2F engine knocks under load. Questions.

[3pits]

in my 62 Fordson Diesel tractor I get a huge knock when the timing has slipped,, of course no dist, so this may shed some light on things,, knocks can be just wrong timing detonations

get some hi octane gas
adjust the carb to correct mixture
play with it! timing that is, make sure things are tight, dont want the dist moving under load, make sure it is not creeping out,,,,

my .02
good luck

 

[60wag]

Doc B - your engine sounds a lot like my engine - 84FJ60 w/ rebuilt 2F, shaved head, fully smogged. It pings a bit around 3k rpm, somtimes. I've tried low, med and high octane gas, switched to a cooler than stock NGK plug, verified EGR, timing advance, HAC, etc function. It still comes back evertime I think I've fixed it. One odd thing I've noticed is that is seems to be worse at the beginning of a long trip than farther into the trip. This makes me think (and hope) that it is carbon buildup. I'm going to try a Seafoam treatment soon. One other idea I read recently suggested a cracked intake manifold could cause pinging that goes away as the engine heats up. I hope that's not it. This is a great thread!

BTW - what is involved in recurving a distributor? Different springs? Shaving the weights? I had my distributor apart a while to see if anything could be loose. I noticed that the two mech advance return springs were diferent - one heavier than the other. Is that right? Can I buy different springs to stiffen the advance ?

 

[DocB]

Put in stock plugs, ND W14EX-U; gapped to 39 (per Haynes Manual). Still pings under load. Filled up with 91 Octane and added "Octane Booster." Still pings under load. I will try retarding the timing just a bit, to see if it helps. I may end up recurving my distributor or putting in another one. Then I will look at the carb. Not ready for that can of worms today. Good news is, the engine has lots of power.

 

[theo]

BTW - what is involved in recurving a distributor? Different springs? Shaving the weights?

Yes. Springs determine the rate at which centrifugal advance increases with RPM. Check advance at a number of rpms between idle and 2500. This generates an xy plot (curve).

The weights determine total advance. Check advance at 2500 rpm (or whatever rpm is enough to throw the weights out as far as they will go.)

Vaccuum advance (and retard) disconnected and plugged during test.

Not sure about your other questions.

 

[IDave]

Doc B, you might want to invest in an OEM engine manual for your trucks. The Haynes manual contains a number of errors, and if you are going to work on it, these should be avoided. For instance, if it is the '77 2F we are talking about, the spark plug gap should be .037. The gap increases on later models. It may not affect your problem, but that's the sort of details Haynes sometimes gets wrong.

Also, to do your timing, you may want to get an advance type timing light. I have found it very helpful for me, since timing by feel can be difficult when you are compensating for altitude as well. I live at 5150 feet, and find that 12 degrees before top dead center works for me. You may find that somewhere between that and the standard 7degrees is best for you.

Also, for my purposes, I found that putting the leaner/smaller/"high altitude" jets in my carb has been an improvement. The carb otherwise ran too rich, and tended to leave carbon deposits on my spark plugs and (presumably) cylinder walls. The carbon predisposes to (!) preignition and pinging. You might look at your plugs and see if they are carboned up. It will happen pretty quickly if you are jetted too richly.

 

[DocB]

Also, for my purposes, I found that putting the leaner/smaller/"high altitude" jets in my carb has been an improvement. The carb otherwise ran too rich, and tended to leave carbon deposits on my spark plugs and (presumably) cylinder walls. The carbon predisposes to (!) preignition and pinging. You might look at your plugs and see if they are carboned up. It will happen pretty quickly if you are jetted too richly.

Yes, my plugs have major carbon deposits after just a few hundred miles. I am probly running rich; are the jets hard to change? Is there a diagram of the stock carb somewhere to show me which screw is idle mix, which one is idle speed, etc, and to show me which vacuum port to plug the distributor into and hose routing for other vacuum ports?

 

[Robert LaDuke]

I think the best step by step diagram for the carb is in the OEM engine manual. I used it when I rebuilt my carb.Lots of other good info in there too. I bet CDan could get one for you.

 

[IDave]

DocB, I'm an F1 man, and don't know my way around the later carbs enough to tell you specifics. But I agree with Robert LaDuke on the Engine Manual (and would add the Emissions Manual) and CDan on this board for getting them. A number of the other guys who have contributed to your thread here, and some others can guide you as well as anyone in the country.

Since you know you are carboned up, you might get some "SeaFoam" (available at finer parts stores) and use it to clean out your carb and cylinders. The directions are on the can, but you basically run half of it directly into the carb and half through a tank of gas. It might even make your pinging go away (until it carbons up again).

 

[jwest]

are the jets hard to change?

Just a word about this.
A lean condition itself, can cause pinging. That is, too much oxygen in the air/fuel mixture either from carburetion or from a vacuum leak. Running richer will actually tend to reduce pinging. However, too rich and it becomes a perfect environment for carbon deposits.

I think a distributor recurve or the use of a non-us distributor is a must do for at least a couple of reasons. Firstly, there's no more EGR for which the US distributor was desiged to compensate, and the advance springs on your distributor may be loosing tension and advancing too far. You won't see this statically.

If the compression ratio is bumped to 8.5 or higher, which I suspect it is, I think you'll have to settle on using premium fuels.

A spark plug's heat range is a numerical code within the part number. The higher the number, the colder the plug. For example, for ND W14exr-u, the next colder plug would be 16 and so on.
For NGK BPR4EY, the next colder plug is 5.

Getting rid of the carbon is another must do. Can you see where the fuel level is in your carburetor sight glass? It should be half way, assuming it's an aisin. It it's above, you're surely running rich.

The above post about heat is also on the money. A weak fan clutch or cooling system causes alot of problems.

 

[Mark W]

A spark plug's heat range is a numerical code within the part number. The higher the number, the colder the plug. For example, for ND W14exr-u, the next colder plug would be 16 and so on.
For NGK BPR4EY, the next colder plug is 5.

Getting rid of the carbon is another must do. Can you see where the fuel level is in your carburetor sight glass? It should be half way, assuming it's an aisin. It it's above, you're surely running rich.

I'd have to take a look at several brands to be sure, but on Autolights for example a higher number is a hotter plug, not a colder one.

The level of fuel in the bowl has nothing to do with the rich or lean status of the engine. This is dependent on the size of the jets.


Mark...

 

[jwest]

I noticed that the two mech advance return springs were diferent - one heavier than the other. Is that right? Can I buy different springs to stiffen the advance ?

I think that's right. One spring has twice as many coils as the other.
I've even heard it's possible to make the weights heavier with adhesives, slowing down the advance.
Anyone?

 

[DocB]

Today I tried several things. First put in new stock plugs and premium gas. Still pings. Then I tried retarding the timing to like 3 or 4 deg BTDC. Still pings. Set it back to factory spec of 7 and then messed with the carb. Ran it lean with the idle mixture screw all the way in (adjusting idle speed to compensate); still ping. Ran it rich with the idle mixture screw all the way out (again adjusting the idle speed to compensate); still ping. I don't know much about carbs, but I suspect adjusting the idle mix does not necessarily adjust the richness of fuel at higher RPM above idle. I could make the rig run smooth at idle and on the highway with all the above settings; just pings under load. The next step is distributor change (I have a non USA on the shelf) and further investigation into the carb; may switch to a rebuilt one on the shelf--SOR rebuild to Non USA specs). Maybe that will do it. Hey, I'm learning something!

 

[Mark W]

You assumed correctly. Idle mixture has little effect on the mixture at higher throttle opening/higher load.


Mark...

 

[jwest]

I'd have to take a look at several brands to be sure, but on Autolights for example a higher number is a hotter plug, not a colder one.

The level of fuel in the bowl has nothing to do with the rich or lean status of the engine. This is dependent on the size of the jets.


Mark...

Funny, when I'm on this board, the only two spark plugs I think of are ND and NGK's.
They may be the few if not the only two who code hotter plugs inverse of their numerical codes. I'll take a look too.

I think they're are two camps regarding the issue of high fuel bowl levels and rich running.
Am I wrong about this?

 

[DocB]

You assumed correctly. Idle mixture has little effect on the mixture at higher throttle opening/higher load.

So Mark, if you cannot adjust the fuel mixture at HIGHER RPMs with the idle mix screw, is there any way to adjust the higher RPM fuel mixture other than re jetting?

 

[Mark W]

The idle circuit always supplies a portion of the fuel. But at higher rpm it is overshadowed by the primary and secondary fuel circuits. The only way to affect them is by rejetting.


The level of the fuel in the bowl has no effect on the mixture unless it is so high that it is simply bleeding out of the vents and getting into the throat of the carb unregulated. Not how it is supposed to work of course.

 

[65swb45]

So Mark, if you cannot adjust the fuel mixture at HIGHER RPMs with the idle mix screw, is there any way to adjust the higher RPM fuel mixture other than re jetting?

The secondaries on your carb will hardly ever come into play, especially if your emissions equipment is running less than optimally. Besides jetting, which is not recommended, there is an intermediate stage of fuel supplimentation provided by the power valve. There is a link in the tech section to a very thorough article on carbs that explains this part, and how it will change the fuel mixture. The 75 and newer carbs control this circuit externally, and it must get the proper vacuum signal to function properly.

You have not addressed the heat question I posed.

 

[Mark W]

If he has completley desmogged his engine (correctly), then the power valve functions automatically just like in the earlier carbs.

I'm not sure what you mean about the secondary not coming into play. Under load with throttle applied (hill climbing I think was specified in the first post(s) it should be opening except at low RPMs. If you mean that the jetting of the secondary probably isn't affecting the situation much, I would tend to agree.

He mentions increased compression. No indication as to whether there is a longer duration cam, or upgraded exhaust flow. The factory jets may well be less than optimum. I don't think that they are the cause of his spark knock however.

The actuation of the secondary is independent of any emissions affected signals.


Unless I'm missing something here?


Mark.

 

[jwest]

DocB mentioned that his plugs are fouling after only a few hundred miles. Since this is a fresh rebuild and compression is good, well maybe a little high, it tends to indicate unwanted fuel going into the system. A bad power valve would cause this, or accelerator pump, but I would track it down before re jetting. Then, set everything, including timing, to spec. and tweak from there. I agree this is separate from the pinging issue.

For the spark knock, I still think it's overly aggressive vacuum advance, and echo what's been suggested about heat.

BTW, is your system completely topped up? Hate to throw more at you but you're head bolts may also be due for retorquing. Any loss of coolant or wax under the oil cap might indicate a slight head gasket leak.

 

[DieselFJ]

I was curious, in the initial thread, he sates that the hash mark(TDC) mark is only 1mm away from the (7 degree timing mark). This is not correct, if the dist was installed as per the wrong TDC mark, this would verify the possibility that the dist was initially was set while not at TDC.

Scott