Page 1 of 2 12 LastLast
Results 1 to 20 of 21

Thread: Pistons too tall

  1. #1
    Join Date
    Feb 2001
    Location
    Omaha, NE
    Posts
    316

    Default Pistons too tall

    I burnt a piston in my ITB Golf due to my stupidity and therefore had to put in new pistons.


    I cleaned out the bores with a hone and replaced the old pistons with a new set of Kolbenschmitts. Ran the motor and was getting what I thought was lifter noise. Replaced the lifters with a new set, and got the same result. Took off the head and thoroughly cleaned the oil passages thinking they may be clogged from piston debris. The result was still the same. Took the head off once more but this time as I was cleaning the bores out, I noticed some marks on the top edge of the pistons. That's when I realized that the lifter noise was actually the piston slightly tapping the head. Good thing I didn't go above 3500 RPM.
    So the question I have is do I need to get it machined slightly or can I just shave a bit off with a belt sander? Looking at the old pistons, they were also ground down a bit. I think just removing .010 in off that edge would keep it from hitting the head.
    Thanks
    Last edited by Ralf; 05-13-2010 at 02:22 AM.
    Ralf
    ITB Golf GT

  2. #2
    Join Date
    Feb 2007
    Posts
    292

    Default

    What is the part #? I have not seen that happen......
    ______________
    Waterhaus Racing is Back!
    NRSCCA Competition Chair
    BOG Member
    "Nebraska organizing committees
    to race in Iowa & Ne board thing "
    Still working on a name...
    X-MVRG Member...
    ITB Rabbit/ITA Miata

  3. #3
    Join Date
    Aug 2006
    Posts
    384

    Default

    somewhere along the line did you deck the block or head? you running a stock gasket?

  4. #4
    Join Date
    Feb 2001
    Location
    Omaha, NE
    Posts
    316

    Default

    Not sure and the head is temp installed right now, so can't get the numbers off the pistons. (Can't really read the numbers on the old pistons, but they are the same.)
    The ridge that you can see on the burnt piston is actually the high point of the piston, not a relief cut. It is actually higher on the new ones then the old pistons.
    Here is a picture of one of the old pistons. You can see some pitting from detonation.
    Ralf
    ITB Golf GT

  5. #5
    Join Date
    Feb 2001
    Location
    Omaha, NE
    Posts
    316

    Default

    It was a motor I bought from a Prod guy that had it in his ITB car. I'm assuming the head and block were decked. I was told it was built by a reputable shop. I'm using a metal head gasket.
    Ralf
    ITB Golf GT

  6. #6
    Join Date
    May 2001
    Location
    IT.com "First Loser" Greensboro, NC USA
    Posts
    8,607

    Default

    Too funny! We had exactly the same thing happen with an engine we had built for a rally car back in the '80s. It sounded like a diesel when we started it up...

    The solution was for the guy who built it to pull the head and whiz off a few thou from the tops of the pistons with a 3M pad on a die grinder. I was appalled but he bolted it back up and it ran strong for several years...

    K

  7. #7
    Join Date
    Jan 2001
    Location
    Buffalo, New York
    Posts
    2,942

    Default

    That piston in the first Pic looks pretty well damaged. I am not sure a post-relief cut, shave or grind will save any damage to the ring lands, but you never know.

    If it were me and that happened, I would bite the bullet for new pistons, relief them before final assembly and rebalance.

  8. #8
    Join Date
    Feb 2001
    Location
    Omaha, NE
    Posts
    316

    Default

    I have new pistons in there now. Its the new pistons that I'm having trouble with. Those pictures are of the old pistons that I pulled.
    Ralf
    ITB Golf GT

  9. #9
    Join Date
    Mar 2001
    Location
    Connecticut
    Posts
    7,381

    Default

    Given the unknown history of this engine, I would:

    - Measure the distance the pistons are protruding from the block, and have them shaved by that amount plus a margin to account for stretch and slack; I'd have to look it up, but I think .003" is the norm

    - Remove the pistons and rods, and have the pistons machined

    - Replace the rod bearings; you probably damaged them with the pistons hitting the head.

    - After block assembly, do a full cc of the engine to ensure that the compression ratio is legal. This block has obviously been machined, and it doesn't take much to increase compression by the legal 1/2-point; I'd bet a dollar that your compression ratio is illegal for Improved Touring.

    GA

  10. #10
    Join Date
    Sep 2008
    Location
    FL.
    Posts
    1,384

    Default

    The guy that built that engine, usually used the cheap, 1 pc thrust bearings. As said, replace the rod bearings, check to make sure that you are using the 6 pc thrust bearing. Pop out the pistons, cut and balance. The felpro head gasket is about 066. thic. Figure for 030 head to piston gap, min.
    Try doing a search for "head saver" head gasket. I have never used one on a VW or know if anyone makes them.
    Deburr the sharp edge off of the top of the block and the edge of the head, match to the gasket..
    An uncut, stock head, should be close for the compression numbers.IMHO. MM
    Mike Ogren , FWDracingguide.com, 352.4288.983 ,http://www.ogren-engineering.com/

  11. #11
    Join Date
    Jun 2005
    Location
    Kansas
    Posts
    532

    Default

    Quote Originally Posted by Greg Amy View Post
    Given the unknown history of this engine, I would:

    - Measure the distance the pistons are protruding from the block, and have them shaved by that amount plus a margin to account for stretch and slack; I'd have to look it up, but I think .003" is the norm

    - Remove the pistons and rods, and have the pistons machined

    - Replace the rod bearings; you probably damaged them with the pistons hitting the head.

    - After block assembly, do a full cc of the engine to ensure that the compression ratio is legal. This block has obviously been machined, and it doesn't take much to increase compression by the legal 1/2-point; I'd bet a dollar that your compression ratio is illegal for Improved Touring.

    GA
    So I think I missed something... where in the ITCS is the allowance to machine (or otherwise modify) the tops of the pistons? Or is this a normal repair/replace procedure that is outlined in the VW shop manual?
    Gary Learned
    MiDiv
    Volvo 142E
    http://www.youtube.com/user/denrael

  12. #12
    Join Date
    Jan 2001
    Location
    Tijeras, NM
    Posts
    579

    Default

    Quote Originally Posted by Gary L View Post
    So I think I missed something... where in the ITCS is the allowance to machine (or otherwise modify) the tops of the pistons? Or is this a normal repair/replace procedure that is outlined in the VW shop manual?
    Same goes for the "head saver" gasket. The material is free, but the compressed thickness must match stock.

  13. #13
    Join Date
    Feb 2007
    Posts
    292

    Default

    Harlan and I ain't going to protest......you need every illegal point of compression to get past Gary's Blue Brick! See ya at the track!
    ______________
    Waterhaus Racing is Back!
    NRSCCA Competition Chair
    BOG Member
    "Nebraska organizing committees
    to race in Iowa & Ne board thing "
    Still working on a name...
    X-MVRG Member...
    ITB Rabbit/ITA Miata

  14. #14
    Join Date
    Feb 2001
    Location
    Omaha, NE
    Posts
    316

    Default

    Cheating is not something I'm willing to do. I know that I would probably never end up anywhere near the Runoffs or ARRC but I'm not going to build a cheater car so i can win regionally. This is why I'm asking here to get clarification.
    Ralf
    ITB Golf GT

  15. #15
    Join Date
    Feb 2007
    Posts
    292

    Default

    I have a NON-Decked block laying here......
    ______________
    Waterhaus Racing is Back!
    NRSCCA Competition Chair
    BOG Member
    "Nebraska organizing committees
    to race in Iowa & Ne board thing "
    Still working on a name...
    X-MVRG Member...
    ITB Rabbit/ITA Miata

  16. #16
    Join Date
    Feb 2001
    Location
    Omaha, NE
    Posts
    316

    Default

    I've got a stock head that hasn't seen any machine work that I'm going to try. Since the contact is only on one edge, I think it is only contacting the head by a few thousands.
    Ralf
    ITB Golf GT

  17. #17
    Join Date
    Feb 2001
    Location
    Omaha, NE
    Posts
    316

    Default

    Quote Originally Posted by Gary L View Post
    So I think I missed something... where in the ITCS is the allowance to machine (or otherwise modify) the tops of the pistons? Or is this a normal repair/replace procedure that is outlined in the VW shop manual?
    You got me looking in the book Gary.

    "Cast or forged equivalent pistons shall provide the same dome/dish/valve relief
    configuration, ring groove width and spacing, pin height relationship,
    weigh no less than the factory standard bore pistons."


    "Balancing and “blueprinting” of the engine assembly are
    permitted. Lightening of parts beyond the minimum material
    removal necessary to balance is prohibited.
    "

    So the way I read this is that the replacement piston can't weigh less then the standard size piston. Since the replacement pistons are oversize I would imagine that there is more material and therefore weigh more then the stock standard piston. Now since one can balance and lighten to the lightest stock piston, one can remove material from the new pistons. What prohibits one from taking material off the top of the piston to lighten? As long as you don't change the dome/dish/valve relief configuration, there shouldn't be a problem.
    I'm by no means an engine builder/machinist, so I have no idea and that is why I'm asking. Better for me to be clear about something then to do it and be illegal later.

    Give me your thoughts on the way I'm reading the book. Like I said, I have stock head I can try first so I may not have to touch the pistons anyways.
    Ralf
    ITB Golf GT

  18. #18
    Join Date
    Jun 2005
    Location
    Kansas
    Posts
    532

    Default

    Weight/balance aside, seems to me you'd be changing the " ...dome/dish/valve relief configuration", if nothing else. And maybe the " ...pin height relationship", as well? I'm with you - not an expert - that's why I replied to the GA's post specifically. Greg, where'd you go?

    Meanwhile, to Hell with this technical crap... you tellin' me we might have 4 (FOUR) ITB cars at MAM next week? They may have to give us our own run group!
    Gary Learned
    MiDiv
    Volvo 142E
    http://www.youtube.com/user/denrael

  19. #19
    Join Date
    Feb 2001
    Location
    Omaha, NE
    Posts
    316

    Default

    I certainly hope I'll have this back together again by then. MAM is local for me.
    Ralf
    ITB Golf GT

  20. #20
    Join Date
    Sep 2008
    Location
    FL.
    Posts
    1,384

    Default

    Cutting the tops off is not legal. If the piston has a higher than stock squish band, and you matched it to the stock piston, you may be considered legal , by the result, not by the method.
    Any head will hit the piston, cut or not cut. I said to use an uncut head to get near the legal compression limit, not to miss the pistons.
    You need to measure the piston to head space by deduction. You can use the clay method or the washer method. Take a 030 thic washer, or a valve spring shim washer( Iuse a 5/16 grade 8 washer). Place on the piston squish zone. Set the head and gasket on, and bolt it on at 25# torque. Rotate the engine, without the cam in, and feel for any touch at TDC. Do both ends of the engine, one at a time. Take the head back off and look for hard marks from the washer. I use permanant marker on the head and piston to show interferance.
    You can also measure the piston protrusion with a pair of the 030 washers and a straight edge. This is quick and easy and works at the 030 gap size, if you run less space(under 020), the actual space should be measured, IMHO.
    Measure the head gasket. It will be about 070( @ 25#) for the Felpro. Remember that the HG wil be about 066 at full torque value.
    You will need to cut the piston tops off to get any room. I suspect that the engine will not be legal.
    I assume that you would want to be as legal as you could be within the spirit of the rules. The head saver gasket and the stock size head may be close to legal compression and you would make any cc test if you were to go fast enough to get taken apart. In reality ,the SCCA seldom takes any cars apart. My circle burner gets taken apart every time we run it.
    As you get more races and start to go fast, find a good block and builder(me) and go fast legally. HTH, Mike Ogren/Protech
    Mike Ogren , FWDracingguide.com, 352.4288.983 ,http://www.ogren-engineering.com/

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •