A bent valve can be very subtle, and it’s very rare that only one valve gets bent as often many cycles take place until its noticed, sometime the “bend” is only a couple of thou and will partial seal on the seat due to the spring pressure flexing the head almost back into place, sometimes this doesn’t cause issue for a while……..until the valve head has seated half a million times, then metal fatigue takes place and the valve head falls off onto the piston top and then all hell breaks loose.
The "problem" with a compression test is that if for example you had a slightly bent valve in each chamber then you would still get a relatively The leak down test will give both a direct measure of how well the cylinder/chamber holds pressure plus an audible indication of any leakage path.
Do the test with the piston at TDC on the compression stroke of number 1 cylinder when the valves are closed (cam lobes at 10 to 2), you will need to lock the crank with something as the air pressure (through spark plug hole on the piston crown) will tend to rotate the crank due to the pressure on the piston crown. Once checked rotate so that number 2 is on the compression stroke and repeat until done.
When you apply pressure get a short length of pipe, open the butterflies of the carbs and listen at each carb mouth, if all is ok then you will need to do the same with the exhaust, separate it at a suitable joint and listen for a tell-tale hiss, if you pass these tests then you’ve been very lucky.
As with any testing like this ensure the engine cannot inadvertantly start up.
Best of luck, hopefully all is well plus at the end you have learnt some valuable skills to boot.
The "problem" with a compression test is that if for example you had a slightly bent valve in each chamber then you would still get a relatively The leak down test will give both a direct measure of how well the cylinder/chamber holds pressure plus an audible indication of any leakage path.
Do the test with the piston at TDC on the compression stroke of number 1 cylinder when the valves are closed (cam lobes at 10 to 2), you will need to lock the crank with something as the air pressure (through spark plug hole on the piston crown) will tend to rotate the crank due to the pressure on the piston crown. Once checked rotate so that number 2 is on the compression stroke and repeat until done.
When you apply pressure get a short length of pipe, open the butterflies of the carbs and listen at each carb mouth, if all is ok then you will need to do the same with the exhaust, separate it at a suitable joint and listen for a tell-tale hiss, if you pass these tests then you’ve been very lucky.
As with any testing like this ensure the engine cannot inadvertantly start up.
Best of luck, hopefully all is well plus at the end you have learnt some valuable skills to boot.
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