Another Knucklehead Build

Discussion in 'A Work In Progress' started by mayhugh1, Mar 22, 2018.

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  1. May 27, 2019 #301

    Rustkolector

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    Why couldn't a flow limiting orifice in the line or lines to the heads be used to control excess oil flow to the top end?
    Jeff
     
  2. May 28, 2019 #302

    mayhugh1

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    Jeff,
    An additional short restriction in the output would just result in the velocity of the oil increasing during the time its flowing through the restriction. The restriction would have to be small enough or long enough to force pump to max out at its maximum possible pressure before the flow would be limited. I'm already restricting the output with 14 inches of 1/16" i.d. copper tubing, the pump pressure during 200 rpm cranking is at 80 psi, and I don't know how much higher this pump is capable of going. I'm probably dangerously close to breaking something (or maybe damaging the crankshaft) especially if they engine were started at this point. The solution has to involve a pressure relief valve. It's bad engineering to not include one in a constant displacement pump that has a submerged inlet. If I weren't worried long term about the pressure, I'd just raise the height of the pump's inlet and allow it to pump a limited amount of oil to the top end at its maximum flow rate during cranking and then let the pump starve after the engine starts. This would be a quick fix, but it would require keeping a specific level of oil in the engine and not quite how I'd prefer to handle it. - Terry
     
    Last edited: May 28, 2019
  3. May 28, 2019 #303

    Rustkolector

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    Terry,
    Sorry, I forgot you don’t need any oil pressure to the bottom end. Okay, so you add a low pressure by-pass valve directly to the pump discharge. Use a generous sized relief port discharging straight down and the pressure adjustment screw access facing horizontal toward the pump case cover. Once set the pressure should not require change. To keep from putting a hole in that beautiful pump cover, you can set the bypass pressure by trial and error using a temporary see thru plexi-glass pump cover panel with plugged adjustment access hole. I have used such covers to good advantage to make rod dipper size and oil viscosity selection for very slow speed splash lubricated engines.

    BTW…absolutely beautiful work.

    Jeff
     
  4. May 28, 2019 #304

    scottyk

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    I did this on my car wash once, just drilled small holes, progressively larger, and more in quantity in the pressure side of a pump housing until I got the pressure I wanted. No regulator, no plumbing and it was mounted in it's own reservoir just like this. I've also seen shock absorbers for cars with internal bypasses in them which is basically a groove machined into the bore, something similar to reduce the efficiency of your pump, might be a bit more elegant than drilling holes. But as you know these aren't PRESSURE regulators just simple bypass ports which will affect flow rate at all rpm
     
  5. May 31, 2019 #305

    mayhugh1

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    The most significant oil leak(s) turned out to be between the rocker boxes and the valve boxes. O-rings were used between them, but I evidently didn't have them under enough compression to handle the top end flooding that's been going on. Thin (.010") teflon back-up washers reduced the leaks to minor seeps that will likely disappear after an over zealous oil pump is tamed.

    With all four valve box covers installed and the leaks apparently solved for now, I was able to perform a slightly longer (30 sec) cranking test. The results were essentially the same as before: approximately 5 cu in/min flow to the top end and 1 cu in/min return to the sump. In 30 seconds the pump moved a whopping 2 cu in of oil into the top end.

    If a restriction is added to the output of a constant displacement pump, it will respond by increasing its head pressure. Depending upon how well (or poorly) the pump was machined, it's capable of absorbing significant power from a small engine. My experience with these little pumps is that they can easily generate over 100 psi. I tried to measure the Knucklehead's cranking pressure, but my 60 psi gauge was immediately pegged.

    The pressure required to produce a particular flow rate through a tube can be calculated using Poiseuille's Law:

    Q = (pi * P * r^4)/(8 * n * L),

    where Q is the flow rate, P is the pressure across the tube, r is its inside radius, L is its length, and n is the fluid's viscosity.

    Rearranging the equation to solve for the pressure needed to pump 5 cu in/min through the Knucklehead's 14 inches of 1/16" i.d. tubing and assuming 200 centipoise (sorry!) for the viscosity of 5W20 oil, a little math (and some gymnastics with conversion units) produces a cranking pressure of about 80 psi.

    The power taken from the engine by the pump during cranking can be calculated by multiplying the pressure times the flow rate (just as with electrical current). At 50% pump efficiency, the result is 1.5W which is responsible for about .15 amps of the starter motor's current. Once the engine starts and begins idling at say 1000 rpm, the power will attempt to reach 7.5W although slip or even stall will likely occur first.

    With such a low oil return rate to work with, it would have been difficult to solve the entire problem using a single pressure relief valve. The solution I eventually arrived at was to reduce the pump's head pressure to 15 psi with a relief valve and to raise the height of the pump's inlet. Reducing the head pressure reduces the load on the crankshaft to a negligible amount, and raising the pump's inlet creates a protected sump for the engine's bottom end.

    With these changes, the pump will still operate well ahead of the return rate while running, but flow to the top end will be cut off as soon as the oil level falls below the pump's inlet. The top end, which doesn't require much oil, will continue to be lubricated by the small amount that the pump will maintain there. Priming/re-priming isn't an issue for an internal oil pump.

    A pressure relief valve is a simple device intended to sit across the pump's output. This particular one is just a piece of brass hex stock bored for a spring-loaded ball and a return-to-sump path. Shoehorning it into the space available inside the engine was more of a challenge because of the precise tubing work required around it.

    For a given ball size, the valve's minimum working pressure is limited by its relief spring. A 3/16" ball was as large as I could comfortably work with in the space available. The ball's cross-sectional area transforms the oil pressure into a force that the spring must balance at the valve's tipping point. The spring that produced the 15 psi tipping point was already uncomfortably light, and I didn't feel I could reliably go any lower.

    In order to avoid some difficult tubing work, construction of the valve began by creating a soldering fixture using as a template the pump assembled to its already fabricated head pipe. After bolting the assembly to the fixture, the pipe was cut in half using a Dremel abrasive wheel so the valve could be soft-soldered between the halves. A notch was also required for clearance around the dipstick.

    In order to avoid defacing the gear box for the valve's one-time adjustment, the spring tension was preset in a bench set-up using a pressure gauge and a 50ml syringe as a pressure source. The set point established by the spring appeared to be very consistent, and the same pressure was obtained using either air or oil in the syringe. For good measure, a weep hole was also drilled through the center of the adjusting screw.

    The height of the pump's inlet was raised by cutting off enough of the existing pickup tube to guarantee a 40 ml (2.5 cu in) sump. Filling the gear box to the existing mark scribed on the dipstick adds an additional 10 ml (.6 cu in) which is available to the top end.

    With 50 ml of oil in the gear box, a portion of the pump's external drive gear starts out under oil and initially splash lubricates the contents of the gear box. With the cranking flow rate reduced roughly to the return rate, the oil level now changes much less during cranking. Tests showed the level dropping by only 10 ml during a 1 minute cranking test and returning to normal less than a minute later. With so little oil being pumped to the top end, the return measurement is now more sensitive to oil dripping off parts inside the gear box.

    During running, the pressure regulator is visible through the dipstick hole and its return-to-sump could be seen working as expected during the cranking tests. Even though the spark plugs were removed for these tests, it was apparent from its sound that the starter is now operating under less load.

    The very apparent crankcase pressure pulses that I can feel coming from the dipstick hole have me wondering if the ventilation added earlier to the dipstick is going to be sufficient. The top end oil returns, although high in number, are gravity fed and only 1/16" in diameter, and they won't function as intended if the crankcase is pressurized. Fortunately, though, with the changes just made they won't be as important during running as they once were. - Terry


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  6. Jun 1, 2019 #306

    Scott_M

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    Outstanding ! A very elegant solution.

    It won't be long now :)


    Scott
     
  7. Jun 1, 2019 #307

    stragenmitsuko

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    As an illustration of what a gear pump is capable of .
    I once made a mistake installing an oil temp sensor on an 136Hp audi 5 cilinder engine .
    That sensor replaces the bolt that holds the pressure regulator spring in place .
    Part of the regulator was assembled backwards , basicly disabling it .
    Stupid I know , but helas mistakes do happen .

    So I started the car and it would idle for a few seconds and die .
    Then the starter would hardly crank the engine . Tried that several times , hadn't a clue what
    was happening . So finally I hit the gas , and BAM suddenly the oil filter exploded .

    Later on , with the return valve put in the right way , I found out that most of the white metal
    on the crank and rod bearings was simply gone and oil pressure now dropped below alarm level at idle .

    A costly mistake it was .

    Pat
     
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  8. Jun 2, 2019 #308

    dethrow55

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    outstanding job. been watching this build from day one, been learning a lot ...great work
     
  9. Jun 3, 2019 #309

    mayhugh1

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    With the oil leaks and the pump problem hopefully behind me, it took only a couple satisfying hours to complete the rest of engine's assembly. Everything went together nicely, but I decided to leave the air cleaner cover off until after gaining some experience with the carburetor. For the first test run, the idle and high speed carb screws were both opened one full turn, and the timing was set to 13 deg BTDC. The spark plugs had been installed only briefly for the initial starter tests, and all the oil system tests had been performed without them. After re-installing the plugs, the engine didn't seem to have as much compression as I had remembered. The head fasteners were re-checked but they were still tight.

    Continuing on, I filled the tank with gasoline, switched on the fuel pump and ignition, and then pressed the starter switch. Although the starter had no trouble spinning the engine at 200 rpm, I didn't get so much as a single pop. After verifying the ignition was actually generating sparks, I reluctantly concluded the cranking speed wasn't high enough. Using an extended socket in a battery-powered drill, the engine was spun at some 600 rpm using the contingency hex machined into the flywheel's hub.

    After several seconds of cranking, the engine started right up and continued to run on its own. It was pretty loud and sounded healthy, and there was little if any exhaust smoke. I thought I'd just run the contents of the tank through it without attempting any adjustments and then retire for the evening. After 20 or 30 seconds, though, I began noticing exhaust leaking from between the rear cylinder and its head, so I shut the engine down.

    While turning the flywheel over manually, it was obvious that the engine now had essentially no compression. My suspicion was that both head gaskets had somehow managed to fail even though the head fasteners were still tight. It was late, I was tired and not thinking clearly, and I should have called it an evening. However, I wanted to make a final measurement of the starter so I'd have something to sleep on. In the process, I managed to reverse the battery leads to the control panel at the rear of the engine. This dumb mistake immediately destroyed the DC/DC converters used to power both the ignition module and fuel pump. The damage to the pump's converter wasn't obvious, but a power device on the converter board for the ignition module had actually exploded.

    I knew it was going to be hopeless trying to sleep if I just walked away from the mess I had just created, and so I worked until sunrise inside that over-filled control box that I hoped I'd never have to revisit. I had replacements for the modules, and after installing them I added diodes to protect them from me in the future. After thoroughly testing the repairs, I spent most of the next day sleeping but only after kicking myself a few more times for not installing those diodes in the first place.

    Upon removing the heads, I found two failed teflon head gaskets as expected. Both of them had signs of erosion adjacent to the exhaust valves which are in the hottest portions of the combustion chambers. Curiously, both sides of both gaskets were covered with oil which was unexpected since the run had been smoke free. While I had the heads off, I also vacuum checked the valves and saw no measurable leakage during several 30 second tests.

    My suspicion is that the gaskets had been coated with oil long before the run. With all the top end flooding that went on during the oil system tests, oil had likely made its way past the valve guides and into the combustion chambers.

    My current theory is that instead of both head gaskets suddenly failing at the same time, neither of them had actually been properly compressed during assembly. As shown in one of the photos, each head has a .015" deep recess that accepts an identical diameter boss machined into the top of the cylinder. I reserved a portion of this recess for registering the heads to insure proper and consistent mounting flanges for the intake manifold that's attached to them. The manifold's built-up construction has a number of soldered joints that are best left unstressed by consistently mounted heads. The original plans recommend using .015" thick copper head gaskets which would have completely filled these recesses. I didn't use copper because the shallow head fasteners aren't capable of creating the force needed to compress even annealed copper. Instead, I made a set of gaskets from .010" thick PTFE sheet so I could reserve .005" of the recess for registration purposes.

    It's possible that with so little depth, the heads really didn't end up entirely within their recesses. It's also possible that the cutter used to machine the recesses left enough corner radius that the close-fitting heads bottomed on them before compressing the gaskets. In any event, if the gaskets had been compressed it doesn't seem reasonable that so much oil would have been found on them. The engine's compression at the time of the first run was likely so low that the starter's cranking speed wasn't sufficient to generate enough manifold vacuum to draw fuel through the carb. This lack of fuel would explain the lack of even a single pop while cranking the engine with the internal starter.

    Some .020" PTFE sheet for a new set of teflon gaskets should arrive by mid-week. While waiting, I'm designing a set of dies that will allow me to emboss a sealing ring in a thin sheet of copper. I came across this interesting idea for a copper head gasket in a post made by George Britnell several years ago (post 720):

    https://www.homemodelenginemachinis...el-hit-and-miss-i-c.10091/page-36#post-124258

    I don't know if this has actually yet been tried out on a model engine, but if the heavier teflon doesn't work out, it may become my third attempt. - Terry


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  10. Jun 3, 2019 #310

    michelko

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    Hi Terry
    These are some bad News, but heads up i am sure you will work this out.
    Have you thought About using some gascet stuff like elring ewp 210 for example.
    It can be purchased in different thikness like 0,3- 0,5-1,0mm
    it holds up to 100 bar and 400°C. I used it on my Bugatti build with some good results.

    Michael
     
  11. Jun 3, 2019 #311

    tornitore45

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    You are not the first to connect a battery backward. I bought a replacement LED position lights for my trailer and the silkscreen on the PCB was wrong polarity, but I caught this blunder before powering.

    There are to way to protect. A series diode like you used, but for higher currents applications the diode loss or the V drop is not acceptable. In that case a backward diode across the input preceded by a fuse will blow in case of battery reversal.
     
  12. Jun 3, 2019 #312

    gbritnell

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    Hi Terry,
    Over the course of many years I have tried all different types of materials for head gaskets. For my hit and miss engines I settled on Teflon and due to the nature of these engines have had good luck with this material.
    For my higher compression multi-cylinder engines I tried Teflon, Copper and other assorted materials. From my full sized engine experience I made copper gaskets with a raised ring created with a die. When the head was tightened it would compress the raised ring and create the seal. This type of gasket worked for non water cooled engines but for my engines with liquid cooling the copper wouldn't seal everything properly, even with the slightest silicone ring around the water openings.
    When I worked as a Patternmaker our shop used a lot of different material for gasketing. I had a piece of one of the materials and gave it a try. It worked great. It sealed the compression, held up to the heat and pressure and sealed the water openings. I have used this material for all my water cooled engines since.
    The original piece had a name on it and I was able to track down a supplier in Cleveland. When it talked to someone there he said they only sold it in 4'x4' sheets but he would see if he could find some drops to send to me. That didn't pan out.
    At that point I went to my go-to supplier, McMaster-Carr and searched through their sheet gasket material and came up with what seemed comparable to the other material that I had.
    It's labeled as: Oil resistant high strength Aramid/Buna-N gasket material. The product number is 9402K21
    It has worked great on my engines. My 302 has at least 30 hours of running with the same gaskets. I have used it for my flathead and so far I have about 2 hours of running with no problems.
    I'll send you a PM to my direct email in case you have any other questions.
    gbritnell
     
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  13. Jun 3, 2019 #313

    gbritnell

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    Terry,
    I can't find a way to send you a PM so contact me at: gbritnell@yahoo.com
    gbritnell
     
  14. Jun 5, 2019 #314

    mayhugh1

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    While waiting for the .020" teflon sheet to arrive, I performed a few rough calculations to better understand what to expect from teflon as a head gasket since I had no previous experience with it. The reason for its popularity as gasket material has to do with its ability to deform under pressure and fill imperfections in the mating surfaces to be sealed. Up to a certain point, teflon will compress elastically which means it will return to its original thickness when the pressure is removed. At higher pressures it will deform plastically which means it won't return to its original condition. Teflon has another and annoying property, however. Under pressure and over time, it will creep or cold flow and continue to plastically deform a tiny (for us) amount.

    In order to estimate the magnitudes of these deformations, the applied pressure is needed. Each aluminum head has five 8-32 fasteners whose maximum recommended torque in aluminum is 10 inch-lbs. If I assume that I'll be able to torque them to 5 inch-lbs using my calibrated wrist, I can expect about 175 lbs of clamping force from each of them. With five fasteners and a 2 square inch gasket, the applied pressure will be close to 450 psi.

    Using 50 kpsi for the modulus of elasticity of virgin PTFE predicts almost two tenths deformation for a .020" thick gasket under such clamping pressure. I've included a graph of the stress/strain relationships for PTFE at a couple temperatures of interest for a head gasket. The changing slopes reflect the deformations' transitions from elastic to plastic, but the important take away for a head gasket application is the effect of temperature.

    Interpolating the 300F strain (a reasonable upper temperature for a model engine's air-cooled head) for a 450 psi stress gives 3% which translates to a .0006" deformation for a .020" gasket. If the heads are allowed to reach 400F, the deformation will increase to over a thousandth. In any event, after the heads have seen such operating temperatures, the fasteners will likely need to be re-torqued some 5-10 degrees.

    Since the machined recesses in the heads are .015" deep, I selected .020" for the gasket thickness in order to completely fill the recesses and to keep the heads off the cylinders. I originally tried using .005" of the recess's depth to register the heads for mounting the intake manifold. This created an issue since the cylinders didn't seem to properly settle inside such shallow recesses, and I had leaks while trying to use .010" gaskets. Now, with no recesses for registration, the head fasteners will have to be torqued with the intake manifold in place to insure its proper alignment. It now becomes very unlikely that the cylinders will end up centered over the recesses. So, it becomes important to insure the heads don't end up bottoming on the cylinders due to gasket deformation as this would again cause a loss of gasket seal. The above calculations show this shouldn't be a problem.

    Before tearing the engine down (again), I took a final set of photos with it fully assembled. Except for the plug wires that still need to be shortened, there shouldn't be any significant changes to the engine's exterior. - Terry


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  15. Jun 5, 2019 #315

    bigearl91

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    Enjoying the attention to detail on the ancillaries!

    Just out of curiosity - would this mean that you would need to periodically check the torque of the bolts/studs to make sure they are within spec to avoid any potential burst gaskets down the line?

    Ta
    Earl
     
  16. Jun 6, 2019 #316

    mayhugh1

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    Earl,
    A handbook from a gasket manufacturer that I read recommends re-torquing a teflon gasket 24 hours after initial installation. Those gaskets, however, sometimes contain a filler and aren't made from pure teflon. In a model engine we aren't applying much pressure as you can see from the stress/strain graph, and so I would think a re-torque after the gasket has seen high heat would be worthwhile. After that, not much is going to change. I'll let you know what my experience is, though. - Terry
     
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  17. Jun 6, 2019 #317

    propclock

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    I recommend you investigate Gortex. It is an expanded? PTFE It has all the
    advantages of PTFE but the creep is limited. I use it for head gaskets, no failures
    so far. I don't know if you can get it that thin though.
    Your engine is beautiful, both inside and out.
    Thank you for documenting your work.
     
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  18. Jun 7, 2019 #318

    mayhugh1

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    The new sheet of teflon arrived and, after installing the new .020" thick gaskets, the engine's compression returned with a vengeance. Compression is now so high that I can barely grip the flywheel tight enough to rotate it through the engine's compression bumps. After sitting for a day or so, there didn't seem to be any change.

    For a first run with the new gaskets, I filled the sump with 50 ml of 5W-20. The internal starter turned the engine over, and this time I got a few pops, but I ultimately had to use the drill starter. The engine started and ran on its own, but there was a huge amount of smoke and oil coming from the exhaust. We're currently having messy wet weather down here in central Texas, and so all my testing is being done inside my shop. I had to shut the engine down after only 10 or 15 secs while the air in the shop was still breathable. Before ending the run, a few throttle blips had no effect on rpm - maybe not surprising since the only carb adjustments so far have been to blindly open the low and high speed needles a single turn. Early indications are that no fuel is being drawn through the high speed jet.

    Since an unreasonable amount of smoke accompanied the improvement in compression, I performed a test to see if there was still a top-end flooding issues with oil being sucked past the valve guides. A run with the external feed line disconnected from the top-end and diverted back into the crankcase through the threaded dipstick opening showed no change in the exhaust.

    Each two-ring piston has a machined groove containing an array of radially drilled holes located just below its lower ring for oil control. This design is fairly common in multi-cylinder model engines and, although effective, appears to be overwhelmed by the 50 ml sump. I've included two CAD drawings showing 50, 30, 20, and 10 ml oil levels overlaid across the crankshaft components. With a 50 ml sump the counterweights are well into the oil which also kisses the connecting rod at its lowest position in the crankcase.

    Another test using 30 ml, a level that's actually below the pump's inlet, placed the rims of the counterweights just under the oil's surface. The smoke was reduced but was still not acceptable. Such a result wasn't expected because I've been underestimating the windage inside the crankcase. Unlike other engines I've had experience with, this one has very little crankcase volume in comparison with the large amount of air being shoved around inside it by the asymmetrical motions of the two pistons. The result is a vigorous storm inside the crankcase with oil laden air being alternately exchanged between the crankcase and gear box through the seven distributed vent holes between them. An unexpected bonus, though, is a nice lubricating mist inside the gear box.

    After a few more runs, I had experimentally determined the optimum sump level to be an unexpectedly low 10 ml. Keeping in mind that the crankshaft bearings are ball bearings and the rod bearings are roller bearings, my definition of an optimum oil level is one that creates just a hint of smoke in the exhaust to show the bottom end isn't running dry. To maintain this level, I made a new inlet pick-up tube that I soldered to the pump.

    The full-size engines used similar bearings, and their narrow crankcases likely created similar oil control issues. I can now appreciate why, even with the engine's high impact loads, the designers chose roller bearings over sleeve bearings whose lubrication requirements would have created the issues that I ran into.

    To verify the new pick-up, I filled the gear box with 20 ml of 5W-20 which provided 10 ml or .6 cubic inches to be pumped to the top-end. (This level may be later increased to 25-30 ml after some of the other issues are worked out.) The exhaust is now well behaved, but issues remain with the starter and carburetor. (For this last run, I opened the carb's high speed needle another 1-1/4 turns but still with no improvement in throttle control.)

    So far, the head fasteners have remained tight. Although I'm probably going to tackle the two known remaining problems out of logical order, my nest step will be to take a look at the starter issue. - Terry


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  19. Jun 7, 2019 #319

    stragenmitsuko

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    Quite odd then that it didn't smoke on your first attempt , and now with basicly just a thicker headgasket it does .
     
  20. Jun 7, 2019 #320

    mayhugh1

    mayhugh1

    mayhugh1

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    The (huge) increase in compression compared with what I had using the original poorly sealed gaskets must have have affected the pumping action enough inside the crankcase to account for the difference. The compression had fallen so much at the time of that first run that I thought it was a waste of time to even try starting it. I admit, though, I'm having a hard time making my peace with what happened as well. - Terry
     

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