TDC actual vs. mark on fan Options

[jmargush]

Has anyone experienced the mark on the fan being off from where actual TDC is ?

Last time I had the engine out I put a dowel in cylinder #1 and found TDC and the factory mark was approx. 3/8" tot he left of where I feel TDC on #1 was.


I am going to recheck it and see if I made an error the last time I did it.

[barefoot]

I've seen where the fan is displaced from intended position with partially sheared woodruff key.

[930cabman]

I've seen where the fan is displaced from intended position with partially sheared woodruff key.

after 1/2 century of DAPO's, anything goes

the dowel method should get you close.

are you adjusting valves?

[mjrrti]

Has anyone experienced the mark on the fan being off from where actual TDC is ?

Last time I had the engine out I put a dowel in cylinder #1 and found TDC and the factory mark was approx. 3/8" tot he left of where I feel TDC on #1 was.


I am going to recheck it and see if I made an error the last time I did it.

There should be a groove on the flywheel that you can see in the little opening on the bell housing top and bottom that will get you dead on. I like to get it on TDC and use a center punch to mark the flywheel @ 180 from under the car also. That really helps for valve adjustment.

[GregAmy]

I've seen where the fan is displaced from intended position with partially sheared woodruff key.

Yuuuuup.

http://www.914world.com/bbs2/index.php?sho...=367703&hl=

[jmargush]

I've seen where the fan is displaced from intended position with partially sheared woodruff key.

after 1/2 century of DAPO's, anything goes

the dowel method should get you close.

are you adjusting valves?

Checking timing and this lead to questioning the marks. there seems to be a bit of range around the TDC mark where both valves are still closed So I feel pretty good about the adjustment and leak down numbers have been good with the mark I made using the dowel to find TDC

[technicalninja]

Depending on year/application the fans are marked differently...

My 75 1.8L is ONLY marked at 7-9? (red). (IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/headbang.gif)

The 73 2.0L fan I replaced it with was marked at both TDC (white) and total timing (27-30? red).

I made a second TDC mark 180 degrees from the original (black) to allow LD testing on the opposing cylinders.

[GregAmy]

See if this helps.

http://www.914world.com/bbs2/index.php?showtopic=339759

[930cabman]

See if this helps.

http://www.914world.com/bbs2/index.php?showtopic=339759

very informative thread, thanks for finding this

[jmargush]

I just checked it with a dowel again.

What I think I am seeing is a bit of dwell at the top of the stroke. Dowel stops moving a bit before the factory mark on the fan.

Once it moves past the factory mark the piston starts to travel downward again.

Does this sound logical/possible?

[GregAmy]

I just checked it with a dowel again.

You can't calculate TDC with a dowel; to do it correctly you need a dial gauge and a cam degree wheel.

If you have a hard piston stop (another tool used for degreeing in cams) then you can rotate the engine until the piston taps the stop, mark the pulley (or read the degree wheel) then rotate the engine the other way until it taps the stop and mark the pulley (or read the degree wheel). The halfway point between those two marks is TDC.

https://www.summitracing.com/parts/sum-900189

GA

[ClayPerrine]

Please don't use a chopstick........ (IMG:style_emoticons/default/lol-2.gif) (IMG:style_emoticons/default/av-943.gif)

http://www.914world.com/bbs2/index.php?act...&and,broken

[emerygt350]

Or just don't be an idiot. You guys all have an idea of precision on your ability to set your timing dead on while juggling a light and holding the throttle and turning a dizzy that probably isn't justified. There is so much variation in these engines that just getting in the ballpark and returning to a previous setting is all your looking for. 30 for me is probably not actually 30 etc... even with Bluetooth, you set it to what the engine wants, not some absolute number. No tech is going to put a motor on the Dyno and set the timing to some preconceived number and keep it there.

Don't use the starter and a chopstick is fine. 5th gear moves it nice and slow.

[bkrantz]

Has anyone experienced the mark on the fan being off from where actual TDC is ?

Last time I had the engine out I put a dowel in cylinder #1 and found TDC and the factory mark was approx. 3/8" tot he left of where I feel TDC on #1 was.


I am going to recheck it and see if I made an error the last time I did it.

There should be a groove on the flywheel that you can see in the little opening on the bell housing top and bottom that will get you dead on. I like to get it on TDC and use a center punch to mark the flywheel @ 180 from under the car also. That really helps for valve adjustment.

This, for sure. Set the flywheel at TDC and see where the fan is.

[JamesM]

Or just don't be an idiot. You guys all have an idea of precision on your ability to set your timing dead on while juggling a light and holding the throttle and turning a dizzy that probably isn't justified. There is so much variation in these engines that just getting in the ballpark and returning to a previous setting is all your looking for. 30 for me is probably not actually 30 etc... even with Bluetooth, you set it to what the engine wants, not some absolute number. No tech is going to put a motor on the Dyno and set the timing to some preconceived number and keep it there.

My timing holds like someone is shining a laser pointer on my fan. No dizzy twisting required, or even possible. (IMG:style_emoticons/default/biggrin.gif)

[emerygt350]

That is a very pretty engine you got there.