351M Blown Head Gasket Test?
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From: San Mateo USA
351M Blown Head Gasket Test?
Yesterday I got a 1980 F350 2WD with a 351M/4-speed that I plan on fixing what's broken so I can use it for swapmeets, dump, supplies runs. Bought it as is & the yard monkey suggested that the engine might have a blown head gasket & some burnt valves. I only ran it long enough to drive it from the street into my driveway and although it ran rough, I didn't see any evidence of water in the exhaust (the exhaust out of both duals was smoke/steam-free). I have found some plug wires in bad shape (broken wires) so I plan on replacing them, the plugs, cap, & rotor. I am checking the cylinder compression tomorrow since I have all the plugs out. Are there any "back-yard mechanics" tests I can do to check the head gaskets and valves without pulling the heads? Thanks!
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From: Indiana
351M Blown Head Gasket Test?
[updated:LAST EDITED ON 21-Jul-02 AT 03:18 AM (EST)]I think you are on the right track with a good tune-up. I don't know if your previous owner gave you any actual history or just his own speculations to the problem.
You will need to warm the motor thoroughly before doing your compression check.
Inspect the plugs when you remove them, look for signs of rust on the tips. You have already discovered bad plug wires.
You may get lucky and it just needs a really good tune-up, and maybe a carb kit thrown in for good measure. Use a good cap & rotor, & plugs and wires.
But doing your compression check will tell a lot. Put a vacuum gauge on it too, if you have one. Leaking valves and head gasket problems will show here with a bouncing needle on the vacuum gauge.
You will need to warm the motor thoroughly before doing your compression check.
Inspect the plugs when you remove them, look for signs of rust on the tips. You have already discovered bad plug wires.
You may get lucky and it just needs a really good tune-up, and maybe a carb kit thrown in for good measure. Use a good cap & rotor, & plugs and wires.
But doing your compression check will tell a lot. Put a vacuum gauge on it too, if you have one. Leaking valves and head gasket problems will show here with a bouncing needle on the vacuum gauge.
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From: San Mateo USA
351M Blown Head Gasket Test?
[updated:LAST EDITED ON 21-Jul-02 AT 04:09 PM (EST)]"You will need to warm the motor thoroughly before doing your
compression check."
Hey Dave, why a warm engine? If it's just a cylinder compression check... won't checking it cold give the same results?
Thanks!
By the way: I did not get any history with the truck, it was a lien sale from a towing company. The owner history indicated the truck originally might have been taken good care of but possibly neglected the past couple of years. All private owners, non-business. The mileage reads 87k... most likely 187k, but ya never know
compression check."
Hey Dave, why a warm engine? If it's just a cylinder compression check... won't checking it cold give the same results?
Thanks!
By the way: I did not get any history with the truck, it was a lien sale from a towing company. The owner history indicated the truck originally might have been taken good care of but possibly neglected the past couple of years. All private owners, non-business. The mileage reads 87k... most likely 187k, but ya never know
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351M Blown Head Gasket Test?
But Superdave, I hate working on hot engines! 
A compression test (even on a cold engine) should tell if you have a blown gasket. The vacuum gage is good for valve problems. Run those tests b4 U put much money in it.
A compression test (even on a cold engine) should tell if you have a blown gasket. The vacuum gage is good for valve problems. Run those tests b4 U put much money in it.
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From: San Mateo USA
351M Blown Head Gasket Test?
Welp, didn't get the opportunity to test live. Replaced the radiator and connected the heater, added minor tune up parts, fired her up anticipating doing a "warm" compresssion test and wallah... 5&6 filled up with antifreeze. Starting the tear down tomorrow, I have all the gadgets off (removed my BRAND NEW 3-row radiator). May end up pulling the whole thing out tomorrow (this next weekend for sure), after I remove the intake & drivers side head. Any bets on whether it's a gasket or a cracked block? Anybody able to tell me what block and heads are compatable? I know where there are a few Rancheros that still have 351M engines in them that I might be able to get parts cheap. Thanks! (are these old trucks worth it?)
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351M Blown Head Gasket Test?
You are correct Superdave, but I still hate working on hot engines -hehe
But then with the weather around KC lately you don't have to run an engine to get burned under the hood.
Ed- Sounds like you have your chores to do! Use the search function to look for head info. It has been discussed hundreds of times here. Replace heads as a pair so you get matching head cc's. 351M/400 heads are all basically the same. You can get a pair at any salvage yard or rebuild yours.
But then with the weather around KC lately you don't have to run an engine to get burned under the hood.
Ed- Sounds like you have your chores to do! Use the search function to look for head info. It has been discussed hundreds of times here. Replace heads as a pair so you get matching head cc's. 351M/400 heads are all basically the same. You can get a pair at any salvage yard or rebuild yours.
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From: Indiana
351M Blown Head Gasket Test?
Ed, I believe all the 351M blocks are the same as well as the heads. Look for them in the pick-ups and big Fords, Lincoln's, and probably the Merc's from the late 70's. You will find the 400's in the same vehicles. If you wind up swapping it out grab a 400. Its a direct swap. Just use your brackets off your current motor.
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From: San Mateo USA
351M Blown Head Gasket Test?
I appreciate all the feedback so far! I'm waiting for the Pick-Your-Parts run til I get the heads off! It seamed like all the F250s and Rancheros that I saw all had 351s. Managed to pull the intake last night and so far... so good. Nothing abnormal yet... very clean & no junk or signs of cracks inside. Keeping fingers crossed it's just a gasket, but I'll still do the heads and lower end and check the rings. Thanks!
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