Rv8 4.6 - changing valve stem seals in situ?

pupp · Post by **pupp** » Thu Jul 17, 2008 10:25 pm

Puffing some smoke on overrun and suspect the stem seals... anyone done them without pulling the heads? Technique?
Ta

ChrisJC · Post by **ChrisJC** » Fri Jul 18, 2008 7:09 am

I seem to recall that at least part of the technique is to feed some rope through the plug hole, then raise the piston up to hold the valve in place.

But then I suspect you'd have to make a tool for compressing the valve spring and getting the colletts out. I've certainly never heard of one.

Should be doable though.

Chris.

Post by **katanaman** » Fri Jul 18, 2008 8:31 am

There is a post here somewhere (maybe on old forum)with all the details and links to the compression tool needed.

TVRleigh · Post by **TVRleigh** » Fri Jul 18, 2008 9:49 am

any reason you don't want to remove the heads, would be a lot easier if you did. also may work out quicker in the end.

sidecar · Post by **sidecar** » Fri Jul 18, 2008 9:49 am

I though that smoke on the overrun was due to oil getting passed the rings. On overrun there is a high vacuum above the pistons and this sucks the oil up from beneath the pistons.

I guess the inlet stem seal will also 'see' this vacuum on the inlet stroke as the carb or EFI butterfly is closed and the inlet valve is off it's seat.

Just distroyed my own argument!

The other way of holding the valves up is with compressed air.

Pete

CastleMGBV8 · Post by **CastleMGBV8** » Fri Jul 18, 2008 10:45 am

Before you start pulling it apart it would be a good idea to check that your crankcase ventilation system is working properly.

If there is excess pressure in the crankcase and valve covers, oil will be pushed down the guides, I had this on a rebuilt engine and found I had a faulty PCV valve, replaced it and problem solved.

Kevin.

ramon alban · Post by **ramon alban** » Fri Jul 18, 2008 2:53 pm

I think this is the science of what happens!

1 Smoke on startup = worn valve stem and/or damaged stem seals.

Reason, oil runs down the valve stem at rest and pools at the bottom. Engine starts and sucks in pooled oil.

2 Smoke on acceleration = worn piston rings.

Reason, big bang with very high pressure in any chamber forces gasses past piston rings into crankcase where increased pressure forced some oil up past other piston rings in chambers that are not banging.

3 Smoke on overrun - most likely worn valve stems.

Reason, very high induction vacuum sucks oily air plus oil down from inside the rocker covers.

Alternatively if piston rings are very badly worn then some oil might be sucked up from there also as a combination of 1 and 2 above.

Regarding replacement of seals without removing head.

Remove the battery so the starter cannot function.

Remove all plugs.

Put long piece of soft rope down one plughole (dont lose the free end of rope down the hole

).

Bring to TDC on the firing stroke, by hand .

Bear down on the spring/collet end with a lever, see below.

Pop out the collets.

Fit new seal.

Re-assemble.

Remove rope.

Repeat 15 times - or is it just a total of 8 for inlet valves only - I cant remember?

paul c · Post by **paul c** » Sat Jul 19, 2008 12:34 am

You can either use rope or a compressed air fitting in the spark plug hole, but if using air make sure you dont break the seal of the valve. There are several tools for removing the valve springs

I have this one

http://www.powerbuilttools.co.uk/enginedrivetrain.htm