hydraulic vs mechanical head - What's the difference? - page 1 - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• hydraulic vs mechanical head - What's the difference? by hipifreq on 04 Feb, 2008 19:48
• Forgive the newb question, but searching here and elsewhere didn't provide much info:
  
  Can anyone help explain what the difference between a mechanical and hydraulic head are? What ways I can tell whether or not a head (or block) are designed to be hydraulic or mechanical? Post photos of the differences between the two? What are the implications for the two?
• #1 by KTZed on 04 Feb, 2008 20:35
• I asked this same question when I first joined.
  Generally speaking '86 and up came with hydraulic lifters. They require no adjustment, just use oil pressure.
  Mechanical lifters require adjusting every *30,000 kms* (this number's just from memory and could be wrong...get the Bently check it for the service interval and adjustment procedure).
  Theres a extra oil gallery on the front of the head (and consequently, the block) commonly referred to as the extra hump or bump seen circled in red.
  
  Bump = Hydraulic
  No Bump = Mechanical
  
  
• #2 by dieselsnowmobile on 04 Feb, 2008 20:55
• Mechanical Heads are said to have a hair more power.
• #3 by hipifreq on 05 Feb, 2008 00:43
• KTZed: Thanks for the photo, that helps ID the difference. The cam and followers in your photo look similar, but does it have the shims that my mechanical head does?
  
  Anyone have a good link to schematics with description of what's going on with the hydraulic? Without one in front of my I have a hard time "seeing" what's going on.
  
  Yes, I've read a few different ideas about the hydraulic vs. mechanical debate. There's some that seem to think mechanical has extra power, but the need to check and adjust clearance seems to be a downer. Guess they never loved an air-cooled VW before. I'd check and adjust clearance every oil change with my old '71 bus.
  
  The down side of hydraulic some people have stated is under high RPMs the oil gets compressed, which can affect the valve clearance as it doesn't lift as much.
• #4 by mufflerbearing on 05 Feb, 2008 01:15
• hydraulic heads have 4 cam bearings where solid heads have 5.
  
  im not too keen on how the hydraulic lifter actually works, but on a solid head the shim sits right on top of the lifter and is held in place by a small skirt around the edge of the lifter.
  
  -j
• #5 by jtanguay on 05 Feb, 2008 01:21
• hydraulic lifters can become 'sticky'.. using a high quality oil can minimize this from occuring though.  i bet running a very good synthetic oil such as royal purple or lubro moly or one of those high end oils can minimize the need to adjust the valve clearance.  i found that my mech lifter engine was a work horse... it could haul some serious weight and not sweat like my current one with hydraulic lifters...  even if people say its a 'minor' boost in power, the butt dyno approves  
• #6 by hipifreq on 05 Feb, 2008 15:56
• The picture of the hydro head agrees with libbybapa: One of the caps is off, but it definitely has 5 bearings.
  
  So I've head about converting hydro to mechanical and vice versa. Is that an easy thing to do? I'm guessing it would involve plugging the oil gallery and replacing the followers with mechanical shim type, but no changes to the cam or other parts of the engine.
  
  Does the hydro block have a different oil pump in order to get extra oil to head?
• #7 by jtanguay on 05 Feb, 2008 16:34
• yes the hydraulic engines should have a bigger oil pump as hydraulic heads 'leech' quite a bit of oil.
  
  would be neat if there was a way to convert 1.9TD/TDI heads to mechanical  :wink:
• #8 by foxracer1 on 05 Feb, 2008 17:19
• The picture shown is a gasser head.
• #9 by jimfoo on 05 Feb, 2008 17:56
• No, it's one of the newer integrated glowplug injector models  :lol:  :lol:
• #10 by subsonic on 05 Feb, 2008 18:02
• Quote from: "jimfoo"

  No, it's one of the newer integrated glowplug injector models  :lol:  :lol:

  
  
  Nice.
• #11 by KTZed on 05 Feb, 2008 21:02
• Better?....Jeez
  
  
  As far as im concerned hydraulic head is hydraulic head as long as it gets the job done....im not picky  :wink:
• #12 by Baselyne on 06 Feb, 2008 00:32
• Quote from: "jtanguay"

  yes the hydraulic engines should have a bigger oil pump as hydraulic heads 'leech' quite a bit of oil.
  :

  
  
  I was wondering on pre 82 mechanical engines would it be possible to adapt the larger oil pump? its stright trade>?
  
  are there two different vac pumps and oil pump shaft lengths?
• #13 by jtanguay on 06 Feb, 2008 09:05
• i've heard of some GM guy's modding the actual oil pump to increase the pressure... is this do-able with our vw oil pumps??? there must be a way!
• #14 by Baselyne on 06 Feb, 2008 16:58
• perect thanks for the reply...
  
  I wonder about the modding about the vac pumps too...
  
  I assume the shaft on the gassers oil pumps are shorter as there would be a distributor there? Just a hunch.... anyone?
  
  When and what size gears did they change to on the gassers?
  Just so someone could get possibly the larger gears version off one of those non diesels