| [ Total Views: 1256 | Total Replies: 9 | Thread Id: 110790 ] |
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 roofchop
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| posted on April 5th, 2016 at 12:26 PM |
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How to check cam duration?? Engine not starting.
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
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psimitar
Son of Jim - Creator of Good
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| posted on April 5th, 2016 at 06:55 PM |
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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.
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hellbugged
A.k.a.: Daimo Pell
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| posted on April 5th, 2016 at 07:30 PM |
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Try the dizzy 180' around
Or swap no 3 lead to your current no1 dizzy position, then re install the rest in order
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 vw54
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| posted on April 5th, 2016 at 07:49 PM |
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yep
| Quote: |
Try the dizzy 180' around
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roofchop
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| posted on April 6th, 2016 at 06:18 AM |
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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....
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dangerous
A.k.a.: Dave Butler Muffin Man
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| posted on April 6th, 2016 at 07:47 AM |
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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.
| Quote: | Originally
posted by westi
That's mad Alan.
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psimitar
Son of Jim - Creator of Good
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| posted on April 6th, 2016 at 11:26 AM |
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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 |
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roofchop
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| posted on April 7th, 2016 at 06:41 AM |
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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
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psimitar
Son of Jim - Creator of Good
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| posted on April 7th, 2016 at 01:25 PM |
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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
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kombiwhisperer
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| posted on May 4th, 2016 at 07:16 AM |
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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
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