Steps to scratch build a VW

Discussion in 'Hangar Flying' started by Little Scrapper, Aug 13, 2019.

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  1. Aug 20, 2019 #201

    fly2kads

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    Once again, good answer from Hot Wings. Shims at the bases of the cylinders, thickness selected to get the deck height you need. Those get a thin coat of sealant to keep the oil in. The cylinder/head interface is left bare, no gaskets or sealant.
     
  2. Aug 20, 2019 #202

    Hot Wings

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    I haven't done the math for an annealed copper head gasket so I don't really know. I suspect, based on similar calculations of the VW cylinder surfaces:

    That the copper will crush, and work harden, when the engine is brought up to operating temperature.

    If the head is then re-torqued it could then be a good and permanent seal provided the work hardening raised the physical properties enough that it would no longer crush under the higher load at operating temperature.

    I don't have the time right now to gather the data and do the math...Got a fence to finish. :(
     
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  3. Aug 20, 2019 #203

    Vigilant1

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    If I can skip ahead a little: Is there a consensus here on Nikasil cylinders?
    The promise: Spend about $1000 for four Nikasil (aluminum with special silicon embedded coating) cylinders and save 10 lbs total engine weight, get better cooling (aluminum conducts heat better than steel), no corrosion in cylinder bores when engine sits between running (a big deal for most recreational aircraft), and better cylnder-to-cylinder head seal because they are then both made of AL and expand/contract at the same rate. As used in expensive Porsches . .
    The experience: They worked for some folks, and Scott Casler and Great Plains still sell them as options. OTOH, the experience in the Sonex community was not good (they seemed to "slump" at the case/cylinder junction), they caused a lot of problems and are no longer sold by Sonex and a lot of folks have removed them and are now back running iron cylinders. I've heard some folks opine that the greater thermal expansion rate of AL (cylinders) compared to steel (studs) may have resulted in excess pressure and crushing when the cylinders got hot--the studs just didn't elongate as much and the cylinders crippled at the case joint, or got smashed deeper into the magnesium case.

    Opinions? Experience? Maybe brand-specific issues?
     
    Last edited: Aug 20, 2019
  4. Aug 20, 2019 #204

    Little Scrapper

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    If you used a copper head gasket wouldn't that create an environment where you would need to check the head bolts frequently?
     
  5. Aug 20, 2019 #205

    Pops

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    On the 1835 cc , 60 HP VW engine in the SSSC I used a combination of shims under the cylinders and the copper O-ring gasket between the cylinder and head to set the CR of 7.55 to one. The copper gasket can be bought in sizes to fit the different bores available. The O-rings squash down to .060 in working out the CR.
    The copper O-rings were standard on the 1200 cc, 40 HP engines of 77mm bore. I have never had any problems with leaks using the copper gasket or any problems with loosing torque on the cylinder studs. I check the torque of the head studs at the first 25 hrs and at 50 hrs and they didn't change. I think all of those problems are caused by high temps like most problems with the VW. Run the engine at the proper temps and most problems go away.
    https://vwparts.aircooled.net/Coppe...d-Engines-p/copper-head-gasket-type-1-set.htm
     
  6. Aug 20, 2019 #206

    Hot Wings

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    Opinion only. NO real world experience:
    I won't use them for some of the reasons mentioned....And due to a Solidworks FEA simulation compared to iron. There was so much 'ripple' between the fins and general 'ballooning' under combustion load I can't think the rings manage to stay in contact with the cylinder wall between the fins. Ring land wear could also be accelerated compared to iron cylinders.

    A Nikasil plated iron cylinder might be worth the expense?
     
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  7. Aug 20, 2019 #207

    Pops

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    Never used the aluminum cylinders, the steel cylinders work to good to spend the large amount of extra money, will save weight somewhere else.
     
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  8. Aug 20, 2019 #208

    12notes

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    What type of sealant?
     
  9. Aug 20, 2019 #209

    Hot Wings

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    Have to defer to Pops on this one. Real world experience trumps speculation.
    If he says copper works, on an engine that hasn't been overheated, spending the time to do the math is probably wasted time.
     
  10. Aug 20, 2019 #210

    Little Scrapper

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    Ok, let's recap.

    Hot wings uses no gasket, no sealant. The VW factory on the Type 1 1600 used no gasket.

    Pops uses a copper O-ring gasket and they crush to .060" and he works out the compression ratio.

    What does GPAS, Hummel and Sonex do?

    Sounds like a builder could do both with success?
     
  11. Aug 20, 2019 #211

    Vigilant1

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    GPAS (per their engine build manual):
    -- Shims at the case/cylinder joint. Use 518 Loctite or Hi-Temp Permatx sealant here.
    -- Hand-lapped direct (no gasket) joint at cylinder-cylinder head. I'm not seeing any sealant called out for this, but may have missed it.
     
    Last edited: Aug 20, 2019
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  12. Aug 20, 2019 #212

    Vigilant1

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    Sonex (Aerovee) per their assembly manual:
    -- Shims at the case/cylinder joint. Use high temp silicone sealant here.
    -- At cylinder-to-cylinder head joint, use .06" copper gaskets. No sealant is mentioned.
     
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  13. Aug 20, 2019 #213

    Mcmark

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    +1 Lapped no sealant. One of mine has taken 25lbs of boost.
     
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  14. Aug 20, 2019 #214

    Pops

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    Can't remember for sure but I have built about 5 or 6 VW aero engines. First one was for my KR-2 in the mid 70's and it was a 1600 cc engine ( no head gasket, stock CR). Bought the plans from Ken Rand when he started sell the plans. Second was for a Teenie- 2 , also a 1600 cc Aero engine ( no head gasket, stock CR) that was flown from the east coast to the west coast and back. Then rebuilt a 1600cc Aero engine for a Volkplane,( no head gasket, stock CR, then a 1915 cc Aero engine for a Fisher Koala ( also used cylinder shims and copper head gasket for 7.5 CR). Then my 1835cc for the SSSC with the cylinder shim and copper gasket ( for 7.55 CR). Never any problems except for the Volkplane because the owner used a prop with to much pitch causing heating problems.
    Also forgot-- The first 32 Hrs on the SSSC was with a 1200 cc, 40HP Aero-engine that I built. ( stock copper heat gasket) No problems, sweet running engine.

    Auto engines, have no idea , built engines and sold VW Bugs as a side business for several years. Of all the engines I had one come back, after about 6 months the flywheel can loose, I know it was torqued correctly, but it still came loose. Put in new crank and flywheel and no more problems.
     
  15. Aug 21, 2019 #215

    Little Scrapper

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    Since my last post I’ve been reading about heads. Man, lots of people argue about heads.

    What manufacturer makes the best predictable quality head? Seems like some manufacturers have really put out some garbage. I’ve been on Samba and studying the threads it seems either nobody agrees or nobody knows. MOFOCO is close to me but I’ve heard mixed reviews on quality. GB Performance? Same.

    Or do people who build these for aviation use prefer to get the original German made single port heads? This is really a confusing subject. AeroVee, Casler and GPAS all use MOFOCO heads from what I gather. Is that true? How many actual manufacturers exist? Regardless of price does a manufacturer exist who makes a superior product?

    I’m getting the feeling like the best was the original German made head.
     
    Last edited: Aug 21, 2019
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  16. Aug 21, 2019 #216

    Hot Wings

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    In the 40 or so years I've fiddled with VWs I'd have to say that, other than some high dollar specialty heads, it's not just a feeling - it's a fact. :(
    An untouched original German head is worth whatever $$$s the person that has it is asking.

    There have been other heads worth using but finding a reliable continuous source is nearly impossible.
     
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  17. Aug 21, 2019 #217

    dmar836

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    I bought a set of the new Panchitos when they first came out. Finally, some newly made heads with reportedly good cooling that didn’t have monster valves and runners. Companies design for flow at street rpms and not for peak efficiency at low rpm. Understandable as that won’t sell. Then everything you read on the Samba will likely be from guys where the heads are the bottleneck to their strokers with big cams and dual carbs. Even if not, the prevailing advise there is to go bigger and you can “grow into them” with dual carbs and all. If you can rework a set of good stock heads go for it. If uncracked they are desireable. I’m always afraid I’ll miss the cracks. I’ve passed on a few and would continue to pass on a pair reworked and cleaned up for eBay sale.
    I’m different than most. I don’t want dual plugs and all that that entails.
    It’s hard to find good heads that are new and higher quality(designed to cool better, etc) without all the upgrades for a performance street motor.
    I’m also convinced that many who have overheated stock heads didn’t spend the time on baffling that they should have. Just a hunch.
    Dave
     
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  18. Aug 21, 2019 #218

    Pops

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    Have to agree 100%.
     
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  19. Aug 21, 2019 #219

    Little Scrapper

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    What does this mean for average homebuilders wanting to build a VW powered airplane? I'm not being snarky either, haha, it's a legitimate question.

    It's so weird how after all those years the HB sector doesn't have a standard go to head manufacturer. Again, I'm not being snarky, I'm just saying.

    I'm not sure what to do about that. Try to locate NOS heads in a box somewhere?

    Let's figure out a way to change this, so VW powered homebuilt aviation can continue and possibly grow.
     
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  20. Aug 21, 2019 #220

    Pops

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    AeroVee, Casler and GPAS doesn't have a choice but to use after market heads except to have their own heads made and the market to very small for that expense. But Revmaster went in that direction.
     
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