Unleaded Conversion

[William2]

I am having my Elan SE spec engine rebuilt and I'm wondering whether to bother with unleaded valve seats, etc. Some people say that if the car is for road use only then the standard valve seats are perfectly good enough to use with unleaded petrol.Is the engine likely to pink using unleaded fuel with standard compression. I know this is a complex issue but I would be grateful to hear owners comments.

[jono]

You may need new seats anyway due to valve recession.

If you're re building the engine I would say it's a bit of a no brainer as the cost is going to be fairly marginal in the grand scheme of things.

Jon

[AHM]

technically they will be fine.

The questions are:
a. How much life do they have left? - how thick are the shims? - you can't grind the valve stems - make sure your mechanic knows this.
b. what sort of engine rebuild you are doing - a freshen? or a chequebook job?

To have all done is about ?250 - money saved if they are good to go again.

[UAB807F]

I think I'd go with Jon, if you've gone to the trouble of removing the head and having some head work done, then I'd do it myself.

I'm on uncertain ground here, but I don't think the OEM valve seats are related to engine pinking, I thought you fitted harder seats to combat valve recession. And if only for the thought that I'd get longer between having to adjust the cam bucket shims, I'd willingly spend the money on harder seats !

Brian

[Chancer]

I doubt that the new seats would be any harder.

valve recession was only thought to be a problem with say a X/flow head that didnt have valve seat inserts, just a chill hardenening of the casting which was lost the first time the seats were recut, even then I know of many X/flows that are still running unconverted with no valve recession.

The twin cam engine already has adequately hardened valve seat inserts fitted into the aluminium casting and in my opinion they are suitable for high speed intensive use with unleaded fuels, I dont see a benefit in repacing them, on the contrary even with the best equipped and competent machine shop there is always the risk that a new seat may go walkies with catastrophic results.

Dont mess with things that dont require messing with!!!!

Happy to be proved wrong on the above.

[Jeff@Jae]

You'll probably need new valve seats due to repeat valve jobs unless the engine is very low miles. Contemporary valve seat material is much tougher than the original, soft austentic iron seats. Unleaded fuel has never been an issue on the original seats but they are soft, prone to pitting and require a rather broad 45 degree seat to survive. New seats can be done to very fine racer type seat cut profile and survive very well and you'll find that valve clearance adjustments are few a far between. The real key here is how precise the the cylinder head shop practices are. Seat bore/seat installation/valve guide to valve stem clearance/concentric alignment of all the above and precision seat cutting are the key to a great Twin Cam head. A common problem is not getting the installed valve height correct, sloppy guide fit and seats not fitted to the seat bores correctly.