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Registered
Join Date: Jun 2015
Location: Chicago, IL
Posts: 3,111
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Finding TDC for #1 without a distributor
I coulda swore I asked about this a few years ago, or found an answer to it somewhere, but I seem to be wrong about this.
My car is running normally again, or at least as it was last summer, but the sort of low wub-wub-wub note is louder than ever and I'm checking that. I want to check the valve clearance on the left bank, particularly exhaust side (compression is a little lower in that cylinder than in the others) so I jack the left rear up and took the valve cover off and realize I'm not confident in having cylinder #1 at TDC. I can set the pulley Z1 mark at the tick on the fan housing but I have a Megasquirt with EDIS, so no distributor. So best thing I can think of is either look at the valve and rocker position, or take the plug out and stick something like a magnetic stick inside to see piston position. Any better suggestions?
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'80 SC Targa Avondale, Chicago, IL |
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07-19-2022, 09:37 AM
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Banned
Join Date: Mar 2014
Posts: 10,751
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If you've got the valve cover off and can see the cam that's all you need. If the crank is at Z1 but it's not on TDC for #1 the intake lobe should be just pushing up against the rocker. Remember the cams turn counter-clockwise. At TDC for #1 the rockers will be on the back sides of the lobes.
If you turn the engine over with the valve cover off it'll be obvious when you're at TDC for #1. Only other way to see is to pull off the chain housing cover, and that's just unnecessary work. Edit: Wait how does the electronic ignition measure timing? Last edited by David Inc.; 07-19-2022 at 09:49 AM.. |
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07-19-2022, 09:47 AM
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OK, glad I didn't miss anything! And yeah looking at the rocker on the cam is easier than looking at the valve.
The car has a 36-1 toothed wheel with a Hall-effect sensor on it to measure crank position.
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'80 SC Targa Avondale, Chicago, IL |
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07-19-2022, 10:12 AM
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Join Date: Mar 2014
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Ah okay, so it just does spark on two cylinders at once based on crank position?
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07-19-2022, 10:51 AM
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Racer
Join Date: Oct 2010
Location: Franklin, TN
Posts: 5,885
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Or you can have full sequential with one spark at a time with both a crank position sensor and a cam position sensor....
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Scott Winders PCA GT3 #3 2021 & 2022 PCA GT3 National Champion 2021 & 2022 PCA West Coast Series GT3 Champion |
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07-19-2022, 11:04 AM
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Registered
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Location: Chicago, IL
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Quote:
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'80 SC Targa Avondale, Chicago, IL |
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07-19-2022, 11:15 AM
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Registered
Join Date: Mar 2001
Location: Marysville Wa.
Posts: 22,431
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Pull #1 plug and stick a compression test hose in there. Turn the engine until compression blows out of the hose. You can put your finger on the end when you turn the engine if that helps. Then continue turning until the Z1 mark on the pulley lines up with the notch.
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https://www.instagram.com/johnwalker8704 8009 103rd pl ne Marysville Wa 98270 206 637 4071 |
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07-19-2022, 11:16 AM
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Not having a compression tester my method is to remove the inlet valve cover over 4,5,6 bank (it's easiest on my car) rotate the crankshaft pulley until Z1 aligns with the mark on the crankcase. Either #1 or #4 is now on compression (firing). If the rocker on #4 is tight (valves must be open) then #1 is on compression. Rotate pulley further 360 deg. otherwise.
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1959 Bristol 406 (bought in 1972; sold in 1977) 1966 Porsche 2.0 coupe (bought in 1977; sold 1981) 1978 Porsche SC coupe (bought in 1993) |
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07-19-2022, 11:37 AM
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Porsche
Porsche
