1956 S120 4x4


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Post Wed Sep 28, 2016 12:54 pm

1956 S120 4x4

Here goes a '56 S120. It's almost all orginal, but noticing some little things here and there that were replaced with silly alternatives (notice the parking lights). Going to start with a rewire and replace the glass. The engine is running and she limps around gingerly. Compression tested and pressures came in at 82-90 psi. I believe the BD240 should be somewhere around 130 psi with a 7:1 ratio. Also having a hard time shifting the twin stick crankcase. Hi and Low lever seems to be working but 4WD stick seems to be stuck in 2WD. Gauges are shot and I will be looking for vintage replacements during the rewire. Any tips you guys can give would be greatly appreciated.
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Golden Jubilee
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Post Wed Sep 28, 2016 1:21 pm

Re: 1956 S120 4x4

:
How do you convert compression ratio to PSI?
A:
QUICK ANSWER
To calculate the pounds per square inch (psi) from the compression ratio, one needs the compression ratio and the atmospheric pressure measurement. Then, the first number in the compression ratio is multiplied by the atmospheric pressure, then divided by the second number in the ratio.
Your compression in PSI may be just fine. Those old engines are very low performance and hard on fuel.
I would rather have tools I do not need than to need tools I do not have
Thinking risks being controversial and possibly being offensive
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Golden Jubilee
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Post Thu Sep 29, 2016 8:19 am

Re: 1956 S120 4x4

looking forward to reading about another project :) We love pictures

Golden Jubilee
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Post Sat Oct 01, 2016 7:06 am

Re: 1956 S120 4x4

James, I have 120 lbs in each cylinder on my 240BD, I do have some miles on it.

Golden Jubilee
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Post Sat Oct 01, 2016 11:06 am

Re: 1956 S120 4x4

tradition compression testers can be thrown off by cranking speed. Most aircraft mechanics and many auto mechanics use a better test to check cyl condition.
It is called a cylinder leak down test, where the piston is placed at TDC compression and a measured amount of air is fed into the cylinder and % of leakage is measured. The amount (%) that is deemed acceptable depends of bore diameter.
It has the added benefit that you can listen and hear where the compression is escaping. (crankcase= rings/piston, intake/exh = valves)

Golden Jubilee
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Post Sat Oct 01, 2016 11:36 am

Re: 1956 S120 4x4

Compression tests are usually viewed as comparative. The actual compression psi number isn't as important USUALLY as the COMPARATIVE values. However, on a non-running engine multiple low compression cylinders can point to valve TIMING issues. THEN the number might be important.
For example, on a six-cylinder engine you may have 119-127 psi compression in the first four holes but only 55psi in the last two. Obviously, something is wrong in the last two cylinders--possibly a blown headgasket.
It's USUALLY not important that all cylinders have EXACTLY the same compression on a good engine, either. They should be well within say...twenty percent of each other.
CB is right again, cranking speed is huge on compression checks...best to run a battery charger before and while you crank. Also, take ALL the plugs out unless you are in a huge hurry, disable the ignition AND fuel systems (exhaust can fill up with fuel during all that cranking and then backfire) and hold throttle wide open with choke wide open.
Try to test each cylinder the same way. Compression gauge malfunctions are common (schrader valves stick) so do each cylinder TWICE.
Checking compression WITHOUT checking overall performance while driving, checking idle vacuum, ignition timing, etc. is asking for trouble. Relative compression should be always be ONE point of consideration not THE point of consideration.
In my little auto diagnosis world at work I use all my senses just as much as the great diagnostic machines I own.
On Friday I had a customer with a low-mileage PT Cruiser he just bought. Nice car! Won't pass smog because of P0304 engine misfire (yes, it misses) although every possible tune-up issue had been covered.
I told everyone in the shop to be quiet and I began to crank the engine. On and off. On and off. Every once in awhile I could hear a different sound from the starter...it was like it suddenly had nothing difficult to turn...HA! Low compression!
Caused a very glum customer but saved everyone hours of work removing intake manifold to gain access to spark plugs (for compression test) just to give customer a big bill and bad news.

Golden Jubilee
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Post Sat Oct 01, 2016 4:27 pm

Re: 1956 S120 4x4

Hey guys,
I have done leak down tests, compression tests, Pre TURBO, and after TURBO, they have been the same, ___I think I'm lucky. I have Snap-On gauges and I feel they are accurate.
So it don't matter to me, opinions are welcome, my old truck runs great.
BTW, trying to help the poster out

Golden Jubilee
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Post Sat Oct 01, 2016 4:46 pm

Re: 1956 S120 4x4

When I was working on cars commercially I had both tools in my tool box. In a situation like MM had, where the customer wanted an answer but not necessarily and diagnosis, a quick compression test could show a cyl out of wack with others.
If they wanted to know what the problem was, and how much to fix it, I would spend the time to do a leak down.
I remember one, a 2.3 Ford that was burning oil. Customer insisted it must be valve guides/seals and wanted to have the head pulled and re done, The leak down showed without a doubt it was the rings/bores that was the problem. Saved a lot of time and frustration for both myself and the customer. IIRC we ended up putting a long block in it. He had done a compression check and found it to be within acceptable range and made the assumption that guides must be the cause of the oil consumption. In fact, the compression was fine, it was the oil control that was the problem!
On one of my own cars, I went from burning a qt every 25 miles to every 1500 only changing the rings. The engine had over 350,000 miles on it and the bores were tapered, the ring grooves worn but it still made a difference.

Golden Jubilee
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Post Sun Oct 02, 2016 2:51 pm

Re: 1956 S120 4x4

CB89, That's amazing,

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Post Mon Oct 03, 2016 10:02 am

Re: 1956 S120 4x4

Thank you all for the insight. This is such a great community and forum. I was able to adjust timing and make some carb tweeks. Shes running a bit better now. I suspect the old fuel may also be a problem. I am going drain and flush the tank. I will keep you posted.
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