100 Octane leaded gas, cheap

[dadsbee]

Okay.. you win, I know nothing about what wears out valve guides after 25 years of wrenching aircraft. 80/87 that had almost no lead in it would let an engine go to TBO (1800 to 2000 hours) without much maintenance and when they stopped making it and everyone had to switch to 100LL (that has about 10x the lead as the 80/87) you're lucky if you can get 300 hours out of a cylinder before the exhaust valve guide to stem clearance is so bad it's like throwing a wiener down a hallway! As I also noted earlier, the other issue with 100LL is it will dry out all your rubber parts that are designed for auto fuel.

 

[Bee1971]

Let’s see - Heat Heat Heat

Air cooled cylinders on most piston aircraft versus liquid cooled cylinders / heads on our vehicles

And how pilots allow those air cooled cylinders and motors to stabilize before shutdown and full power on take off

No , not an A&P , but have seen it a million times

Have been pumping 100LL for 32 years and hang out in the maint hangar just about every day talking to the guys

Student pilots kill cylinders along with charter pilots who don’t own their own equipment

 

[Slap Stick]

I said nothing about valve guides. I asked what caused the VALVES to burn.
116 octane race fuel never burned valves in our race cars.

 

[Slap Stick]

It wears out the valve guides first because it's like sand paper, at least in aircraft air cooled engines, and then the valve seat stops sitting straight. Next thing is blow by and then burnt seats and sealing faces. Next comes cracked valve heads..

That is a failed guide causing the valve to burn.
The problem is there isn't enough compression to burn off all the deposits.
If lead is so bad for aircraft engines why is it used?

 

[slimt]

That is a failed guide causing the valve to burn.
The problem is there isn't enough compression to burn off all the deposits.
If lead is so bad for aircraft engines why is it used?

A aircraft engine is constantly under high revs . and can burn off the fuel .A car engine is not unless it has a high compression ratio .

My old boss is highly skilled AME and has been in the industty for 50 years and very much a car guy as well in mechanics as well for 65 years with the AME included in those years. My info came from a person with more knowledge than most.

Av gas is a good fuel for aircraft. But you have to remember those go there 100 hour checkups and in most cases do get torn down for filings in crank cases to valves pitting .Cars usually never see a tear down until there just worn out .

 

[Slap Stick]

A aircraft engine is constantly under high revs . and can burn off the fuel .A car engine is not unless it has a high compression ratio .

2800 rpm....very high......they cruise at lower rpm...if I leave my Dakota in 3rd at 60 it will spin that fast....and you made my point about burning off deposits. And I said deposits not fuel. Thank you.

 

[Photon440]

If you can read it...

 

[J5 GTX]

As far as aircraft engines wearing valve guides, cylinder wear ,etc. That all depends on how you operate the engine.
The company I work for had 5 Beech Barons, twin engine, IO-520 engines. I saw that fleet go to TBO 3 separate times. That's 30 engines with a cumulative 51,000 operating hours. All but 8 went TBO without replacing any cylinders or cylinder work. (I know, you A&P's just said "ah bull****!). None received a top overhaul. (Except for 2 engines with the EQ cylinder AD. That was due to a machining error by the mfr.)
Incorrect mixture leaning will cause oil crystallizing and lead formations, that will cause valve guide problems.


Worked for a different aviation company, that replaced cylinders due to valve guide wear on a weekly basis. No joke.(lean until it runs rough and push it in 2 clicks, doesn't cut it.)
For the A&P crowd:
2300 rpm cruise, 23" Hg manifold is standard ops, here.

 

[Slap Stick]

2300 is high rpm.....I guess 8200 rpm is astronomical!

J5, you aren't the only one with that experience.

I would still like to hear from our A&Ps why is lead added if it is detrimental.