308 ignition problem, what am I missing

Very interesting......but if they were 180 out would you not have valves and pistons hitting?


Coincidently the cams drive pulleys were replaced, post the engine rebuild and test run, and pre engine install...... I wasnt there when they were done so I havent seen under the cam covers. however 1- 4 is lined up - as seen through the oil filler cap and external markings. There are no visible marks on 5-8 inlet or outlet on my car that I can see.....

I have 190 psi in all 8 cylinders which means no pistons and valves have met!

The myestery deepens.

Need to do the strobe check against timing on single back running to see what happens

 

No...but you would have a scenario as Tim describes above, where the ignition timing and cam timing aren't in synch. For my money, I think Tim (2NA) hit the nail on the head...

Best of luck,
David

 

Rotate the crankshaft one more revolution and check for marks on 5-8. This is a 4-cycle engine, the crankshaft turns twice for each revolution of the cam. If the cams are somehow 180 off on the rear bank you'd still get compression but the plugs would be firing at the end of the exhaust stroke instead of the compression stroke.

 

David


BINGO!!!!


When everything else is ruled out, there can only be one other possibility....... that which people said was impossible!

The cams on bank 5-8 are 180 degrees out of synchronisation with the cams on bank 1 - 4..........

I took the cam cover off bank 5-8.

The flywheel is set at PM 1-4 mark, the inlet cam on 1-4 lines up (as seen through the cam cover oil filler hole)

The cam marks (for TDC) on 5-8 are not visible on the cam shafts. Turn the engine crank 180 degress and they line up.


You cannot imagine how angry I am at the moment......... interesting conversation to be had with engine rebuilder on Monday!

Thanks for your help.

 

Glad to see that you're working it out. An interesting conversation for sure but if compression is good it doesn't appear any real damage was done.

For the record, I don't think anyone stated that this was an impossible scenario, just not the first thing to be checked.

 

You're welcome.
When posed with many "odd" situations in my shop, I always start with the basics, no matter what I'm told is "correct". Too many years of chasing my tail on well-intentioned assumptions!

The good news is that this is a simple fix...and the chance of any engine damage really is zero.

Here's the fix, just in case your builder has any questions:

Engine at TDC 1-4
Verify Piston 1 really is at TDC 1 on compression stroke
Quick check: Cam caps marks on 1-4 bank line up

Important! Do not turn engine over!!!! (We're still at TDC 1-4) As I recall PM 1/4 is the factory mark...

Remove both cams on 5-8 bank
Reinstall with marks aligning with caps.
Replace 5-8 timing belt

Degree all cams

Turn key->Enjoy your car.

Best,
David

 

Tim,

Not suggesting anyone here said impossible............ my engine rebuilder did!, much egg on face now