Unleaded Conversion??

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Unleaded Conversion??

Post by SteveW » Thu May 21, 2020 8:54 am

I thought that I would post this question hear rather than clutter up my engine rebuild thread.

It's a simple question but might provoke debate. Is it worth going to the expense of getting the head converted to run on unleaded fuel given that it will be driven as a classic and not raced hard or for high mileage. Are the fuel additives any good as an alternative?

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Steve Simmons
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Re: Unleaded Conversion??

Post by Steve Simmons » Thu May 21, 2020 8:58 am

Personally I would at least do the exhaust valves, but there are those who say it isn't necessary. The expense isn't that high compared to having to pull the head and do it later. Just my opinion though.
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Re: Unleaded Conversion??

Post by timberstone » Thu May 21, 2020 9:57 am

The last 2 heads that were done recently had 1 with and 1 without the conversion.
The machinists in both cases said the conversion was not necessary, but the 1st was done from inertia.
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Re: Unleaded Conversion??

Post by timandgerda » Thu May 21, 2020 1:09 pm

I had mine done at the same time as the head was skimmed - it wasn't too much to get it done at the same time and the lapping in of the valves was better than anything I could have done at home (I have been building engines for 45 years but don't have the tooling that the engine shops have). I had to 'blue check' them just because that's me and they were perfect!

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Re: Unleaded Conversion??

Post by Ray White » Sat May 23, 2020 6:00 am

The withdrawal of tetraethyl lead from petrol has led to a belief that ALL engines need to have their valve seats replaced with hardened inserts (Stellite) in order to prevent valve seat recession. This is not necessarily the case. Lead also helped as an anti knock agent at a time when engine development was enabling cars to run with higher compressions. As a general rule, I would say that if an engine was designed before Thomas Midgley developed leaded petrol in the early 1920s then it will not require the fitment of hardened valve seat inserts.

I believe the engines in our cars were intended to run on leaded petrol. Consequently, if the car is to be driven as intended - even with slightly retarded ignition - then the head should have hardened valve seats.
Last edited by Ray White on Sun May 24, 2020 2:44 am, edited 1 time in total.

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