• 1 Vote(s) - 5 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Time for an engine rebuild?
I recently completed a restoration on a '73 fastback for my son. His first car. We pulled the motor during the process but didn't rebuild it as it ran O.K. (No smoking, compression in the 132-151 range, stock motor, about 90,000 miles. Never rebuilt that I know of.) The car ran even a little better after we put it back in. (rebuilt the 2 barrel motorcraft carb, new timing chains, pulled the valve covers and cleaned out what we could get to, swapped the manifolds over to 4 barrel manifolds.
Last week the car didn't want to turn over. It would crank, but spit and sputter like it wasn't getting gas. Checked the fuel pump, and changed the fuel filter, no issues there. Pulled the plugs and not surprisingly they were fouled. (The distributor is stuck in the block and is in a slightly advanced position, another future fix). I was getting a little white smoke, so I though maybe the head gasket blew. Here's where things got interesting.
I pumped 120psi into each cylinder to see if any air would bubble up through the radiator fluid to see if the head gaskets were bad. No bubbles. But during the test on some cylinders I had air blowing out of the carb, and on others had air blowing out through the breather on the valve cover. I read that air coming out of the carb indicates a valve job is needed on the head, and that if air comes out of the breather it indicates badly damaged rings and pistons. TRUE?
I did a second compression test and I'm still in the 132-151 range, so I'm not thinking it's a head gasket. I cleaned and replaced the fouled plugs, leaned out the carb a little and got it running again, but it has never run as well as I thought a 351C should. Am I looking at a rebuild here? Any other suggestions on what I might want to check? Thanks all!!!
The compression range seems good.. I would look for something else because you stated the engine ran well. It is possible that the intake manifold is the culprit. If the plugs were fouled, was it due to a rich mixture or oil fouling.. ? Also you mentioned getting air up thru the carb when pumped into the cylinders.. Again, I suspect the intake manifold is the problem.. the gaskets may have slipped out of position, or not sealed to the combustion chambers..

White smoke out the tail pipe indicates a coolant leak.. Grey smoke indicates an oil leak and black smoke indicates a rich fuel mixture..

Hope this helps
Question, when you pressurized the cylinders did ensure that the valves were closed on that cylinder and then rotated the motor as you tested the others? Is it still points and condenser. You mention that you put a 4V manifold in but you rebuilt the 2V carb, what manifold did you install and why did you change it if you used a 2V carb?

351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,
C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

Some Mod pictures can be seen at:

I think this sounds like another ignitiion issue. I mentioned on another thread where I had my old Galaxie start acting up randomly and chased my tail until a buddy suggested I change the condensor. This is all contingent on your car running the stock type ignition system!

Also, as jobgo referenced, pressurizing the cylinders can tell you things, but your results suggest that perhaps the valves on certain cylinders were not closed. When you test each cylinder, you need to slightly rotate the engine to make sure that both lifters are on the cam base circle so that both valves are closed.

I'll also throw in that when performing a compression test, the engine should be at operating temperature, and all of the plugs should be out. While you are looking for an even balance in the pressure readings from cylinder to cylinder, the test can suggest where issues lie. For example, if you have a low cylinder reading, squirt some oil in the cylinder, rotate the crank over a few times and re-test. If the reading increases, it suggest that the ring clearance is excessive, that there is an issue with the rings/ bore. If it does not change, that cylinder is a good candidate for a leak down test, which as you reference, can detect compressed air leaking past what should be seated and sealed valves...

Sorry if I'm rehashing stuff you already knew....

Let us know what you find!
If you have ever torn down and engine that has sat for extended periods you have probably seen rings on the pistons that were stuck and did not expand when the pistons were pulled from the cylinders. Moisture in the air makes the aluminum in the pistons corrode and the cylinder walls can also rust. You might try mixing up some WD-40 and Marvel Mystery oil. You can get the WD in a squeeze or squirt bottle, gallons or even 5 gallon sizes. I would mix two parts WD-40 to one part MMO. Idle the engine up and spay into the carb while running. Make sure to get in all bores in the carb. This will probably make the engine run rough and will foul the plugs but keep pumping it in and flood the engine out. Let it stand for several days and start it up and bring to operating temp. Pull the plugs and do the compression checks again and clean the plugs and go back together.
When I am going to let an engine set for long periods I always do this to help prevent valve seats rusting, valves sticking and rings sticking along with rust in the cylinders. Might save you a rebuild.
Would at least try before pulling the engine.
We put MMO, WD-40, transmission fluid in a Studebaker engine in a 1930's model that had sat for 40 years. We got it to turn over but it was in really bad shape from sitting outside and I think eventually went to scrap.

When a man is in the woods and talks and no women are there is he still wrong??
check your timing at idle.

remove and plug the distributor vacuum advance and check your timing at idle.

i would put some kroil oil around the distributor every several hours for 2 days then ry to break it loose . . your not going very far f you cant adjust the timing.

once the distributor i free, advance the timing 4 degrees with the engine idling and see if the rom increases much.
Share Thread:  

Possibly Related Threads...
Thread Author Replies Views Last Post
  351 engine tear down Manu Mach1 82 12,137 05-09-2019, 07:39 AM
Last Post: jowens1126
  What's an ok C6 Rebuild kit? Fabrice 6 192 05-07-2019, 06:11 PM
Last Post: Fabrice
  Headers to fit '72 Mach 1 w/400 engine MeanMachine 8 352 04-14-2019, 06:38 AM
Last Post: MeanMachine
  basic engine temps SteveO_71 5 259 04-05-2019, 04:00 PM
Last Post: tony-muscle
  Post your burbling bit (Engine) 1sostatic 7 384 03-26-2019, 10:26 AM
Last Post: 1973machi
  Engine breakin oil question EvilPuppetMaster 10 346 03-25-2019, 09:36 PM
Last Post: EvilPuppetMaster
  351C 4V - 72 Mach 1 Engine fan baz70 16 657 02-21-2019, 09:13 AM
Last Post: Stanglover
  Engine/dyno/speed programs mbrew2 3 290 02-03-2019, 09:28 AM
Last Post: c9zx

Users browsing this thread: 1 Guest(s)