How to Measure Cylinder Head Clearance
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  1. #1
    R/C Newbie Big Bro's Avatar
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    How to Measure Cylinder Head Clearance

    Ok, if you're a racer, or into tweaking the performance of your engine, you're going to want to know the cylinder head clearance. Here's a tip I learnt this week from an RC Boat buddie of mine for measuring cylinder head clearance.

    1. Take off the cooling fins and glow plug and rebolt the button back down onto the engine.


    2. Take a short length of solder wire, and bend a small hook into it.


    3. Insert the hook end of the solder wire into the glow plug hole, and push and hold the solder against the cylinder wall. It is important to ensure the solder is hard against the cylinder wall, as the head is tapered, and this is the area of lowest clearance.


    4. Crank the engine over once. It will be quite hard to do, because when the piston is near TDC, it will be crushing the solder.


    ...hold your horses guys, to be continued in the next post...
    Morphy's Savage SS Monster truck, .28 SH engine
    Albatross 2.0m electric glider
    Generic high wing (trainer) petrol plane, .46 OS engine
    Control line trainer, .15 ASP engine

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  3. #2
    R/C Newbie Big Bro's Avatar
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    How to Measure Cylinder Head Clearance - continued

    5. Remove the solder, and measure with a set of vernier calipers, or a micrometer. Try to measure this as close as possible to the end of the solder that was against the cylinder wall, as shown below. Due to the taper on your cylinder head, this area will be the smallest clearance between your cylinder head and piston.
    Here are my results, showing where I measured the wire, in 0.97mm, or 38 thou:



    Ok, hope you find this easy to do...I'd be interested if you were willing to post any measurements on cylinder head clearances to this thread. Perhaps, for comparisons, please provide:

    * Engine Brand and Size
    * Age of engine
    * Clearance obtained mm (inch)
    Morphy's Savage SS Monster truck, .28 SH engine
    Albatross 2.0m electric glider
    Generic high wing (trainer) petrol plane, .46 OS engine
    Control line trainer, .15 ASP engine

  4. #3
    R/C Newbie Big Bro's Avatar
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    Here's my results:
    Engine: SH .28
    Age: 4+ years, done a bit of work
    Clearance: 0.97mm (.038")

    Good luck, enjoy.
    Morphy's Savage SS Monster truck, .28 SH engine
    Albatross 2.0m electric glider
    Generic high wing (trainer) petrol plane, .46 OS engine
    Control line trainer, .15 ASP engine

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  6. #4
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    Quote Originally Posted by Big Bro View Post
    Here's my results:
    Engine: SH .28
    Age: 4+ years, done a bit of work
    Clearance: 0.97mm (.038")

    Good luck, enjoy.

    Well as the aforementioned boat buddy I thought I'd better put my engine info in here

    Engine: K&B .21 Outboard
    Age: 13 years (but only the crank and flywheel are original). Custom rod and piston.
    Clearance: 0.23mm (.009")

    Set up to run on 60% nitro. This is only really achievable with the help of watercooling, and we need the extra torque of high nitro in the boats, as there is constant load on the engine. Don't aim for the same figures in a car engine!

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