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Old February 19th, 2013, 18:42   #1
vwmilo
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Default should I clean and reuse or replace my pistons?

Hello, first time rebuilding a TDI. its an 02 jetta TDI with about 100k. engine oil gummed up and solidified causing serious problems (ticking noises and low compression on 3 & 4). not 100% sure why this happened but, I think the combo of old engine oil, a veggie oil conversion, engine running cold (stuck open thermostat? veggie conversion heat exchanger?), and pre-existing excessive blow by...

Pulled the head and oil pan and pushed pistons out through top. pistons were very dirty. stuck rings on 3 & 4 with galling on pistons and cylinders. I honed the cylinders until vertical galling marks were barely visible.
Should I replace the pistons? or at least these two? I think they are re-usable. I can sand the galling off the pistons easily (it's pretty light).

If I do re-use, is there a good method to cleaning the carbon off the pistons?

pulled a couple main bearing caps and the bearings look new so I put them back. I intend on replacing the rod bearings along with the rings and all bolts (they are TTY right?).

thanks for any pointers!
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Old February 19th, 2013, 19:11   #2
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First....all the bolts you are using are shot. TTY.

Second, you cannot sand and hone at random. you need to take detailed measurements and make sure they are equal all around or you are just tossing your money in the toilet.

Third, Dump the freaking WVO system in the trash. There is NO REASON AT ALL an ALH motor should need rebuilding at 100K.
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Old February 19th, 2013, 19:28   #3
vwmilo
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Thanks Jason. hard to say what the life of the car was b4 I got it. I have been measuring as I go. luckily, I didn't have to remove much at all. obviously 3 & 4 had to receive a bit more honing than 1 & 2. would it be problematic if 3 & 4 are a thousandth or so larger in diameter? how much variation would be acceptable? I could hone 1 & 2 a bit more to be exactly same diameter...
any pointers on the pistons? clean and re-use or no?
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Old February 19th, 2013, 19:29   #4
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As Jason said, all those bolts are trash now............and, no justifiable reason for an ALH engine to need a rebuild at 100,000 miles .........gees!

I'd use Joy or Dawn dish washing liquid, scrubb pad, brush with nylon bristles, etc........ keep the damn sand paper off them. Lots of elbow grease until they are clean. Yeah, you can use some Wally World carb cleaner too.

I'm no expert on cylinder wall honing, but you need to heed Jason's advice.

Lastly, any time of Vegetable Oil has no place in a TDI engine............. unless it has been commercially converted to Bio-diesel. Read and learn about the % level of Bio-diesel that's acceptable to be blended with conventional diesel fuel!

Hope this helps!
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Old February 19th, 2013, 19:41   #5
vwmilo
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I've seen DIY vids on using wire wheel to clean off carbon but I dont have a warm fuzzy about that. I'll proceed with the scrubbing and will use a piston ring to clean the grooves.
the veggie system is a second tank system and can simply be switched off. I am curious how much of this problem is related to that though. I've seen plenty of these systems in ALH's go 100's of thousands without problems. I think the set up in this car, using coolant to heat the oil, caused the engine to not ever heat up to normal op temp and burn off oil contaminants. either way, I dont think I'll use it any more.
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Old February 19th, 2013, 20:43   #6
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Something like Awesome, Simple Green, Power Clean, etc., will dissolve the carbon. However, do not let that stuff dry on the pistons. Use eye protection and rubber gloves, maybe even a cheap face mask (don't breath the vapors). You can mix it with Dawn or Joy without any adverse affects. It may take an hour to clean one piston.

Of course, I suppose you can always take them to a shop with a hot tank. I'd steer away from a chemical clean, other than what I described above.

Yeah, the engine needs to warm up right away, otherwise, carbon can build up as well as condensation never leaves the engine via the CCV system. No telling how much water (suspended) was in the WVO as well as the glycrin.
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Old February 19th, 2013, 22:07   #7
vwmilo
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thanks. thats about what I figured I'd be doing. I'll just have to set up in front of a movie and spend a couple hours cleaning.
I think your right about the glycerin and water. the few times I drove the car, it never reached normal temp and took a long time to warm up at all. the oil even smelled like glycerin. turned it solid like congealed gravy. seems like the thermostat should have caused the engine to warm right up WVO system or no since the T to the heat exchanger is right after it. seems more and more like a $5 thermostat is the culprit >
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Old February 20th, 2013, 05:33   #8
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I can guarentee it's all related to the WVO set up.

I have LOTS of cars that go 15K+ miles and come in with just over 2 qts in the sump run for hundreds of thousands of miles. Grease run improperly, no or incorect purge and tank mixing along with lots of other bad habits due to the warm climate cause absolute carnage to the system. Just make biodiesel and call it a day. Seriously.

Good luck with the rebuild.
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Old February 20th, 2013, 06:56   #9
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Id be a little concerned about honing to remove galling. Do you have an inside micrometer? Honing is really only intended to polish after boring. If you're not real careful you could end up with a bulge in the mid cylinder area or create an indentation in an area.
You need to take a measurement in 4 directions or more at many heighths up the cy... especially at the gall and just past. When the honing balls hit the gall they have a tendency to get "knocked back", then they "spring forward" causing an impact point just past the gall. This can create an every so slight indentation. With the HIGH compression these engines require.. tolerances are critical, and an indentation will cause a compression nightmare. Gas engines are not "AS" critical due to lower compression. Compression Gas is 150-200+psi no less than 100, and no more than a 30% difference between highest to lowest reading. Compression Diesel new is 350-450psi and no less than 276, and no more than a 20% difference between highest to lowest reading.

A mechinist ruler as a straight edge placed vertically on the cy. wall and a small pen flashlight (gun bore flashlight) moved around can find these imperfections.If you see light under the ruler, you have a indentation.
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Old February 20th, 2013, 09:58   #10
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IF you can get the rings off, and that is a BIG IF, you will have what is referred to as pyrolysis. That is what happens to the glycerine from the WVO that will not burn, cokes up on the rings making them stick. The pyrolysed oil also gets into the turbo bearings, rod, mains, etc.

The only thing that takes the gunk off is high heat and/ or mechanical force. Don't reuse galled pistons.

This is what you should expect:
1. the cylinders will need boring and oversize pistons.
2. your injectors will not work and the #3 won't ever operate correctly.
3. The cylinder head needs rebuilt.
4. the VE pump will leak and have galled components.
5. In other words, you need a complete overhaul.

Better yet, go to the junk yard and find a complete engine. You'll save yourself a lot of headaches.
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Old February 20th, 2013, 10:01   #11
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The problem with vegetable oil is that 99% of the people don't use it properly, with deadly (to the engine) consequences. Gummed/carboned rings, valves, pistons, etc- and if the veg oil contaminates the engine oil, it turns the engine oil into a viscus goo that looks a lot like black jello, and there go all your bearing surfaces due to oil starvation. I for one would never, ever buy a TDI if I knew it had been run on veg oil, unless I got it for scrap metal pricing. - And I do have some experience with this, having expiremented on both IDIs and TDIs from 1998-2009. I have never run my TDI Getta on anything but 98% diesel and 2% commercially made biodiesel, and have never run the 86 IDI on veg oil either.
When re-building an engine you really need to mic everything - pistons, cyl walls, bearing surfaces, etc. - the eyeball is just not accurate enough. You can use plastigauge on the bearings to check tolerances. Everything needs to be brought back to factory tolerances, or you are wasting your time and money. Remember if you buy new pistons, that each piston and rod has been balanced at the factory to work with it's individual placement on your crankshaft. So, if changing out a piston or rod, go get your assembly professionally re-balanced.
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Old February 20th, 2013, 10:37   #12
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Quote:
Originally Posted by Franko6 View Post
IF you can get the rings off, and that is a BIG IF, you will have what is referred to as pyrolysis. That is what happens to the glycerine from the WVO that will not burn, cokes up on the rings making them stick. The pyrolysed oil also gets into the turbo bearings, rod, mains, etc.

The only thing that takes the gunk off is high heat and/ or mechanical force. Don't reuse galled pistons.

This is what you should expect:
1. the cylinders will need boring and oversize pistons.
2. your injectors will not work and the #3 won't ever operate correctly.
3. The cylinder head needs rebuilt.
4. the VE pump will leak and have galled components.
5. In other words, you need a complete overhaul.

Better yet, go to the junk yard and find a complete engine. You'll save yourself a lot of headaches.
Here one thing we actually agree on!
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Old February 20th, 2013, 11:43   #13
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Quote:
Originally Posted by jasonTDI View Post
Here one thing we actually agree on!

Off to buy a lottery ticket... the planets are definitely in some weird form of alignment today.
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Old February 20th, 2013, 13:01   #14
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lol!!
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Old February 20th, 2013, 13:06   #15
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Same thing happened to this BRM:

http://forums.tdiclub.com/showthread.php?t=255131
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