Posted by R Davis on Tuesday, December 19, 2000 at 02:43:54:
In Reply to: Valve Guides/valve seats/overhaul/leadedgas posted by John J Conrardy, D.C. on Sunday, December 17, 2000 at 09:52:23:
I also agree with Gordon,and anyone who knows his back ground would do well to take heed to his opinions and advice. Before me set two(2) books
(1.)The automotive repair manual:1950
(2.)The automobile engine:1961
Both books are full of data to support Gordon's statements.They also contain formulas and info that one could pert near start from scratch and build an engine,refine and test fuel,and more than I care to mention at this time,Very extensive info!
Book(1.) Octane rating:The ability of a fuel to resist detonation is called its octane rating.It is claimed that a straight run gasoline from asphalt base crude oil has better antiknock value than one from paraffinc base crudes.Cracked gasoline generally has less tendancy to knock than straight run gas.All marketed gasolines are a blend of straight run and cracked gasoline,so unless their blending is controlled,their antiknock qualities will vary.If the octane rating of gas is naturally low,the fuel will detonate as it burns and power will be applied in hammer-like blows.The ideal power impulse is that which pushes rather than hammers against the piston.Engines with a compression of between 5:1 and 6:1 will usually operate satisfactorily on a fuel having a octane rating of between 65 and 75.As the compression ratio increases so must the octane rating of the fuel used.
Antiknock Compound-Tetraethyl Lead:Detonation may be overcome to a great extent by mixing an antiknock compound with the gas used for fuel. the most commonly used compound is called tetra-ethyl lead and gas so treated is referred to as "Ethyl Gasoline".
Book(2.)States:Ethyl gasoline,an important additive placed in present day fuel is a chemical mixture of tetraethyl lead,ethylene bromide,ethylene dichloride,and a small amount of soluble coloring.It has been found through experimentation that an Ethyl mixture added to engine fuel reduces the detonation at higher compressions.The Ethyl fluid does not speed up or slow down the burning process,but for some unexplainable reason,it lessons the detonation.Before a fuel can be called Ethyl or high test,it must first perform satisfactorily with a minimum octane rating.
Higher Compression:When fuels are used that allow the engine to operate at its highest compression and most advanced spark position,the engine will run at a slightly higher temp.Burning gases at their highest possible compression results in a more forceful and power producing push,and this greater amount of energy expended produces more heat.It is poor economy to burn a low test fuel in a high compression engine with retarded spark to reduce knocking.The car will give better mileage and performance if the spark is advanced to its greatest possible extreme for the high test fuel recommended for that engine.
Valve and seat lubrication was just a added side effect of the type lead used.The compounds used today as a lead substitute for lead as an antiknock additive are very corrosive to the older valve seats and as the hot rod mags suggest,have your older engine heads (or blocks) retro-fitted with hardened exhaust valve seats to extend their life due to the corrosive nature of modern unleaded fuels.I have read that these new compounds are just ,if not more dangerous than the once used lead,but dissapate from the atmosphere much faster than lead.The years past unleaded or "white gas" is not the same as todays unleaded.
These books contain so much more tech info I wish I could Or had the means of up loading it for all to search through and down load.
When folks ask for answers to tech questions,give factual info you can backup or at least say "this is what I heard or was told or always believed",not hearsay or old sit around the stove at the shop bull.Your well meaning friends,dad or granddad could have been passing on misinfo they got from a bad source themselves.