1971 Boss 351 Engine & Trans O/H

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1971 Mustang Boss 351
I’m going to share my recent engine and transmission overhaul in hopes it may be helpful or interesting to some of the members. The project has taken much longer than expected due to COVID and being hit with two hurricanes. I’ve owned this car for 20+ years. Prior to recent drivetrain work, the engine had never been removed and the car was pretty much original, except for a new coat of paint earlier in it’s life. The car has 78k original miles. I pulled the engine and trans due to a failed speedometer gear on the trans out put shaft and a change in oil pressure during idle. I have a number of pictures, mainly due to the need of having to refer back to them during reassembly. I will post a few at at time. I hope my post will help others.
 

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Joined
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1971 Mustang Boss 351
Hooked up to the lift and ready to come out for the first time in nearly 50 years. Engine still ran well but I had noticed my oil pressure was lower than normal at idle. The transmission has been removed and I’ve removed the grill as to not bang it with the lift.
 

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Engine is out and I get my first good look at the engine bay. A couple of pics of the rear of the engine while it is hanging. Notice the factory paint marks on the rear of the aluminum intake.
 

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1971 Mustang Boss 351
Mounted on the engine stand and ready for the tear down. I’m interested in finding the source of my reduced oil pressure at idle. As you can see, I’m limited on work space so you just have to make the best of what you have. I overhauled the Lycoming engine out of my Cardinal back in 2019 in this same spot. Surprising how you can manage with a small work space.
 

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Joined
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1971 Mustang Boss 351
I soaked the exhaust bolts with Kroil and managed to remove all of them without snapping any off. Piston tops and bores look good. I’m unable to remove the distributor at this point. It will come up about an 1/8 inch then binds. Found bearing material in the oil pan. Very concerning. You can see some flakes on the oil pump pick-up screen. Timing chain and gear have seen better days.
 

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Joined
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Crank, cam and pistons out. Crankshaft journals all looked good considering the age of the engine. The bores will require only a minor cut in order to clean them up. All of the crank bearings looked good. My source of metal was coming from the front cam bearing. Nearly all of the soft metal is gone. Some of the bearing material welded itself to the distributor shaft. Mission Speed shop in San Antonio will be working the components. John raced a Boss 351 during the early 70’s and knows them in and out. I‘m staying as close to original as I can.
 

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Joined
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The car had 75k when I purchased it in 2001. I’ve only added the miles while attending local car shows. The car has always been trailered out of town. There is a price to pay for not driving a car! The one and only engine o/h is probably the result of not driving the car often enough. The lower oil pressure issue at idle occurred after the car was started after sitting 12 months inside the car hauler. NO GOOD. Should have pulled the distributor and primed the engine to prevent a dry start. I knew better!!!
 
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1971 Mustang Mach 1 M code 351 4 speed
I am breaking my head trying to figure out why that cam bearing would fail like that after 50 years and 78K miles. The not starting it for 1 year should not be an issue. I have worked on a tons of vehicles that have not been started for way more than a year and I have never seen a cam bearing do that. The fact that all other bearings are fine, should be an indication that you not starting the car for a year probably did not cause the issue. My understanding is that on a 351 Cleveland the first thing that gets oil from the pump is the #1 main bearing and the front cam bearing. If this was just oil starvation related because of long term storage, you should be seeing this happening towards the back of the engine, which is what gets oil last.
My gut feeling is that this did not happen due to this one time when you started the car after one year of sitting. I would also bet that this would have happened even if you did pre lube the engine. This is a failure that has probably been years if not decades in the making. that bearing has probably been loosing material for years, maybe decades, and it finally gave up the ghost when you got the car out of its one year hibernation. So, do not feel bad, you probably had nothing to do with this cam bearing failing. I don't know if the super stretched nylon timing chain, and all the vibration that it probably produces as the engine is running had anything to do with it, but I have never heard of a stretched timing chain damaging cam bearings.
 
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71 Project….. you are probably correct. Actually, rest of the engine internals looked fine. The engine shop was surprised the original camshaft was still in new specs. The crankshaft journals also did not require any work and we only took a .006 cut on the bores to clean them up. Apparently, the 3 prior owners before me maintained their oil changes.
 
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At this point the engine has been disassembled and taken to the engine shop in San Antonio. They will inspect, clean and do what ever work is required for rebuild. I will reassemble it myself. We did discuss mods to obtain more power but I told the guy I wanted to keep it as close to original as possible. I did go with the hardened valve seats on the rebuild of the heads and we went with new pistons and kept the original compression ratio. I burn 100LL Av gas in it. I dropped the top loader off with David Kee for a complete rebuild. The transmission did show signs of someone being in it earlier. Now on to the engine compartment. The surprise comes when I remove the battery tray. The panel shows some eat through due to a battery leak at some point in the cars past. And it will only get worse from here. More to come.
 

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Joined
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Location
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1971 Mustang Mach 1 M code 351 4 speed
At this point the engine has been disassembled and taken to the engine shop in San Antonio. They will inspect, clean and do what ever work is required for rebuild. I will reassemble it myself. We did discuss mods to obtain more power but I told the guy I wanted to keep it as close to original as possible. I did go with the hardened valve seats on the rebuild of the heads and we went with new pistons and kept the original compression ratio. I burn 100LL Av gas in it. I dropped the top loader off with David Kee for a complete rebuild. The transmission did show signs of someone being in it earlier. Now on to the engine compartment. The surprise comes when I remove the battery tray. The panel shows some eat through due to a battery leak at some point in the cars past. And it will only get worse from here. More to come.
It seems that most, if not all of these cars, have the apron under the battery tray rusted out. It is really rare to not see this specific part of almost every Mustang rusted out. The batteries in the 60's, 70's, and into the 80's leaked, and you had to maintain them by filling them with acid. I still remember that every auto parts store sold battery acid in those soft sided plastic containers with the fil caps. It seems that you always had some battery acid going all over the battery when you opened the fill plugs and then tried to fill them, plus those batteries always seemed to leak a bit.
 
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Now this project starts to get interesting. I AM NOT a body repair guy. But I do have a good buddy that is and he gave me instructions and kept me straight. I also got to use the mig welder I purchased 10 years ago for the first time! After removing the passenger side front fender, I decided to also remove the drivers side since I was concerned over some rust areas. On to replacing both front compartment panels.
 

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Removed the front panel on the passenger side. I will end up also removing the same panel on the drivers side and weld in two small patches on the rear panels before I’m finished. I ordered new panels for both sides at the firewall but decided it would be too much work and the rust area were small in size.
 

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Joined
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At this point in August of 2020 the Boss project was put on hold following the landfall of hurricane Laura. Delta followed six weeks later. We took direct hits from both Cat 4 and 2 storms. We were fortunate in that we still had a roof on the house. Many of hour neighbors were missing theirs. I’ve included a couple of before and after pics. We arrived back home the day following the storm.
 

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Sheriff41

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Glad you were able to dodge as much of those storms as you did! Many were not as fortunate.

Based on your experience would you recommend Mission Speed? (I'm thinking it is the machine shop associated with Mission Auto Parts & Machine on Roosevelt Ave). I have a set of DOAE-N heads that need machining and have been researching machine shops in SATX. Finding a machine shop that knows 351Cs is not as easy as one would think!
 
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I got my engine parts back from San Antonio and decided regardless of dealing with storm issues, I needed to get the engine back together and sealed up. It also provided me a chance to focus on something more enjoyable. I’ve installed the cam and crank.
 

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Engine continues to go back together. The engine shop took a .006 inch cut to clean up the cylinder bores. We had many discussions over trying to reuse the original pistons but when it was all said and done I decided to go with replacements. I stayed with the original head design but did go with hardened valve seats. I also put the original camshaft back in. Went with a new timing gear set-up and had the original balancer rebuilt. The engine shop had supplied me with a high volume oil pump but I had clearance issues between the pick up screen and oil pan. I decided to go back with an original design.
 

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