17 replies to this topic

[kez_19]

i have bought this. head gasket set and in the kit is 8 old type valve stem oil seals and 4 new inlet stem seals

question is now do i fit

the old type to all the valves and the new ones to the inlet valves or

just the new type or

just the old type

thanks michael

[Guess-Works.com]

Just the new type on the inlet valves.... which does mean you'll need to remove the valve springs...

As standard there is no seal on the exhaust valve.

[kez_19]

so do i throw away the old type seals then ??

as for the valve springs i have the head in bits anyway as i am rebuilding the engine and have had to change the valve guides and one was broken

cheers

michael

[Guess-Works.com]

If you've changed the valve guides you should get the valve seats re-cut to match the new guides.

[kez_19]

not sure if we are talking about the same thing now i have fitted theese

and as far as i know then i dont need to re grind anything

obviously i need to grind the valves to their old seats but that should always be done after de-coking the head

michael

[Guess-Works.com]

unfortunately the link does not work, but if you mean this sort of thing...

http://minispares.co...ty=pb&pid=37123

then yes the seats will need re-cutting...

The reason for this is the seat is centred and cut using the valveguide as a guide, when you change them, due to manufacturing tolerances, the centre of valve may well be offset from the centre of the existing seat. You can try and recentre them using valve paste, but expect to be at it for a few hours, and if it has hardened unleaded exhaust seats, you've got no chance.

It's another one of those things which are often over looked, or more to the point.... "ah it can't be that far off, don't matter" type thoughts, but what will happen is the valve head will attempt to sit in the seat square, which means it may be twisted slightly, this in turn will cause the new valve guides to wear on one side, eventually making your newly pressed in guides, oval.

Extract from workshop manual..

[attachment=82846:Valve_seats2.pdf]

[Dan]

obviously i need to grind the valves to their old seats but that should always be done after de-coking the head

Not really and as Guessworks says if it's an unleaded head it's pretty pointless to even try grinding in the valves. Unleaded seats have to be cut, not ground.

[Pauly]

I think metro 1275 heads didn't have valve stem oil seals on the exhausts, but mini heads did (my SPI did). Most aftermarket gasket sets will only supply 4 (I tend to use the orginals on the exhausts) but the payen gasket sets come with 8 and are a good quality set.

Paul.

[Guess-Works.com]

if you want to use seals on the exhaust valve stems, then use silicon ones... they are not affected by the temperature so much which is what causes the rubber to degrade...

They probably came in to use on the exhaust stems when the cat was introduced, as oil which does leak down them, is obviously shot out the exhaust pipe and the cat don't really like that...

[kez_19]

ok i have a mini from 86 so it isn't unleaded

and these are what i have fitted hope the link works now

http://www.minispare...ty=pb&pid=36203

as for grinding in the valves i had no idea that they could be off centre still find it a bit strange that something that is pressed in to the head and is cast and presumably lathed to within tolerances should need to have the valves re ground in to the seats but it does mention it in the link that guess works supplied

so i suppose i will have to try to find some one that can re centre the valves in to the old seats

thanks for the help

ps guessworks do you have any more links to that workshop manual looks very useful

michael

[Paul Wiginton]

so i suppose i will have to try to find some one that can re centre the valves in to the old seats

Got that backwards mate, the seats need grinding to suit the valve position which will be slightly different now because of the new guide. It will only be a few thou but thats enough for the valve to not seat properly

Paul

[kez_19]

is that a common tool that machine shops will have ??????


michael

[dklawson]

is that a common tool that machine shops will have ??????

michael

Any machine shop that works on engines will have the equipment to re-cut the valve seats and re-grind the valves.

The link below shows a picture of the old, manually operated cutters for heads without hardened seats. The long skinny rod goes down into the valve guide which acts as a pilot to keep the cutter centered.
http://i21.ebayimg.c...b/6b/7c29_1.JPG

The link below shows a machine powered seat cutter. You can still see the skinny pilot but you have to look carefully to see the hardened cutter insert for cutting the seats. It's a single blade on the right side of the pilot. This type of cutter is suitable for the hardened seats which can be seen in the picture.
http://www.flowspeed...seat-cutter.jpg

I don't believe anyone mentioned this above, but there is one other machining step required now that you've installed the new guides. Before the seats are cut, the machine shop will ream the inside of the guides to size. As you pointed out, these are a press/interference fit with the head. The guide bores collapse a bit on insertion. They are reamed to size after installation.

I've worked on heads a few time (port matching and chamber matching) but I've never bothered to do anything more than lap valves at home. The machine shops can cut valve seats and re-grind valves so much more effectively than I can that I consider it money well spent.

[mini7boy]

I think the point has already been well made, but I just wanted to second(or third) the idea of redoing the valves sets, whether cutting or grinding, anytime the guides have been swapped for new ones.

It seems implausible, but if you have ever seen photos of new guides that were freshly machined, it is appalling just how "off center" the bore in the guide can be, thus causing poor valve seal.

DK Lawson was spot-on in mentioning the need to ream the guides after installation. Failure to ream the guides is one of the leading causes of valve seizure in the guide and massive damage to the head and piston, at least, if it all goes wrong.

[kez_19]

right i have been in touch with a few machine shops up here and i have had a quote for grinding the seats so at £128 for the work i started looking at courier prices and found that it costs £25 so ship it to sweden i figured that i would be better off buying a replacement head in england and shipping it over

so now i have the question of what do i look for as a replacement

i have a 998 from 1986 and i have these numbers on the head and block


ECAM 4004

4 C6

and a big A

thats all that is on the head

the engine number is

99H834AJ

thanks michael