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Concensus on unleaded fuel

Simon.AU

Enthusiast
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I did start replying to Steve's reply in the R4 upgrade topic, but figured it would be going a bit too far OT.

What is the concensus on unleaded though? On my R4 with a 1964 type 800-01 three bearing motor, with 8.0:1 compression (checked when rebuilt, very close to) that has been run exclusively on 91 octane unleaded with no additives since it was rebuilt 20,000 miles ago. It has been used in extremes from town to fast intercity trips (500-800 miles at a time, around 60-70mph).

I've also got a 1975 R12 with 810-05 Sierra motor, basically a "big block" 4GTL motor. That has been run exclusively on unleaded for the last 20,000k's (12,000 miles), mainly as an unleaded experiment on 98 octane with no additives, again in a number of extremes, and again no signs yet of VSR.

I've tried cross referencing things like R5 Series 1 heads, but have drawn a blank as I've not got a parts catalogue for the US Le Car unleaded versions. Things like the Renault 15/17 used a completely different head for the US market unleaded versions, and valve seats are not listed separately so that didn't help either.

Hence the using of my 12 as a personal unleaded test bed, also no pills potions, lotions, or Ebay sourced magnetic additions have been added on the 12, it is basically stock with nearly 300,000km's on the clock. The motor having been rebuilt 120,000k's ago, the valve seats were unchanged, but new stock valves were installed at that time, and it was still running on leaded petrol.
 
I phoned up a Renault service department for the official view. They didn't seem to know. They were aware that timing might need to be retarded by around 4 degrees and suggested an additive for valve seat lubrication to be on the safe side.

Cars most vulnerable to valve seat recession were the ones with cast iron heads (and hence cast iron valve seats). The Renault engines have aluminium heads and a valve seat insert of a harder material. These inserts tend to be quite hard, so unleaded is generally OK for cars with aluminium heads.

However... I had a valve burn out on an engine after a 4,500 trip flat out around Europe a couple of years ago. I haven't pulled that engine apart yet, but a previous engine (run for 15,000 miles on unleaded) had a burned valve but the valve seat was still usable.

There are other reasons for burning valves - the lean mixture that R4s seem to run would make for high upper cylinder temperatures. I believe unleaded further increases temperatures.

Not an authoritative answer there. My own approach is to use unleaded without additives and avoid driving everywhere at maximum speed. A safer approach would be to do as the dealer suggested and use one of those octane boosting and valve seat protecting additives (phosphorus based not manganese based as manganese can turn the petrol into jelly if given enough time).

:mrgreen: :mrgreen: :mrgreen: :yellowre:
 
My experience with my '75 R4,800-01 engine fitted with the "later" type head (with the cast-in pushrod guides).I ran on 95 RON unleaded for 30.000 kms then overhauled the engine.No signs of valve/seat wear,however I put on a set of four exhaust valves I had (genuine Renault) and lapped them on the seats,no machine grinding.I shaved 0,4mm off the head (warped due to overheating) and assembled the engine with otherwise stock settings (ignition timing and valve gaps).I have done around 40.000 kms since then,again without anything alarming happening.No pinking,normal temperature and no decrease in valve gaps (I check them every 10.000 kms).Not much top speed driving,mostly city traffic.I think original valve seats are safe with unleaded,beware if someone replaced them with cast iron ones at a head repair.
 
I was speaking to a Hillman Imp owner in the pub last night. Apparently Imps have aluminium heads with valve seat inserts but they can suffer from valve seat recession.

Imp owners reckon the problem is heat dissipation from the exhaust valves. Lead in petrol improved the contact between the valve and valve seat, letting the heat transfer away a little better.

Their fix is to change the valve guide from steel to bronze to improve heat dissipation. Not sure what material newer Renault 4 valve guides are made from.
 
I have never seen a R4 head with bronze valve guides, be it 845 or 1108cc (maybe the latest ones?). From my knowledge,lead (more accurately tetraethylic lead) makes a coating on the valve-seat contact face (with use) that prevents the two parts from being "welded" together under the very high temperatures that they have to withstand.This "welding" makes small pieces of the seat break when the valve opens,producing seat wear (generally valves are made of tougher materials for a number of reasons).The way to reduce this is to make the seats of a material with better properties at high temperatures ("hardened valve seats") or even to harden the valve seat area only on a cast iron head (induction hardening-that was the way some American heads of the '70s were made). Actually, putting good quality valve seats had something to do with the manufacturer wanting or not to invest money on engine longevity,I think.Renault engines seem to have good material quality throughout. Fiat Twin cams of the same period,for example have VSR problems running on unleaded, even though heat dissipation is way better (cross-flow head,larger valves,better head design etc).I don't think British engines of the '60s and '70s had very high material quality, I have seen extensive VSR on all 8 valves on an early MGB engine running on leaded petrol.Also, engines designed to run on unleaded "by default" were aircooled ones since their manufacturers took a lot of precautions in material selection to compensate for the higher operating temperatures and worst heat dissipation.
 
switched head

Hey guys, my Rosy had her head switched in the past from her original 850cc to the earlier 747cc. Will this cause a problem when using unleaded?
 
I don't think you will have any problems.Since 747 and 845 engines were being produced at the same time, they must use the same valve seat materials (which is known to be OK with unleaded). Of course this does not apply if someone replaced the exhaust valve seats in the past and put cast iron ones.
 
In my case there were no problems with regular unleaded (the stuff we get here in Colombia). After 300.000km (some 180.000 run on unleaded) and one or two overheats because of a coolant leak. I had the engine disassembled for overhaul and there were no signs of abnormal wear or damage on the seats or valves, but they were replaced anyway. During those 300.000, very often I went as high as 5500rpm and did a lot of high speed driving.
Unleaded with no aditives sounds OK to me.
I also have a 1974 R12 1.3l with 180.000km of which maybe 80.000 were run on regular unleaded. It's doing fine as well.

Simon: would be nice if you came by and said hello on our R12 site: http://renault12.esarmiento.com
 
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