I have a 1980 F150 with a 351M. The truck originally came with a 302 but was changed out prior to my ownership. A number of issues.

At about 50 miles per hour the valves clatter (not pinging but a mechanical clatter) This engine doesn't burn any oil at all and not sure what to do. I'm running 15w40 diesel oil in it. I know this engine is difficult to set the timing on without knowing the exact year and I don't. It has a C6 transmission that is leaking some and need to change the filter and gasket on.

Any comments on the transmission?

Any advice on the clattering valves would be helpful. I hate running it over about 55 because of the clattering noise.

Thanks

 

The M/400 has a very unique oiling system and it didn't work out too well as many/most have low oil pressure compared to other engines. And valve clatter is sometimes caused by not enough oil to the lifters - exactly the problem the oiling system creates.

So, what oil pressure are you running? And if you say the gauge doesn't work I won't be surprised as many of them don't. If that's true, then I strongly recommend an inexpensive aftermarket set of gauges.

I'm not sure what your question is on the tranny, but I do suggest changing all the fluid, inc that in the torque convertor. And, install a drain plug kit in the pan while you have it off.

Also, most M's had 6 degrees BTDC as the static timing.

 

Thanks for your reply - at 50 mph I seem to have plenty of oil pressure - the gage doesn't register a oil pressure number but seems to have good oil pressure when traveling at that speed.

Could the issue be due to a timing issue? I am at my wits end with this and am considering selling the truck for what ever I can get out of it..]

 

It could actually be ignition as some detonation or spark-knock does sound like valves or lifters. But, an exhaust leak can also sound like valves. In fact, Dad's truck had an exhaust leak at the rear of the driver's side exhaust manifold and he was convinced it was a lifter.