MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB GT V8 Factory Originals Technical - V8 valve seals

I have stripped 2 Rover V8s and niether had valve stem seals. the Manual I have mentions replacing the seals. I know some later engines had guides machined to take seals. Is it possible to fit seals to the P6/ SD1 engines.
Also I'm going to use 10.1-1 ratio pistons... do you think this will cause problems with UK spec fuel?
Thanks again
Brian
Brian Bourne

The factory V8 manual doesn't show seals, FWIW.

The higher the compression ratio the more likely you are to get pinking on any grade of fuel. You may need to use the higher grades i.e. 97/98/99 and still set the timing to give no pinking on any combination of throttle opening, revs or engine load, which is what I have to do on my 4-cylinder. The factory V8 being 8.26:1 has no problems with the standard timing even on 95 octane. However different engine designs will react differently to the same compression and fuel grade, 4-cylinders engines of the early 70s seem particularly prone to pinking, it may well be that the V8 isn't.
Paul Hunt 2

Brian,

The early pre 4.0/4.6 engines had small O ring seals on the inlets only, and do not require any machining of the valve guides.

The early high compression pistons P5/P6 were 10.5/1 which is a bit too high for road use with ordinary 95 Ron fuel, you could use composite gaskets which will lower the compression to approx 10.1/1 which is the figure you quoted, were you intending to use the composite gaskets anyway?

The ratio is still a little high but the Rover is quite tolerant to timing and compression issues being of all alloy construction. Alloy headed engines can generaly run a compression ratio one full point higher than a iron headed engine ie 10/1 Alloy 9/1 iron. The SD1 Vitesse engines ran 9.75/1 without problems I believe.

Kevin
Kevin Jackson

Paul/ Kevin, many thanks.
My intention was to use the best combination of of bits from the Rover and SD1 engines that I have. I recall that putting the high Comp pistons was a cheep tuning trick in the 70's, but I was concerned that any HP gains could be lost because of altered timing to cure pinking. The use of composite gaskets might be a good compromise ...or should I just use the orig SD1 pistons?
Couldnt see any valve 'o' rings - whereabouts a should thy be?
Cheers guys
Brian
brian

Brian.

The O ring seals just slip over the inlet valve stems, push them down so they sit on top of the guides before you fit the springs of course, they will self adjust when the engine is turned over.

You can get the seals and comp gaskets for a 3.5 from Real Steel.



Kevin.
Kevin Jackson

Kevin Many thanks,
Real Steel are fairly near to me.
Sound like the seals are a bit of an after thought when the engine was designed... I guess they probably help somewhat.
Cheers
Brian
brian

Comp Cams sells a seal exactly like the later Rovers, part #506-16. It requires a .494" guide top cutting tool however, that most performance shops should have as this seal is useful on a triple spring applications. In the mid 90's Rover had trouble with the seals coming loose. Rover's fix was to replace all the guides but I discovered that the actual problem was that the guide was not cut small enough (about .010" too big) and the seals were being distorted during assembly, only to come loose later. Instead of changing all the guides, a nightmare on a Rover, I simply cut them to the correct OD, problem solved.
Dale

Dale
Many thanks for the info. This is exactly what I was searching for. Cheers
Brian
Brian

Hi
Just to clear up something here--Dale's suggestion is definatley the best way to go in my opinion. but if not going that way and only fitting the little o rings on the inlets the correct method is to --
Compress the valve spring and cap assy down over the valve stem, then fit the o ring to the stem just below the collets , fit the collets then release the spring,this will allow the cap to come up and seal off the gap between the cap and the stem against the collets. Fitting the seals this way prevents the oil that sits on top of the cap from running down the stem. Any oil that splashes through the valve springs on an ordinary road car is minimal and doesn't cause any problems. However for any competition or fast road car or just peace of mind go the Comp Cams seals Gary
Gary

This thread was discussed between 07/03/2008 and 24/03/2008

MG MGB GT V8 Factory Originals Technical index

This thread is from the archives. Join the live MG MGB GT V8 Factory Originals Technical BBS now