My Ford 7.5 carburated motor is running rough

[Bilito]

Originally Posted by whem2fish

One thought while your in there dave said something I thought about if you can get a socket on the crank pull no. 1 plug make sure 1 piston is on top when timing mark is lined up that would rule out the chain I bet po timed by ear

It is too hot to do much until later when it cools a tad, I have painted that big bracket, it's dry to the touch but I want to give it a few more hours before I mess with anything.

The help and advice I am getting here is invaluable. Slowly I am getting to the bottom of this rough running issue, then I can get back to finding the bad wire in my generator. Who would have thought the timing could be so far off? I think when2fish was right about the PO timing it by ear.

Sitting in the wheel well with a timing light is about the same as standing next to a jet at full power, It just echoes the sound everywhere, not to mention scary.....

[Bilito]

Originally Posted by whem2fish

One thought while your in there dave said something I thought about if you can get a socket on the crank pull no. 1 plug make sure 1 piston is on top when timing mark is lined up that would rule out the chain I bet po timed by ear

This picture is about how far advanced the timing was. The white line is at 8 degrees BTDC, it was way off, we have it almost even with the pointer now, about the thickness of that white line away.

Now we have a new issue, the bolt that locks the distributer in place is under the vacuum advance, if it isn't one thing, it's the other

[Dave78Chief]

Please check to see if your harmonic balancer has not twisted on it's hub. pull #1 plug. Insert a long rod into the #1 plug hole to use as a gauge. Use a large socket on the center balancer bolt to turn the engine until the #1 piston is at Top Dead Center (TDC). Verify the harmonic balancer 0 deg line lined up to the timing pointer. Happens rarely but the rubber section between the inner and outer section of the balancer can fail/twist which throughs the timing mark off.

Dave

[trashman1995]

One thing to check when you have the timing light on the timing mark on the harmonic balancer, is to see the amount of centrifical advance in the timing when the RPM increase and when looking at the timing mark see if the mark is going up and down indicating your timing chain could be worn and that might give you a rough idle.

Trashman

[Bilito]

Originally Posted by trashman1995

One thing to check when you have the timing light on the timing mark on the harmonic balancer, is to see the amount of centrifical advance in the timing when the RPM increase and when looking at the timing mark see if the mark is going up and down indicating your timing chain could be worn and that might give you a rough idle.

Trashman

Lets make sure I got this right

If I manually turn the crank until zero degrees on the balancer is lined up with the pointer and the piston in number one is at TDC, by checking that with a long rod or a coat hanger.
I will know that part is OK?

Also, with the motor running, (I assume we are talking about warmed up and at idle), I should be using the timing light to see if there is any movement of the mark up and down, movement will mean the timing chain is worn.

When I have it set at 8 degrees BTDC I know that should that be with the vacuum line on the vac advance off and the line plugged.
What about the centrifugal advance?

Besides checking if the vac advance works by sucking on a line attached to it to see if it moves, we can check it with the light to confirm it works by revving it a little and watching it advance

Right now we have it down from almost 25 degrees BTDC down to about 10 and that explains a lot to me, the back fire when revving it up, the hesitation when it is starting before it fires, The engine running rough, it also explains why I have had so many start solenoids sticking, they must be burning up trying to crank that engine over while the spark is trying drive the pistons down way too soon before they reach TDC

Tomorrow when my neighbor comes over we will check this info and then install that big bracket and the alternator, we are sure we can tighten down that distributer bolt with a thin open end 1/2 which is now under the vac advance rendering that special distributer wrench unusable, All this leads me to think that somewhere along the line the PO has installed the distributor one gear off.

When this RV had about 20K miles they had an issue with the motor and replaced the whole motor with a long block, the new motor only has around 10k miles on it. I don't think the timing chain would be an issue but I will check it.

Gotta do all this with me in the wheel well with the motor running, talk about fun.....

If we cannot get it any closer then 10 degrees it should be OK after all that is a lot better then 25.....

[Dave78Chief]

If I manually turn the crank until zero degrees on the balancer is lined up with the pointer and the piston in number one is at TDC, by checking that with a long rod or a coat hanger.
I will know that part is OK?

Piston goes up and down in the cylinder. Long rod (ie coat hanger) is just used to confirm the piston is at the top of the cylinder. When #1 piston is at top of cylinder, the the pointer and the balancer mark should line up.

Also, with the motor running, (I assume we are talking about warmed up and at idle), I should be using the timing light to see if there is any movement of the mark up and down, movement will mean the timing chain is worn.

Centrifugal advance - AT idle you have 0 degrees centrifugal advance. As engine RPM increases weights and springs inside the distributor get thrown outward resulting in advanccing the timing. This is typically from 0 degrees at idle to about a max of 25 deg at around 2500RPM. You have to ignite the mixture earlier as RPM increases so that the mixture completely burns. Because you have to increase the RPM a lot to see this, you could only perform this check once you get the alternator reinstalled.
Vacuum Advance - is added in on top of centrifugal advance and is dependent on engine loading at a given RPM. You can have upwards of 50 degress advance total (Centrifugal + Vaccuum @ say 3000RPM) in a light load condition like on a slight downhill situation where you have to still give it a little gas to keep the speed up. (It is still a big heavy RV prone to wind resistance)

Timing chain slack is measure with engine off once you know that the timing mark pointer and harmonic balancer mark are lined up at TDC on #1. While one person watches the rotor, another pperson turns crank to TDC, stops, then turns the crank in the opposite direction until the rotor moves. You then use the degree marks on the balancer to determine how many degrees of slack are in the chain. A few degrees is normal. 5-8 is not real good. Above 8 definitely replace the chain and gears. (going from memory so I may have the degree numbers off a little bit).

Dave

[Bilito]

Originally Posted by Dave78Chief

Piston goes up and down in the cylinder. Long rod (ie coat hanger) is just used to confirm the piston is at the top of the cylinder. When #1 piston is at top of cylinder, the the pointer and the balancer mark should line up.



Centrifugal advance - AT idle you have 0 degrees centrifugal advance. As engine RPM increases weights and springs inside the distributor get thrown outward resulting in advanccing the timing. This is typically from 0 degrees at idle to about a max of 25 deg at around 2500RPM. You have to ignite the mixture earlier as RPM increases so that the mixture completely burns. Because you have to increase the RPM a lot to see this, you could only perform this check once you get the alternator reinstalled.
Vacuum Advance - is added in on top of centrifugal advance and is dependent on engine loading at a given RPM. You can have upwards of 50 degress advance total (Centrifugal + Vaccuum @ say 3000RPM) in a light load condition like on a slight downhill situation where you have to still give it a little gas to keep the speed up. (It is still a big heavy RV prone to wind resistance)

Timing chain slack is measure with engine off once you know that the timing mark pointer and harmonic balancer mark are lined up at TDC on #1. While one person watches the rotor, another pperson turns crank to TDC, stops, then turns the crank in the opposite direction until the rotor moves. You then use the degree marks on the balancer to determine how many degrees of slack are in the chain. A few degrees is normal. 5-8 is not real good. Above 8 definitely replace the chain and gears. (going from memory so I may have the degree numbers off a little bit).

Dave

I understand

We got the big bracket and the alternator back in, belt attached.
plugged what we thought was all the open vac lines, After we got the alternator back in we realized we forgot to check for zero with the pointer and the balancer and a coat hanger, cranked it anyway and it ran rough. we let it run for a few minutes to see if it would smooth out, nope, so we shut it down and called it a morning. We will get back to it later today when it cools off a few degrees
You cannot believe the heat and humidity down here so early in the season

[Dave78Chief]

I just wish the rain would stop here. Crazy weather this year.

Dave

[Bilito]

Originally Posted by Dave78Chief

I just wish the rain would stop here. Crazy weather this year.

Dave

Just an observation and a possible question
When we do the check with a coat hanger, balancer pointer at zero shouldn't we also make sure the distributor rotor is pointing to the number one plug????

What could possibly cause these things not to line up. I thought the balancer was slid on over a Keyway and can only go on one way, I know that timing chains have marks that must line up during assembly, what could go wrong????? Other then the distributor being a tooth or two out of place?? I have heard of very worn chains jumping a tooth. Outside temps are down to 92 right now, will get back at this when they drop below 90

[jmerritt]

Yes rotor should be pointing at number one with timing mark at TDC with cylinder 1 at top using the coat hanger wire. Not sure if this helps but idle adjustment screws on the Motorcraft (Holley 4160/4180) are located at the front of the carburetor down under the primary fuel bowl. A real bitc* to get at they may still have the limiter caps on them which you probably will want to remove. They should be brittle enough to crack and break off but you need to be careful you don't mess up the idle screws. Don't know why Ford moved the idle screws down under from up on the side of the fuel bowl which would make it a lot easier. Sounds like your having some tough times. While you have the distributor cap off check the advance weights and springs to be sure no rust, broken spring, or anything making them stick. Power valve is definitely a possibility for some of your problems they rupture easily on backfire through the carb and once blown they cause rich mixture all the time. If the mileage on your engine is as you say chain and gears should be OK but wouldn't hurt to check. Ford put a fiber gear on the cam which is notorious for wear and with chain wear they jump easy. Just had my chain and gears changed to all steel on my '87 460 while repairing a front timing cover gasket replacement.

John

[Bilito]

Originally Posted by jmerritt

Yes rotor should be pointing at number one with timing mark at TDC with cylinder 1 at top using the coat hanger wire. Not sure if this helps but idle adjustment screws on the Motorcraft (Holley 4160/4180) are located at the front of the carburetor down under the primary fuel bowl. A real bitc* to get at they may still have the limiter caps on them which you probably will want to remove. They should be brittle enough to crack and break off but you need to be careful you don't mess up the idle screws. Don't know why Ford moved the idle screws down under from up on the side of the fuel bowl which would make it a lot easier. Sounds like your having some tough times. While you have the distributor cap off check the advance weights and springs to be sure no rust, broken spring, or anything making them stick. Power valve is definitely a possibility for some of your problems they rupture easily on backfire through the carb and once blown they cause rich mixture all the time. If the mileage on your engine is as you say chain and gears should be OK but wouldn't hurt to check. Ford put a fiber gear on the cam which is notorious for wear and with chain wear they jump easy. Just had my chain and gears changed to all steel on my '87 460 while repairing a front timing cover gasket replacement.

John

I was surprised when I replaced the distributor cap and did not see points and a condenser which is what I was expecting to see.
There is just this reluctor thing which I am totally unfamiliar with.
Is there any preventive maintenance for that thing? Does the base plate move back and forth from both the weights and the vac advance? Can I give it a shot of WD-40 under the plate to lube things up a bit?
When you say Ford put a fibre gear on the cam are you talking about the big gear above the crank gear that the chain runs around? I always thought they were both steel. Why did they do that, to make it quieter?

This is off the subject but back when I was Kid in the USAF I had a 53 Merc with a V-8 flathead and it started to make a lot of noise, sort of a howling sound, went to the local Merc dealer and was told I had to replace the cam gear. There was no chain on that motor, just one small gear driving the big gear, they gave me, or sold me, the gear and a gasket set for the job, the gear was made of something called Mica or something like a plastic or fiber material. When I got the job done, not only was the motor super quiet,. but it had a boat load of extra power. The teeth on the old gear were worn way down and I could see a big diff between old and new. That was my first engine repair where I actually tore something down, other then an oil change etc.

[Dave78Chief]

Is there any preventive maintenance for that thing?

You can only adjust the gap. I provided the links in thread http://www.irv2.com/forums/f65/my-fo...ml#post1605065 to describe how all that works.

Does the base plate move back and forth from both the weights and the vac advance?

Yes. That is how the timing is advanced based on RPM and vacuum. With engine off, you can pull a suction on the vacuum can and watch the plate move.

When you say Ford put a fibre gear on the cam are you talking about the big gear above the crank gear that the chain runs around? I always thought they were both steel. Why did they do that, to make it quieter?

Big gear yes. Quieter yes.

Can I give it a shot of WD-40 under the plate to lube things up a bit?

I would only use a spray silicon lubricant that that drys. WD-40 will attract dust and dirt.

I thought the balancer was slid on over a Keyway and can only go on one way, I know that timing chains have marks that must line up during assembly, what could go wrong?

Harmonic balancer also acts a vibration dampner. There is an inner steel ring and a outer steel ring. The rings are held together with rubber. The rubber can degrade and allow the outer ring to slip resulting in the outter steel ring no longer being at the proper position relative to the inner steel ring. If that happens the timing marks engraved on the dampner will be off by the amount the ring has slipped. The coat hanger check is to verify that the outter ring has not slipped.

Other then the distributor being a tooth or two out of place?

Being a tooth off doesn't actually change the timing. Just means the rotor button will not be in the original designed position. You end up turning the distributor body farther to account for the offset. In your case, moving it back one tooth would assist you by placing the vacuum can in a position that does not cover up the hold down bolt. You just have to make sure the can does not hit something else preventing from adjusting the timing. You can accomplish the same thing by rotating each plug wire around by 1 position. You simply turn the distributor body around to account for the new #1 plug position.

Chain jumping results in the camshaft being out of alignment with the crankshaft. Valves open/close at the incorrect time. Affects distributor also because the cam drives the distributor.

Dave

[jmerritt]

Yes fiber gear is the large cam gear and Ford did that to reduce noise but honestly in our motorhome and in an 82 460 E-250 Club Wagon that I replaced the gears with all steel I could not tell any difference. Vacuum and weights move the advance plate and the springs are to resist advance. Lubing them is OK just be sure the plate moves freely and none of the weights stick or any springs are off or broken. You could at one time get a distributor mod kit with various springs to change the advance curve but you had to be careful so as not to cause preignition but you could improve performance. Since your engine is carbureted it must be an early 1988 or earlier since Ford went with EFI in 1988. My motorhome is a 1988 but the engine is 1987. Sounds like your compression is good and most of your problem is in the carburetor. You might try taking some Lucas injector cleaner and squirting it in directly to the fuel bowls and the let it set overnight and see if that helps. Jets and orifices could be partially varnished over and the Lucas does a great job cleaning that up without ruining any non metal parts. I will bet that your power valve is ruptured and needs replacement. On the Ford vans and trucks you could get at the power valve by removing the front fuel bowl and metering block but on that motorhome you will probably need to remove the carb. Might as well rebuild it while you are at it since it is pretty easy to do. A nice thing about the Holley is its simplicity, easy to modify and easy to rebuild.

John

[Bilito]

Originally Posted by jmerritt

Yes fiber gear is the large cam gear and Ford did that to reduce noise but honestly in our motorhome and in an 82 460 E-250 Club Wagon that I replaced the gears with all steel I could not tell any difference. Vacuum and weights move the advance plate and the springs are to resist advance. Lubing them is OK just be sure the plate moves freely and none of the weights stick or any springs are off or broken. You could at one time get a distributor mod kit with various springs to change the advance curve but you had to be careful so as not to cause preignition but you could improve performance. Since your engine is carbureted it must be an early 1988 or earlier since Ford went with EFI in 1988. My motorhome is a 1988 but the engine is 1987. Sounds like your compression is good and most of your problem is in the carburetor. You might try taking some Lucas injector cleaner and squirting it in directly to the fuel bowls and the let it set overnight and see if that helps. Jets and orifices could be partially varnished over and the Lucas does a great job cleaning that up without ruining any non metal parts. I will bet that your power valve is ruptured and needs replacement. On the Ford vans and trucks you could get at the power valve by removing the front fuel bowl and metering block but on that motorhome you will probably need to remove the carb. Might as well rebuild it while you are at it since it is pretty easy to do. A nice thing about the Holley is its simplicity, easy to modify and easy to rebuild.

John

Found my vacuum hose routing decal and took a picture at 10 megs, I have no idea what most of those abbreviations are.

Just was running the engine and looking for vac leaks and found that since I removed the two air pumps to get to the distributer and timing marks, all those little steel lines going into the exhaust manifold are forcing exhaust gas back up the lines and coming out of the disconnected 1 inch hoses and it was a good pressure, I held my thumb on the tube and I could feel the air behind my thumb getting warmer

When you look at the decal you will not believe how many vac hoses I have to deal with.

MY RV was made in 6/91 and the Oshkosh chassis with motor was made in 8/89 and I have the documents for both, the motor was changed in March 1999 with 26K miles, it now has around 30 something miles on it