351/400m
Thread Starter
|
New User
Joined: Feb 2008
Posts: 3
Likes: 0
351/400m
I am new to this forum and I have a couple of ?'s about my motor. How do you know the differance between the 351 or 400, I own a 1980 F-350 Dump Truck. It overheated and I think it blew a head gasket on the exhaust side. It has white smoke coming out the exhaust, but no water in the oil or radiator. The engine tag reads 351/400M, I assume it is a 400 since it is a 1 ton, but I could be wrong. I would like to repair it since the truck is restored and I use it alot.
If the heads are warped or cracked I have a local machine shop that can rebuild them, but if they are fatal, what heads will work on it?
Thanks Wayne
If the heads are warped or cracked I have a local machine shop that can rebuild them, but if they are fatal, what heads will work on it?
Thanks Wayne
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
Yeah, the sticker says:
Engine Family: 351M/400
Displacement: 400 cid (6.6 liters) OR 351 cid (5.8 liters)
If nothing else can be seen, there is no other way to tell by looking. Everything is identical on the block, including bore size.
Other heads that will work on these engines with stock intake are: 351 Cleveland 2V, other 351M or 400, or Australian 302C quench heads. Junkyards are still full of these motors with exception to the latter heads, of course! If you want a pick-me-up in power, the Aussies will be a treat. Increases compression ratio, even with stock pistons.
By the way, there is only one 351M. The 400 has no letters after it, and was the first one built (1971), preceeding the 351M by 4 years. Some refer to these two engines as 'M-blocks', as a general reference.
Engine Family: 351M/400
Displacement: 400 cid (6.6 liters) OR 351 cid (5.8 liters)
If nothing else can be seen, there is no other way to tell by looking. Everything is identical on the block, including bore size.
Other heads that will work on these engines with stock intake are: 351 Cleveland 2V, other 351M or 400, or Australian 302C quench heads. Junkyards are still full of these motors with exception to the latter heads, of course! If you want a pick-me-up in power, the Aussies will be a treat. Increases compression ratio, even with stock pistons.
By the way, there is only one 351M. The 400 has no letters after it, and was the first one built (1971), preceeding the 351M by 4 years. Some refer to these two engines as 'M-blocks', as a general reference.
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
Well the good news is, if you are pulling the heads to do gaskets, you can easily measure the stroke of the piston when at BDC up to the top of the cylinder. 4 inches and you know you have a 400. Half an inch shorter is a 351.
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
351M and 400 are the same dimensions 100%, including deck height. The intake manifold is therefore wider than the 351 Cleveland. Does that answer your question?
All they did to the 400 to make it a 351M was chank the crank to a shorter throw and put in taller pistons to make up the difference.
Here are some excellent resources for you to study:
https://www.ford-trucks.com/article/...00_Engine.html
and:
http://www.projectbronco.com/Technic...e_build_up.htm
and:
http://www.projectbronco.com/Technic...the_rumors.htm
and finally:
http://www.fordcobraengines.com/Modified%20History.htm
All they did to the 400 to make it a 351M was chank the crank to a shorter throw and put in taller pistons to make up the difference.
Here are some excellent resources for you to study:
https://www.ford-trucks.com/article/...00_Engine.html
and:
http://www.projectbronco.com/Technic...e_build_up.htm
and:
http://www.projectbronco.com/Technic...the_rumors.htm
and finally:
http://www.fordcobraengines.com/Modified%20History.htm
Last edited by trinogt; Feb 9, 2008 at 10:35 AM.
Trending Topics
Senior User
Joined: Dec 2007
Posts: 269
Likes: 0
i have discovered 9just yesterday) that the harmonic balancer differ from the 351M and the 400.
The 351 has a counterweight and a small convoluted ring, and the 400 had the same counterweight, but the convoluted rinh is almost twice as wide, so it covers the counterweight fully up.
in other words: if you "see" your couterweights when rotating the crank, its a 351M, if not (and the ring is approx. a inch wide) its most likely to be a 400.
Hope that helps.
No guearantees naturally, but it's a step in the right direction of finding out.
The 351 has a counterweight and a small convoluted ring, and the 400 had the same counterweight, but the convoluted rinh is almost twice as wide, so it covers the counterweight fully up.
in other words: if you "see" your couterweights when rotating the crank, its a 351M, if not (and the ring is approx. a inch wide) its most likely to be a 400.
Hope that helps.
No guearantees naturally, but it's a step in the right direction of finding out.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 10 Fords at 2026 Carlisle Ford Nationals
Joe Kucinski
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
Yes, this is in one of the links I posted today:
"The 351M uses a different harmonic balancer than the 400 -- It is best to buy a new 400 harmonic balancer to go along with a 400 crankshaft. You can use a 351M balancer, however, you will have to rebalance the 400 crankshaft by adjusting the counter weights to bring the assembly into balance. Also, the timing marks on the 351M balancer will be nearly useless on a 400 crank -- I know because the engine shop used the 351M balancer on my engine. I had to set my timing at 20+ degrees to get the engine properly timed."
credit to: projectbronco.com
So basically, buy yourself a new balancer for a 400 and be done with it.
"The 351M uses a different harmonic balancer than the 400 -- It is best to buy a new 400 harmonic balancer to go along with a 400 crankshaft. You can use a 351M balancer, however, you will have to rebalance the 400 crankshaft by adjusting the counter weights to bring the assembly into balance. Also, the timing marks on the 351M balancer will be nearly useless on a 400 crank -- I know because the engine shop used the 351M balancer on my engine. I had to set my timing at 20+ degrees to get the engine properly timed."
credit to: projectbronco.com
So basically, buy yourself a new balancer for a 400 and be done with it.
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
His question has already been answered (what heads will work on it). These other posts are just extra information for anyone with a 335 series engine who wants to know more about the 351M and 400.
Thread
Thread Starter
Forum
Replies
Last Post
Fords and Dolmars
1973 - 1979 F-100 & Larger F-Series Trucks
7
Aug 12, 2017 04:11 PM
yankeerebel
1973 - 1979 F-100 & Larger F-Series Trucks
0
Jun 19, 2016 05:15 PM
BuiltFordTough100
1973 - 1979 F-100 & Larger F-Series Trucks
24
Jun 1, 2012 01:43 PM
