Checking cam timing on assembled engine

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Fuzzy Dice

Fuzzy Dice

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Is it possible to check the cam timing on an assembled engine? I have low vacuum of 8"-9" at ~15* advanced initial timing with distributor vacuum advance and brake booster both unplugged and capped. I've had it apart twice this year to replace the timing chain and the intake manifold gasket. Neither helped with the low vacuum issues or changed how the engine ran.

'69 340, Edelbrock performer intake, Holley 4bbl carb (600 or 650 can't remember) with spacer, unknown cam
 
Welcome from Waterloo. You may be able to check cam timing but you won't be able to adjust it without taking the front of the engine apart. The "unknown cam" is likely your problem especially if it has a lopey idle. You have a video?
 
I know I won't be able to adjust it. I just don't want to pull the engine apart again only to find out it's fine, been down that road twice already with the intake gasket and timing chain.

The cam is not lopey at idle. If it's not stock I would guess it's a very mild cam.
 
It is possible to check cam timing but most likely a waste of time if you don't know the cam specs.
The vacuum your getting is typical to a performance cam with long duration.
 
It's impossible to check it properly without exposing the timing chain. Sorry.
 
Sounds like maybe you suspect the timing chain may have jumped a tooth ?? Compression test may give you some confidence one way or another.
 
Whats keeping you from advancing it further or is that when it taps out making vacuum? Most large cams like more advanced timing. Were are you measuring vacuum from?

Like others have said without a cam card or the ability to get one and the front cover removed you can't degree it.

I take it power brakes are why you need vacuum?
 
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You MIGHT be able to show some useful info since it "doesn't lope." I would start out with some basic factory cams, and "assume" it might be one of them, IE stocker 360, stocker "stick" 340 and see how close you can come to that. you will of course need some way to insure the lifters are not collapsing, is the intake off?
 
Have you tried plugging the PCV hose to see what happens to the vaccum? And have you sprayed carb cleaner around the carb base to see if the idle speed increases with the cleaner at some point?

You can measure the cam timing if:
1) You find true TDC of the #1 piston and mark it on the damper; that part is easy. This gets used as your reference point for setting up the timing wheel.
2) You mount a timing wheel on the front of the crank; takes a small bit of work but very doable.
3) You put solid lifters in place of the hydraulic ones on #1 cylinder and find a way to support the 2 pushrods in place. Not too hard with stock heads.
4) You get/borrow a dial indicator and mount it up to accurately measure the movement at the tops of the 2 pushrods.

If you do all the above, then you can measure the opening and closing angles at the .050" lift points on both the opening and closing ramps of the intake and exhaust lifters. You would then compute the intake and exhaust centerlines, and then know the LSA, and have the .050" durations very closely, and can compute timing. And you can get a close reading on advertised duration by measuring the .005" lift angles, opening and closing. With all that, you will know the timing and the cam specs with good accuracy, and can then know the cam's characteristics and what to expect for idle vacuum.
 
It would be difficult to read a degree wheel in the car if you could even get one mounted in there...
 
Yes, you wold be pulling the rad and belts and pullies and perhaps the water pump. Put the pointer in a place where it is clear and set up a mirror. It ain't nearly as easy as on the engine stand for sure, but is all doable.

I sure would look everywhere else first.
 
Maybe I missed it, but how does this engine perform currently? Under load? As is.
 
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