Mystery bolt

[bill1957]

New Englander:

Very nice work with the safety wires. As an engineer, I can appreciate this. Can you post a picture of your 786? I'll do the same, as I've got some "before" and "after" photos.

[Bulldogred]

As an a/c mechanic myself,that safety wire job looks straight out of the 65-9a,and using .040 safety wire to boot.Those bolts will be tight when mother earth reclaims her.

Thanks Red!

I don’t do much aircraft maintenance anymore but I do take the yearly training to keep my Inspection Authorization – a fallback in case my current gig goes away.

Jim N. brings up some valid points and I agree with most.

Let us flash back to A&P School, almost 40 years ago.

In the middle of engines, 101, one student asked why some engines had pal nuts on the cylinder hold downs and some did not. He replied “you don’t need them any more” and produced a bulletin from Pratt & Whitney stating so. He also stated that all the other manufacturers said the same.

Since he was on the subject, he went on to produce a paper from some engineers that said that lock washers did no good either. Those of us who had actual mechanical experience didn’t believe him and it was apparent that he also had doubts. None of us had ever seen a lock washer on a head bolt though or a wing bolt, for that matter.

After reading the paper, some switched to the lock washers are useless camp. I was certainly headed that way. The paper said that once the washer was flattened it was effectively a flat washer; who could argue with that?

The instructor devised an experiment. He produced a dozen new AN bolts and a half dozen locks. We were to screw them into an old engine case and carefully torque them with a dial-type wrench. They were dutifully screwed into an old Wright engine, every other one. The results were telling. The breakaway torque of the washer equipped bolts was marginally higher. More importantly, the washer equipped bolts resisted loosening, showing some torque, for some further degrees of turn whereas the plain bolt resistance fell off as soon as it broke free.

I suppose any loss of torque represents a failure. Certainly very few lock washers are used on aircraft. I remember most being star washers, nothing structural.

Oh yes,next year will be 30 yrs since I attended South Ga Tech's a&p course.Couple of projects on my o&p consisted of timing valves on a 3350 and tracing the path of fuel and air thru a Bendix pressure carb off a 2800,fun times!Mechanically,I haven't touched one of that caliber recip since.Would love to have that opportunity.

[New Englander]

Oh yes,next year will be 30 yrs since I attended South Ga Tech's a&p course.Couple of projects on my o&p consisted of timing valves on a 3350 and tracing the path of fuel and air thru a Bendix pressure carb off a 2800,fun times!Mechanically,I haven't touched one of that caliber recip since.Would love to have that opportunity.

During my General Aviation stint, I worked on R985, 1340, 1830, 2800 P&Ws 1820 and 2600 Wright, and R755 Jacobs as well as a couple of round Continentals. That business started falling off and we saw more lighter planes with flat engines.

When I went to an airline the only round engines were turbine - much more reliable!

Some of the older guys there remembered the R3350 turbo-compounds on the Super Connies and DC7Bs not too fondly; they called them turbo-incendiary!

[New Englander]

New Englander:

Very nice work with the safety wires. As an engineer, I can appreciate this. Can you post a picture of your 786? I'll do the same, as I've got some "before" and "after" photos.

It's not much to look at as it's obviously been an outdoor working tractor.

As with just about everything I own, I won't be able to leave it that way. It will get cleaned up and painted after I get all the mechanical bugs out of it. It still has to work some more this fall.

I just sold a loader and a pretty JD B. That will make some room to keep this inside with the rest.

[Bulldogred]

Oh yes,next year will be 30 yrs since I attended South Ga Tech's a&p course.Couple of projects on my o&p consisted of timing valves on a 3350 and tracing the path of fuel and air thru a Bendix pressure carb off a 2800,fun times!Mechanically,I haven't touched one of that caliber recip since.Would love to have that opportunity.

During my General Aviation stint, I worked on R985, 1340, 1830, 2800 P&Ws 1820 and 2600 Wright, and R755 Jacobs as well as a couple of round Continentals. That business started falling off and we saw more lighter planes with flat engines.

When I went to an airline the only round engines were turbine - much more reliable!

Some of the older guys there remembered the R3350 turbo-compounds on the Super Connies and DC7Bs not too fondly; they called them turbo-incendiary!

Their Achilles heel was the fuel enrichment switch during start,pilot's and mechanic's both would overprime during start,one backfire and you had a raging inferno.We had a P2V Neptune at school and this is exactly what happened during a start oneday.It burned the wire harness's off the engine,melted the distributer blocks and ruined the mags before they got it out.It was that classes big project for the rest of their powerplant class to rewire that engine and get it back operational.They were successful.