Unleaded question - sorry!

[JonB]

Hi

I run my car on unleaded petrol and so far I've done 200 miles without adding additives, which is not enough to show symptoms of valve wear. The PO said he alternated a tank with additives, then a tank without and he'd run it for 3 years. Not sure the mileage, looks like 1200 going by the past MOTs.

I have read many conflicting views on different forums. Quite a few of them say it is OK to run on U/L as the valve seats / guides will have "lead memory" which I think is leftover lead compounds deposited when the car was fed unleaded. I saw very few reports from people who'd had problems, but their cars are (I guess) mostly steel heads, and the Twink is aluminium. There is a receipt ( dated Feb 1991) that details work that was carried out on the head as follows:

• Strip & decoke
• New valve guides / exhaust seats
• Recut seats, reface valves, grind in
• Blend exhaust seats into throats
• Minimal skim, clean & reassemble

Problem is I don't know if the valve guides / seats were hardened or not - besides, exhaust only. The engine was also rebuilt at QED at some point (same owner who had the head overhauled) though there is no documentation of the work carried out. I called QED but they do not keep history, however the chap I spoke to said they fitted hardened seats / guides as a matter of course since the '80s when doing rebuilds, so there is a chance it has them. I was advised to run on unleaded and pay for new seats if the engine started losing power (or compression?).

So the question is.. should I follow his advice?

[alan.barker]

Imho the exhaust seats fitted by QED should be alright. On my Sprint which has original valve seats i just run it on unleaded 98 ron and no problems.
If you have doubts check the valve clearances to see if the seats are burning + compressions.
On a +2 it tends to be exhaust n?4 that burns it's seat first (take off for brake servo = weaker mix).
Alan

[fatboyoz]

Hi Jon,
I had my cylinder head overhauled by QED in 1991. All the valve seats were replaced. I also made enquiries in regard to whether or not they were hardened seats, and I obtained the same answer as yourself. Other people have also stated that steel valve seats fitted to aluminium heads have always been hard enough.
A test carried out by The Federation of British Historic Vehicle Clubs (FBHVC) prior to the demise of leaded fuel in the UK had these results: http://www.mgb-stuff.org.uk/lead_replacement.htm
If you read through it, you will read that the product that did the best job was Superblend. The active ingredient in Superblend is Potassium. Superblend now has a slightly different name: http://www.morrislubricantsonline.co.uk ... itive.html
I have been using Flashlube here in OZ for the last 40,000 miles: https://www.flashlube.com/en/products/v ... fluid.html
It's active ingredient is also potassium. The engineer who does a lot of work on LCQ member cars, also uses Flashlube. If you look through the website, there is an agent in the UK.

Cheers,
Colin.

Hi

I run my car on unleaded petrol and so far I've done 200 miles without adding additives, which is not enough to show symptoms of valve wear. The PO said he alternated a tank with additives, then a tank without and he'd run it for 3 years. Not sure the mileage, looks like 1200 going by the past MOTs.

I have read many conflicting views on different forums. Quite a few of them say it is OK to run on U/L as the valve seats / guides will have "lead memory" which I think is leftover lead compounds deposited when the car was fed unleaded. I saw very few reports from people who'd had problems, but their cars are (I guess) mostly steel heads, and the Twink is aluminium. There is a receipt ( dated Feb 1991) that details work that was carried out on the head as follows:

• Strip & decoke
• New valve guides / exhaust seats
• Recut seats, reface valves, grind in
• Blend exhaust seats into throats
• Minimal skim, clean & reassemble

Problem is I don't know if the valve guides / seats were hardened or not - besides, exhaust only. The engine was also rebuilt at QED at some point (same owner who had the head overhauled) though there is no documentation of the work carried out. I called QED but they do not keep history, however the chap I spoke to said they fitted hardened seats / guides as a matter of course since the '80s when doing rebuilds, so there is a chance it has them. I was advised to run on unleaded and pay for new seats if the engine started losing power (or compression?).

So the question is.. should I follow his advice?

[JonB]

OK, here's another question.

I have a cheap boroscope here. I'm thinking that if I push it inside one of the intakes (carbs off) or exhaust ports, I may be able to look at the valve seat by turning the engine over. Will I be able to tell by looking at it? I'm guessing not but thought I'd ask anyway.

[Orsom Weels]

Hi Jon,
I had my original seats re-cut & new guides fitted in the late eighties & have been running on 95ron unleaded without any additives since 4 star disappeared from most forecourts, probably well over 25,000 of the 40 odd thousand miles I've done since the rebuild. Never had a problem with the seats, but it's about ready for a new set of guides now, I get a BIG cloud of smoke on start up. I set the ignition timing in the same way I do on my old motorcycles which have no timing marks & little info on figures anyway. I add a little advance until the engine just pinks pulling up a hill, then back it off a degree or so. With modern fuels, the original factory settings should only be used as a starting point anyway. What I have discovered is with ethanol free unleaded I had to retard the ignition about 3-4 degrees, but with ethanol I have had to add about 2-3 degrees back on, so closer to factory figures again.
I think a few people made a lot of money out of a lot of people by spreading scare stories about valve seats & unleaded fuel, A good number of us in the Norton world have done seriously high mileages on Commandos without any head mods at all with no issues. We were all warned of the impending doom, but chose to ignore it & see for our selves. The only things I have know to have problems are engines where the seats are cut directly into the cast iron head, & even then it's taken years & lots of miles to happen.

Regards, Tim

[The Veg]

I think a few people made a lot of money out of a lot of people by spreading scare stories about valve seats & unleaded fuel, A good number of us in the Norton world have done seriously high mileages on Commandos without any head mods at all with no issues. We were all warned of the impending doom, but chose to ignore it & see for our selves. The only things I have know to have problems are engines where the seats are cut directly into the cast iron head, & even then it's taken years & lots of miles to happen.

I think the truth is somewhere in the middle, depending on the engine in question. This issue was quite real for BMW motorcycles (my other obsession), many of which saw serious valve recession on unleaded. Thank goodness their heads are so easy to remove; most of them that old have been converted by now.

[JonB]

Thanks all, I am reassured.

In the UK there is Unleaded (RON 95) and Super Unleaded (RON 98). Is it worth buying the higher octane Super?

Slightly moot point right now as the car is up on stands with no front suspension!

[alan.barker]

Hi Jon,
on my classic cars here in France i use RON 98 when i can get it with no problems.
Lotus Elan Sprint, TVR 3000S and TVR 3000M
Alan

[nmauduit]

In the UK there is Unleaded (RON 95) and Super Unleaded (RON 98). Is it worth buying the higher octane Super?

octane rating selection is primarily based on engine specs, mainly compression ratio, to avoid detonation or knocking

[Chancer]

We were all warned of the impending doom, but chose to ignore it & see for our selves. The only things I have know to have problems are engines where the seats are cut directly into the cast iron head, & even then it's taken years & lots of miles to happen.

Regards, Tim

Amen to that!

All original and OE valve seats inserts were hard enough to not need the secondary protection of leaded fuel.

The engines like the X/flow that had seats cut directly into the cast iron only needed the tappets resetting one time only and the then larger surface area of the seat resisted further recession, the few problems were always where the tappet clearances were already tight, were not readjusted and a valve burned out through not closing properly.

It was an early millenium bug false news money spinner

And its still making loads of money for the snake o?l additive sellers!

[Orsom Weels]

In the UK there is Unleaded (RON 95) and Super Unleaded (RON 98). Is it worth buying the higher octane Super?

As stated in my earlier post, I always use std 95 octane with no additives. I have tried some of the 'super' 98 octanes & various additives, but I can honestly say that I haven't been able to tell the difference in the way the cars run, so for me, no, it's not worth the higher cost of the 'supers'.
Experiment with both 95 & 98 octane & various brands & see if you notice a difference, then try some of the additives as well, you can then decide for your self. As has been said, compression ratio has an effect on what your particular engine will require & be happy with.
Regards, Tim

[tedtaylor]

Here in USA, I've been using "regular" unleaded at 87 octane. Am I doing any harm to my original engine build?
I always thought the modern regular fuels far outweigh the fuel composition of 40 plus years ago.

[denicholls2]

Unless you're an obsessive personality, there's another way to look at this regardless of whether recession is a problem or not: The work involved is basically the same as a head overhaul, and you will definitely know when the work is needed, if ever. The rest of the engine is not going to be ruined by the valve seats going somewhere warmer than a combustion chamber in a handbasket.

So save your money, drive your car, and hope for the best. Worst case, your car will need a head overhaul someday. If you're not spending money on additives, you should have it in the bank when you need it. With the expected lifetime of a set of Twink valve guides, it's just something you check when dealing with those wearing out.

[JonB]

Yes, I do agree. I never liked the idea of using expensive additives. Anyway, I've overhauled heads before so not too worried. Might have to get an engineering firm to press on new guides/seats, though.

I should do a compression test so I have a baseline.

[denicholls2]

Tedtaylor, 87 octane is fine as long as you are tuned for it by retarding the spark to avoid knocking or pre-ignition. Typically, this detuning costs more than a few horsepower, which is why Lotus owners usually don't go there. It also has a negative effect on fuel economy that serves to offset the cheaper fuel to some extent.

My Europa's 10.5:1 compression ratio won't let me get away with regular and still climb hills.

Running on low-octane fuel and allowing substantial knocking can advance valve-seat recession and in extreme cases blow a hole in a piston. So tuning to low horsepower makes sense if you're cheap, but allowing for lots of detonation doesn't.

Occasional detonation, like lugging a bit climbing a hill before you hear it and downshift shouldn't be a big problem. I'll opine that if you hear detonation above about 3,000 RPM or frequently below that engine speed, then you have an octane or spark advance problem (or both) and need to take corrective action.

Here in the U.S., Congress has thrown an expensive bone to the corn farmers by requiring alcohol in gasoline at varying percentages depending on where you live. While in general this results in accelerated engine wear and is unconscionable for that reason and because it offers no real benefit except to the corn industry, this fuel is higher in octane than straight gasoline.