camshaft with no overlap??

**Sam_Q** · 15-09-2007, 06:46 PM

I had a good look at my 7afe head yesterday and I noticed that there is no overlap at all, and when I say none I mean not even close. I thought all engines has some sort of overlap built into them. Not only that they have an unusually large amount of lift: from what I have measured so far: 8.7mm on the intake and 7.9mm on the exhuast!! apart from the lift is this common on economy engines?

I figure this would be great for fuel economy at very low speeds and for very low range power, or would it? what do you guys think toyotas reasoning was behind this bizare profile?

if I had a head that had a good inlet system and had these cams, then I changed to a profile like one of a 20v (250 degrees duration) but with more lift on the intake what would happen? heaps I am guessing

**oldcorollas** · 17-09-2007, 11:53 PM

no overlap at all?

is this when rotating the cams by the crankshaft?
are they in correct position?
it seems odd to have no overlap at all.

**Sam_Q** · 19-09-2007, 11:52 AM

well I checked it, the dots line up for the cam gears to be in sync with each other.

I checked it by spinning the drive belt gear which turns the 2 scissor gears.

**myne** · 19-09-2007, 12:44 PM

The old EB motors on the Civics had 10* of both valves closed at TDC.
They also idled quite low for such a small engine with such a light flywheel.
I mean, 700rpm idle with a flywheel that was like 10" round and pretty light is quite impressive.
I imagine that's what it's for. Really good low rpm response

**Ben Wilson** · 19-09-2007, 01:22 PM

Not meaning to be rude, but did you check the compression, or exhaust stroke?

**Sam_Q** · 19-09-2007, 02:24 PM

myne: thanks, sound about right.

ben: I have just a head and thats it, I am roting at it by hand and visably looking at it. I should of said i didnt have the rest of the engine. Thats what you meant yes?

**myne** · 19-09-2007, 03:18 PM

me? I went by the engine's specs
exhaust closes 5* BTDC inlet opens 5* ATDC

**TC1600** · 19-09-2007, 09:35 PM

You should still have some overlap, the exhaust going out helps draw the intake in. If you had a pair of dial indicators set up you would most likely see some overlap, but it may be small enough that it's not visible by eye.

**Sam_Q** · 20-09-2007, 05:02 PM

no way I had the head of the valves looking at me and I stopped in the middle to check it out, if i cant see it then it would make no difference to how the engine runs