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post #1 of 17 (permalink) Old 06-16-19, 11:18 AM Thread Starter
Jim Robson
 
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Problems with 300CI straight sixes

Hi all, I have caused myself a few problems with my engines and I'm wondering if anyone has suggestions. My first engine had a blown head gasket and I found a good head and had it inspected by my machine shop and it passed with flying colors. Flat as a pancake, didn't need a valve job and passed a magniflux test. Soon after I installed it, I ran the cooling system dry and it broke down on the Interstate. I nursed it home by adding water and driving about a mile at a time until I was home. It was very noisy but I never had an official diagnosis and I decided to replace it. I still have it. I found a replacement at a quality used Ford parts house here in Jacksonville (Rusty Acres). They have a great local reputation and the engine came with a no questions asked 90 day warranty. I got preoccupied and let the warranty expire. When I finally installed it, it would run for about 2 minutes and then lock up and stall. It had the correct oil level and water level. Soon thereafter it wouldn't start at all. The starter motor was bogging down and turning it by hand was nearly impossible. I pulled the head and the binding was still there.

Where should I go from here? Which engine would be the best bet to repair? The truck is a 1981 F-100 Custom short bed.

Thanks, Jim

I take full responsibility for my predicament, please no guilt or shame. I feel bad enough as it is.


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post #2 of 17 (permalink) Old 06-16-19, 02:49 PM
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Re: Problems with 300CI straight sixes

Best judgement would be from whoever gets to look at the crank and bearings. Both situations sound like either one could be a basket case, but the 300 was always pretty durable, one of them may surprise you.
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post #3 of 17 (permalink) Old 06-16-19, 04:04 PM
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Re: Problems with 300CI straight sixes

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Originally Posted by CatSkinner View Post
Best judgement would be from whoever gets to look at the crank and bearings. Both situations sound like either one could be a basket case, but the 300 was always pretty durable, one of them may surprise you.

I have to agree about the 300. I had one that lasted to 550,000 +/- miles before the head literally blew off the block. They're comparable to the old Dodge slat six, practically run forever if taken care of...
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post #4 of 17 (permalink) Old 06-16-19, 08:20 PM Thread Starter
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Re: Problems with 300CI straight sixes

One of my local mentors advised me to drain the oil and observe the color. Look for metal flakes and grey oil to predict the condition of the lower engine. Can you guys add anything or comment on that advice? Thanks, Jim

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post #5 of 17 (permalink) Old 06-17-19, 01:16 AM Thread Starter
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I drained the oil and showed it to my friend and he said that it looked perfectly normal. No metal flakes and no discoloration. I then showed him pictures of the cylinder head and the cylinder walls. He said that the head was fine, but he was concerned about the condition of the cylinder walls. He said that they looked as if they had been starved of oil. I felt them with my finger and in my inexperienced opinion, they didn't feel too bad. I'm tempted to put a quarter cup of Marvel Mystery oil in each cylinder just to see what happens.

Any ideas? Thanks, Jim
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post #6 of 17 (permalink) Old 06-17-19, 02:16 AM
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Re: Problems with 300CI straight sixes

I have had some engines where they seized up due to timing tensioners collapsing and jamming up . But I believe yours has fiber and phenolic timing gears. If correct with that engine we had some with that set up on a few Ford models way back in time . I had a few where the fiber teeth on gears had sheared resulting in further damage and jammed up engine .Not 100% sure with your engine though but either timing set up failure can cause this . Cyl. bores dont look too clever but hard to judge from pictures and may clean up .

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post #7 of 17 (permalink) Old 06-17-19, 01:40 PM Thread Starter
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Re: Problems with 300CI straight sixes

I'm real anxious to pull the oil pan. but I have a small problem. My neighbors are getting upset about me doing extensive work in the car port. "It's not that kind of neighborhood". So I have to reconfigure my privacy fence to allow me to put the truck in the back yard. That will cause a several day delay. Sorry to get everyone involved and then have a delay. I'll let you guys know when it's time. It might be this weekend. Thanks, Jim

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post #8 of 17 (permalink) Old 06-19-19, 04:42 AM
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Re: Problems with 300CI straight sixes

Although hard to tell from that pic, the cylinder walls look a little scored so may have worn/loose wrist pins that are hitting the walls; in any event check them. Also check the piston rings are in the right order and have been properly gapped (the gap might have been made too small or they may not have been filed to fit at all); something looks wrong. They also appear to have a ridge at the top that needs reaming away and may have been dislodging rings.

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post #9 of 17 (permalink) Old 06-19-19, 05:00 AM
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Re: Problems with 300CI straight sixes

According to this https://www.jalopyjournal.com/forum/...00-six.572178/
Quote:
the 300 is prone to breaking the ring lands from pre-ignition

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post #10 of 17 (permalink) Old 06-19-19, 04:39 PM
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Re: Problems with 300CI straight sixes

Given what we're seeing, I'd strongly recommend honing the cylinders and getting a good look at the journals. As a tech tip, I generally run a magnet through the used oil. Majority of what ends up in the oil is nonmagnetic, but there is ferrous, but generally if your picking up magnetic debris, it's toast.
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