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How to check cam duration?? Engine not starting.

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roofchop Seriously Crusin Dubber

177 posts · joined Jan 2011 ·

#1025160
OK, just rebuilt motor with an Engle 110, new lifters, hd springs.

Will not start, got sparks, fuel and compression. (ran fine on stock cam)

Checked timing many times, No1 both valves closed on TDC, rotor pointing to No1

Correct firing order, no explosions at all. Even swinging the dissy left or right.

Swapped wires over a few times, still nothing.

Started looking at cam opening times.... All from TDC No1 rotating engine clockwise.

No1 intake starts to open at 450 degrees (full rev plus 90)

Stays open for 270 degrees (back to TDC)

No1 exhaust starts to open at 200 degrees.

Stays open for 310 degrees.

Seems horribly wrong, am I measuring correctly?

During assembly I set the cam in the correct position, sure it did not move.

What stupid mistake have I made?

Cheers
Dave

psimitar Son of Jim - Creator of Good

2,506 posts · joined Jan 2009 ·

#1025179
When you re-installed the dizzy drive gear did you make sure that No.1 was at TDC of compression stroke?

The valve timing is all relative to what part of the cycle the piston is on. So from the VW manual each cylinders valves do the following:

Inlet opens 2.5 BTDC
Inlet Closes 37.5 ABDC
Exhaust Opens 37.5 BBDC
Exhaust Closes 2.5 ATDC

So if you take the top of the exhaust stroke then at 2.5 before TDC of the pistons travel the inlet opens and 2.5 after TDC the exhaust closes.

Then say the inlet closes 37.5 after the piston has reached the bottom of it's travel.

So if you add the degrees of revolution from the TDC at which the spark plug firing is taken from then yes you will get large amount of degrees for the valves operations.
madness is in the eye of the beholder 👍

hellbugged 48's and straight cuts

5,080 posts · joined Apr 2003 ·

#1025183
Try the dizzy 180' around

Or swap no 3 lead to your current no1 dizzy position, then re install the rest in order

roofchop Seriously Crusin Dubber

177 posts · joined Jan 2011 ·

#1025204
Cheers, swapped the leads straight away, and a few more times, still nada....

The dissy drive is not where it should be, I over looked that during install, but it just means the rotor points to a different place to whats in the manuals, as long as I arrange the leads correctly (I have, ten times) all should be well..

No matter how I interpret the opening and closing of each valve they are no way near the W110 specs, surely if it is supposed to open at say 10 degrees before tdc I should be able see that or close to it, but I am many many degrees away from all specs... The duration is close but not where it should be...

I need more knowledge....help....

dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 ·

#1025210
You need to check the cam at .050" lift with a dial indicator.

Take the rockers off and put the dial on the #1 inlet push rod tip.

When you rotate the engine make sure the dial has enough travel to reach full lift,
then 'zero' it when it is at the low point.

Rotate the engine a few times to make sure your zero is repeatable.

Lift to .050" and look at the pulley number.
It should be about 19 degrees before TDC.

Continue rotating past full lift and then back down till it is .050" from zero on closing,
and look at the pulley again.
Should be 48 degrees after piston passes BDC.

Check the exhaust the same way with the card numbers:
http://images.thesamba.com/vw/gallery/pix/853809.jpg

I have seen cams 10 degrees out and they still ran, but it should be within a couple of degrees to work as intended.
westi wrote:That's mad Alan.

psimitar Son of Jim - Creator of Good

2,506 posts · joined Jan 2009 ·

#1025218
Um, here's an interesting question.

When you bolted the new cam to the timing gear did you absolutely make sure the timing mark was in the correct position relative to the orientation of the cam?

IIRC the VW lump is a non-interference type engine so the valves will never hit the pistons. Hence if the cam is installed out of sequence to the crank then it will still rotate freely with no valves locking up against the piston.
madness is in the eye of the beholder 👍

roofchop Seriously Crusin Dubber

177 posts · joined Jan 2011 ·

#1025244
That will be my stoopid mistake...Thanks Mr simitar..

In my defense, I just 8 doweled my crank, and it has an offset pin so the flywheel will only go on in one position.

When bolting the cam to gear, I thought I lined up the holes and only one lined up, then rotated 120 degrees, still one then again and they all lined up ( I thought)

Seemed obvious that one hole would be offset to ensure the gear could only go on one way.

I obviously am more blind than I thought I was....

Anyhoo, engine out and do it all again.

Thanks to everyone and Mr simitar!

Cheers
Dave

psimitar Son of Jim - Creator of Good

2,506 posts · joined Jan 2009 ·

#1025254
That's ok dude. I would've thought the holes would have been drilled so they only align one way but if the valves are opening at the wrong time then either the timing gear dots weren't aligned or the cam is bolted up incorrect.

I really do hope this is your problem and you can get it all remedied 🙂

Cheers,
Mike
madness is in the eye of the beholder 👍

kombiwhisperer Seriously Crusin Dubber

131 posts · joined May 2012 ·

#1025961
Hey, simple check, before you tear it down

Rotate engine till no. 1 is on overlap TDC(or on the rock), so piston at top dead centre, exhaust closing and inlet opening, both valves should be within 0.020" of each other or even lift

Anything will start at that🤪