TIMING QUESTION Mercruiser 260

[Buck Horn Deer Farm]

Why does the engine run smoother and higher rpms at an idle when I move the distributor to way before tdc? the timing mark is like at 30 before tdc and when I move it lower than 8 it will want to stall out.

 

[stackz]

Re: TIMING QUESTION Mercruiser 260

sounds like the distributor is off a tooth. cant remember but base timing on a chevy v8 is supposed to be either 10btc or 6btc.

if you are stalling out at around 8btc, you are likely off a tooth (advanced) if I remember correctly. how old is the engine? makes me wonder if the timing chain is stretched.

 

[John_S]

Re: TIMING QUESTION Mercruiser 260

Why does the engine run smoother and higher rpms at an idle when I move the distributor to way before tdc? the timing mark is like at 30 before tdc and when I move it lower than 8 it will want to stall out.

Assuming you have thunderbolt IV or earlier ignition, the initial timing of 8 degrees BTDC is probably correct. When you set it to that, did you go back and adjust your idle mixture and idle speed? In general, advancing the timing further from stock, with no load will increase rpms. Inititial timing is not determined by the highest rpm location. Now, I wouldn't expect you engine to stall at 2-8 degrees BTDC either. It could be just an adjustment, or many other things.

 

[Don S]

Re: TIMING QUESTION Mercruiser 260

It may sound smooth, but it sure won't run under a load like that. The back pressure alone when setting in the water would make it hard or impossible to get started. No power, probably suffer from preignition and eat the pistions if you tried to run it like that.

 

[Buck Horn Deer Farm]

Re: TIMING QUESTION Mercruiser 260

This is a 1977 Chevy 350. The dist only has one wire to it and no vacume advance. I had the dist out to clean it and put it back in with the 1 piston on comp stroke tdc and the rotor pointed at 1 wire on the cap. Can moving one tooth on the dist to cam do anything but cause you to twist the dist to get timing?

 

[stackz]

Re: TIMING QUESTION Mercruiser 260

I had the dist out to clean it and put it back in

and there's the missing the piece of information. as said, you have it one tooth off. you may have thought you had it spot on but obviously the way it is running says otherwise.

put the engine back to TDC and then pop off the cap and look at the rotor, I'm pretty sure you'll see that its not pointing where it needs to be. when you pull the distributor, you turn the rotor ahead a little and as it sets back down in...due to the curvature of the drive gear and camgear, the rotor will be pulled back into proper alignment against the teeth.

 

[stackz]

Re: TIMING QUESTION Mercruiser 260

Can moving one tooth on the dist to cam do anything but cause you to twist the dist to get timing?

yes, just because there's no vacuum advance doesnt mean there arent internal timing weights inside. you will still have a total timing advance if it has internal weights and they arent locked out.

 

[Buck Horn Deer Farm]

Re: TIMING QUESTION Mercruiser 260

So when the motor is at tdc, the rotor should be pointing directly at #1 wire on the cap?
It seems to me that if it is off one tooth that you could twist the dist so the rotor lines up with #1. Does that work?

 

[stackz]

Re: TIMING QUESTION Mercruiser 260

So when the motor is at tdc, the rotor should be pointing directly at #1 wire on the cap?
It seems to me that if it is off one tooth that you could twist the dist so the rotor lines up with #1. Does that work?

you've already done that and seen where it got you...you base timing when it was running good was like 31 instead of 8. which will throw off your total timing if you have internal weights which will lead you right into the problems Don S talked about.

like I said. rotate the engine back to TDC and then pull off your cap and you'll see that its a tooth off. then just pop the distributor up carefully to just off the camgear teeth and you will be able to feel when you rotate the distributor rotor as you glide across the tooth you are on to the next tooth. then you should be either on the right tooth or two teeth off lol as I cant remember which way a chevy engine rotates (I'm a ford guy )

or dont listen to us and just run it as-is and you'll quickly see why your "rotate it until it points right" decision isnt good.

 

[FreeBeeTony]

Re: TIMING QUESTION Mercruiser 260

It seems to me that if it is off one tooth that you could twist the dist so the rotor lines up with #1. Does that work?

I believe you are correct.....being "off" one tooth does not matter as long as the dist is aligned correctly at #1 TDC.......

 

[John_S]

Re: TIMING QUESTION Mercruiser 260

I believe you are correct.....being "off" one tooth does not matter as long as the dist is aligned correctly at #1 TDC.......

I believe Tony is correct, but I have always gotten mine back in original location. If you do reposition, keep in mind that the distributer will not sit back down flush to the intake, until you rotate the engine one revolution. This will allow the distributer drive to drop into the oil pump drive slot.

 

[Kareo]

This thread was super helpful. Couldn't figure out why my timing mark was so far off. I even bought a TDC tool and verified my TDC mark was correct! This is exactly what the problem was. Lifted it, one notch over, now I can actually use my timing light to verify my timing!