Thread: gm sent wrong engine??

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Hey Found Somemore Info From Pace Perf. Target Motor And 290/350 Both Use The Same Casting Number Those Two Casting Numbers Basically Mean The Same Thing, Only Diff In Motor Is 290/350 Has Cam Used In Corvette And Camaro. Only Way To Tell Is To Check Lift At The Pushrod. Sux That I Cant Have Enough Confidence In Gm To Trust That They Sent The One With The Right Cam!!!!!!!!!!!!!!!!

Are you running a vacuum advance distributor?

Pull the distributor vacuum line, plug it then shoot the timing.

Be aware you have to have the engine idling reasonably slow - 500 - 600 rpm so the centrifugal advance doesn't add any timing.
You're shooting for the initial timing point here.

Suppose you have 8 degrees initial timing BTDC.
With the vacuum line still disconnected run the engine up to 3000 rpm or so until the timing shows "all-in" at 34 degrees or so.
In other words as far as it will go with the centrifugal advance.
And . . . stay out of the plane of the fan blades, have one of them come loose and the injuries can be very severe.

Replace the distributor vacuum line while the engine is idling.
You should hear the rpm increase a bit, maybe 200 rpm or so.
Shoot the timing again.
You'll see quite a bit of advance on, maybe 24 - 34 degrees BTDC (Before Top Dead Center).
That is correct and GM engines need a lot of advance at idle or they'll overheat at idle or in traffic.

Wing the engine - just snap the throttle open a little ways for a quick rpm increase and release.
You only want to gain a few hundred rpm.
Watch the timing with a light and you'll see the vacuum advance back off and the centrifugal advance come up a little bit due to the rpm increase.
It's easy to tell the difference.

If you know where true TDC (Top Dead Center) is, one thing that will help is to install a timing tape on the harmonic balancer.
Clean the balancer well before the install or it'll come off in a short period of time.

You need a timing light to see what's going on, especially if you're somewhat new at this.
Timing with a vacuum gauge and by ear is only for very experienced people.
Even then, they can't tell if the centrifugal and vacuum advance mechanisms are working correctly.

Keep in mind that some dial-back timing lights will show about 20 degrees off if you're running an ignition amplifier like an MSD box.
Other dial-backs work fine.
In my case, I had a regular Sears Penske timing light and bought a Sears Penske dial-back timing light and there was a 20 degree disparity shown between the two.
I took the dial-back, back.


Like Dave says, 30 degrees retarded on cam timing -which is an entirely separate issue from ignition timing - and the engine won't run.

About 4 degrees is the max factory retardation on camshafts.
Performance cams are many times installed 4 degrees advanced.

I bought one of the first engines off the line and had the exact problem. After months of diagnosis, I tore down the block and measured the cam against the prints GM faxed me and discovered the cam slot was ground ~ 30 degs out. After asking various gm parts managers, one confirmed that this was a small 'production problem' that was caused in production where a bad run of cams were installed. He knew of 20+ cases. They replaced the cam and lifters and it times up correctly.

We had ordered a 454 from GM and then bought the fly wheel from a different Gm dealer, after 8 months (they told us there was a piston shortage and had to wait for more) after we got it running it would shake bad, we popped the cam plug read the #'s, and the block #'s ...What the heck, They sent use a 427! Neither dealer would return the now used flywheel! Last parts we ever bought from those dealer. The 427 still worked good in the Vega

Pat