quick question-stem seals

[DanRodd]

currently reassembling my 295 head and i need to know something quick!
am i right in assuming that the new umbrella type stem seals fit over the top of the valve guides?seems to be the only way that they will fit securely

[bpr81a]

The ridge at the base of the seal fits into the groove round the top of the guide - assuming you've got the later guides to go with the later seals.

[bmcecosse]

But on a 295 head you won't have the grooves - however - well worth fitting them anyway - to the inlet valves - leave them off the exhausts - just use the normal O ring seal there. You want a bit of oil going down the exhaust guides - and they are not under 'suction' effect from the inlet stream.

[DanRodd]

ive just fitted the cap type seals over the valve guides,were all a nice tight fit.is this right?couldnt see a way of fitting them at the top like the originals and i couldnt see how this would keep oil out of the valves as the seal would be at the top?

[bmcecosse]

Yes - they go over the guides - but without the groove they may come off in time. The little O ring seals are in the valve cotter groove - and are simply designed to limit the amount of oil that can run down the stem of the valve. The guide seals keep it out at the guide! As I said above - best to NOT fit these guide seals on the exhaust guides - just on the inlets.

[DanRodd]

so would it be a good idea to fit the o rings as well?think they came in the gasket kit

[bmcecosse]

NO! But you should fit O rings to the exhaust valves - INSTEAD of the 'top-hat' seals. Certainly don't fit both - you may starve the stems of all lubrication - leading to rapid wear and possible sticking valves.

[ADO16]

currently reassembling my 295 head and i need to know something quick!
am i right in assuming that the new umbrella type stem seals fit over the top of the valve guides?seems to be the only way that they will fit securely

You might try these they seem to work great! Scroll down the page until you get to "Cylinder Heads & Oil Consumption" and read up on the Viton valve guide seals...they work great.

http://members.tripod.com/austin_america/id82.html

Cheers M8

[DanRodd]

one last problem ive decided to just fit the 4 standard type o rings onto the inlet valves,where should i fit them?from what ive read in some manuals it says to fit them just below the cotter groove,which i have done,but they look pretty free to slide up and down.on my spare normal minor head the seals are sort of fitted into the spring retainer.help!

[bmcecosse]

You should fit the 'top hat' seals on the inlet guides! They do a good job there - and will cut oil consumption and blue smoke production. Only fit O ring seals on the exhausts - and they go on the reduced diameter section of the valve stem - and then you pop the cotters in - slyghtly higher up on the stem. The O rings can't go anywhere - they are trapped in place.

[DanRodd]

the top hat seals i have have no wire in them and i dont have grooves in my guides,so they would just come off.
i managed to suss out the method you just said Roy and its worked perfectly,ive fitted 4 o rings to the inlet valves,should i fit them to the zorsts as well?

[bmcecosse]

You should do - yes - but you should have stayed faithful with the top-hat inlet seals - they are better!

[DanRodd]

im going to keep it standard for now,my valves are a very nice tight fit in the guides so not too worried about oil leaking through,right then,i shall fit the remaining 4 seals to the ezhaust valves,now i know how to do it! (good thing i had a spare pack,only get 4 in a gasket set.

[Declan_Burns]

This discussion has me slightly confused and perhaps I have missed out on something. I cannot figure out how an O-ring in the valve cotter groove limits the oil to the valve stem. I'm not questioning Roy by any means-I just don't understand how it works and want to get it right. Looking at the minispares website they state that the top hat seal is a "must" for the exhaust valves.
http://www.minispares.com/Product.aspx? ... itle=VALVE STEM TOP HAT OIL SE...
Has anybody a cross sectional sketch or drawing showing the location of the O-ring. The link above posted by ADO16 mentions the viton seals being for both inlet and outlet.
Quote:
"Modern valve stem seals made with Viton.
Viton is designed to be used in caustic and hot chemicals.
Viton has a max temp rating of 450*F.
These seals have the correct dimensions to fit over A-series engine guides and valve stems, without any modification!
These seals will fit inside dual valve springs.
These seals fit either your existing original guides, or the new guides made of either bronze or steel.
These are designed to be used on all 8 valve stems.
These control the oil that gets down the guide, they don't eliminate it.
These will not cause your exhaust valves to hang up or gall"

Any comments or have I misunderstood something?
Regards

[DanRodd]

hi declan,the type usually supplied by the mini people have a small wire spring around he side of the rubber seal,which fits over the guides,this is usually enough to hold onto guides which do not have a locating groove for the seals.the type sold by minor people do not have the spring and therefore are at risk of coming off standard,ungrooved guides.
the original o ring fits in the valve spring retainer and is meant to limit the oil that runs down the stem.not exactly sure how it works but it was presumably adequate for a fair few decades.

[bmcecosse]

As above - the O ring is just intended to form a wee 'dam' at the cotters - and stop excess oil pouring down the stems. Obviously the top hat seals are far better - they stop the oil going into the guides. But to do this on the exhausts risks them seizing up from lack of oil, and there is no 'suction' on the exhaust ports to suck in excess oil (as there is on the inlets) - and so certainly for stressed engines - I strongly recommend NOT fitting top hat seals on the exhaust guides. O ring seals will be ok though, and should be fitted - since they don't do all that much anyway!

[Declan_Burns]

Thanks,
Are they retained by the base of the collet or can the move on the valve stem? A sketch or a photo would be helpful of the position of the O-ring relative to the collet. I will by picking up a 12g940 head on Tuesday so I will need to order the O-rings as they were not supplied with the 1275 gasket kit-only the top hat seals were included.
Regards

[DanRodd]

right,fit the valves and springs,and the retainer,then apply your valve compressor.compress the spring as far as you can,insert the o ring and push down to the base of the retainer.then fit the collets,and slowly release the compressor,then totally release it.the collets trap the o ring between them and the retainer,and it pushes the o ring perfectly into the end of the retainer.

God,ive just got my head off,what a bodge job!various washers missing,all the head studs were loose,and the supposedly decarbonised pistons appear very crusty!yet another job to do before the new head can go on

[bmcecosse]

The 940 heads never used the O rings - there is no space for them. They use the top-hat seals -on the inlet valves only is my preference, but many do fit them on the exhausts too.

[Declan_Burns]

Thanks Roy,
It's beginning to make sense to me now. I'm only familiar with the 940 head due to recent experiences. I haven't removed the 202 head yet-hence the questions. While on the subject, double or single valve springs? I was going to go for single to minimize the wear on the cam drive train but would like a second opinion. I'm only interested in an improvement in performance not a race engine.
Regards