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MG TD TF 1500 - Unleaded Head Conversion

Although I'm specifically writing in regard to a TF1250 what is the general opinion regarding having a head "converted" to unleaded. A local mechanic has referred to a problem with valve seats breaking free. The consequences of this happening could obviously be catastrophic on a virtually irreplaceable item.Thoughts please.
JK Mazgaj

I have this done on every head I own. If done properly there should be no issues.
Steve Simmons

A "conversion" to use unleaded fuel means only that hardened valve seats are installed in the head to avoid the valve recession that is said to take place when using today's fuel that lacks the lubricating lead.

Opinions differ whether hardened seats are even necessary. There are those who argue that it's a fairly inexpensive job, and the peace of mind is worth it. If the existing seats are badly worn and corroded, seats will have to be installed anyway, so why not use hardened ones?

But on the other side, there are those who argue that if valve recession has not already happened (and I can't say I have ever seen an XPAG head where it had), it probably never will, considering the annual miles we drive our cars. If you are a vigorous and frequent driver over extended distances it probably makes sense to do, but for the average driver my personal opinion is that it is unnecessary.

I recently pulled apart an engine I rebuilt 55,000 miles and two decades ago (originally rebuilt due to overall wear, this time it was worn-out cam and lifters), and there was no noticeable recession on the un-modified cylinder head (see above comment on mileage). And, of course, if machine work is imperfectly done and a hardened seat comes loose, the head will indeed be damaged/ruined, and probably a piston and maybe a valve will break, causing major distress.

So my approach is that if the head is worn or if seats need to be re-done anyway, I have hardened seats installed. Otherwise, if the existing seats can be happily ground, I don't bother with hardened seats.

Of course, your opinion may vary...

Tom Lange
MGT Repair
t lange

back in 1985, when my son and I rebuilt the TD we had hardened inserts installed. By then the engine had been sitting for 16 yeas. The speed shop said the valve seats were pitted and not usable.
We also had bronze guides installed.
When I went to put the head together, one of the seats fell out!.

I was being laid off so the head went on with a mental note NOT TO RUN IT!

Segway to 2014. The was was pulled and semt to Dave Jacks. (https://davejackracing.com/heads)
He had custom inserts made in California and installed them. He made sure the guides were aligned and took a chip off the head.

So far I have only 61 miles on the rebuild. No issues although I don't like the valve clatter. I will try again to set the clearance, when I get back from the hospital. (Electro-conversion, nothing really serious.)

(Trouble is I have no idea of my cam grind I have been setting at 0.015, but I think I will try 0.012.)

My point is, if you have it done, be sure of the shop first. XPAG's are not 305's

Jim B.
JA Benjamin

If you have seat recession, then have new valve seats fitted. If you don't, there is no point unless you plan on a huge mileage. Seat recession is a slow process and most classics don't do enough miles to matter.
Dave H
Dave Hill

My head has hardened seats fitted 20 years ago because of damage and have had no problems.
My 1954 BSA motorcycle has not and is a much more advanced motor regularly revved way beyond an XPAG. I have used Castrol Valvemaster for 15 years with no sign of seat recession so for peace of mind that would help.
If you replace the seats make sure you use a machinist used to XPAG's
Ray TF 2884

Ray Lee

I’m a long way from home so can’t check my records but, from memory, after lots of measuring and discussion with the machine shop I use, we decided to keep the lightly worn guides and inlet valves but fit new larger exhaust valves with seats to match. They suggested that seats were unnecessary on the inlets and I suppose this strategy reduces the chances of a valve seat dropping out by 50%!
Having seen what the pieces of a valve seat look like when embedded in a piston crown of my brother’s Morris Oxford it is something I would like to avoid.
Chris
C I Twidle

Tom. The valve seat recession on my XPAG was dreadful, so new seats were essential. Unfortunately I took no photos. However a high mileage seems likely as I am on +0.080" on the bores. B&G did mine (or whoever they contracted it out to).
Dave H
Dave Hill

JA the valve clatter I tried to get rid of was actually loose push rod ends. Got a new set from Tom Lange and have been running like a fine sewing machine for a few years now.
Peter Dahlquist

Thanks peter, If setting things at 0.012 does not work I will try that.

Jim B.
JA Benjamin

Jim, Make sure the rocker arm tips were resurfaced and are not cupped out. That is common reason for clatter- the feeler bridges the concavity and you are not setting actual clearance. George
George Butz III

This thread was discussed between 08/07/2018 and 09/07/2018

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