piston protusion ?'s noobish - page 1 - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• piston protusion ?'s noobish by Possum79 on 19 Dec, 2009 21:09
• I have a pretty dumb question but I don't know the right answer. I have been in the process of taking my little 1.5 apart and just started to tear into the bottom end. I put cylinder 2 and 3 at tdc and i noticed that one cylinder is slightly lower then the other maybe by like 1/16". Is that normal? I was kinda rushed to leave and didnt really check it out. Is it just the operation of stroke its at? one on combustion one on exhaust or what ever?
• #1 by Vincent Waldon on 19 Dec, 2009 21:19
• Due to machining differences it's normal for the piston protrusion to be slightly different across all 4 cylinders.
  
  Having said that, if one is very obviously lots lower*and* there's signs of impact (impression of valves in the top of the piston (etc) it can signify a bent rod. 
  
  I don't think I've ever seen what the maximum allowable difference is... hopefully someone wise will weigh in.
  
• #2 by theman53 on 20 Dec, 2009 11:18
• X2
  and show us some pics that would be neat to see.
• #3 by rabbitman on 20 Dec, 2009 11:25
• I've heard the pistons are a matched set in order to have the same protrusion so it could be a piston out of another engine then.
• #4 by Possum79 on 20 Dec, 2009 12:51
• Ill try and get some measurements tonight along with pics. I mean I can visually see a difference and went wtf. I say 1/16" because I dont think I would notice anything smaller. This kinda sucks. I have no signs of piston contact. When I took the head apart I did find three broken lifters. When I rolled the bottom end over on my stand I saw some small chunks of metal bits fall out. Now this is really started to make me sad.
• #5 by Vincent Waldon on 20 Dec, 2009 18:06
• Unfortunately broken lifters are a pretty reliable sign of valve-piston contact (and the resulting bent rods in some cases) but lets see what your measurements yield.  Pics of the top of the pistons would be great as well.
• #6 by Rabbit on Roids on 21 Dec, 2009 09:22
• 1/16th inch? there has to be something bent or squished.
• #7 by maxfax on 21 Dec, 2009 18:14
• Quote from: Vincent Waldon on 19 Dec, 2009 21:19

  I don't think I've ever seen what the maximum allowable difference is... hopefully someone wise will weigh in.
  

  
  I can't say that I'm wise, but I've always been under the impression that the max allowed difference is the range given for choosing the HG thickness..  For example, a 3 notch HG is used for a piston protrusion of .033 - .036MM..   That seems like a rather small range, but then again it doesn't take much to make the compression uneven....
• #8 by Possum79 on 21 Dec, 2009 18:36
• SON OF A B WORD! After looking harder at the bottom side with the oil pan off it does look like a bent rod to my untrained eye. Anyways as far as measurements go I had piston #3 sitting .026" above the deck. And piston #2 was well over .035" under the deck. I gave up and cried a little inside. It looks like a bent rod and I did get pics but I dont think you can really see the bend. anyways here is the small size ones and Ill link to bigger ones if you want to take a better look. Im need of some new stuff here if anyone is feeling generous!  
  
  This was my problem cylinder too but I was getting coolant to flow into this and screw everything up. When I took the injectors out to compression test I had coolant fly out at me. I was gonna say no valve contact but I feel like an idiot. It probably hydrolocked on me and bent that rod. Still doesnt explain where the coolant came from.
  
  
  
  
  
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• #9 by Possum79 on 21 Dec, 2009 19:42
• It makes sense though doesn't it? I had a problem of coolant getting in the cylinder and when I tried to compression test the thing I didnt take out all of the injectors at once just one at a time. And when I got to #2 I noticed coolant spraying me in the face. Hydrolocked with the injector still in there and bent the rod. If I would have taken all the injectors out at once I think I would have been in just for a resurface of the head. I cheaped out and didnt bother the first time to get the head checked out.
  
  
  ~Lessons learned.
• #10 by rabbitman on 21 Dec, 2009 20:20
• Correct me if I'm wrong but isn't the white blobs from coolant?
  
  If it's for sure coolant then I'd say your hg went. Possibly another rod is all you'll need.
• #11 by 745 turbogreasel on 21 Dec, 2009 20:24
• at least your block is vent free.
• #12 by Possum79 on 21 Dec, 2009 20:37
• Quote from: rabbitman on 21 Dec, 2009 20:20

  Correct me if I'm wrong but isn't the white blobs from coolant?
  
  If it's for sure coolant then I'd say your hg went. Possibly another rod is all you'll need.
  

  
  I have had the head off the block for a while so its possible that its from taking the head off. I noticed some scrapes on the head when I took it off so I think thats where its leaking. I replaced the gasket a few months back and the one I took off wasnt broken at all other then being old and crusty. I replaced it with a new and it ran good for 5 minutes then I heard a cough and started to smoke and run like crap. When I took the head off this time I noticed the small scrapes but the gasket looked great.
• #13 by Vincent Waldon on 22 Dec, 2009 09:58
• Quote from: Possum79 on 21 Dec, 2009 19:42

  Hydrolocked with the injector still in there and bent the rod.
  

  
  Which is why there's no valve impression marks... it all makes sense, unfortunately.
  
• #14 by Vincent Waldon on 22 Dec, 2009 11:44
• Yeah, I was wondering the same thing.
  
  Until they actually open they're pressing against a virtually uncompromisable mass... so I can see it happening.
  
  I'm thinking it would be exhaust lifters that would bear the brunt?