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Blown Motor?

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Old 11-01-2017, 12:55 AM
1974 f100 1974 f100 is offline
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Blown Motor?

Just picked up a 73 f350 scs with, supposedly, a blown motor. The 390 2v turns over fine but won't start. May be some knocking in the bottom end while trying to start. PO stated it overheated and burnt up. Shows 65k on odometer so no telling miieage, but generally looks like someone took care of it before PO. He owned it a couple years. Rad is full, no sign of oil. Oil looks good, no milkshake. Strange. Haven't done a compression test yet, but why would an overheating episode cause low compression? I'll post photos later for you, but I'm still running my 74 f100 with a 360 2v. Considering swapping the 360 into the 73scs. Opinions? Many thanks.
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Old 11-01-2017, 06:05 AM
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Overheating can cause the oil to thin so much that pressure drops or the film strength is broken. Either way, you can end up with bearing wear and/or cylinder bore wear.

See what the oil pressure is with fresh oil and compression test the cylinder as well. It might be failing to start because of fouled plugs so check those, too.

I'd definitely see what is up because there may be very little wrong - good luck and fingers crossed!

Cheers - boingk
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Old 11-04-2017, 11:20 PM
1974 f100 1974 f100 is offline
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Thank you. Will check it out
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Old 11-05-2017, 06:19 AM
Justinb1984 Justinb1984 is offline
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When an engine is overheated badly enough the cylinder head gasket can blow, cylinder head itself can crack or warp. Either of these will cause low compression.
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Old 11-05-2017, 06:29 AM
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To make a 360 into a 390 is only the crank, connecting rods, and pistons or maybe 2 of those 3, ICR.

If you are pulling a 360 out, it would be a good time to swap the parts and get fresh bearings and put it back in as a 390
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Old 11-14-2017, 08:29 PM
1974 f100 1974 f100 is offline
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An update. A compression test revealed the following:
1-185
2-155
3-60
4-140
5-185
6-130
7-150
8-90
Don't think I have a bad head gasket. May have a couple of burnt valves, but this thing should start. Moving to looking at the coil or if pointless distributor module failed. Please share your opinions. Thanks
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Old 11-14-2017, 09:33 PM
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There's also the pick-up in the distributor.
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Old 11-14-2017, 09:44 PM
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Have you checked for spark yet?

After installing a new water pump, I left mine idling in the drive to get it fully warmed up when it just died. I checked for spark, had none so replaced the DuraSpark module. Fired right back up so out for a test drive. Died again a half mile from home at Budget Batteries. This time it only had spark when the key was first turned and when it was released. Turns out this is the classic failure mode for the pickup coil in the distributor. Thinking it was gonna be a special order, I had it towed home only to find one at O'Reilly's down the street a half hour later. It now starts better than it has in years.

Michael
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Old 11-14-2017, 10:29 PM
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Guess i'm still a novice at electronics. What does the "pick up in the distributor" look like? My 73 f350 has an after market module. Not sure where they ended up putting it, perhaps somewhere under the dash. Was not aware there was something else in the distributor. Help me out a bit here. Thanks
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Old 11-14-2017, 10:33 PM
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Does it have the stock distributor in it or an aftermarket like an MSD?
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Old 11-14-2017, 10:37 PM
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The inside of a factory distributor would look something like this. My magnetic pickup had a broken wire in mine at one point and wouldn't start. It would crank all day long, but wouldn't even sputter due to no spark.

https://www.google.com/search?rlz=1C...Pr3Ym8Ym7gWOM:
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Old 11-14-2017, 10:47 PM
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I'm guessing you have a points style converted to electronic. Maybe a Crane or Pertronix. If so, The above about pickup coils won't be useful.

Look something like this?,


Michael
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Old 11-15-2017, 08:16 AM
fe390pc fe390pc is offline
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The scary part is that you can here banging in the lower end why cranking. I would drop the oil pan and look at the rods before trying to start that engine. If it does have a bad rod bearing you could destroy that engine starting it. Could be beyond repair now, but maybe not.
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Old 11-15-2017, 09:57 AM
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#3 and #8 cylinders have issues according to your compression test. I would drop the pan and have a look because of the knock.
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Old 11-15-2017, 09:56 PM
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Thanks to all for input here. Storming here on Pacific coast. Will take next step in a few days......
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