Every 351M i've ever seen or heard of has had a rod knock and low oil pressure. Is there a reason these bottom ends are so weak and is there anything that should be done to the oiling system during a rebuild to make them hold up?

-Jon

 

There's a known problem with 351C blocks and oiling, perhaps it's the same on the M? The fix involves running an external oil line from an oil galley near the oil pump to a tee screwed into the oil pressure sensing port at the rear of the block. I don't really know which ports are involved, I'm not a 335 owner, but hopefully this will give you enough info to search the web for an answer.

 

its not in the block


the crankshafts are the MAJOR culprit where 351m's and 400's are always having lower end problems...

bad crankshafts

soft as puppy crap..

the 351 Cleavland has the good crank


if you want a 351M or 400 to survive get a steel aftermarket crank

anything else is just a waste

...zap!

 

The 351M uses the same cranks as the 351W. If that's the problem, why aren't the 351W's notorious for oiling issues?

It's been my experience that most 351M/400 engines were overworked because of their applications, often replacing a big block, and wear excessively. Excessive wear reduces oil pressure, which leads to engine failure. The cheap fix is to install a high volume oil pump, but the real solution is to rebuild the engine (if you can bore it out).

 

after some digging and asking the right people..(uncle was a service manager for ford...and dad built engines for 45 yrs..)

he said the cranks that were destined for the M'S and the 400's were sent to a diffrent heat treater for treatment and the crankshafts were just not hardend the right way

thus the "soft" tag

the M's the 400"s and the windsors have the same diameters for the mains(2.99 o.d.)

the cleavlands have a 2.74 diameter mains

...zap!

 

But does the "M" block share the oil galley layout of the "C"? They're both 335 blocks, so I'm guessing it probably does. If so, then the problem is likely related to the oil starvation seen on the C and the fix would be the same.

The C used smaller main bearings to reduce bearing speed. The load rating of a sleeve bearing is proportional to the contact speed and the contact force. By reducing the diameter by about 8% ford increased the RPM potential of the engine by a similar amount.

 

But does the "M" block share the oil galley layout of the "C"? They're both 335 blocks, so I'm guessing it probably does.

that i'm not sure of...

more digging coming up

...zap!

 

I'm definitely going to do a complete rebuild, just want to make sure that the problem doesn't happen again. Supposedly this engine was rebuilt 8 thousand miles ago so who knows what i'll find inside. It was an amateur rebuild so i'm sure the guy didn't change the cam bearings so that could be part of the low oil pressure problem. If it's true that the 351M had softer cranks, i think i have an extra windsor crank i can toss in there. I guess i'll know for sure once it's out.

-Jon