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So I gather this is a question that gets asked quite a bit. Myself for one asked it recently. I wasn't happy with the answers I got as to me the common one of lining the keyway up at 90degs is going to be vague at best. Also, I gather it is not wise to remove the pulley on and installed engine.
So if you motor is built it can be a bit of a ball ache to check your timing marks. and if it's in the car even more so.
Hopefully I think I have the solution for you all that will be accurate to within a degree as long as you have good eye sight!
I need to thank a fellow club member Pavel very much for his assistance getting some measurements from his own engine. These were then used on mine to check my marks as I had suspicion they were out. As it happens they were bang on using this exact method.
You will need a protractor a similar size to the pulley wheel. Or one you can stick on and make pointer for as I have done. If you engine is in the car you will need a small flashlight and a mirror also! and of course a spark plug removal tool.
The principle is this:
We position a rotor tip in the centre of the Trailing plug hole on the front rotor. As the hole is small it is quite easy to get a good judgement on the centre. Anymore than a degree or so of engine rotation either way and it is clearly off.
Once you have this you rotate the engine 100 degrees counterclockwise and this gives you the leading timing mark. Of course you can also mark TDC by going 5 degrees past this and trailing timing by going 15 degree back.
You can do it two ways.
1) Mark the pulley in line with the pointer on the front cover where the apex seal is aligned centre to the trailing plug hole. Then remove the pulley and use a protractor directly seated on the pulley to mark the leading mark by measuring 100degrees around.
2) Alternatively, you can set a protractor up mounted on the pulley with a wire pointer and then find the trailing plug hole position and rotate the engine around 100degrees and then mark the pulley with leading timing mark in line with the pointer on the front cover.
Here are some pictures to show in practice.
So here are the measurements taken from Pavels 20B engine. you can see all the pulley markings and where the Apex seal comes up centre of the trailing plug hole. He also got a measurement for the leading plug hole for a double check but we don't need to use this. It is a bit more inaccurate due to the size of the hole as well. I made a slightly different measurement on mine but it could be the angle I am looking at with the engine in the bay. So good job the trailing plug has a nice small hole!
So this is mine setup to measure back and check my engine. You can see I bent up a welding rod to make a pointer and double sided a protractor onto the front of the pulley. (tip#1 crack the spark plugs on all the rotors and you can rotate the engine by hand quite easy.)
Here are a couple of images showing the rotor tip in the trailing plug hole. You can see it nice ad central. (tip#2 to get you in the ball park position remove only T1 plug to start with and listen for the air compressing and bleeding out as the rotor comes around.)
Then you mark this position on the pulley with a marker and note the degrees where the pointer is at on the protractor.
So now you can use the protractor to rotate the engine 100 degrees counterclockwise to position your leading timing mark.
As you can see mine was spot on. I didn't actually look at the mark until I had stop rotating the engine. I was quite surprised it wasn't even a degree out!
So there is it done. You can now remove the pulley and make some more permanent marks and use a protractor to add any other markings you which such as Trailing timing and TDC.
You are now good to go with your CAS install.
I hope this helps some of you guy's out there. As I understand this principle should work for 13B as well but I have no means to verify this. maybe someone will check there engine and post up to complete the thread.
Great job documenting this Lee! Hopefully it leads to helping others in the future and I'm happy to contribute with the pictures. Maybe the experienced engine builders can chime in and correct or approve of this. By the way the 360° protractor I used that fit inside the pulley is 12cm. Rotor on!
11-04-16, 07:13 PM
