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MG TD TF 1500 - White deposit on exhaust valve

While changing the gasket I'd spent a look into the chambers. I recognized a white deposit on exhaust valve of cylinder #1. The other valves show only a little bit of this white deposit. I use a lead additive. What may be the reason for this deposit?





W_Mueller

... an other valve


W_Mueller

It looks like a white ash combustion product. It will vary between cylinders according to mixture and temperature of the individual cylinder. Such deposits were not unusual in the days of leaded petrol, so I imagine the additive you are using may well be a cause. I use unleaded petrol and no additives, if you are worried about valve seat recession - its a slow process and unlikely to be a problem on a classic car unless you cover a lot of mileage.
Dave H
Dave Hill

Thank you Dave

I hope valve seat is good. Last compression test didn't show any issue.
W_Mueller

Before I'll fit the manifolds - any other thing I should have look at from this point of view?
W_Mueller

I don't think so, but over time the hard ash deposit on the back of a valve can get so thick on the valve stem, that it jams in the guide and the valve fails to close properly, causing a backfire. It may be worth taking a look in the cylinder through the spark plug hole - easy with a fibre optic type camera (very inexpensive) attached to a mobile phone, just to check all is OK.
Dave H
Dave Hill

Hi Dave,

if you say backfire - do you mean misfire in direction of the carburetors or is banging in the exhaust also a possible issue? The last is what my car does without acceleration.
W_Mueller

You can't mistake a proper backfire - a loud bang down the exhaust from unburnt fuel mixture meeting hot exhaust gases. Caused by an exhaust valve not closing properly.
Dave H
Dave Hill

Thank you Dave

it bangs only while driving without acceleration (mostly downhill). A tip at the accelerator and the show stops.
W_Mueller

Back fire is back through the carbies . After fire is out the tail pipe

Regards, Tom
tm peterson

A backfire applies equally to the exhaust over here.
Dave H
Dave Hill

'Normally' a light carbon colour like that would indicate an over lean mixture- If it's the only cylinder (what colour is the matching cyl. on that carb.)
If the other 3 are normal you could have a leaking manifold gasket
A leaking gasket will also cause backfiring on the overrun
willy
William Revit

I agree with William. I think your engine is running a little lean.
John...Sydney
J Walton

This thread was discussed between 15/11/2017 and 27/11/2017

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