VW Rocker arms: Loss of power due to broken adjuster. Install 'em right!

Discussion in 'Volkswagen' started by Vigilant1, May 29, 2017.

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  1. May 29, 2017 #1

    Vigilant1

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    The attached link (here) provides some discussion on a loss-of-power incident (no one hurt, but damage to the aircraft on landing). The engine builder had apparently installed the rocker arms in such a way that the adjusters needed to be backed out >far< too much. (Maybe the pushrods were cut too short, or too many shims under the rocker arm supports). As a result, the hole in the adjusters that allows oil to pass from the rocker arms to the bearing was not in position and instead may have been entirely outside the rocker arm. This had two results:
    -- No lubrication to the bearing that rides on top of the valve stem. It was frozen on the affected engine
    -- The valve adjuster was weaker due to the drilled hole being outside the rocker.

    [​IMG]


    (See above. Only a tiny bit of the valve adjuster is visible above the lock nut on all of the cylinders. Not right).

    As a result, the adjuster broke and the engine suffered from reduced power.

    There are very good instructions, photos, and videos of how to build these engines, but it's important to pay attention to the details when doing the work.

    The NTSB report noted that there were burrs on the crossdrilled hole where the adjuster failed, and that this might have increased the likelihood of a stress fracture there. Does anybody here routinely de-burr these holes? I guess it wouldn't hurt anything, but it would seem unnecessary if the adjusters are correctly installed (since that portion of the adjuster shaft should be well inside the rocker arm and not be under appreciable stress).
     
  2. May 29, 2017 #2

    Pops

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    I have found in the past if you have the correct length pushrods and then switch over to the ball type adjusters all that is needed is the 1/16" thick spacer washers that is supplied with the new type adjuster.

    I used that type of adjuster for several years on an aero-vw engine and decided to go back to the stock VW adjusters. VW engineers had many years to perfect the engines and after driving over a million miles without any problems with the stock adjusters along with several other aero-VW engines that I built.

    With the rocker arm geometry being off your engine was not developing the power it would if the geometry was correct. Also increase valve guide wear, etc.
     
    Last edited: May 29, 2017
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  3. May 29, 2017 #3

    radfordc

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    I once found this when I did a valve adjustment. I'm sure they were adjusted properly. Sometimes stuff breaks.

    [​IMG]
     
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  4. May 29, 2017 #4

    TFF

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    Just looking at the adjuster, it reads done wrong. A friend bought a plane that supposedly had a pushrod AD done. Nope. Mag check was fine. The plane fully loaded barely got off a 3500ft runway. Thought it was fouled plugs, landed and checked mags again. Took off with the same effect; landed and picked alternate transportation to get where he was going. Intake pushrod collapsed; 3 cylinder engine in a plane that really needs 4 if not 4 bigger ones. It goes back to alternate engines being a hobby unto themselves. Its not a VW problem, its a builder problem. All the Ps and Qs matters, not just good parts.
     
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  5. May 29, 2017 #5

    cheapracer

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    Seriously?

    Anyone who can't see that's way out of parameters and just plain wrong shouldn't be touching engines.
     
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  6. May 29, 2017 #6

    Hot Wings

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    The mistakes illustrated are hardly "details". Someone should lock that mechanics tool box.
     
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  7. May 29, 2017 #7

    Vigilant1

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    Sure. But I can see how it could happen to a person building their first engine. He cut the pushrods (too short as it turns out) but he got the valve lash to come out right, so "no harm done". And, "hey, look, they aren't screwed down all the way into the lock nut. If this is too far in, why did they make the adjuster stud so long?" Except harm WAS done because the oil hole was now in the wrong spot and (surely) the geometry of the valve/rocker arm was far off (leading to extra stress on the valve stem, valve guides, and the adjuster).

    Pops, I don't know the reason that these ball swivels are used on some VW aero engines. I know racers that use strong springs like them because they reduce side force on the valve compared to the stock solid adjusters. But I think the springs on a VW built for airplane use could be stock (due to our moderate RPMs). Maybe aftermarket heads for large bore cylinders just come with ball adjusters by default because such products are normally used at higher RPM (on the street)?
     
    Last edited: May 29, 2017
  8. May 29, 2017 #8

    Pops

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    Yes, you are right. Made for higher rpm for street use. But as you know we are building for low rpm, high torque for a straight drive engine. Even the dual port street heads hurt low rpm torque at straight drive prop rpms for a VW of below 2180 cc and below 3K rpm. You can buy new single port heads from here. https://aapistons.com/collections/c...-of-stock-head-single-port-w-seats-and-guides
    Another big plus for the single port heads is no problem with cracked heads between the spark plug hole and valve seat area as on the dual port heads. When I get my 2180 cc flywheel drive VW engine finished it will have single port heads.
     
  9. May 29, 2017 #9

    Hot Wings

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    Maybe acceptable if it's his first engine and it's a ground bound unit. For an aircraft it's inexcusable. Where was his advisor/mentor/EAA designee? Even solo a google would have lead him to Hoover's blog. A look at the pictures would show something wasn't right. At this point not looking for some qualified help indicates way too much hubris, or ignorance.
     
  10. May 30, 2017 #10

    Vigilant1

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    We had a thread some time go regarding what a "purpose-built" head for a VW airplane engine would look like. So, for a 2180cc engine, what would you think about:
    Single ports: Previously you mentioned that you thought the single ports might hurt torque in an engine with displacement somewhat higher than 1994cc. I also found that Limbach's aero engines used single ports in their 1994cc engine, but had gone to dual ports for their 2400cc model. It sounds like you now think a single port would be best for a 2180cc engine.
    Stock springs (? everything I've read says the stock springs with their "progressive" rate do a very good job at opening quickly and sealing well at our RPMs)
    Stock (solid) valve adjusters
    Beefed up fins for adequate cooling, esp around the exhaust port.
    Valve size? It would be nice to have a little more meat between the valve seat than we have with 40mm intake/35.5mm exhaust valves, IF these valves are really overkill for the RPMs we are running.

    Idea: Maybe "Timecert" steel thread inserts for the spark plugs as part of the initial build. They are head and shoulders better than helicoils, and they take a lot of the worry out of changing the spark plugs in our AL cylinder heads. Some racers are putting them in on day one--it's lots easier than doing it as part of a repair later on.
     
  11. May 30, 2017 #11

    Pops

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    I am going to use single port heads on the 2180 cc 75 HP engine for the reliability factor of no crack heads and take the small power loss. The 2180 will have my STOL airframe over powered so I can take the loss. Yes, stock valve springs for the lower rpm's. Long ways from any valve float. Stock head fins will be OK because of the low continuous HP used in the airframe and good cooling baffles. Full HP just used for a short time in take-off. On the 1835cc 60 HP engine in the SSSC I was using about 32 HP continuous in cruise at 80 mph by the fuel burn along with a WOT ROC with my fat butt of 1200+ fpm @ 42 knots.
    On every head I use a sparkplug steel thread insert similar to the "Timecert" but with a larger top flange that is drilled for a steel dowel pin to lock it in. Similar type used in small Cont cylinders. Local machine shop will supply and install for about $30 each. Well worth it.

    Plan on building another SSSC but putting more effort in reducing weight. I can use the first wings that I built for the SSSC with the smaller wing fuel tanks. I had built another set of wings for the SSSC with long range fuel tanks along with the added weight. I know I can save a few pounds over the 141 lbs firewall forward weight of the SSSC and save as much weight as possible on the airframe. Think I can get a EW of 425 lbs over the 450 lbs of the SSSC with the short range fuel tanks.
     
    Last edited: May 30, 2017
  12. May 30, 2017 #12

    pictsidhe

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    A lot of performance parts are used when they aren't needed. Many are less reliable than stock. People will buy stuff because it's "race spec", billet etc, without having a clue whether it is needed or even beneficial. Engine manufacturers have gotten pretty good at balancing life and wear. Back in Wales, I heated my house entirely with logs cut with a chinese cheapo chainsaw for 5 years before it needed a fresh $25 barrel and piston. If it ain't broke, don't try to fix it!
     
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  13. May 30, 2017 #13

    Vigilant1

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    +1. The "better" car manufacturers (most reliable, not necessarily more expensive) develop relationships with suppliers and work hard to improve the quality of components by rewarding suppliers who produce high-quality parts and by incrementally improving them over the years. At the very least, a "stock" auto part has had the benefit of tens of thousands of fielded units each operated for hundreds of hours per year, and if it is crummy that will be obvious. The complicating factor with the VW Type 1 at larger displacements is that the stock engines were never that large nor operated at these HPs, so non-stock parts are required,so we need to depend a bit on what the hop-up guys have learned (where it can be discerned from hype/marketing/lore, which ain't easy). But our moderate-RPM use in airplanes differs from the typical VW racer, so even some of their valid lessons don't apply to us. Unless a builder of a VW airplane engine is a truly knowledgeable engine expert, he/she is dependent on a "guru" for advice, published specialized books for detailed guidance, and on recommendations of the guru for reliable non-OEM parts. Luckily, good parts are widely available and inexpensive for the Type 1.
     
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  14. May 30, 2017 #14

    Pops

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    Back in the mid 1970's I did a redneck test on a 1600 cc engine that I built. All stock except I balanced the pistons, balanced each rod end and used a matched set of rods for distance between piston end opening and crank end opening. Put the engine in a 1966 VW bug beater with the lower ring and pinion ratio. Used 40 straight weight Valvoline racing oil. Changed oil and adjusted valve tappet clearance once in a while if I had the time and thought about it. At the time I was driving about 1100 miles a week to different job locations. I put it to the floor for WOT as I was getting on the interstate and ran WOT until getting off the interstate. ( Gov was not quite as money hungry as now so never got a speeding ticket) at around 100K miles I was running WOT ( 87 mph on level ground) when the engine exploded, valve head came off and went thru the piston. Rear wheels locked up and the car almost swapped ends 3 very quick times before I got the clutched in. Engine parts all over the interstate. Nothing left of the long block that wasn't damaged.
    So in my test, valve guide wear was the weakest point. The reason I have a spare set of heads ready to put on at 500 hrs of easy running on the airplane. Then I'll rebuild the old heads for the next 500 hrs.
    In MHO the 1835 cc 60 hp VW engine is the most bang for the buck and the most HP for the reliability. For the first 32 hrs on the SSSC I used a 1200 cc, 40 engine, great little engine but I decided I wanted more ROC. Could always put the 83 mm bolt on oversize pistons and jugs for about 45 hp for the same price if needed but I went to the jump of the 1835 cc, 60 hp. The 1200 cc is the height of reliability of all the VW engines. I would not go over 2180cc in a type1 VW engine and put it in an airplane.
     
    Last edited: May 30, 2017
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  15. May 30, 2017 #15

    Pops

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    Everyone that is thinking of using a VW engine should read this post. Very well said.
     
  16. May 30, 2017 #16

    Vigilant1

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    So, you got about 1150 hours of WOT operation at something like 3800 to 4300 RPM using well-balanced stock parts, with no rebuilds, valve jobs, etc. Wow. Of course things will be different if we ask for more HP, but it certainly hints at the basic reliability of these little engines. We just have to respect the limits that previous aero VW builders have identified over several decades. There's lots of great, inexpensive flying fun to be had within those limits.
     
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  17. Jun 11, 2017 #17

    N8053H

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    I just checked the valves on my 1700cc vw engine. This is a full vw engine not the 1/2vw. But I found on each side one intake valve that the adjuster was turned all the way in. I needed a little more clearance and could not get it. Seeing how I only needed a few thousands clearance, I removed the rocker arms and on that one rocker arm I filed that one down to get the clearance needed. If I was building a hot rod engine all these would be machined flat anyway. I did not want to shim the rocker arm shaft away from the head for the reasons that the OP states.
    Seeing how I found these adjusted like this or all the way in not out. I would say this has been like this from day one. But still I am concerned about this. I am getting ready to take this airplane on a few hundred mile trip and why I checked the valves. This is a new to me airplane, I have put close to 20 hrs on it now. It runs a lot better after I did the valve adjustment. Idles a lot smoother and now I feel each compression cycle as each piston comes to TDC. Before not so much. But after finding this, I am not sure I want to take this airplane far from home. But this may not be of any issue.

    Tony
     
  18. Jun 11, 2017 #18

    pictsidhe

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    The correct shims under the rocker pillars would get the adjusters where they are supposed to be. The geometry may be slightly out, but it already is.

    In a low revving aero engine, softer valve springs would stress the valvegear less and give a tiny hp increase. Once the springs stop valve float at max revs, any more increase just wears stuff out and uses power.
     
  19. Jun 12, 2017 #19

    N8053H

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    Correct and why I did not want to put shims under the rocker arm shaft mounts. All the other rocker arms are correct. Only two intake valves, one on each side were out or where I could not adjust them. This is way I am concerned. I could have two valve seats that are sinking into the head. It could also just be its happening to both heads. I will watch this, but my plan is to replace both heads this winter. I am going to send the engine to Scott Calser and have him look it over and replace these heads.

    Tony
     
    Last edited: Jun 12, 2017
  20. Jun 12, 2017 #20

    N8053H

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    As to the oiling of these rocker arms. I would like to see a colored schematic or flow chart of the oiling system of these rocker arms. I really want to see a flow chart. If these adjusters are screwed in all the way, will they produce the same results as being screwed out to far and starve other parts of oil?
    I know next to nothing about these split case air cooled engines and have no problem admitting that. Why I post here. Why I refuse to try and built one to put into the air. I can do some maintenance but that is it. It would be nice if someone offered training for these VW engines that go into the air. I would be standing in line for that training.

    Tony
     

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