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MG TD TF 1500 - Thermal event # 2

Too lean AGAIN! I melted another piston on the way to Gatlinburg. I will now go richer (Again) & use a thermal barrier coating on the piston crowns.Also looking for Stu Keene, ( R. e. piston failure) Lean Len
Len Fanelli

Sorry to hear about that, Len. I have two email addresses for Stu - and . Not sure which is the latest. Stu's car and mine were on the assembly line together.
Bud Krueger

Wow Len

I burned a set of valves when I put to lean a needle in my TD and tried to go over the grapevine pass going to a GOF in San Diego in the 70's, but a piston?

Is there a reason you are not running stock? (i.e. a souped up engine)
Bruce Cunha

Yes Bruce, it not stock. A Chet Herbert Roller cam, big valves, head work, 1 1/2" carbs., w/ H1 needles, #200 closed, #3oo open valve springs. Etc.... a few people with supercharged T types have have been supprised how well it runs.
Len Fanelli

I would try GJ needles, I use these on my TF 1500 with 9.5 comp ratio ( stage 2 tuned) 74 HP at 5000 RPM.
The H1's could be too lean at speed.
Don Harmer

I used to do a lot of my own maintenance on my 275 GTB/4 Ferrari (regrettably, sold a few years ago - ditto my 250 SWB).

The Ferrari dealer once showed me the resuts of "doing one's own maintenance" with a melted piston fused into the cyl. wall of Lampredi engine (Ouch!), as a result of running it too lean and a bit too much advance.

I learned a lot from that. I ran into Len at Gatlinburg, and in fact, he helped out one of our Rockburnians who was having ignition problems. Many thanks, Len.

Timimg, plugs and mixture can be crtitical, especially when running the engine near its design limit, like Gatlinburg where the temp ran to 36° for several days running.

The WSM specifies for the XPAG and the XPEG
GJ for Normal
HI for rich
Gl for weak (lean)

Like Don, I run GJ in my hotted-up XPAG - nary a problem; and N5C plugs set to .028

Gord Clark
Rockburn, Qué.

Gordon A. Clark

I've been told that the spark can be advanced 6-10degrees due to improvements in gasoline. Is this risking overheating the engine?
Russ Oakley

From what is see, the H1 needle is richer than the GJ, wich i took out. The LS1 seemed too rich, i may try a # 5, & perhaps an O2 sensor in the front pipe.
Len Fanelli

Hi Len, sorry to hear about your meltdown. When you get it going, maybe do an old fashioned plug color check. I don't think it is as accurate as it was with gasoline of old, but it still gives you a good idea. I had a valve briefly (and luckily) stick on the way home from the GOF here. The only thing I could find was the front two plugs were really white and had been running way too lean and hot. Don't know if my carb efforts fixed it yet, as I decided to redo the car and it is all over my garage at the moment. George
George Butz


I think this applies mainly to engines equipped with solid-state ignition; the thinking being that because it is more responsive, it can fire at full compression.

Gord Clark
Rockburn, Qué.
Gordon A. Clark

I am simply amazed that you can burn a hole in a piston in the XPAG engine.
What are you guys doing to this little, mild HP engines........running them with NO2.

I have heard of burnt pistons in racing engines with high compression heads, etc. But the XPAG!
These are'nt sophisticated engines, they are vintage 30"s stuff, very low tech.

My 54 year old TF has never had the carbs fiddled with, and still has the original points in it. Sure it runs a little rich, hardly ever needs a choke. It never overheats and runs like a dream.

Timing....... I set by the old "up the hill in 4th" 'till it knocks a bit, and then a back it off a tad. Tuned to the fuel (regular Mobil)I use.

Colin Stafford

That would explain it Len

Way over my knowledge level. I am still having problems figuring out why I have no idle oil pressure in my rebullt (stock) TD engine.
Bruce Cunha

Geeze Len,
You got a seriously hot engine, proof of the old adage that better breathing = higher rpm = more power. I guess you are running at 5500/6000 rpm regularly? What about the other bits that tend to fly apart at 6000+ steel crank? solid little end?
On needles have you tried the A1 which was the prototype TF 1250 needle in the H4s?
TD/C 7822
G.D. Smith


What would be the estimated Hp output with your current configuration? My assessment is that a well tuned setup can match a supercharged motor, at the higher end of the rev range.
P S Falconer

Years ago I bought an exhaust gas analyzer. It only cost a couple of hundred dollars and has been really useful over the years. You can get a very accurate idea of mixture, even drive around with it hooked up.
Would be a good investment if you are messing around with a modified engine.
Regards, Richard.
R Payne

Russ, what you want is 34 or so, degrees total advance, about 5 or so degrees advanced static. G.D. I don't quiet run it that fast, on a regular bassis, but almost. Stock, later type crankshaft. No brains & a big foot. At the Nova Scotia GOF hill climb, a member told me, I used to run my XPAG that hard, untill i broke 2 crankshafts!A1, #5, #6 & fx needles may be in the future, thanks for the A! tip.P.S., i doubt if it has as much HP as a supercharged one, in propper tune.
Len Fanelli

I've had a eureka moment on your lean problem - fair chance it could be fuel frothing in the float chambers!! What put me onto this is a reprint of V W Derrington ad for tuning mods in the latest issue of TTT No 16 see P 23
here is the URL for the TTT index
Derrington advises for 'Racing Tuning' - "The float chambers should be flexibly mounted to prevent fuel frothing"
You will recall also that fuel frothing was the Achilles heel of mga twin cams running on SUs - massive weakening of the mixture during high rpm frothed the fuel and melted pistons. I recall an article in (I think) Safety Fast about 2 years ago detailing a mod. Annular recess machined in the face of the inlet manifold (where the carb mates to) and a beefy 'O' ring was set in the recess.
Dont know of a source of flexible mounting for float chambers, but a fellow forum buddy may be able to help?
This could be your answer?
Good Luck
Graham (Honorary Dave)
TD/C 7822
G.D. Smith

Len/Graham - in my recent project of rebuilding the MKII carburetors that turned out to be MGA carburetors I ran into something that you might want to consider. The float bowls for an MGA are mounted via a rubber bushing, whereas the MKII uses the standard bolt/washers as used with H2s. You might want to try the MGA bowl mounting. The project is at .
Bud Krueger

Bud, my carbs on my TD are mounted via the MGA system. I always assumed it was because a PO decided he wanted better sealing... Now I wonder if he wasn't trying to acheive something else! You can learn more here by accident...

the neoprene gasket system is visible in this shot:

Dave Braun

This thread was discussed between 16/07/2006 and 08/08/2006

MG TD TF 1500 index

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