hey guys, my friend has a 78 f150 with a 351m and something sounds pretty messed up. it has a new starter, when he tries to start it, the engine turns over fast as if it was gonna start but suddenly locks up. after it locks up if he tries to start it, it sounds like the starter and flywheel are grinding or something. it just keeps doing this in a cycle, turns quickly, locks up and grinds. what in the world is wrong with his truck?
thanx
gc

 

[updated:LAST EDITED ON 19-Apr-02 AT 02:49 AM (EST)]Will the motor start at all? If not, from what your describing, it sounds like a jumped timing chain to me.

 

the motor will not start. it attempts to, but then locks up. what causes a jumped timing chain??
thanx
gabriel

 

[updated:LAST EDITED ON 19-Apr-02 AT 11:44 PM (EST)]The factory cam gear has a hard plastic like material on it where the teeth are and the teeth break off after years of service ( there are small nub teeth on the actual cam gear under the plastic ones, barely enough for the chain to grab on). It allows slop to develope in the timimg set which will allow the chain to jump (slip) teeth on the gears. When the chain jumps it usually slips on the cam gear which allows the gears to get out of sync. Then it will crank as you desribe, because to motor is out of time badly. Aftermarket replacement sets can wear out too eventually, if they have enough miles on them. Bring your number one cylinder to TDC and verify it on the dampner. (if it has not sliped on the rubber sleeve). Trace the number one plug wire to the distibutor cap, then pull the cap off and see if the rotor was lined up under the number one tower on the cap. If not, it has jumped time.

 

>The factory cam gear has a hard plastic like material on it
>where the teeth are and the teeth break off after years of
>service ( there are small nub teeth on the actual cam gear
>under the plastic ones, barely enough for the chain to grab
>on). It allows slop to develope in the timimg set which will
>allow the chain to jump (slip) teeth on the gears...

I second that. Many years ago the 400 in my Ranchero had gotten a bit tired and I had made an appointment with a mechanic to overhaul the engine. Being 19, I decided to have a bit of fun with it on the way to drop it off with the mechanic. I went by the high school I had graduated from and noticed that the hill out front had a few 25 foot or so lazy J's - with standard tires. I had pretty wide tires - and the engine was pretty beefy at the time (4 Barrel, headers, intake, dual exhaust, open air cleaner, etc). I stopped at the top of the block long hill, and let it start rolling down - got to the bottom, dropped in drive and nailed it.

Should mention that I had a shift kit which prevented the C6 from shifting until you let off the gas. When it finally made it back to the top it was still smoking, and smoked a bit past the top - perhaps 300 feet in total. I then drove directly to the mechanics, about 5 miles away. He opened the door, I started to drive in and it stalled halfway in the door. The timing chain jumped right there - lucky it didn't do it on the hill!

I later talked to some high school students and they were wondering who had that wide of tires and that kind of power. The moronic things that you do as a kid.

Those composite timing chains are the worst thing invented - though the ones on the Cleveland were much better than the ones used on some 4 bangers, such as the Chrysler 2.2L and 2.5L. You'd be lucky to get 60-70,000 on one of those - they are actually on the maintenance charts to replace them regularly. I could never figure out why they did not just use metal if they knew how often they wore out.


Tom
1972 Ranchero GT 351CJ+ (Third Ranchero)