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Looking for help with a Flathead six


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I'm looking for some advice/suggestions on my 251ci flathead. The truck is a 1957 Fargo and it has been running great since putting it on the road over a year ago but has just recently started having issues. About 3 weeks ago while on my way home from a cruise night the throttle linkage fell off the carb causing the engine to go to full throttle very high rpms, I tried to shut it down as soon as it happened but it still revved for probably 15 seconds or so. I got it coasted off the road and found that the clip/pin had fallen out of the linkage, I was able to make shift a pin to get me home that night. The problem now is that the engine is puffing blue smoke (oil) when accelerating though it doesn't seem to smoke at steady higher rpm (ie: if I rev the engine manually from under the hood it smokes every time if I "crack" the throttle, but if I take the rpms up above idle and maintain it manually it doesn't seem to smoke, I have had someone stand at the tailpipe to watch for the smoke). The engine still runs great other than the smoke, I am not sure where to start as with my knowledge I would think if it was rings it should be smoking typically at all speeds, the smoke when "cracking" the throttle would typically point toward valve seals on an overhead valve engine but I know the flatheads are a different setup and don't use seals. So am I looking at possibly a broken ring, a bad valve guide or ?? This smoking issue was not there prior to the throttle sticking open! I thought at first that maybe it had sucked some oil in from the oil bath air cleaner but it still hasn't cleared out so I'm doubting that is the case. I hope someone on here has more experience with these engines than I do (which isn't much, lol). I have not yet done a compression test though it hasn't changed in the overall performance of the the engine power wise just smoking. Thanks in advance

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I would start with the compression test, and pull the valve covers for inspection to see if anything got bent.

Next would be pull the head to inspect cylinders wall. I suspect a piston(s) scored a cylinder wall.

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2 minutes ago, P15-D24 said:

I would start with the compression test, and pull the valve covers for inspection to see if anything got bent.

Next would be pull the head to inspect cylinders wall. I suspect a piston(s) scored a cylinder wall.

Thanks! I will check all of these suggestions as all sound possible! It hit some really high rpms even though it was only a short period of time it has obviously done some kind of damage. It is very frustrating as it has always worked so well and we have driven the truck over 2000 miles and never an issue until this happened. I guess it's just one of those freak things, but unfortunately it looks like it might turn into an expensive fix. Thanks agian

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I have had similar incidents over the years and one with a 57 Fargo.    If the compression tests out all right I would just keep driving it.

You will not have done your engine any good, but maybe not much harm either.   At the worst, it could have broken some top rings ( top ring striking the ridge)  .  It is easy to re ring this engine  right in the truck.

I drove two 57 Fargos continuously over a period of almost 30 years.   Have a 52, now.     The second 57 got a 273 Dart v8.  It  worked really well. This truck is pictured in The Standard Catalog of American Light Trucks

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For less than 25 bucks you can get a borescop ap and hardware for your smart phone or tablet computer.  This would all you to pull the spark plugs and get a look at the top of your pistons and cylinder bores without needing to pull the cylinder head.  A head gasket is going to cost you about the same.  The scope you can use again, pulling the head is an expense you may not need to add to the situation.

https://www.google.com/search?q=borescope+app&client=tablet-android-lenovo&sa=X&biw=962&bih=601&tbs=vw:l,ss:44&tbm=shop&prmd=svin&srpd=5881436639666328147&prds=num:1,of:1,epd:5881436639666328147&ved=0ahUKEwj6mZyq1sXVAhXMRyYKHYF3DzQQgjYI2AQ

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54 minutes ago, Reg Evans said:

Plus you can do your own colonoscopy and save some big bucks there too. :eek:

I wont even began to tell you how much fun it was to have a camera stuck up the number one hole. All I will say is never again. It did help that the nurse was really cute.

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So I still haven't confirmed anything for sure on my smoke issue, though I did finally get a chance to do a compression test today. I don't have the luxury of keeping my truck at home as I live in an apartment so needless to say I don't to work on it as often as I'd like to. I did the compression test both Dry and Wet and did find cylinder number 3 is a bit low but had very little change by adding oil to the cylinder. I believe this should rule out any issue with the compression rings though it still wouldn't rule out an oil ring problem, though if I'm not mistaken a bad oil ring should cause smoke at all times not just coming off of idle like mine is doing but I could be wrong. My mechanical knowledge is very good but not so much when it comes to internal engine problems unless it's something very obvious. The compression test results are as follows:

DRY

#1 - 95,   #2 - 100,  #3 -70,  #4 - 90,  #5 - 95,  #6 - 100

WET

#1 - 100,  #2 - 105,  #3 - 75,  #4 - 90,  #5 - 110,  #6 - 110

Hopefully someone can give some direction as to the next step prior to a tear down. This engine has been rebuilt at some point in it's life though I have no idea how long ago, but based on these numbers it looks like it would've been a long time ago. I say that it's been rebuilt as the pistons are stamped made in England and are 30 Thou oversize neither of which looks like something that would be factory original for when the truck was built, but I could be wrong. The engine running very smooth and quite so I have a hard time thinking it would be anything related to the valves, not saying there might not be an issue there but it does run very smooth which if it had bent a valve I would think it would be running a little rougher than it is.

Thanks in advance for any help with this

Edited by dodgefreak73
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I haven't had a chance to investigate any further on my engine yet, but I did find another complete enigine that I can get! The problem with this other engine is I'm being told that it is a 251ci (it was rebuilt within the past few years), that it was in a car but the seller claims he checked the stamp numbers and that it is a 1960 truck engine. The concern I have is that any info I can find about the numbers the truck engine stamp starts with "T" though most of what I can find is for USA built and I know some stuff was done differently here in Canada. I know the original engine in my Fargo is stamped with a "T" but then I also have found information suggesting that 1958-60 were stamped differently again so I'm getting confused. This engine does appear pretty fresh and the price is very reasonable but I don't want to buy it if it's not a 251ci! I know that if it did come out of a car I'll likely have to change the oil pan and exhaust manifold which is no big deal, I just don't want to spend the money if it isn't correct. 

The block stamp is P1D1 - 33657C  I'm hoping someone here can shed some light on what this engine really is before I decide. The deal is too good to pass up if it is what I need but don't want get a boat anchor smaller cube engine. Thanks in advance

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Edited by dodgefreak73
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