hoohaa Posted June 25, 2007 Share Posted June 25, 2007 I am rebuilding a VG30 out of a JDM 95 pathfinder and I found melted pistons. The pistons had worked their way into the cylinder walls toward the fore and aft of the motor, not all the way around. On some pistons it was so bad I could not get the rings out. The pistons left a nice little aluminum deposit in two spots on each cylinder wall. I honed out the bores and most of the aluminum came out. You can still see a bit of aluminum on the top of one of the bores in the following pictures. I am now dealing with scratches on a couple of the cylinders which can also be seen in the pictures. This is the first and worst cylinder. All the aluminum came out of this one and these score marks are what's left after about three minutes of honing. They are just deep enough to sort of catch the tip of your fingernail if you run it over the scratches. The rest of this cylinder looks great. There is one other cylinder with a bit of a problem. It can be seen here: What do you think about these cylinders? Boring out the block is not an option, as this is a budget build. I will hunt for a better block before boring out cylinders. If I just need to spend more time with the hone I will do that too. Are those score marks too bad to run? I'm replacing bearings, rings, and gaskets with OEM Nissan stuff. Quote Link to comment Share on other sites More sharing options...
hoohaa Posted June 25, 2007 Author Share Posted June 25, 2007 Sorry for the huge pictures. It's WAY easier to see the scratches with the larger picture size. I will shrink 'em down after I get a few responses. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted June 25, 2007 Administrators Share Posted June 25, 2007 First off, PLEASE oh please shrink the pics down to at leasst 1024x768, or 800x600 would be better yet. With the huge by large pics, the text also wraps requiring side scrolling as well as down scrolling to read. Sounds like a major melt down. How does the crank and the rods look? Were the bearings squished out at all? Any scoring on the crank journals? If detonation was present during the melt down, you might want to have the main webs of the block and the crank magnufluxed for cracks as detonation to the point of total melt down is typically quite severe, i.e. cracked block and or crank. How do the heads look, in particular, the valves and valve seats? Pending the parts are reusable, not broke, the cheap way out is just kiss hone the bores, (as you have already done, don't hone any further unless you plan to over bore and don't forget to verify piston to wall clearance and ring-end gaps) , re-ring and fresh bearings, the scrathes will still be there, the engine will run and the cylidners will make compression, it just wont be "right" if you know what I mean. As an engine builder/machinist, if this were my personal engine, and if the crank and main line is still in good condition, I would either overbore this block or just find another good core block. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted June 25, 2007 Share Posted June 25, 2007 Those are non usable as shown in the pics IMHO. You'll need to find another block. Quote Link to comment Share on other sites More sharing options...
hoohaa Posted June 25, 2007 Author Share Posted June 25, 2007 The crank is good, all journals were nice and smooth, the bearings were all good. I don't think this was detonation. This is a NA VG30E block. I'm thinking perhaps the oil was contaminated, or the motor was run with little oil. The pistons melted from friction with the cylinder walls, not from excessive heat from lean conditions IMO. I am guessing the damage happened very quickly from the way the internals look. The guy I bought it from had replaced a "blown head gasket" on the motor previously, but then the motor siezed very soon after the HG replacement. I know some of the damage was already done before the HG replacement because someone tried to remove those aluminum deposits from the bores with scotchbrite or something. Not sure exactly what this means, but I'm guessing the "blown head gasket" led to contaminated oil, which led to too much piston friction, which led to aluminum deposits, and by that point replacing the head gasket was not enough, the damage had already been done. Here's my thinking on this situation: this is not a high dollar engine rebuild, it's a budget bearing, ring, and gasket job. If the motor blows up, which is likely for reasons other than the scoring (first time tuning with boost), then I probably won't cry. I'd probably just do another budget rebuild job, but try to find a better looking block. Thanks for the comment BRAAP, that's kinda what I was looking for. Yes it won't be "right", but it will probably run fine... That's good enough for me for this motor. Quote Link to comment Share on other sites More sharing options...
mtcookson Posted June 25, 2007 Share Posted June 25, 2007 Personally, I would just grab another VG. They are so cheap anymore that it would be cheaper to get one in good condition than to rebuild one in most cases. Quote Link to comment Share on other sites More sharing options...
hoohaa Posted June 27, 2007 Author Share Posted June 27, 2007 Well theres been a change in plans. I've decided that since I have a block with a couple scored cylinders I will be considering the motor "disposable". I am going to slap it back together with the cheapest ebay bearings, rings, and gaskets I can find. When I pull the running VG30 out of my pathfinder to swap this one in, I can tear that down and hopefully it will be in good shape. Then I can rebuild that one to factory spec with all OEM stuff. I will take the time to do that one right. I see two advantages to doing it this way: 1. I don't have to worry about blowing up a $600+ motor while learning to tune the MSII, and 2. I will have extra money for rebuilding the running VG30 correctly since the gaskets, bearings, and rings for the junk block will only cost me $160 total from ebay. I am going to feel MUCH better while tuning knowing that I can be as rough on this motor as I want to. We'll see how much boost this thing can take. Quote Link to comment Share on other sites More sharing options...
Careless Posted June 27, 2007 Share Posted June 27, 2007 Well theres been a change in plans. I've decided that since I have a block with a couple scored cylinders I will be considering the motor "disposable". I am going to slap it back together with the cheapest ebay bearings, rings, and gaskets I can find. When I pull the running VG30 out of my pathfinder to swap this one in, I can tear that down and hopefully it will be in good shape. Then I can rebuild that one to factory spec with all OEM stuff. I will take the time to do that one right. I see two advantages to doing it this way: 1. I don't have to worry about blowing up a $600+ motor while learning to tune the MSII, and 2. I will have extra money for rebuilding the running VG30 correctly since the gaskets, bearings, and rings for the junk block will only cost me $160 total from ebay. I am going to feel MUCH better while tuning knowing that I can be as rough on this motor as I want to. We'll see how much boost this thing can take. why not atleast give it a nice hone to see what you can make of it? the first pic (last score on the right) looks to be the deepest. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted June 27, 2007 Administrators Share Posted June 27, 2007 Those pics are of the block already honed. If he hones the bores further, especially to the point of removing the scratches, that only makes the bores larger which means more piston slap, wider ring gaps which is more blow by, and the rocking pistons due to the excessive pistons to cyl wall clearance accelerates ring wear considerably. It really needs the next size up pistons. Neither route is the right way to go about this and he is fully aware of that, but as a disposable engine, as he coined it, the scratches are the lesser of the two evils. Quote Link to comment Share on other sites More sharing options...
mtcookson Posted June 28, 2007 Share Posted June 28, 2007 Well theres been a change in plans. I've decided that since I have a block with a couple scored cylinders I will be considering the motor "disposable". I am going to slap it back together with the cheapest ebay bearings, rings, and gaskets I can find. When I pull the running VG30 out of my pathfinder to swap this one in, I can tear that down and hopefully it will be in good shape. Then I can rebuild that one to factory spec with all OEM stuff. I will take the time to do that one right. I see two advantages to doing it this way: 1. I don't have to worry about blowing up a $600+ motor while learning to tune the MSII, and 2. I will have extra money for rebuilding the running VG30 correctly since the gaskets, bearings, and rings for the junk block will only cost me $160 total from ebay. I am going to feel MUCH better while tuning knowing that I can be as rough on this motor as I want to. We'll see how much boost this thing can take. That's something I'd definitely do. Quote Link to comment Share on other sites More sharing options...
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