Checking Cam Timing with Engine In

[RogueEngineer]

I just finished a 3.4 rebuild (my first) and have been trying to start up for several days with no success. I'm beginning to think I set the cam timing wrong. Currently getting spark and fuel, but so far the only success I've had was about 30 seconds worth of running on cylinders 1-3. Very frustrating - but gotta keep moving forward!

I was confident that I set up the timing correctly, but since it was my first time there is definitely a chance I did it wrong.

Any recommendations on checking the cam timing with the engine in the car?

- Ian

[yelcab1]

You need to remove the muffler, the engine tins, engine mount bracket from the car (after supporting the engine so it does not drop). Remove the intake valve cover and the timing chain housing cover. Mount the gauge to the top of the valve, and do your valve timing measure.

Where did you get the spec?

[RogueEngineer]

Spec came from the Webcam's spec provided with the cams. As I understand it, its Webcam's 'stock Carrera' spec regrind. Something like 1.4-1.7mm lift at TDC. When I set it I believe I was able to hit 1.55mm on the money for both sides.

[lvporschepilot]

Can also try a compression test. If things are extremely low on a new albeit unrun engine then it's definitely cam timing.

[RogueEngineer]

Just checked compression - 155-165 across all cylinders. I'd say that's about perfect for a 9:1 engine that isn't broken in.

[john walker's workshop]

Just need to pop off the upper covers to check cam timing.

[yelcab1]

Originally Posted by john walker's workshop

Just need to pop off the upper covers to check cam timing.

True, but if you need to adjust it then it is a lot more work.

[john walker's workshop]

He said check.

[yelcab1]

Originally Posted by john walker's workshop

He said check.

yes.

[boyt911sc]

Checking the cam timing is totally different from adjusting it. You could perform a quick test by following John Walker’s advice. Why removed the muffler and the engine tin? You might not even need them removed after all.

Tony

[Eagledriver]

You might have one cam 180 degrees out. Both banks would be trying to fire at the same time.

[JSV798]

Originally Posted by Eagledriver

You might have one cam 180 degrees out. Both banks would be trying to fire at the same time.

Wouldn't valves hit pistons if it's that far out? But the ignition timing could be 180 degrees out.

[RogueEngineer]

Found one problem - perhaps it helps identify the other

My distributor was misaligned - I aligned it to TDC on cylinder 1.

Engine fired up right up but ran very sooty and didn't want to rev. Upon shutting down, I noticed that exhaust pipes for 1-3 were hot - but 4-6 were still cold.

I 100% measured lift of the intake valve on 1 and 4, at TDC - but I'm questioning whether or not I spun the engine 360, or 720 when starting to set the timing for the right side (bank 4-6).

Could that cause and ignition timing & intake/exhaust valve opening mismatch that would prevent combustion?

[ben parrish]

Stupid question... are you sure your plug wires are in the correct position? 100% sure?
I just reinstalled my motor after a lot of work that included retiming the cams...I had the wires in the wrong position when I reinstalled and tried to start the car...it happens.

[rokemester]

Yep did the same thing recently. I swapped plug wires 1 and 5. I hope it’s that easy!!

[RogueEngineer]

Originally Posted by ben parrish

Stupid question... are you sure your plug wires are in the correct position? 100% sure?
I just reinstalled my motor after a lot of work that included retiming the cams...I had the wires in the wrong position when I reinstalled and tried to start the car...it happens.

Unfortunately for me, I've checked the easy stuff! Fuel pressure, spark (and wires), injector power, compression all look good. Just no combustion on 4-6.

[john walker's workshop]

When you set #1 intake clearance, mounted the dial gauge and rotated the crank 360°, did #4 intake then have some valve clearance so you could mount the dial gauge, or did you have to rotate the crank to get it?

[yelcab1]

Originally Posted by RogueEngineer

...

I 100% measured lift of the intake valve on 1 and 4, at TDC - but I'm questioning whether or not I spun the engine 360, or 720 when starting to set the timing for the right side (bank 4-6).

...

If you have to ask yourself that question, then 90% you did not do it right. Go back and check.

Get #4 TDC, zero the dial indicator, spin it one revolution, read the overlap. I bet 20$ that is your issue. And if you have to redo the cam timing, then ... the exhaust does have to come off.

[RogueEngineer]

Thanks Yel - going to give this a shot. I believe what I should be looking for is that the valves on #1 should be completely closed (rocker slop) while #4's valves are starting to peak open (timing point - beginning of intake stroke).

I suspect that I will find that #1 and #4 will either be both in the process of opening, or both closed (AKA timed the same and not 360 deg out).

Fortunately, the exhaust is simple to remove at this point! (see pic)

John,

I don't recall right off hand what I did as its been 2 months or so since I set the timing. I do remember installing the cams 'key side up', putting on the sprockets/chains and beginning the timing process on #1 - I don't remember futzing with #4 until I moved to that side to time it.

I believe I zero'd the dial indicator when the valve was closed (rocker slop) and rotated the crank through TDC until I got the lift I was looking for. I unbolted the cam and rotated the crank back to TDC - then locked the cam. Spun crank 720 to recheck - and then moved to #4. I actually did this at least 2 times in order to perfect the measurements on both sides. I suspect that, as Yel pointed out, that I had the #4 in the wrong stroke for proper timing.

[yelcab1]

Oh man, that thing looks totally non-stock. Turbo and all. Since you are going through the trouble, check both sides.

Bring it to top dead center number 1. See if there is any valve slop on the rocker arm.
Install your dial indicator, and zero it.
Turn it 360 degrees, read the over lap.

Then, bring it to number 4 TDC (technically, you are already there from the last step), check for rocker slop.
Move the dial indicator over to bank 2, zero it
Turn the engine 360 degrees, read the overlap.