Unleaded conversion

[Jono]

Hi,

I am building a motor for road rallying based upon a 1300GT engine.

I would like to do some light porting myself and have been thinking about the valve seats. I have built a few Lotus twin-cam engines and had hardened seats fitted along with new stainless steel valves and cosilbro guides. However in Lotus circles there are divided opinions on the strict necessity for fitting hardened seats. The heads are expensive though so I have tended to take a comprehensive approach.

Paul Exon has done all my Lotus head work and I will probably have him do the machining for the short A series motor - he's ex MED I understand and his work has always been first rate.

An A series head is a very different animal and, whilst simpler, I am less familiar with it.

So, what is the best advice - new seats and valves or can I get away with some porting, cleaning valves in a lathe and re cut the seats? The head, valves and seats are actually in good condition. My thoughts are that pulling and re doing a mini head is easy and cheap so this approach might be worthwhile on the basis that I don't mind getting my hands dirty again down in future if I have to pull the head.

What compression ratio would you advise to skim it to?

Thanks in anticipation.

Jon

[Andrew1967]

Hi Jon,

I've been running my 850 and 1275S engined cars unconverted for several thousand miles (and without additive) and have not to date had any problems with valve seat recession. If anything, the valve clearances have got wider in the usual, to be expected, manner.

I have similar thoughts to you. A Series heads are easy to lift off and convert later IF the need arises.

Highly recommend running on Super Unleaded, even the 850.

[Jono]

Many thanks for your comments Andrew

I would welcome any views on CR

Jon

[Spider]

I think there was some discussion not long ago on unleaded fuels and whether to fit hardened seats or not. It can depend on what country you are in and the blend of fuels available.

I always fit them these days and never had an issue from having done them, however I have and I've seen many issues issues from not having them. Mind you, if they are not fitted properly, you'll wish you'd never heard of them!

Another small point is that from about 86-ish, they were factory fitted to all Minis. If it wasn't needed / warrented, they wouldn't have fitted them.

In regards to CR, need a bit more info, like what fuels are available to you and what Cam are you considering fitting?

Rather than work to a Static CR, I work them out on Dynamic CR.

[carbon]

Jon,

If the valve seats in your head are in good condition then personally I would leave them and run using a good additive and decent petrol. I use Castrol Valvemaster with the Shell 99 octane.

Also before doing any skimming to the head I would strongly recommend measuring all of the combustion chamber volumes, to make sure are exactly the same capacity (or at least within 0.1cc). Best doing this after you have cleaned and lapped in all of the valves.

The last 1300GT head I worked on had one of the chambers almost 0.5cc less than the rest, and had probably been like this since it left the factory. Now runs a lot smoother...

[andy1071]

As has been said many times in many places, if you re-cut the seats you are more likely to get valve recession.
-I have run/thrashed an old engine on unleaded without any additives, and had no problems, but if I re-built a head, I would always have inserts installed.

-The use of the engine also affects the valve recession: lots of high revs is not good -but most people don't use their classics to the full (apart from all Mini owners, of course... )

Regarding seat inserts: "all inserts produced over the last 60 years (since WW2), for all alloy-headed engines, are hard enough for unleaded, so do not need to be updated" -this was the feedback from the chief engine designer at Jaguar some years ago, when asked.

[Spider]

I think there was some discussion not long ago on unleaded fuels and whether to fit hardened seats or not. It can depend on what country you are in and the blend of fuels available.

viewtopic.php?f=3&t=9827&p=74537&hilit= ... ats#p74537

Another aspect that comes to mind in regards to weather seat erosion will occur or not is combustion temps and in particular, exhaust valve temps, ignition timing can have quite an effect here.

[surf-blue-850]

An engine run on leaded petrol will have 'lead memory' and will run on un-leaded fuel for some time before recession occurs.

Grind the valves and seats and the memory is lost, the valves and seats will happliy wear away pronto.

Do the job properly, fit new guides and seats and forget...