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Cylinder Head Unleaded Conversion

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Hi All, I'm after a bit of advice...


I have removed the engine from my TR2 as it is having a full respray including engine bay. Whilst the engine is out I am going to take the opportunity to get the cylinder head converted to unleaded (plus other jobs).


I believe the U/L conversion involves fitting hardened valve seats, is this just to the Exhaust valve seats or all? To do the work the valve guides are removed and replaced? Do I need to replace the valves if they are not damaged?

I am trying to understand what needs replacing as I have asked a few places over the phone and they want to replace valves, valve springs, valve guides.


The engine is a standard early TR4 unit fitted in 1975 and has done 28k miles.




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Hi Ade,


You have a PM.


Mick Richards

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The simple answer is don't do it until necessary.


Despite the hype about unleaded fuel, a road-going engine that rarely sees the upper end of the rev band will last a long time on unleaded fuel, without the need for an additive. The only reasons to fitted hardened exhaust valve seats for unleaded would be:


1. The head needs to come off anyway, or...


2. There is recession of the exhaust valves, shown by the valve clearances closing up.


If you do go ahead, it's the exhaust valve seats that need to be replaced with hardened steel. Unless seriously worn, the existing valves can usually be cleaned up, refaced on a lathe and used again. Replace the valve guides if they're worn, and it's worth replacing the valve springs as a matter of course.


When reassembling, use a genuine Payen head gasket.




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The machine shop uses the valve guides to center the tool for machining out the recess for the hardened seats and for facing the new seats. So the accuracy depends on how good the guide bores are. Given the low cost of guides, I would replace them. I fitted phosphor bronze ones which was probably unnecessary on a mildly tuned road car.


Some things, particularly if difficult to get at afterwards, and are relatively inexpensive, are a no brainer to replace........valves, springs and guides and I would take a light skim off the head face too.


Then fit and forget for at least 100,000 miles.

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If the head is off, but you elect not to go for hardened exhaust seats, resist the temptation to lap the valves.

As Nigel says, the seats are protected for a very long time by a "lead memory", pounded into the seats over the years before unleaded, and unless stressed by prolonged high speed driving you won't get recession.

But remove that thin layer of 'leaded' iron in the seat and you remove the protection.



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Nigel - where do you buy genuine Payen 4 cylinder gaskets? JJC


Are they hard to find for 4 pot TR's? Rimmers list a 'Payen Type' head gasket for TR2 - 4A:




Don't know exactly what Payen type means but said to be made on the original tooling. I've also seen genuine Payen listed on eBay occasionally.




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Mine is not converted, & I use no additives.


Still running just fine. If & when The valves recess, then I will take the head off & do something about it, but not before.



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In 1990 when I was finishing the restoration of my 1958 TR3A, I lapped in the valves (some were still the original valves with over 80,000 miles) from new. This was during the engine rebuild. Then everyone started to write about unleaded petrol burning the valves and the valve seats. I decided to run an experiment. I would run the TR on unleaded and see when I would be forced to convert the head. By this I mean 8 new valves, 8 new valve guides and 4 inserts for the exhaust valves.


I was able to drive 43,000 miles with the original configuration.


Since the conversion, I have driven an additional 72,000 miles and rarely have to re-gap the valves - maybe 0.001" every 2 or 3 years on 2 or 3 valves.

Edited by Don Elliott
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