Tootie Pang

iTrader: (2)

Is there a way to positively check for a misaligned timing set without taking the front cover off? I did the timing set a year ago and I want to double check it. What sort of symptoms would happen if I was off one cam gear tooth (half a crank tooth)?

paulo57509

You can try rotating the crankshaft mark to TDC and taking the distributor cap off and noting where the rotor is pointing. It should point to either #1 or #6. But I don't know if the resolution using this method would be fine enough to detect a half or one tooth off situation.

NoEmissions84TA

iTrader: (1)

Tootie, not much time right now, so a quick answer.
If you knew your camshaft specs, (let's use the EXHAUST because #1 EX valve is easiest to see with the valve cover removed) and you knew EXACTLY the number of degrees of crank rotation for that valve to be at max lift, then you could accurately attach a degree wheel to the crank and see what you measure. I believe 1 tooth off would be 10 degrees. You would also have to take into account if the cam was ground advanced and whether you physically advanced or retarded it by use of a multi keyway timing set.

Edit: To add a little more info, A typical stock timing chain set for a small block Chevy has 36 teeth on the cam gear and 18 on the crank gear. There are 360 degrees in a circle, so (360/36) = 10 camshaft degrees per tooth. Whatever the tooth count, a 2:1 ratio is mandatory because the crankshaft rotates twice for every 1 turn of camshaft rotation.
So what does 10 degrees look like? Look at a clock face. 1 minute is 6 degrees (360/60). 2 minutes is 12 degrees. Will you be able to "see" 1 tooth off (10 degrees) without having a degree wheel attached. Doubtful.

GeneralDisorder

iTrader: (1)

I think you would ultimately have to put a degree wheel on it which requires a lot of disassembly just to do that and not have it hit a bunch of stuff.... and then you would need to know the exact cam specs as mentioned..... I think the clarity of this method precludes drawing a foregone conclusion from the testing. You will forever be questioning so many aspects of this test that it's probably a waste of time. And once you are down far enough to swing a degree wheel on the engine you are pretty close to just removing the cover.

GD

OrangeBird

iTrader: (1)

And of course the question here to the OP is , what exactly leads you to believe that you may have misaligned it ? Running poorly ? low power ? Backfiring ?

If a proper compression test shows good readings , and if a manifold vacuum check shows within spec , you likely did get it right .

Tootie Pang

iTrader: (2)

Thanks everyone. Bone stock 1989 LB9 with Bosch D3s and an adjustable FPR. I've checked all the vitals- vac, fuel pressure, etc - exc compression and the cat looks clean (used a camera). It runs rich and idle is bumpy in closed loop. Seems to make all the power expected when the throttle is down. Scott Hansen is doing a custom tune to try to dial it in. I've replaced every sensor/module and all gaskets except head gaskets. No error codes exc EGR which is blocked off and is being tuned out anyway.

I'll eventually do a compression test but for now I think everything is in order. I was just wondering if there was an easy way to triple check the cam/crank timing. I did replace the valve stem seals and springs recently as well so getting the valve cover off is not my favorite thing to do. I could probably read the lifter/rocker through the oil filler port and add the correct degrees

sofakingdom

iTrader: (1)

The cam being mis-timed by one tooth will not cause the symptoms you describe.

Generally, a cam that's advanced, will move the torque peak RPM downward A WHOLE BUNCH. It will tend to have very high idle vacuum, make the motor feel very peppy off-idle, shift earlier and harder than normal esp at low RPMs, and seem unwilling to wind out. Basically the tractor motor effect. Retarding it will have the opposite effects; it'll have very low idle vacuum, feel very lazy off-idle, sluggish overall at lower speeds, but will seem to pick up more at higher RPMs, without really having any more power than it would if it was right. Subject in both cases of course, to the properties of the intake system and so forth; neither direction of misalignment would likely be considered an overall "improvement". As NoEmissions points out, it's a DRASTIC mistake, and the effect is ENORMOUS... it's a 10° mistake, whereas a 4° adjustment such as with a 3-slot crank gear is considered a substantial tuning change.

Think for a minute about valve events vs crank position. For each cylinder, there are 2 instances of TDC during the complete engine cycle; one is firing, the other is the end of the exh stroke and beginning of the int. As the motor passes through TDC therefore, on that 2nd instance, you will see the exh valve just reaching its closing point and the int just beginning to open. At exactly TDC, the 2 valves should be very close to the same lift, which will be very little but still detectable. If this is true, then your cam is properly phased to the crank. If the exh is still open quite a bit but the int hasn't started to move yet, then the cam is retarded; if the exh has closed fully and the int opened significantly already, it's advanced. This isn't a "perfect" or "absolute" observation by any means since it's dependent on the details of the particular cam, but it's PLENTY close enough to expose such a gross malfunction as that assembly error.