Wagz Posted July 25, 2005 Share Posted July 25, 2005 So, after a fair bit of work, I finally get the 260Z fired up. I picked this thing up for waayyyy cheap and towed it home a few months back. It was in a lot of pieces and came with many boxes of new and used parts. It's got an N42 block and head and I'm running 4-screw round top SUs. Anyway, the guy I bought it from had the head re-worked by a local shop years ago before the whole project was shoved in a corner of his garage and forgotten. The head had obviously been tanked and cleaned. The valves looked like new. The cam looked like it was original with minimal wear. Anyway, I looked it over, did a cold check on the valve lash and it looked to be in good shape. I planned on doing a hot adjustment after I got the carbs adjusted and synched up. I got the car fired up and it seemed to run pretty darn well right out of the gate. I synched the carbs and did a few turns around the neighborhood. There was no valve noise beyond what is normal for the L6 motors I've had in the past. I was pretty happy. The next morning I go out to do some more work, fire it up and... WTF???!! A TON of bad clattering! I quickly shut it off and pulled the valve cover. I found two lash pads and the keepers (split colletts) for one valve. SH!%@*! Pulled the head and found this in the number 5 hole (not the quarter - just the damage): The number 2 intake valve didn't lose it's keepers, just the lash pad so, there wasn't piston to valve contact. I'm considering reinstalling the lash pad on number 2 and replacing the bent intake valve on 5. I don't know if the rebuilder put in incorrect lash pads, or if I screwed-the-pooch when I checked the lash when it was cold, or??. I'm leaning toward not replacing this piston and seeing if I can make this bad-boy run for now while I scare up another motor to rebuild. Opinions on my cutting corners? Quote Link to comment Share on other sites More sharing options...
Guest DoTheDrew888 Posted July 25, 2005 Share Posted July 25, 2005 As long as you fix the head the engine should run fine. A slightly damaged piston shouldn't cause any problems and no noticable performance differece. I ran a piston with a valve ding in it and it worked fine. I even checked the compression and it showed up even across the board. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted July 25, 2005 Share Posted July 25, 2005 I've had that exact same thing happen, and found that it was the result of very old fuel residue/gunk built up in the fuel tank. the 240 I have now, was sitting in some guys garage for 13 years when I bought it. I put my newly rebuilt motor in there, and just drained what little fuel there was in the tank and thought that'd be good enough. After driving for a few days I started having that same problem, the lash pads started popping off the valves. Fast forward a bit.... after it happened a couple times and I couldn't figure out what was causing the problem, finally a valve got stuck and hit the piston and got bent. On later inspection after taking things apart, I found that not only were the valve stems all gummed up with varnish from the old fuel residue, but my SU's were also badly gummed up as well... every part of the fuel system was. These were newly rebuilt SU's, and again, the motor was recently rebuilt so that varnish build up was DEFINATELY a result of dropping the engine in the 240 and from the old fuel residue in it's tank. So you might want to have a look and see if this caused your problem as well... needless to say I couldn't run the motor again until I dropped the tank and had it cleaned, had the entire fuel system flushed, and had to rebuild the carbs, replace the bent valve and hot tank the head again. Quote Link to comment Share on other sites More sharing options...
Wagz Posted July 25, 2005 Author Share Posted July 25, 2005 Bastaad - I'll bet you are right on the money. I can all but guarantee that old gas varnish was the problem here too. I had the same scenario, car sitting for 10 years, decided to cut-corners and not drop the tank and clean it, drained the old gas and put in 5 gallons of new stuff. Everything was gummed up from the SUs to the tops of all the pistons and everything in-between. Lesson learned. I stopped at the local Nissan dealership this morning and ordered up a replacement intake valve, keepers and upper spring seat. I'll be dropping the gas tank this week... Damn, cutting corners can get to be expensive and time consuming! Quote Link to comment Share on other sites More sharing options...
Here comes trouble Posted July 25, 2005 Share Posted July 25, 2005 Mark... I would have rather found the quarter than the valve imprint. Keep the piston.... Wreciking yard fellow told me that the gas in the last few years was really prone to gunk and varnish up. Watch this post and I will try to get a photo of proper cam and lifter geometry posted for yoiur consideration when installing the different size lash pads I have a bunch of 280 pistons if you need any http://pg.photos.yahoo.com/ph/larryjohnson97438/detail?.dir=/392a&.dnm=59f1.jpg&.src=ph Quote Link to comment Share on other sites More sharing options...
Phyxius Posted July 25, 2005 Share Posted July 25, 2005 just a side note, the ridges in the piston could cause some pre-ignition if you try to do anything fancy with the motor while that piston is still in there... I'm sure you've already thought of this...just thought I'd make sure Quote Link to comment Share on other sites More sharing options...
Here comes trouble Posted July 25, 2005 Share Posted July 25, 2005 http://pg.photos.yahoo.com/ph/larryjohnson97438/detail?.dir=/392a&.dnm=a4ee.jpg&.src=ph Quote Link to comment Share on other sites More sharing options...
Wagz Posted July 26, 2005 Author Share Posted July 26, 2005 Larry - Thanks for the pictures and piston offer. I'm going to put this thing back together (after I drain and clean the tank) and get it running again. After that, I'll be checking the cam lobe wipe on the lash pads to make sure I'm not running off the end. Now, back to the garage... Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted July 26, 2005 Share Posted July 26, 2005 yeah I agree with Phyxius... if at all possible you might want to smooth out some of the damage to the piston... those rough sharp edges could get glowing red hot and cause preignition. They may also cause dieseling when you shut the car off... that's a real PITA with SU's since they'll just keep sucking fuel, the engine could diesel forever like that if those ridges get red hot. Quote Link to comment Share on other sites More sharing options...
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