351 engine only runs at 30 degrees BTDC

[bluesdude]

The 1987 Subra I just purchased had an engine rebuild before it was sold to me. I have to set ignition timing at 30 degrees BTDC for it to run. It seems smooth and responsive when I throttle with no load. A friend suspects timing gears may be out of sync by a tooth. Compression shows between 110-140 psi. Oil put into a 110 cylinder only brought it to 120. Anybody got any ideas?

 

[Haut Medoc]

Re: 351 engine only runs at 30 degrees BTDC

I suspect that your distributer is off by a "Notch"...
Remove your coil to dist wire....
Ground it to the block....
Remove the #1 spark plug....
Bump the starter until you feel compression with your finger over the #1 plug hole....
Bring it to TDC.....
The rotor (dist cap removed), should be pointing at the #1 terminal on the cap (if it were installed)....
Fords are unlike Chevy's ...
They can be off a little....
Chevy is either in or 180* out.....
Keep in mind Ford numbering of cylinders & dist rotation...
Either the dist is wrong or the position of the ign wires is wrong....JK

 

[Boatist]

Re: 351 engine only runs at 30 degrees BTDC

Are you sure you have timing light connected to plug wire for number 1?
Are you sure you have plug wires on the cap in the right order?
How are you mesuring 30 degrees before TDC? I sure your degree plate does not go that far.

Your low cylinder could be a broken ring, burnt valve, lifter way out of adjustment, hole in piston scored cylinder wall.

Timing gear off by one tooth would not make that big a difference but it is not that hard to check.

One last question, Is it a Ford block?


That one is Joke, chev man myself.

 

[Haut Medoc]

Re: 351 engine only runs at 30 degrees BTDC

8) Ford has a better idea!d

 

[lilmandavis]

Re: 351 engine only runs at 30 degrees BTDC

has a chevy stuck inside it somewhere? chevy injestion! do leakdown and see if its hissin and where.

 

[mkast]

Re: 351 engine only runs at 30 degrees BTDC

How can you tell it's at 30 degrees, most timing marks don't register that high?

 

[Buttanic]

Re: 351 engine only runs at 30 degrees BTDC

Don't confuse a Ford and a Chevy, #1 cylinder on a Ford is on the right side and on the left side on a Chevy. Also a Chevy distributor turns clockwise and a Ford turns counterclockwise. If it has a mechanical advance make sure it is not frozen from rust or lack of lubrication. No such thing as having a distributor a notch off. As long as the plug wires are correct to the rotor position you can install a distributor body in any position.

 

[bruceb58]

Re: 351 engine only runs at 30 degrees BTDC

Distributor being off one notch doesn't have anything to do with what you read timing wise since you just rotate the distributor to make up for it. You could have the distributor off 4 teeth and it still woouldn't matter other than having a more difficult time routing your plug wires.

I assume you are using an advance timing light to measure your timing.

What does your timing measure at 2500 RPM?

I kinda doubt he is on the wrong plug since they fire every 90 degrees.

 

[bluesdude]

Re: 351 engine only runs at 30 degrees BTDC

I'll try to answer all of the follow-ups. I am using the starboard side front cylinder as # 1. When I rev the engine (not sure about rpm, tach needs work too) the timing moves to about 24-25 degrees so I believe the weights are not frozen. The harmonic balancer scale actually goes to 30 BTDC so I'm not guessing there. Is there a way to check the valve timing without going to the gears? Thanks for your help thus far.

 

[Buttanic]

Re: 351 engine only runs at 30 degrees BTDC

I'll try to answer all of the follow-ups. I am using the starboard side front cylinder as # 1. When I rev the engine (not sure about rpm, tach needs work too) the timing moves to about 24-25 degrees so I believe the weights are not frozen. The harmonic balancer scale actually goes to 30 BTDC so I'm not guessing there. Is there a way to check the valve timing without going to the gears? Thanks for your help thus far.

Now I am not getting your problem. You say it moves to 24 to 25 degrees when you rev the engine, what is it at idle. There are two ways to set timing, one is at idle which would be between 4 and 12 degrees depending on the spec. and the other is at about 3000 rpm when the advance is fully kicked in and would be 30 to 36 degrees again according to spec.

 

[bruceb58]

Re: 351 engine only runs at 30 degrees BTDC

Something isn't right here...you say that at idle you have it at 30 degrees and when you increase RPM it goes to 24 degrees?

 

[lilmandavis]

Re: 351 engine only runs at 30 degrees BTDC

i was thinking as i was wandering through my old posts. i bet who ever rebuilt the thing tried to put a huge cam in it. thats why its only runnin set at 30 or so...

 

[Don S]

Re: 351 engine only runs at 30 degrees BTDC

Doesn't Ford's have marks both BTDC and ATDC? Perhaps you're looking at the wrong side of the marks.
And perhaps the outer ring of the dampner has slipped.

 

[Buttanic]

Re: 351 engine only runs at 30 degrees BTDC

Something isn't right here...you say that at idle you have it at 30 degrees and when you increase RPM it goes to 24 degrees?

The only possible way I can see that happening is if the centrifical advance mechcanism is for a reverse rotation engine. Someone may have put the wrong distributor in it.

 

[bluesdude]

Re: 351 engine only runs at 30 degrees BTDC

I took another look at the timing marks. Facing the front of the engine looks like this...ATC i i 10 i i 0 i i 10 i i 20 i i 30 BTC. It idles best at 30 BTC and gradually moves to around 25 as I rev. The distributor is a Prestolite. I don't know if that is Ford OEM or not. The distributor turns ccw with a firing order of 1-3-7-2-6-5-4-8. Is it possible that someone put a wrong harmonic balancer on it?

 

[ParallaxBill]

Re: 351 engine only runs at 30 degrees BTDC

"I suspect that your distributer is off by a "Notch"..."

I believe the distributor could be dropped in WAY off. It was in my 165 Merc and I was getting readings like that until I found #1 TDC and rotated everything including the drive shaft for the distrubutor until it let the distributor drop in like it did from the factory and the mark appeared in the vicinity of where it should on the timing tab. One small adjustment to the factory 6' BTDC and I was back in business.

Proper distributor orientation will solve this type of problem if it is the same way off reading I was getting, for the same reasons.

 

[ParallaxBill]

Re: 351 engine only runs at 30 degrees BTDC

"It idles best at 30 BTC and gradually moves to around 25 as I rev. "

That's definately not right. Should add advance as you rev.

 

[Don S]

Re: 351 engine only runs at 30 degrees BTDC

Did you set the point dwell before trying to set the timing? If not, give it a try.
Also, when it's running and you try to turning the distibutor back from 30 towards TDC, what exactly happens? Does the rpms drop off slowly, or just suddenly stop, any popping or backfiring? What is the minimum rpm it will run.

 

[Don S]

Re: 351 engine only runs at 30 degrees BTDC

You also need to pull the contact plate off the distributor and access the weights. See if they move. My guess is the springs are rusted along with the weights. Since you have a mechanical advance only on that distributor, it has to be in the weight area somewhere (along with possibly some broken bits and pieces). But until you take it apart and look, you never will know why it won't advance properly.

 

[Buttanic]

Re: 351 engine only runs at 30 degrees BTDC

With the cap off, by hand try and move the rotor counter clock wise. If it doesn't move try to move it clock wise. It should move counter clock wise, if it doesn't but does move clock wise it is a set up for a reverse rotation engine.