I have never been able to find any information about when Fiat/FSO started putting hardened valve seats in the cylinder heads to cope with unleaded gasoline.
Just today I ran across a Polish site that gives this information. I have translated the information below.
Here is the original link: http://126p.co.pl/smarowanie-oleje-plyny.html

"126P to the car should be used leaded petrol 95. Due to the fact that currently the petrol stations are only available unleaded petrol, engines older than number 6621475, use the special supplements (available at every gas station). Engines from number 6621475 are already designed to burn unleaded gasoline. Fuel with a lower octane is not recommended, because it can appear dangerous for engine knock, revealing a characteristic clatter, increase engine temperature, which can lead to damage to the drive unit."

In my case both engines should have hardened valve seats. I believe the information because the cylinder head on 6739534 is in very good condition and the valve seats show no recession or wear.
For USA 500 owners, a European octane rating of 95 would be an octane rating of 91 in the USA.
John

Excellent that.
Looking at the other pages there seems to be a lot of practical info.
One of the pages refers to an optional wheel that is available which can be screwed to the generator pulley. Then a rope is attached and you can pull start in really cold weather such as Poland (and Scotland) can experience, thus making a more reliable start when the cold is working against you.

jjacob said:

Engines from number 6621475 are already designed to burn unleaded gasoline.

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MAL_3610 by Peter Thompson, on Flickr

Very interesting article - I have got a 1973 500R with engine number 0169637. I haven't had the car that long so I'm not sure if the engine is original to the car. Anyway, I know I am being a bit thick but am I okay to run unleaded fuel without additives?

Idleboy08 said:

Very interesting article - I have got a 1973 500R with engine number 0169637. I haven't had the car that long so I'm not sure if the engine is original to the car. Anyway, I know I am being a bit thick but am I okay to run unleaded fuel without additives?

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John said on another thread that this was specifically referring to Polish built 126 engines, your serial number suggests that it probably an Italian built engine as it doesn't fit those serial numbers quoted.

It's all a bit confusing as I have a 1997 engine that starts with 6------- and fits in with the correct series of numbers quoted but Peter's starts with a 9------- and doesn't fit but has Polish bits on it? Unleaded was introduced in 1986 and four * leaded banned from 87 so I would imagine any engine post 87 is likely to have hardened seat valves. The Italians stopped making the 126 in 1979, so I would imagine none of their engines have hardened seat valves unless done later by an owner as an upgrade.

Mmmmm I'm still confused.com! My car was built in '73, so assuming the engine is original to the car is sounds like I might need to use the additives. Why are these things never simple?!?

Idleboy08 said:

Mmmmm I'm still confused.com! My car was built in '73, so assuming the engine is original to the car is sounds like I might need to use the additives. Why are these things never simple?!?

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Yes, the "A5" part of the engine number means that it was made as a 594cc; so it probably is original and I think unlikely to have hardened seats.
Everyones' advice seems to be if you don't drive it much, don't worry and if you do then be ready for problems at some point.

Build date of your car means nothing. Engines get changed quite a bit in these cars by this time. Need to go by the engine number. Answer to your question is yes you need to use an additive.
John

Is there such a thing as 'soft' valve seats.

When unleaded fuel was first introduced in Europe there were a lot of scare stories doing the rounds e.g. all 'classic' car engines would need costly modifications including having 'hardened' valve seats fitted otherwise valve seat recession would occur resulting in potentially burnt valves and seats due to valve clearances rapidly closing up.

Many people found that this didn't occur to any significant degree especially with cars which covered low annual mileage and were carefully maintained i.e. valve clearances regularly being checked.
Many did find they needed to retard the ignition timing to cope with the lower octane rating of unleaded fuel, especially with engines whose compression ratio was iirc 9.5:1 or higher. Some used octane booster additives in the fuel.

However the exception was engines with iron cylinder heads which had the valve seats cut directly into the head, e.g. ohv Fords, British Leyland (Austin, Morris, MG, Triumph et al) etc. I've never encountered abnormal valve seat recession on engines with aluminium cylinder heads, which are of course, fitted with valve seat inserts. Whether the valves need to be upgraded to ones of a different material is a different question.

Also afaik, it doesn't seem to affect Japanese motorcycles built in the early '60's onwards many of which had air-cooled engines with aluminium cylinder head(s) fitted with valve seat inserts as standard. - just like the Fiat 500 etc. (I'm aware the older BMW motorcycles can have problems, some even say you must convert to twin plug heads. Hmmmm!).

So, does anyone know if there are different grades of hardness of valve seat material for engines which are used for normal road driving, (not competition)?

Al.

Al, I used lead additive for most of the 16,000 miles that I drove with the 499 engine; the latter part of this mileage was fairly aggressive. The head has inserts but even so, the exhausts have really worn down. As everyone has pointed out, this is no doubt because of my unusual high mileage and because I didn't spare the horses​. But it tells me that running without a conversion to the seats will always be a calculated risk.

F123C said:

So, does anyone know if there are different grades of hardness of valve seat material for engines which are used for normal road driving, (not competition)?

Al.

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My machine shop who has been going years advised my D head would be just fine on unleaded and there was no need to change these seats.

F123C said:

So, does anyone know if there are different grades of hardness of valve seat material for engines which are used for normal road driving, (not competition)?

Al.

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Apparently there are at least two: "Special heat treated alloys are used in the production of these inserts, the two most common being nickel/chromium and vanadium/molybdenum." http://www.burtonpower.com/tuning-guides/tuning-guide-pages/unleaded-fuel.html

Optimisim is great...it's what I was operating on; but there does seem to be a lot of technical information from generic and from Fiat sources which points at the inevitable need for special,replacement valve-seats if you want to be really sure.

The whole thing is quite an academic point for most people though; I wonder how many rebuilt classic engines even get to the point of being "run-in" given that I think Fiat set that figure at 750 miles?

jjacob said:

Build date of your car means nothing. Engines get changed quite a bit in these cars by this time. Need to go by the engine number. Answer to your question is yes you need to use an additive.
John

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So, as I have a Panda 30 Head on my engine (two cylinder engine ran from Mar 80 to Jan 86) I can be slightly more confident that the inserts are capable of dealing with unleaded But, as the engine is tuned I am taking no risks with the added Ethanol problem and am using Millers VSPe Power Plus anyway

Ian.

The answer is that older aluminum heads have harder valve seats than old cast iron heads that have the seats cut into the head.
However, when unleaded gas came along manufacturers put in even harder valve seats. These are induction hardened and usually of different metallurgy than older valve seats.
If you are using your car lightly, not driving at over 80kph (50+mph) for long periods of time, and driving less than 5000 km (3000 miles) per year, then you most likely can get by with the original valve seats and using an additive.
However, if you are running for long periods of time at high speed, driving lots of miles (like our friend Peter in Scotland) then you need modern hardened valve seats.
Also, when you examine your valve seats, pay close attention to the valve and valve seat margin. This is the width of the seat. If it is wider than specification, valve recession will occur quickly.
John