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No surprise here. I suspected burnt valves/seats but I think I know exactly when one went bad as I noticed a distinct loss of power about a week ago. Is it possible to hear some kind of report when a valve cracks?
One of these cylinders was making @ 40 PSI and the other was making @ 60. The others were relatively healthy. The cylinder walls look great as do the lifters, rocker arms, push rods, etc. so I'm hoping it will run fairly well with a new top end.
Rebuilt heads are on the way. I'll rebuild the carb and replace the front seal in the C6 while I wait.
The gang is uncharacteristically quiet so I will give a shot.
No, you will not hear valves crack.
What is the history of the motor? How many miles?
What do the plug tips look like? White is bad. Maybe put up a photo.
What was the timing set at? Too much advance will cause a lean condition and cause your problem. Set up at 6* advance. It would be a good idea to check what the present setting is.
Vacuum leaks? They too will lean and cause burning.
Have you replaced the carb recently?
Since the problem came on suddenly, any change in gas or gas stations?
A lot of top gear uphill lugging?
What I see are two garden-variety harelipped exhaust valves, maybe from age.
But you have to ask more questions about carb jetting at stuff as above that may have caused your problem.
The gang is uncharacteristically quiet so I will give a shot.
No, you will not hear valves crack. I din't think so, but ya never know unless you ask
What is the history of the motor? How many miles? Truck odo reads 35,000, guessing 135,000 tho. Motor prob has one rebuild as I can see flex hone marks on the cyl walls. Truck was in storage from '89 to '14, so the rebuild is an old one but the mileage is low.
What do the plug tips look like? White is bad. Maybe put up a photo. Plugs look normal with gray deposit
What was the timing set at? Too much advance will cause a lean condition and cause your problem. Set up at 6* advance. It would be a good idea to check what the present setting is.
Vacuum leaks? They too will lean and cause burning. no vac leaks. Since it's only two valves that are cracked, wouldn't that rule out a fuel or timing issue?
Have you replaced the carb recently? carb has an older rebuild
Since the problem came on suddenly, any change in gas or gas stations? I should clarify, the motor had a dead cylinder before, but seemed to loose power recently, so I'm guessing there was a new development
A lot of top gear uphill lugging? No, all SC lowcountry, light duty driving
What I see are two garden-variety harelipped exhaust valves, maybe from age. That's my guess
But you have to ask more questions about carb jetting at stuff as above that may have caused your problem.
Excellent response.
It looks like the motor just got tired. Put it back together and drive on.
And yes, timing is a factor. Put on 6* when you restart and post up what it was set at- to add to our base of knowledge.
Good luck.
Here they are, but the color of the deposits is not as I remembered and not the same for all. First the plugs from the cylinders with the burnt valves:
Then the rest:
I should also mention that several of the other valves were seated deeper in the seats that the others, so there probably is some erosion in several of the valve seats.
Those are the cleanest looking plugs I've ever seen. The plug that is next to the end, right side is the perfect color. The over lean condition might have helped burn those valves. Do you know what size jets are in the carb? And is it a 2V or 4V?
It's way too lean. All the plugs should look more or less like the one on the right, at least on a carbureted vehicle.
Originally Posted by GaryKip
Those are the cleanest looking plugs I've ever seen. The plug that is next to the end, right side is the perfect color. The over lean condition might have helped burn those valves. Do you know what size jets are in the carb? And is it a 2V or 4V?
Motorcraft 2100 and it will be getting a rebuild. I have no idea what size the jets are but I plan to replace them anyway. From what I have been told, some experimentation is required to find the proper jet size. ND recommended a #55 or #56, I think.
Aw, I see it's had exh. seats installed on the burnt valves before. May be a sloppy valve job done. Man, I'm surprised that engine did not rattle & ping as lean & clean as they look.
Now you'll have to check the push rods for correct length getting head you know nothing about. It's mostly best to have your heads rebuilt then ask Machine shop how much was shave off the heads so you'll know if you need to shorten the push rods.
F100 & F250 are jetted different as the F100 will have the smaller size jets of the two vehicles with same motor like# 52-54's & the F250 #54-56 for a little more power for towing I guess.
Looks to me like modern fuels combined with improper timing killed your FE.
Colder plug too.? AC makes them.
When you get the valve job done make SURE they install HARDENED EXHAUST valves and seats with special inserts and guides. This is to counter the increased combustion temperatures.
That way you can SAFELY run the unleaded fuels.
ALSO...
Look elsewhere on this awesome site for info on PROPERLY setting the timing on these FE motors using today's fuels.
I have found that the Distributor, timing and curve are set RADICALLY different than what they were the 1970's.
I'm running 12 degrees advance (Compared to 6) because I modified the distributor to provide only 20 degrees mechanical advance.
I added a Crane Adjustable vacuum Advance unit too.
Doing this WOKE THE MOTOR UP!
It runs cooler now, no ping, more lower end power and it provides more vacuum at idle.
Thanks to all for the advice and I will definitely be asking more questions when it comes time to rebuild the carb and set the timing. I still have to get the tranny out and replace the seals and install the rebuilt heads. BTW, the heads do have hardened seats, I made sure of that.
Lookin' good, Coastal.
You clearly have a lean burn condition. What caused it, we don't know. But here is what I would do: replace heads, torque all down, replace all rubber vacuum lines, retime to 6*, smooth out. Run it for 1500 miles, pull a plug, have a look.
Don't change anything more in that motor than you must. Confounding variables and all that.
The problem with rebuilt carbs is that you don't know what is inside. If they are supply chain items you can be assured that anything soft is garbage. As far as jets, you get what was on the last vehicle. Anything will start and run on any sized jet. Problems like yours take awhile to appear. It took me a year to burn a valve in my '34 with a SB because of a lean Carter AFB.
These 2100s are common and cheap. They tend to be garage clutter that we throw away on our periodic cleanings. My suggestion is to pick up a clunker with a tight throttle plate at a swap meet- or wherever- for a ten-dollar-bill.
Dealers still sell quality kits and there are some real smart guys in the carb and induction forum who can tell you exactly how to jet a 2100 for your climate. Rebuilding is a piece of cake.
But first, the heads, timing, rubber lines.
We will get you turning 11-second quarter miles
04-29-2016, 01:29 PM
