M six engine questions
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Cargo Master
Joined: Aug 2014
Posts: 2,594
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From: North Central Arkansas
M six engine questions
I pulled the engine and transmission from the '51 F6 truck today. The engine should be an M series 254 cid six with a T98 4 speed. The engine has the correct pan and maifolds, but the block has a 7HA-6015 casting number. Did Ford use the same block casting for the M and H series sixes or do I have an H series 226 cid engine with M series trim? I will probably pull the head tomorrow to check engine condition, so I guess I will know for certain then. The truck has 22,000 actual miles as it was a tank truck for a local Fire Department, so the engine should be in decent shape.
Thanks, Mark
Thanks, Mark
Hotshot
Joined: Oct 2009
Posts: 16,188
Likes: 4,792
From: Burbank, WA
I don't remember if the casting numbers on the block were the same for both engines, and none of my pictures show that. All my 254 stuff is gone now. The head on the 254 is cast 8MTH, and the rod caps on the bottom end also say 8MTH. The cylinder bore is slightly different, 3.3" vs 3.5", so it's quite possible they used the same casting with different machining.
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Cargo Master
Joined: Aug 2014
Posts: 2,594
Likes: 72
From: North Central Arkansas
I pulled the head a few minutes ago and it is a 226. It has been bored .060 and there are still a few honing marks on the cylinder walls. I wonder why the engine would have been changed with only 22,000 miles? The transmission has never had a PTO, so they weren't using the engine to pump water. My Dad told me years ago that when he worked for Tose Trucking, just outside of Philly, in the '50s that they had a few Ford and International trucks for local delivery. He said that the flathead sixes in the bigger Ford trucks were bad about burning valves. Maybe the F.D. burnt the valves in the 254 and had to replace the engine. When I got the truck the shift diaphragm had been removed from the two speed axle and it was locked in low., so I am sure that it was probably over revved.
Thanks, Mark
Thanks, Mark
Logistics Pro
Joined: Sep 2014
Posts: 4,920
Likes: 21
From: Bothell & Silverdale, WA
Few mid sized trucks back in the day had the luxury of exhaust pyrometers. Keeping egt's within acceptable limits aids in keeping carbon particles from breaking off and getting lodged in valve seats which begins the wire-drawing failure process. Nothing like lugging an engine at high speed to promote that scenario.
Believe Nothing
Joined: Jun 2004
Posts: 7,516
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From: W. Central FL.
Nothing like lugging an engine at high speed to promote that scenario.
Bob, could you explain how this happens, please. Referencing post #5. I have been of the understanding that lugging was a low rpm occurrence. Or are you referencing an engine that is grossly overloaded and run long time at WOT?
Thanks
Bob, could you explain how this happens, please. Referencing post #5. I have been of the understanding that lugging was a low rpm occurrence. Or are you referencing an engine that is grossly overloaded and run long time at WOT?
Thanks
Logistics Pro
Joined: Sep 2014
Posts: 4,920
Likes: 21
From: Bothell & Silverdale, WA
Nothing like lugging an engine at high speed to promote that scenario.
Bob, could you explain how this happens, please. Referencing post #5. I have been of the understanding that lugging was a low rpm occurrence. Or are you referencing an engine that is grossly overloaded?
Thanks
Bob, could you explain how this happens, please. Referencing post #5. I have been of the understanding that lugging was a low rpm occurrence. Or are you referencing an engine that is grossly overloaded?
Thanks
Last edited by Mixer man; Nov 6, 2019 at 12:48 PM. Reason: Ratings
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Cargo Master
Joined: Aug 2014
Posts: 2,594
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From: North Central Arkansas
Bob, I'm sure this truck spent most of it's life with the F.D. overloaded. Besides locking the two speed in low gear, they also cut the rivets on the helper spring brackets, turned them upside down tight against the springs and welded them back on the frame.
Thanks for all the replies, Mark
Thanks for all the replies, Mark
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From: NM
Carb'd inline 6's were notorious for burning exhaust valves in the end cylinders. They ran dangerously lean, while the center cylinders ran so rich the plugs were black. The Chrysler Slant-6's were the only inline 6's that made any attempt to distribute fuel evenly across all cylinders.
Our family had a bunch of Fords with the 144/170/200/240" 6's and they would rarely make it over 80K miles without burned valves on #1 & 6. On one of them the exhaust valve head was burned in half in #6. The intake manifold on those was ridiculously crude, but I'm sure it saved Ford a lot of money.
Our family had a bunch of Fords with the 144/170/200/240" 6's and they would rarely make it over 80K miles without burned valves on #1 & 6. On one of them the exhaust valve head was burned in half in #6. The intake manifold on those was ridiculously crude, but I'm sure it saved Ford a lot of money.
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