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MG Midget and Sprite Technical - Difference in stem seals?

As you may of seen in an earlier post I am replacing my valve stem seals to cure a burning oil issue which seems to appear most significantly when the thermostat opens for the first time.

I have got a full head Gasket set including 4 valve stem seals for £10+vat, yes it is a payen set(unipart) on inquiring about extra seals so I could do the exhaust at the same time they wanted $2.50 each for them.

On looking on minisport there are two types one for 55p each and the other is £2.60 each and is listed for the a+ is one better than the other?
S Riches

S..
Are the 4 seals umbrella type? If not you are still looking at oil burning.
Sandy
Sandy Sanders

Shaun,
I presume you're looking at the ones with a spring around the neck. The more expensive one is made of a rubber(?) compound which does not harden over time I believe. I used the cheaper ones.
You got a good deal price on the gaskets set. Where did you get it from?

Steve
Steve Church

Shaun,
Sussex Classic Cars supply them individually at 65p each.
http://tinyurl.com/5qbxw6

Guy
Guy Weller

http://www.calverst.com/shopopen.htm

Click on cylinder head. The ones in there are as good as you can get.
Nick

I'm not convinced you need oil seals on the exhaust if the valve guides are in reasonable condition. Seals are required on inlet valves because suction tends to pull oil down the guide but the reverse is true of the exhaust - exhaust pressure should keep most oil out. In fact a bit of oil down the exhaust guides is probably a desirable thing. If lots of oil is getting down the exhaust guide then clearly there is a problem with the guide being excessively worn. That being so then oil seals are a temporary fix but the real need is for new guides. As you might guess I don't have exhaust valve oil seals and have no oil burning problem.
I also can't see any connection between the thermostat opening and oil burning - or am I missing something?
Chris H (1970 Midget 1275)

Chris,
In my case, on a newly rebuilt engine, putting seals on the exhaust valves was the only solution that worked, after 6 months' of experimenting with all sorts of other ideas.
I agree, the logic says that oil won't be pulled down the exhaust guides and certainly the original spec for these engines is no exhaust valve oil seals as you say. But I cannot get away from the fact that it worked for me.

The only explanation I can hazard at is that there may be some connection with the valve overlap if, like me, one is using a non standard cam. It may be connected with some sort of pulse or venturi effect of the "plug" of exhaust gas passes through the exhaust port and across the end of the valve guide.

Guy
Guy Weller

I am sure seals on the exhaust valve stem will work - and if that is the only thing that does then I guess you have to go for it!
Chris H (1970 Midget 1275)

But Chris, you are right to point that out. As you say there is an argument for some valve stem lubrication as well.. Sort of reverse argument, this!
Guy
Guy Weller

All good points here. As you say, shouldn't need exhaust seals, but then again long overlap cams could mean your pulling oil down an exhaust guide and with the 5 port head this might even be in a different cylinder! I think for the minimal frictional loss they would cause i'd be tempted (and have done so in the past) to stick them on all valves.
Nick

Hi All my first time on here so here goes, firstly it is possible to have oil consumption from the exhaust as the area at the valve head alternates between pressure and vacuum during the engine cycle all modern engines have seals on all valves. On the midget/Sprite engine stem seals were only fitted to the inlets but on later Minis seals were fitted to all valves to help with enviromental issues As a final point these should not be called seals but an oil control device as oil needs to pass by them at a controled amount to lubricate and cool.
Colin
Colin

Hi Sandy

Chris H is right, you do not need stem seals on the ex valves, in fact we have seen valves nip into ex guides when worked really hard. ...BUT...on Mini transverse use we fit stem seals on the exhaust as the oil can puddle in the head and go down the guides, seems odd but we have been differentiating like this for 10 years. A lot of the problem of oil burning can be due to excess rocker/shaft wear allowing too much oil in the head which can be slow to drain back and cause oil burning.

Peter
peter burgess

Wow! Peter Burgess (the guru)agrees with me!!
Chris H (1970 Midget 1275)

Shaun,

What are the effects when the thermostat opens? Have you done anything to the engine recently?

I can vouch for Peter's comments - I had one of the occasions with nipping exhaust valves, which Peter sorted out by removing the exhaust stem seals in situ(quite 'surgeon like'!), and also suggested running the exhaust valve tappets slightly wider than usual (+0.002"/0.003") until the engine had done 1000 miles or so. Worked, and still works beautifully!

Richard
Richard Wale

This is my first stab at resolving the issue, I do not know the history of the engine but I do know it is something different to standard and as I want to find out what bore the engine is and valve sizes I thought I would try the stem seals and then take I would know what type of head with valves I need to replace it with.
S Riches

This thread was discussed between 10/06/2008 and 19/06/2008

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