23 replies to this topic

[Cooperman]

The majority of people ream guides...

 

This is bad practice as they should be honed, honing gives a better, rounder bore, after all you don't ream your piston bores do you ? 

 

Anyway reaming often gives higher clearances, less round and a rougher surface finish which will let the oil through easily hence the need for 8 seals, however if you hone the guides then the oil flow through he guide will not be enough to cause any issues but will still lubricate the valve stem, F1 do NOT ream guides ! 

 

The benefits of a closer better fit are more even heat dissipation through the surface to the head and cooling is improved, much better smoother running because of the superior roundness and accuracy.

 

Also another plus is a closer fitting valve to guide also seats better and keeps the seal for longer between the valve head and cylinder head seat.

 

Well, welcome back Martin. Hope all is well with you. We have missed your pragmatic advice on here for too long.

 

Pete

[jonlad]

Nothing like a good thread resurrection!

 

I found this thread as I was confused by finding only 4 stem seals in an engine that I am stripping. I think this engine is proof that the oil gets baked on

to the valves and the combustion chamber internals. Looks like I will be fitting 8 seals when it goes back together.

 

Can I wire brush off the baked on carbon rubbish??

 

[gazza82]

Put the valves in a fixed/held electric drill and apply a wire brush as they spin ...

[Dusky]

Are it my eyes, or does that valve look a bit bent?

[jonlad]

Thanks Gazza82, will do.

 

I think its my rubbish phone camera making the valve look bent!

 

 

[Spider]

Not fitting seals to the Exhaust Valves can lead to Exhaust Valve Seat Pitting too.

[carbon]

+1, particularly on heads which do not have valve seat inserts fitted.

 

Worth giving the exhaust valve a quick lap into the head using fine grinding paste. If you see head seat is mostly grey but has small black specs about 1mm across this is likely to be pitting.

[jonlad]

Thanks carbon, i was thinking it'd be worth grinding the valves in a bit.

[tiger99]

I have often found only 4 seals on an A series but always refitted all 8.Even when I was young and inexperienced it just seemed right, and there were 8 in the gasket set.

But the idea of a valve stem seal is somewhat problematic. If you do make it seal properly above the guide the valve and guide will not be lubricated and rapid wear will follow.

In theory the inlet valves might use an internal seal inside the tip of the guide, in the port, so that the valve stem is lubricated, which would need a means of letting the oil circulate, maybe a shallow spiral groove. But how would you make a seal like that work on an exhaust valve?

I wonder if modern engines are all that much better than the Mini in this area? They mostly use much less oil. It would be nice if we could apply some modern techniques to the Mini.