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MG MGA - Valve Guide Wear
|How long can I reasonably expect the valve guides to last? I have 22,000 miles on my 1800 engine since its total rebuild.|
The engine is going really well, excellent compression on all pots and, when I last had the head off about 2 years ago, there was absolutely no wear in the bores.
It is just that I have noticed on the odd occasion that when I have hit the throttle to the floor I get a whiff of burnt oil entering the cockpit (lasts about 10 seconds). Just wondered if I am beginning to get a bit of valve guide wear. Oil consumption is negligible; I rarely have to top up between annual oil changes.
My engine vent system is absolutely MGA standard, not MGB.
As an additional point of interest this has only started to become a minor issue since fitting the stub stacks, so I am wondering if it could be related to better flowing vented gas into the front filter.
|Steve, valve guides should last a lot longer than 22,000 miles unless you have a lubrication problem. Usually blue smoke from the exhaust when you put your foot down is a sign of worn rings, and blue smoke when you lift off is worn (inlet) valve guides. But make sure you haven't got a leaky rocker cover gasket. That can leak oil onto the exhaust manifold and give you that smell, my money would be on that.|
|I've always considered guides as an "engine life" component, c 100,000. Done lots of valve jobs at 50-75,000 without replacing guides, though often saying they are a little loose, but no problem. That's with CI guides & OE "seals", not any modern stuff. |
If you have bronze guides, they might leak more if the seals fail, given the bigger initial clearances.
|For new iron guides 100,000 miles or more, sometimes up to 150,000 (if the cylinder bores and rings make it that far). Bronze guides, I think at least twice as long. So far I have bot been able to wear out a set of bronze guides. I have one cylinder head with hardened valve seats, Stellite exhaust valves, and bronze guides that went 100K on one engine. Then it was transferred to a second engine with only minor touch up of the exhaust seats and new valves, now having an additional 85K on it, and the bronze guides are doing fine. I like the idea of hard valve seats and bronze guides as a one-time life time investment, good deal if you drive a lot.|
|Steve, do you know what kind of valve seals were fitted, were they the better type as per Barney's site?|
|J H Cole|
|Thanks all for the comments.|
I will look on it as a pleasant over-winter task to take the head off and investigate. I want to polish and clean the associated bits anyway to maximise the benefit of my new stub stack performance.
John, I do not know what seals were used during the rebuild. If my memory serves me right I bought a recon head outright from Bob West as my 1800 came without a head.
Lindsay, no external leaks anywhere from the engine. That was the reason for my engine lift out 2 years ago - to sort out a tappet cover leak, clean-up and repaint the engine. Still looks sparkling.
As I said, it's a minor issue for me, no smoke apparent, just the occasional whiff of fumes under reasonably hard acceleration. May be it's just my sensitive nose.
|Steve, are you sure it's an oil smell and not just a burnt fuel smell? I sometimes get fumes drawn into the cockpit, depending on wind direction, usually when I slow down after I've been belting it.|
I've had the rocker cover leak a couple of times, where it sneaks down the manifold side almost invisibly. A tiny drip of oil can make an awful lot of smell once it reaches the exhaust manifold. I cured it by pulling the rocker cover bolts down a little more. I don't like to overtighten them, but it seems like the cork gasket shrinks a bit in its first few hundred miles.
Or could it be a bit of blow-by throwing fumes out of the draft tube? If you are really putting the engine under pressure it could be a possibility. It's probably the turbo-effect of those stub stacks!
|Steve - just my two penneth...|
I had my head 'done' and ruined as I discovered 8,000 mls later. This was where I found over 0.02" slop in some of the bronze guides and the roughest hardened valve seat grinding for the new valves which were replaced at the time by the garage. I also found washers under the valve springs! 6 of one sort and 2 of another; instead of the correct collars.
I managed to source an excellent local cylinder head specialist who was astounded at the state of the head. They do not recommend solid bronze guides due to the bronze rate of expansion. They prefer and indeed fitted cast iron guides with a bronze liner - now that has to be the best way. Lining up on the new guide bores they diamond machine the valve seats with three angled surfaces, to give better valve cooling and flow. While carrying out this machining they also equalised all four combustion chambers too! There is no seat grinding involved, they simply pop the valve in and carry out a simple vacuum test against the manifold face.
These have been perfect now for the last 4 years and when checked, strangely the tappeta are always spot on!
If you want the name of these cylinder head guys send me an email Steve.
|P N Tipping|
I will have a look at the head over the next few months and make my conclusions.
Car was great today. Back at work doing some consultancy for my old boss. How I hate driving in Greater London rush hours. Never had to do it before. Went as fast as I could to get out of it quickly! What I hated most on some of the dipping, winding roads out of Farnborough was 4X4s behind on dazzling main beams.
|Steve, those brilliant white headlights that seem to flash every-which-way need banning. They are highly dangerous, I'm surprised they are legal.|
|Lindsay, a lot of those lights are not legal and changes to the MOT next year are designed to get rid of them!|
|Its changing the subject I know - but that's the best news I've had all year. Those lights just cannot be road legal in the UK - why are vehicles with them allowed to be sold??? Another pet hate is the use of fog lights in clear air - where are the police? Am afraid these lights have ruined any pleasure in night driving. It has simply made the "A" a non-no at night too with the standard mirror and all our shiney chrome reflecting everywhere.|
|P N Tipping|
|Pete, they are not sold (new) with those bulbs, but the bulbs are readily available and a common upgrade for the selfish. See on any modern car forum!|
|Oops, sorry for the thread hijack... erm... your valve guides should be fine Steve!|
Carry on. My sniff test paled into insignificance when blinded by those lights behind. He kept going on to full beam whenever no one was coming the other way, despite me being only about 30m in front of him. I had to turn all my mirrors down, then hit the floor to get some distance. Lost him back to about 200m eventually because he could not or would not hold me on the corners. Must admit some of those corners were pretty sharp (thanks MG for holding traction), and some had me tensing a bit - unfamiliar roads at night with indifferent lighting on the A and cars coming the other way.
This thread was discussed between 06/11/2011 and 08/11/2011
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