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MG TD TF 1500 - Burnt out Inlet Valve?

The TD started to sound rough when I first start and after a few seconds I hear a 'click' and she runs fine.
It sounded like a valve snapping back into the seat. I figured the value guide was a little tight.
Then yesterday the engine made a rough top-end noise from the valve area, I popped the cover and everything seemed to be in order. After about an hour the breakdown man arrived and we fired her up, it sounded ok again and, after I told him of the little 'click' sound he agreed and said the valve seems to have gone back into place.
I drove home ok and popped the head and this is what I've found, the head had hardened valve seats fitted 3,000 miles ago, I've not removed the valve but the seat looks damaged. I'm taking it to my machine shop tomorrow to see what they say but has anyone seen anything like this before?


Cliff Harvey

Running lean? Intake leak? What does the plug look like? I'm guessing white.
David
D. Sander

Hi David,
Strangly no, brown centre with a slightly sooty outer ring, so I'm guessing slightly rich?
Cliff Harvey

Cliff,
It is the intake valve? How tight was the valve in the valve guide? How loose was the valve adjustment? How tight is the tappet in the bore? My guess would be either a tight adjustment or a sticky valve causing hot combustion gasses to burn the valve. The clue is the fact it only went a few thousand miles.
David
D. Sander

A TD with a "round hole" head! It's an exhaust valve, a very burned one at that.

If there's an insert, it isn't obvious from that photo, but you'll know soon enough. Could be a chunk missing under the valve. Hard to tell from picture.

Is there any indication that it hit the piston?

It could be an illusion from your flash, but it appears the valve is not centered on the seat.

When you get the valve back, chuck it in a drill and spin it to see if the head wobbles- bent.

Fortunately, the seat doesn't appear wire drawn and can be cleaned up.
JRN JIM

It's the inlet valve. The tappet is very slightly tight in the bore. I had hardened seats fitted. The bore seems ok but the top of the piston is clean compared to the others but there are little bits of metal embedded in the piston, presumeable from the insert.
Cliff Harvey

Did your machine shop fit bronze valve guides? This is common when unleaded seats are fitted. I had these fitted to the engine in my Lotus but they were reamed to the same clearance as conventional guides. Bronze expands more than cast iron and a greater clearance is needed to prevent the valves sticking and potentially burning.

Jan T
J Targosz

The valve with the part burned away is tan in color, while the other is black. 99.9% of the time the tan one is exhaust. I have never seen an intake valve burn, always exhaust? What cylinder # is it? George
George Butz

I'm pretty certain the bronze guides were fitted so this could be a possible cause of sticking.
George the valve is number three from the back, inlet I think.
Cliff Harvey

Inlet. They run EIIEEIIE from front to back or from back to front. Cheers
Peter TD 5801
P Hehir

Well, that must be the .01% intake that is tan. I too have had a problem with valve sticking with too tight new bronze guide. That was an exhaust, and I had some gunk in the jet causing really lean condition/heat on that cylinder. George
George Butz

Double check the vavle, it is smaller than the other one, right? The spark plug is located closer to the intake than exhaust.
If an intake burned that bad, it would backfire through the intake, very unpleasant.
JRN JIM

looks off center to me like its bent. if it was timing I would guess more than 1 valve would be sad. if it was 1 guide then that would be bad luck ... might be wise to check the follower as well as the rod/tappet/spring?
mog

Maybe we are looking at the number two chamber Jim. The description of "3rd from the rear" "inlet valve" and the location of the spark plug opening doesn't match.

MG LaVerne

OK, big mistake it was the exhaust valve doh and double doh, sorry guys.
I've taken the head to my machine shop, he removed the valve by tapping it from the top, the guide was really tight, not as he built it 3,000 miles ago.
The insert has a chunk missing, something he's never seen before.
From the look of the head he reckoned that the head gasket wasn't making a good enough contact with the head itself around the chamber and thus water was getting into the two rear-most chambers and this is what was the cause of the destruction. I don't know but when I got home I checked the head gasket and it seemed to be upside down, this is to say the raised lip that goes around the edge of each chamber was facing up. According to my machine guy this should face down with the smooth side against the head iself. This could be the reason for the water leak and my problems?
Cliff Harvey

When I first saw your picture, I said to my self, "The insert is broken or missing".
I had inserts installed in my TD head some 20 Years ago in Wisconsin.
When I got the head hove to assemble, some were loose.
I needed to assemble the engine since I knew I was going to be laid off but I made a mental not not to run the engine.
Some 18 years later I had the (unused) head reworked again. Custom inserts were made since the holes had been machined oversize for standard.

Now the exhaust valves see a lot of heat. Although the combustion cycle is (mostly) finished when they open, the exhaust gasses are HOT. The valves need to be cooled before the next cycle. Anything that impedes heat flow from the valve to the head to the coolant will cause a problem.

I believe the heat flow is (mostly but not entirely) valve-to-insert-to-head-to-coolant. The other path; valve-to-insert-to-head-to-head_gasket-to-block-to coolant is longer with two additional interfaces, head-to-gasket and gasket-to-block, that adds additional thermal blockages.

If the valve was not hanging up then, I would suspect that your insert did not properly make contact to the head.

Perhaps it was not seated, or loose, or cracked.

Jim B.
JA Benjamin

Set the head gasket back on the block and note there is only one way it can be assembled and still match the water passage in back and the two ears around the tappet chamber. If the gasket were on up-side-down, there would be zero water circulation, and certainly, with 3000 miles on it, your cooling system was working. That head gasket excuse doesn't fly.
When did this mysterious water leak come up? Have you been dumping water in constantly? If you had some water leaking into a couple of cylinders, the combustion chambers would be remarkably cleaner than normal. If you had a major leak into the cylinders, youe engine would lock up - "hydraulic"- and that was not the case.
My concern wouldn't be too much water, but not enough oil. You'll have to study your rockers and oil spray once it is running again. Immediately pull valve cover after shutting it off to see if here's lots of oil dripping off rockers and running down the head or if it's dry as a desert.
"the guide was really tight" is what catches my attention. Do you still have the valve? If so, see if it is slightly bent. As I mentioned before, if you spin it in a drill, you may see the head wobble. If it is bent, that could explain sticking in the valve guide. Then again, a tight valve guide could explain a bent valve. Which came first, the chicken or the egg.
Test fit a different valve stem in the guide to see if it is the guide or the original stem.
Again, the question, were new guides installed before and were they iron or bronze?
Did that engine set for years by any chance, and you just started driving it? Reminds me of a truck I got that sat 10 years and the valves, springs & rockers were solid rust. I could hear the pistons banging the valves back up!
Did the remainder of the insert fall out or was it tight? One has to wonder if it came loose and flopped around until it broke. The question then is, will a new one fit tight or be sloppy? If a new one presses in snug, you're probably good to go... another 3000 miles?!
JRN JIM

The questions JRN is asking are on the right track. The machinist who originally did the work may be reluctant to accept the blame. The leaky headgasket is probably not the problem. A bent valve stem would explain most of noted problems. How it got bent???
I always compound the valves in and look at the pattern on the contact surface, which will show up most seating problems.
Good luck
Chuck
cj schmit

JRN's comments are 100% correct.
I would like to see a better photo of the other valve. It appears to have an extremely rough surface.I think that it looks somewhat like an exhaust valve from another engine that has been machined to fit.
Sandy
SANDY

Thanks for all your ideas, here's some answers to your questions.
The valves were all purchased new by me along with bronze guides, the head was crack tested and skimmed and then assembled with new hardened inserts by the mechanic (experienced).
The engine was started less than one year after the rebuild.
When we removed the damaged valve in the work shop we also removed it's neighbour, the burnt valve slid easily in and out so not bent. We tried the good valve in the burnt valve's guide and it was tight so it's definately the guide.
The hardened insert appears to be well fitted into the block and although a chunk is now missing it is reluctant to fall out on its own.
His theory is that I had a water leak under the gasket into the chamber causing the problem. I can't quite make the connection, yes, I've topped up the water but probably no more than a cup full over a nine month period. Another thought he had was the that during the 3,000 miles of running to date the engine may have over-heated, possibly blocked water ways?
He suggested I get the radiator water ways checked to make sure all is well there but it was reconditioned (I don't know to what extent) not long before the car was taken off the road in '64.
Last summer I did experience the water gauge going up to 90 (max on the gauge so probably hotter) when climbing a long local road on a few occasions. Perhaps this started the over-heating damage ... if it is heat related of course?
A few weeks ago whilst fitting a heater I examined the thermostat and found it to be jammed in the just open position, I've since replaced it. It made that same long climb but the air temp is now much cooler so not a fair test until the Summer heat returns.
What are folks thoughts on having the block skimmed and crack tested for a second time? Also should I use some sort of sealant either side of the gasket on reassembly just in case of a future leak?
From reading other threads on heater pipe take-offs the hottest part of the engine is the back of the block. I've used the Arnolt fitting on the bottom hose but I'm wondering if it would be worth taking heat from the back of the block/engine to the heater to help keep things cooler?
Any suggestions welcome.

Cliff Harvey

If there was any water getting into that cylinder there would have been a very clean area. Water converted to steam will do a fantastic cleaning job.From your photo there does not appear to have any leaking.
I think your mechanic is trying to transfer blame away from him. Tight valve guide was most likely caused by him overlooking the fact that Bronze guides need greater clearance.
That intake valve is way too black to have any large amount of water leaking into that cylinder.
After over 60 years of involvement with British cars I have seen most problems commencing with my first car in 1947 that was a 1937 Morris 8.
Sandy
SANDY

Geof,
I believe the problem is pretty minor with respect to what catastrophic failures others have reported. ...also hate finger pointing when it comes to mechanical problems. We don't want to flog the guy that has his hand on someones heart! I've had to do CPR on a lot of old machinery.

With that beings said- spin an 8mm reamer in the bronze guide and test fit again. The new guides can crimp tight at the tops on installation, but that has nothing to do with a cracked insert. Chalk it off to a tiny casting that failed. That's rare.

From observations, it doesn't appear there was a headgasket/coolant leak as it wasn't steam cleaned.

The "marks/indications" on the flat surface of the head caught my eye but we can't tell what caused it. Those aren't gouges from a solid object bouncing around, is it? Maybe seat chunk ricocheted around before leaving throught the exhaust port?! Any matching marks on the piston?
The fact that the remainder of the seat isn't out, bouncing, around is testament to a tight fit. GOOD!
I had a single, very loose insert that had been peened all the way around, very ugly, to tighten it in, and that was the only insert some previous machinist attempted. A broken insert is not common.
As for running hot, I had to keep my eye on our supercharged TD before the radiator was recored. We might run 230F/110C steady, on hot days. And once in a while, the 50/50/antifreeze soluions might boil over!!! Never had a serious problem as a result.
Ream the guide; verify free movement with new valve; enjoy the driving season!
JRN JIM

This thread was discussed between 22/03/2015 and 26/03/2015

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