HOT 351m

[SAYBYE]

Hi just put a rebuild 351M in a 79 Bronco. Left off the all the vacum hoses, no emmitions. One hose from side of carb to dist. The motor runs ruff hard starting when cold, get gas in carb starts great. the vale covers get hot to touch. also have a knocking in right cover, like vavles not set right?? things done/tried. new coil,newcap/rotor, new plug wires, new plugs, checkedfor vacum leaks. blocked off EGR valve. new water pump, new radeator. new waterpump, newhoses/belts, thermestat full of coolant, have heat, overflow tank is to the line. timing is 6* BTDC with vac hose off, idle 1000 cold to1200 hot in park. seams low on power not my truck so didn't hammer it. What did I miss? Thanks for any thoughts.

 

[Leadsled]

Hi just put a rebuild 351M in a 79 Bronco. Left off the all the vacum hoses, no emmitions. One hose from side of carb to dist. The motor runs ruff hard starting when cold, get gas in carb starts great. the vale covers get hot to touch. also have a knocking in right cover, like vavles not set right?? things done/tried. new coil,newcap/rotor, new plug wires, new plugs, checkedfor vacum leaks. blocked off EGR valve. new water pump, new radeator. new waterpump, newhoses/belts, thermestat full of coolant, have heat, overflow tank is to the line. timing is 6* BTDC with vac hose off, idle 1000 cold to1200 hot in park. seams low on power not my truck so didn't hammer it. What did I miss? Thanks for any thoughts.

try taking a spark plug reading to see how exactly it is running. the knocking is most likely from a weak spring or one that isnt shimmed correctly. take a plug reading and post back on here what it looks like. its a good starting point. oh yeah i almost forgot. the poor mans way to check the valve springs to see if they are weak or not shimmed right is to try to turn the spring by hand. if you can turn it then its no good. tell us what ya have after that stuff.

 

[SAYBYE]

Update: Talked to somone who put a rebuild 351 in he said that as long as I have oil on top of the valves it sould be ok. They rebuild with tighter tollerances 1 to 2 hours of run time will cool the valvecovers down. I backed the timing to 4 degrees BTDC and took off the right valvecover. The loud tapping was the exhaust rocker on number 1 hitting the valvecover. Dimpled the cover and checked the springs. Couldn't turn them by hand but the rockers were loose. Tightened them to 35 ft pounds. Still didn't seam to have alot of power, droped the exhaust,WOW new motor. The cadlatic coverter was half pluged. Still had alot of exhaust going through, but was pluged enough to cause the temo to rise. Now the water temp is lower, better respond with the loud peddle, idles better. Thanks

 

[Leadsled]

Update: Talked to somone who put a rebuild 351 in he said that as long as I have oil on top of the valves it sould be ok. They rebuild with tighter tollerances 1 to 2 hours of run time will cool the valvecovers down. I backed the timing to 4 degrees BTDC and took off the right valvecover. The loud tapping was the exhaust rocker on number 1 hitting the valvecover. Dimpled the cover and checked the springs. Couldn't turn them by hand but the rockers were loose. Tightened them to 35 ft pounds. Still didn't seam to have alot of power, droped the exhaust,WOW new motor. The cadlatic coverter was half pluged. Still had alot of exhaust going through, but was pluged enough to cause the temo to rise. Now the water temp is lower, better respond with the loud peddle, idles better. Thanks

Did a manual call for 35 ft lbs? That seems a little high to me but if that is what one of the mauals calls for the run it. With it being torqued to much, a valve has the chance to not seal properly and as you probably guessed it, there would be a loss of power. If you dont have to do any smog checks, I would just punch out that cat and call it a day.

 

[SAYBYE]

Sent the 79 Bronco home to it's owner, still runs alittle warm but when I got the new radiator it had plastic tanks and smaller inlet/outlet holes. Nice new replacement. I didn't even go with the cheapest one. I did open up the cat witch was half pluged. Runs more like a new motor should. Thanks for the help.