Gollum Posted March 4, 2013 Share Posted March 4, 2013 (edited) So I was working on our Merc today ('66 250S) and did a compression test trying to figure out why I was down a cylinder. Well, since I had everything out I went ahead and finally got around to testing my DD, the '81 280ZX. This motor now has 250k on the odo and I've put 50k of those on there, which is now officially the most miles I've put on a single datsun motor. I've done a pretty good job at trying to kill it to. I got the car for free so it's been more of a "well if I don't do this maintenance it might explode" type of mind frame. The engine consumes oil about as hardcore as it drinks gas, which also isn't great. It gets about 20-28 MPG depending on what oil I'm running that day and how many cold starts it's endured on that tank. Usually I get around 22-24 for 90% of my tanks. According to a wideband at the tailpipe the O2 isn't doing too bad. Onto the test conditions: Engine HAD been warmed... about 1.5 hours prior. Was probably decently cold again, but as ambient was in the 60's it couldn't have gotten TOO cold in that time. Oil was 20/50w last time I filled it. I was too lazy to get IN the car to turn the key each time, so the throttle was closed. To compensate I get the cylinder testing reach it's compression stroke a good 4 times before taking a reading. (can you tell how much I care for this engine's well-being?) I went ahead and did dry AND wet tests, since I was semi-concerned about my ring wear. So the numbers: Cylinder/Dry/Wet 1.__180__190 2.__190__191 3.__179__182 4.__183__188 5.__182__189 6.__190__196 Conclusion: The numbers are much higher than I expected... FSM says standard is 171, and min should be 128. Also says that the lowest reading should be within 80% of highest. I have a mere 94ish% variance... which utterly shocked me. So, why might the numbers be high? Maybe carbon build up? Maybe the fact that I burn so much oil there's black sludge in my chambers? Maybe my tester is just reading high? (unlikely as the merc numbers were on the money down in the 120 range) Or could my engine be absurdly healthy? (unlikely as well...) Well, here's my plugs before I cleaned them this evening. They read 6-1 from left to right, as you would see them standing on the passenger side of the engine bay. They're only about 5-7k miles old, but this is the first I've pulled them since first install. Next step is to check my valve clearance. It's possible I'm a bit loose and need to tighten things up. That might also bring compression numbers down a tad. Then maybe if I figure out the oil consumption issue I can get on with beating the hell out of this engine for another 50k. I'm debating pulling the head to see if the gasket has been leaking at all. I know this head has seen some serious overheating, before and during my ownership, and I wouldn't be surprised if she's not sealing quite as well as she should. All comments/suggestions welcome. I know this has been an aimless post, but that's because it's more for the documentation for myself and others, rather than solving problems I don't care much about. Edited March 4, 2013 by Gollum Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted March 4, 2013 Share Posted March 4, 2013 (edited) That middles plug looks a tad oily. I've always heard people say and engine performs best right before it goes . You're probably has a lot of life left in it. How much oil consumption are you actually talking about? quart every 500miles? Edited March 4, 2013 by BluDestiny Quote Link to comment Share on other sites More sharing options...
Xnke Posted March 4, 2013 Share Posted March 4, 2013 Those plugs look really oily. Does that thing smoke at all? I am thinking you might want some valve stem seals. (Or a head rebuild, pending a leakdown test.) As others here have said, I've pounded a set of stock pistons and rings through rusty bores and the rings came out without a scratch on them...and after honing all the rust out, the bores were within spec save for the rust pits! Not surprising that these engines last forever as long as you keep oil in them. (Or if you don't, but the bearings don't care for that, much). Quote Link to comment Share on other sites More sharing options...
steve260z Posted March 4, 2013 Share Posted March 4, 2013 I'd put NGK plugs in there. Quote Link to comment Share on other sites More sharing options...
Gollum Posted March 5, 2013 Author Share Posted March 5, 2013 That middles plug looks a tad oily. I've always heard people say and engine performs best right before it goes . You're probably has a lot of life left in it. How much oil consumption are you actually talking about? quart every 500miles? Well see that's the thing... If I keep 'er full she'll eat at least a quart a tank. Run 'er almost bone dry and she'll eat about half that thanks to the lower oil pressure... just gotta watch out for the sound of that cam grinding.... Those plugs look really oily. Does that thing smoke at all? I am thinking you might want some valve stem seals. (Or a head rebuild, pending a leakdown test.) As others here have said, I've pounded a set of stock pistons and rings through rusty bores and the rings came out without a scratch on them...and after honing all the rust out, the bores were within spec save for the rust pits! Not surprising that these engines last forever as long as you keep oil in them. (Or if you don't, but the bearings don't care for that, much). Depends on the oil I'm using. It never smokes enough that I'm making a cloud going down the freeway, but it'll smoke in the morning with lighter oils and people behind me complain about the smell... I currently run 20-50 with a stop-smoke additive (not a super heavy tacifier type). That helps the cold smoking immensely and also allows me to engine brake without killing myself of fumes... . I'd put NGK plugs in there. Considering how this thing treats plugs you can imagine I've tried quite a few in just 50k. I've seen zero difference in how any of them perform/last for this engine. In the end, new plugs are great, and that fresh power feeling lasts about..... 1k and then it's just meh. Quote Link to comment Share on other sites More sharing options...
Xnke Posted March 6, 2013 Share Posted March 6, 2013 Valve stem seals, at a minimum. Probably time for a fresh head, the guides and valves may be worn too. Quote Link to comment Share on other sites More sharing options...
Gollum Posted March 6, 2013 Author Share Posted March 6, 2013 I'd be surprised if the valves and guiders were THAT bad. At 250k this motor is still a yunggin' by some standards. Though I admit, there might be some abnormal wear in some areas due to neglect... I'd imagine the cam/lifters going long before the valves, valve seats, guides. I knew she could use stem seals the first day I got her, about 5 years ago now... IF I actually keep the car long term, which I doubt, I think I'll end up pulling the head and doing a major overhaul on it, just because. I wouldn't mind shaving it down .08 and such, maybe massage the chamber a tad before tossing the valves out. Toss in a mild cam just for fun and wha-la revived little engine. But no matter what I need to buy another car soon, so really it's the question of weather or not this car gets the axe, which is most likely will. Time will tell. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 6, 2013 Share Posted March 6, 2013 (edited) Your numbers are almost EXACTLY what mine were. 1980 280ZX 2+2 with 225,000 miles: 185 across the board. At around 275,000 miles it has not changed. You can smell oil behind it, it burns oil but only smokes on startup and hard throttle on-off. Worse after Big Throat TB conversion removed the BCDD... Personally I think it's stem seals in my engine myself... I'm not in any rush to pull this apart, it just runs too damn good. Pushes my 76 2+2 to rock solid consistent 15.50's all day and night long, gets 22mpg towing an 800# trailer at 80mph, and spun a Dynojet to 147! Yeah, it uses oil, maybe a quart in 1,000 miles. Yours is 4x that... I'd say you got stuck oil control rings, especially with the look of the plugs. My 73 would do that on ONE cylinder after the engine was stored for 5 years. That engine had 26,000 miles on it (yes, you read it right, 26K, not 126K...I pulled then engine and had all the Nissan Maintenance records, bought in Japan out of a 77 Cedric in 1987 42,000 km on it) that engine on the same compression gauge runs 160. Pfffft! Edited March 6, 2013 by Tony D Quote Link to comment Share on other sites More sharing options...
duragg Posted March 6, 2013 Share Posted March 6, 2013 What about try running straight 50wt? Like a VR1 SAE50 I secretly hate multi-grade oil and just switched to straight 50 in my Z due to high temps oil turning to water. Im not sure just how much oil could really get by VG seals? Could you pill a full quart past them? Or more likely past the rings which have a lot more surface area to offer. More importantly, need to see a picture of that 250S and its engine please... Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 6, 2013 Share Posted March 6, 2013 I run single grade based on factory recommendation since it never gets -40 here. My air cooled experience has led me to not trust mineral-based multi-Vis... Synthetics are a different matter. Quote Link to comment Share on other sites More sharing options...
Gollum Posted March 7, 2013 Author Share Posted March 7, 2013 You know, several people have mentioned running a straight weight oil, you guys really got me thinking about it again... And tony, I think I probably DO have some stuck oil control rings. Suggestions? The marvel mystery oil stuff maybe? I'm kind in the same boat though. I can live with the oil consumption since it's pretty trouble free otherwise. And since you asked so nicely duragg: No pics of the engine, I'll have to work on that. I've got to order some parts for it actually. You don't get different thickness lash pads for these motors, but instead they offer different thickness rocker holder dealios that they call "pressure pieces" in the service manual. One cyclinder is reading ZERO PSI because the valve isn't able to seat. I'm going to have to be uber careful about valvetrain wear on this thing. It was rebuilt about 12 years ago, but was only about 2,000 miles ago. So the rings, bearings, rubber parts in carb, etc are all brand new, but this motor has seen AT LEAST 400k miles. Speed stopped working sometime in the 80's. It was the car my wife actually learned how to drive in. No PS, 4 speed manual (floor shifter, kinda rare actually for these cars), and pretty darn gutless. My wife is quite fond of it, so you can imagine that it's not really going anywhere for a while. I'm still weighing the data to figure out how long I have to wait to even THINK about bringing up the IDEA of a swap.......... So far I'm not a huge fan of this motor... And it's not the lack of power that bothers me... Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 8, 2013 Share Posted March 8, 2013 I turned my boost controller up to 17 psi and went tear-assing all over creation intending to blow the engine up... Damned if after 30-45 minutes of that, coming off the freeway I noticed the smoking had stopped. In fact...oil consumption dropped DRAMATICALLY from that point onwards. Engine has around 75 or 80,000 on it now... It sat again...and #5 is acting like it wants to oil foul the plug again every 1,000 miles or so.... So I guess it's time to go beat the hell out of it again and try to kill it. ******** Seafoam ray down the plug holes...hot, thn run it as intake cleaner and in the oil after you go run the hell out of it and change the oil. Quote Link to comment Share on other sites More sharing options...
Gollum Posted March 8, 2013 Author Share Posted March 8, 2013 Well, I guess this looks my to do list: Bottle of seafoam: $13 Straight 40w Oil, 5 quarts: $28 Bosch OIl Filter: $8 Total: Approx $55 w/Tax out the door Then, if that happens to reduce oil consumption considerably... F-Pro Head Gasket: $24 F-Pro Intake/Exhaust Gasket: $11 F-Pro Valve Cover Gasket" $11 F-Pro Valve Steam Seal Kit (box of 12): $20 Consumables (sand paper, razors, grinder bits, etc): $30 Head mild overhaul: Approx$100 w/Tax out the door So for about $150 and a solid weekend of casual work maybe I could fix it... Well, if I was going to do all that I should also change my plugs out, plug wires, cap and rotor, etc. It all banks on how the seafoam handles that oil consumption though. I'm not going to dig into the head just to find out that it's still leaking oil like crazy.... Quote Link to comment Share on other sites More sharing options...
duragg Posted March 8, 2013 Share Posted March 8, 2013 (edited) Don't have any fear of using 50wt either. I Like your Benz. My other toy is a 1988 560SEC. Splitting my time and resources amongst the two projects. Aircraft get stuck rings a lot (huge bores) and I have had good luck by plugging the spark hole with my thumb, and rotating the engine backwards creating a vacuum, then quickly release. Now do it forward-then release. And backwards creating that reverse suction on the rings and just keep doing this. Its easier with a propeller, but using a bar on the crank should work too. That backwards suction seems to snap the junk loose and you can feel the compression come right back up. Then proceed to try to blow it up.. Edited March 8, 2013 by duragg Quote Link to comment Share on other sites More sharing options...
Gollum Posted April 1, 2013 Author Share Posted April 1, 2013 So 3 week later and guess what happens? I swear my car goes on hybridZ at night and stalks my posts.... ...In the last 3 days I've developed a HUGE exhaust leak. I'm fairly certain the leak is at the manifold to lower pipe, but I'll check before ordering a new gasket. I'm also fairly certain this has been a long time coming. Rayapp helped me swap the cat not long ago and we threw in a 3" unit he had from a turbo motor, which meant we had to weld in reducer adapters to my wimpy stock NA pipes. Well I think the movement combined with possibly being a tad short in length might have added undo stress to the upper joint, and slowly burned the gasket out. Anyhoo, I'd already been planning my attack on the head. I figured that since my intake/exhaust gasket was fine that I could get away with changing the head gasket without pulling the manifolds. Speed things up, and make it easier on myself. I'd already planned on unbolting the exhaust at said point of current leak... So we're upping my schedule on this. I've got the parts priced out ready to order and will order them later this week. Parts include: Head Gasket Exhaust Gasket Valve Cover Gasket Valve Stem Seals Degreaser Wire Brush So I'll pull the head, put it on a bench. Clean it up nice and new, pull the old valve seals, install new ones, clean the pistons, and reassemble. If I get it all done smoothly enough in a day I might also do another compression test. On the other hand, once I get to cleaning I can get kinda OCD and might spend all day getting oil stains off my valve cover.... Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted April 1, 2013 Share Posted April 1, 2013 Honestly for the extra hour of taking the manifolds off, I think your back will thank you. Quote Link to comment Share on other sites More sharing options...
Gollum Posted April 1, 2013 Author Share Posted April 1, 2013 Honestly for the extra hour of taking the manifolds off, I think your back will thank you. HA! You think I'm even going to lift the HEAD? You're cray-cray. I've got a cherry picker for heavy lifting. Probably won't ever come unbolted from it either, I'll make a work space right by the vehicle so the head just gets lifted up, and set down. I can use the picker when I need to move/rotate the head around, then just pick it up and plop it on when done. Work smarter, not harder. Quote Link to comment Share on other sites More sharing options...
srgunz Posted April 5, 2013 Share Posted April 5, 2013 HA! You think I'm even going to lift the HEAD? You're cray-cray. I've got a cherry picker for heavy lifting. Probably won't ever come unbolted from it either, I'll make a work space right by the vehicle so the head just gets lifted up, and set down. I can use the picker when I need to move/rotate the head around, then just pick it up and plop it on when done. Work smarter, not harder. I used to have a Maxima with the L28 and the head gasket was leaking. That's what we did. Unbolted and used the cherry picker. Saved a lot of work. Quote Link to comment Share on other sites More sharing options...
slownrusty Posted April 6, 2013 Share Posted April 6, 2013 Duragg = Tom from Benzworld? Quote Link to comment Share on other sites More sharing options...
Gollum Posted July 31, 2013 Author Share Posted July 31, 2013 (edited) Well carbon build up MIGHT have had a role to play in the high numbers... Something tells me that after this top end freshening my numbers might end up a bit low... Cylinder 1 Cylinder 2 Cylinder 4 (not a typo, weird upload order) Cylinder 3 Cylinder 6 Cylinder 5 Overall the gasket actually looked in REALLY good shape, and was a fel-pro, so it'd definitely been changed, just no idea when. I didn't see any obvious signs of leakage, even though I had evidence of mild compression bleed into the coolant system... Going to look again at the gasket more closely in the following days. Changing the valve stem seals while I've got it all apart, along with all sorts of top end gaskets. Many days of scraping ahead of me.... Edited July 31, 2013 by Gollum Quote Link to comment Share on other sites More sharing options...
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