Unleaded fuel effect on 1700 Super Sprint motor

[CSM]

May I gather the wisdom of some technically minded Caterham folk on the need for upgraded valve guide seats to cope with unleaded fuel in a 1700 Super Sprint Cross flow Ford unit? Is this necessary? Thanks in advance.

[Equus]

The obvious answer is to wait and see.

Rates of valve seat recession vary from car to car and driver to driver: if your driving style uses lots of revs, the rate increases dramatically.

Run it until your valve clearances close up beyond adjustment: you can fit hardened seats at that point, and it won't cost you any more than it would if you fitted them immediately.

Just make sure that you check your valve clearances regularly (which you should be doing anyway, with a Crossflow)

[V7SLR]

Do you use an additive?

[RobXjcoupe]

A regular road going engine with just a factory state of tune will need hardened valve seats fitted. I’m sure you are aware that hardened valve seats were fitted to all aluminium heads even when engines were using leaded petrol.
My old Jag engine was also fitted with bronze valve guides as the exhaust valves start to stick with the increase of heat when using regular unleaded fuel.
I was re-building that engine so the extra for the bronze valve guides was a belt and braces approach as I didn’t want to have to take the head off again.

[Mr2Mike]

Equus said:

Run it until your valve clearances close up beyond adjustment:

Letting the valves recess that much will have a major impact on performance. If the OP drives it like it was intended to be driven, then seats should be fitted sooner rather than waiting until it barely runs.

[Equus]

Mr2Mike said:

Letting the valves recess that much will have a major impact on performance. If the OP drives it like it was intended to be driven, then seats should be fitted sooner rather than waiting until it barely runs.

Yes, for sure.

Not sure it'd have a major impact on performance, provided you keep clearances within tolerance until you start to run out of adjustment, but my point was that you can assess the recession as it progresses, provided you check clearances regularly... there's no need to spend money fixing a problem that hasn't even manifested itself.

At the very limited mileages that Cateringvans typically do, it could be literally decades before the engine starts to show significant issues.