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Other work with heads off 351w?

DC_Gearhead

Sr. Member
Joined
Dec 28, 2015
Messages
563
So, I took my baby for it’s first drive around the block and realized I needed to take a look at the motor. It was running, so I prioritized my time to start with suspension, brakes, steering, body, etc. Well....now my trip around the block didn’t go that well...engine wise. On the positive side, everything else worked perfectly....I just didn’t have any power and it had a ticking sound coming from under the hood.

I did a compression test and noticed that 2 cylinders had 0 compression. The rest were right round 135. I figured the ticking was probably a valve hitting a piston, so I took off the heads to look. I was correct. Bent push rods and small rings in top of two pistons from the intake valves. I took them to a machine shop here in DC to take a look. After disassembly they said the guides, valves, a couple of valve seats, and springs all needed to be replaced. Apparently the springs were all at 70lbs when they were supposed to be 82+ for the installed height. Anyways, long story short, I am getting the heads rebuilt.

My question is this: Is there anything else I should do while I have the top end off the motor?

Current specs: ‘69 351w, C90E heads, HEI distributor, PS pump, cast exhaust manifolds, Elelbrock intake, 750 BP Holley, 302 RV cam and lifters.

I can’t check the rings, without installing the heads, so I am gambling that the compression issue is the heads. The heads being so bad, is probably because the motor sat assembled for 25 years before I started it, but I don’t know.

Any advice?
 

KeithKinPhx

Sr. Member
Joined
Jan 8, 2017
Messages
444
Depends on how far you want to go.

Water pump, thermostat, plug and wires if not done recently.

When I did mine I went crazy and did an aluminum intake, cam, timing gear, lifters and push rods. Mine is a 289 so I can't give part # recommendations.
 
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DC_Gearhead

DC_Gearhead

Sr. Member
Joined
Dec 28, 2015
Messages
563
I have new wires, plugs, thermostat, and will have new pushrods.

I guess I’m just arguing with myself on whether I should just jerk it out and rebuild it. In my small garage it would be a big undertaking. I’m hoping someone says “don’t do it...wait until you install the heads and see”.


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Powerbyford

New Member
Joined
Jun 8, 2018
Messages
34
Loc.
Garden City, MO
What do the cylinders look like, any trace of rust or pitting? How much ridge is there at the top? If you can feel a significant ridge it will be on the downhill side of life, but it needs to be measured to know. I can’t explain very well how an okay ridge feels versus a worn out ridge. It’s also possible to get a crude estimate of wear by looking at the gap between piston and cylinder while assembled, but need an experienced machinist to look at it. I would put it back together and drive it a while to see how it runs before going deeper.
 
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DC_Gearhead

DC_Gearhead

Sr. Member
Joined
Dec 28, 2015
Messages
563
Cylinder walls look smooth and polished. No grooves, no rust. There is no lip at the top from ring wear. I cleaned the little bit of carbon off all of them and couldn’t feel a lip at all. The pistons are stamped with “30”, so the motor has been rebuilt. Maybe they just didn’t do any head work. I don’t know. My uncle did tell me there was “something going on with the valves” before he past away.

I’m thinking I’m just going to bolt the heads on and try it out. With any luck it will be fine and compression will be great.


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bronkenn

Contributor
Bronco Guy
Joined
Apr 27, 2017
Messages
2,662
Loc.
Southeast Ohio
You need to check valve to piston clearance. There is something wrong if the valves were bent from hitting the piston. You need to find out why it happened. The cam might have too much lift. Ken
 

Timstrk

Full Member
Joined
Apr 8, 2014
Messages
193
If the guides are very worn it will allow the valve to go somewhat sideways and not straight up and down. The wide end of the valve, very outside, can contact the piston. I have a shattered piston to demonstrate.
 
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DC_Gearhead

DC_Gearhead

Sr. Member
Joined
Dec 28, 2015
Messages
563
If the guides are very worn it will allow the valve to go somewhat sideways and not straight up and down. The wide end of the valve, very outside, can contact the piston. I have a shattered piston to demonstrate.



That’s exactly what the machinist said. You add the fact that they sat for 25 years before me startling, with the added corrosion, you get valves sticking and not gliding smoothly. On top of that, weak springs to pull them back. Lucky for me I only drove it around the block and checked the compression.

It could have been really bad.


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DC_Gearhead

DC_Gearhead

Sr. Member
Joined
Dec 28, 2015
Messages
563
Not bad. Here is a bad pic.

3af5f7c7889691ff9da9cc758eae0786.jpg



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Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
That's a pretty hard hit, and pretty close to the ring land. Probably OK. An minimum there should be some cleaning up of that impact site to take off the sharp edges. Technique would vary depending on what tools are on hand. I would do it with the piston still in the block. If the gouge doesn't clean up it may be a crack. I would avoid pulling the piston if possible and that just gets real deep into the can of worms really fast. I just refreshed an engine last year and refused to pull the heads because if I did I knew it would turn into a full on rebuild. That just for a lifter tick and leaky gaskets. Ended up with a full valve train and new bearings because I just had to look at what shape they were in.
 
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DC_Gearhead

DC_Gearhead

Sr. Member
Joined
Dec 28, 2015
Messages
563
I just got my heads back. Lots of work done. Hopefully I can get them installed and get it started this weekend.

76c471dd0f22971c6413d2998344542f.jpg




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Powerbyford

New Member
Joined
Jun 8, 2018
Messages
34
Loc.
Garden City, MO
One more thing to consider is cam timing. Possible the cam timing is off making the valve too close to the pistons. My bet is that you already have it diagnosed right. Lots of motors that sit a long time end up with a bent valve or two and bent pushrods because the valves are corroded in the guides. Add weak springs and they collide.
 

Pa PITT

Contributor
Bronco Guru
Joined
Jul 15, 2005
Messages
11,252
Loc.
Stephenville TEXAS
I'm with you on just putting the heads back on. If its not correct then I'll have to come out any way . & When it goes to the Machine shop they take it apart & reassemble it.
After doing a bunch of over hauls I now think most of the smoke & blow by comes from bad valve stems & seals Rather than the rings.
 
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DC_Gearhead

DC_Gearhead

Sr. Member
Joined
Dec 28, 2015
Messages
563
We’ll see. I have it all back together. Hoping all is good. I’ll let you know.


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Skytrooper15

Full Member
Joined
Sep 13, 2018
Messages
216
Loc.
Tuscaloosa,Al
If you are worried about the compression my Chilton's manual says that the lowest compression ratio should be within 75% of the highest compression ratio so if you have at least 101 on the two that had bad valves and 135 on the other 6 pistons you will be OK but my guess is that after the valve job you will probably have the same on all 8 cylinders.
 
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DC_Gearhead

DC_Gearhead

Sr. Member
Joined
Dec 28, 2015
Messages
563
If you are worried about the compression my Chilton's manual says that the lowest compression ratio should be within 75% of the highest compression ratio so if you have at least 101 on the two that had bad valves and 135 on the other 6 pistons you will be OK but my guess is that after the valve job you will probably have the same on all 8 cylinders.



Got her back together and she purrs like a kitten compared to before. I thought it was a big cam sound before. Apparently it was the 2 missing cylinders. Haha. It started right up and vacuum is good at 16-18. It’s steady but bouncing a little so I decided to check compression. Not the best but ok. It ranges from 105 to 125. I’m not racing this sucker so I think I’ll be fine.

Any thoughts?


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DC_Gearhead

DC_Gearhead

Sr. Member
Joined
Dec 28, 2015
Messages
563
Sounds like a standard low compression smog era engine. That's just what it is. They run, just nothing exciting about them.



Took it for a drive after adjusting the carb and timing. Seems to have enough power for me until I rebuild it in a few years.


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Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
I have one sitting in my driveway right now. Functional. Even with carb and timing set it still lacks a lot of the fun. It is crying out for another point or so of compression. When rebuild time comes it will get it.
 
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