, 2011 Report Share Posted October 15, 2011 Doug that 2-3% is only true at the TDC position don't forget. Just for giggles set the piston at BDC or even lock motor in gear with the parking brake on and test with piston half way down the cylinder. The cylinder could be oval or tapered or damaged in some way allowing gasses out further down but not at the top. I guess you will have to temporarily pop the rocker arms off that cylinder. Quote Link to comment
Sealik Posted October 15, 2011 Author Report Share Posted October 15, 2011 Doug that 2-3% is only true at the TDC position don't forget. Just for giggles set the piston at BDC or even lock motor in gear with the parking brake on and test with piston half way down the cylinder. The cylinder could be oval or tapered or damaged in some way allowing gasses out further down but not at the top. I guess you will have to temporarily pop the rocker arms off that cylinder. Yeah I know.... :) I'll do another leak down test later today Quote Link to comment
Sealik Posted October 15, 2011 Author Report Share Posted October 15, 2011 Maybe with the engine cold...? Not warmed up. Quote Link to comment
datzenmike Posted October 15, 2011 Report Share Posted October 15, 2011 Clearances wider so should leak more... besides right now thew leak down looks fine while in practice it 'blows ass'. Quote Link to comment
Sealik Posted October 15, 2011 Author Report Share Posted October 15, 2011 I know what I'll be doing this winter..... :angry: Pistons at BDC...bottom of stroke, Tester set at 90lbs/compressor at 100lbs 1...83 lbs...8% loss 2...79 lbs...12% 3...79 lbs...12% 4...82 lbs...9% All pistons half way down (or up) 1...82 lbs/9% 2...77 lbs/14% 3...80 lbs/11% 4...82 lbs/9% As usual...No 2 plug fouled during warmup. Quote Link to comment
datzenmike Posted October 15, 2011 Report Share Posted October 15, 2011 H-m-m-m Well that's shitty but expected for the amount of blow by. Sorry Doug. Quote Link to comment
Sealik Posted October 15, 2011 Author Report Share Posted October 15, 2011 Yeah...that's what I thought. Plan B Leak down test on a cold engine. I'll test with cylinders at TDC and BTC, any variances should confirm cylinder taper....? Quote Link to comment
merlin Posted October 15, 2011 Report Share Posted October 15, 2011 shoot that effing machinist... Quote Link to comment
datzenmike Posted October 15, 2011 Report Share Posted October 15, 2011 Inside caliper would confirm taper. Cylinder bored too wide Abnormal ring wear. Quote Link to comment
Sealik Posted October 16, 2011 Author Report Share Posted October 16, 2011 More numbers. Checked 1 and 3 cold Tester set at 90lbs No 1...80lbs/ cylinder up, 80lbs cylinder down. No 3...76lbs cylinder up, 76lbs cylinder down A little less than with the engine warm yesterday....1-3 lbs That's the 'good' news.... :blink: The bad news is my readings at TDC have also gone for a shit....not 2-3 percent loss anymore This time when I did the leak down test (engine warm), I did No 3 first No 3 23 lbs piston up...23 lbs piston down, intake valve is leaking. Can hear the leak trough the carb and TC cover Checked twice...rockers removed No 2 About 76lbs No 1 Around 82lbs No 4...didn't bother.... Basically all the pistons have the same shitty numbers...up or down in cylinder Which would explain some of the issues.....engine is cold/choked and 'no' leaking intake valve.....not too bad of a miss. Engine warms up....choke opens, No 3 intake valve starts leaking(???), combined with these less than stellar leakdown tests...runs like shit Quote Link to comment
datzenmike Posted October 16, 2011 Report Share Posted October 16, 2011 Maybe removing the rocker by prying on them disturbs the valve seating. Hit top of spring with plastic hammer to seat them before testing. Quote Link to comment
Sealik Posted October 17, 2011 Author Report Share Posted October 17, 2011 Yeah that's what I figured....I did open and close it with a bar a few times, with no improvement. Was kind of loosing interest and or hope about that time though.... :( And yes...I did feel like hitting (smashing) it with a plastic (steel) hammer... :D Could be some crud that dislodged keeping the valve from seating. I'll do a leakdown test on No 3 without removing any rockers. That 'blowby' was there when I first started up the engine. I mentioned it in another thread...and was suggested that there will be a little until the rings seat. Never thought anything about it again until I started the engine a couple of weeks ago without the oil fill cap. Then I noticed.... Compression was low just after I got it running...around 125 Kept creeping up to about the 170 it is today. So...I'm thinking that if I didn't have any issues, the compression readings would be closer to 200? Piston to cylinder clearance is .025-.045 (.0010-.0018) Double that and add to piston size...equals appropriate bore? Correct? Sure as shit they overbored.... Maybe.... :blink: ...Hopefully, then I would have some (more) proof of their incompetence... :D Shall be measuring...ASAP Quote Link to comment
datzenmike Posted October 17, 2011 Report Share Posted October 17, 2011 Piston to cylinder clearance is .025mm-.045mm (.0010"-.0018") Double that and add to piston size...equals appropriate bore? Correct? Between 1 and 2 thou inch all the way round I think. No piston is exactly 89mm and can range from 88.965 to 89.015mm. That's just shy or 2 thou inch. This is why the piston for any cylinder should be supplied to the person who is doing the boring so he can measure them. Best if they are just under and you hone the difference out. Quote Link to comment
Sealik Posted October 24, 2011 Author Report Share Posted October 24, 2011 Pulled the engine/head....noticed a lot of carbon on the backside of the intake valves and stems. Exhaust valves are clean. Assuming this is from the PCV connection sucking that crap (blow by) though the intake....? Notice the tops of the pistons are not all the same....No 1 is a lot cleaner. Quote Link to comment
datzenmike Posted October 25, 2011 Report Share Posted October 25, 2011 Doug, you used Z24 pistons? Thought you put KAs in there. Quote Link to comment
Sealik Posted October 25, 2011 Author Report Share Posted October 25, 2011 Z24 pistons Mike.... My theory on that carbon buildup is 'worthy'....? :D Quote Link to comment
MicroMachinery Posted October 25, 2011 Report Share Posted October 25, 2011 Yours is having issues too? Eeegh.. sorry man :( I just finished hauling the rest of the 280zx I cut up for scrap. Probably pull mine out here in the next week or so. Quote Link to comment
datzenmike Posted October 25, 2011 Report Share Posted October 25, 2011 Z24 pistons Mike.... My theory on that carbon buildup is 'worthy'....? :D Maybe but why would it all go to the #1 valve? That buildup could be from a worn valve guide or seal. Intake vacuum sucks oil down the stem. Quote Link to comment
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