23 replies to this topic

[bikenutmart]

Really quick question, should I put 4 or 8 valve stem seals on my 1275 A+ head(12G940) Mart.

[ACDodd]

8 for a road engine.

Ac

[Wim Fournier]

There is a reasoning for answering 'four'; only on the intake valse. Because, when the outlet valse are open there is pressure beneath the halve stem and, when the inlet halve is open, the eis suction beneath the halve stem.

[nicklouse]

There is a reasoning for answering 'four'; only on the intake valse. Because, when the outlet valse are open there is pressure beneath the halve stem and, when the inlet halve is open, the eis suction beneath the halve stem.

almost but nope.

 

oil into the combustion chamber has an effect on power. oil into the exhaust only makes smoke.

[racingbob]

don't know why but was told on all 8 but leave off the little spring clip on the exhaust

[fenghuang]

Can someone elaborate on this a bit please?
I'm planning on renewing the valve stem seals when I change my head gasket. I've not done it before and assumed there was a seal for each valve, but now I'm a bit confused.

[gazza82]

I was told to fit to all eight and no-one I know has taken the spring off! I'm fitting the newer A+ cap type seals, not just the rings

[Gr4h4m]

8 for a road engine, people leave the exhaust valve oil seals off for a number of reasons, high powered, high heat environments the idea is to allow so lubrication to the hot exhaust valve. It's a common thing to do on turbo/ supercharged engines.

If you not building a racer / high up turbo/supercharged engine fit all 8 and use the higher spec ones from mini spares.

[Cooperman]

I've always used all 8, including on high output and high revving engines.

[Spider]

8 should always be fitted. Any Oil going down the exhaust valves will burn and usually bake on to the valve.

[bikenutmart]

Many Thanks, need to buy 4 more then. Mart.

[carbon]

There is a reasoning for answering 'four'; only on the intake valse. Because, when the outlet valse are open there is pressure beneath the halve stem and, when the inlet halve is open, the eis suction beneath the halve stem.

 

In my experience using just 4 valve stem seals on a road engine just on the inlet, and none on exhaust gives following results:

- significantly higher oil consumption

- visible exhaust smoke at start-up

- carbon baked onto exhaust valves, as mentioned by Moke Spider

 

This was on a 1330 unit, with brand new exhaust valve guides reamed to size. When the engine got hot it could burn through an incredible amount of oil, I think the record was over 4 pints in 250 miles on long motorway trip.

 

The only advantage I can see by not using exhaust valve guide stem seals is the rustproofing effect from all that oil coating the inside of the exhaust.

[HUBBA.HUBBA]

8 for a road engine, people leave the exhaust valve oil seals off for a number of reasons, high powered, high heat environments the idea is to allow so lubrication to the hot exhaust valve. It's a common thing to do on turbo/ supercharged engines.

If you not building a racer / high up turbo/supercharged engine fit all 8 and use the higher spec ones from mini spares.

Can leaving the seals off the exhaust valves let much oil down after the engine has stopped? I ask as I am getting blue smoke on start up only. It's a new head without seals on the exhaust valves. I do get a lot of oil in the rocker area and I wondered if this might be caused be having the rocker cover venting to a catcher tank, therefore encouraging the oil to work its way up too easily.

Supercharged, by the way.

Edited by HUBBA.HUBBA, 02 February 2016 - 08:58 PM.

[MRA]

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.

[Gr4h4m]

I went from the advice on the guy that built the head. I guess you need to do a bit of investigation as to your consumption.