12 replies to this topic

[stormduck]

I'm in the process of stripping the cylinder head fitted to my 998. I have all the exhaust valves removed using the valve spring compressor, but the collet on each of the inlet valves will not budge! I've tried tapping the top of the compressor, banging the top of the compressor, smacking the top of the compressor with a large hammer against a block of wood but still they don't budge!! i had to tap all of the exhaust valves a bit, but the oil would start showing around the top of the valve then it would come loose. I've had nothing like it on the inlets....any ideas??

I've also snapped a thermostat bolt. The bit that's snapped is inside the thermostat nelly the elephant looking thing, so it won't come off. I did get it turning, so maybe if i can somehow get nelly off, a pair off mole grips on the stud might get it out! Any ideas!!??

Finally, the valve seats of the exhaust valves look quite pitted. The valves leaked liquid when i filled up the ports, hence the reason for stripping it. What are my options with the head on the whole, bearing in mind i'm on a budget and do like doing things myself...although the stories of grinding a valve to seat it properly is putting me off a bit!

[ian]

why is it putting you off? its not a hard job just dont rush it, think you can get the wooden stick thing and the paste from your local halfords.
what ever you do though make sure you get every bit of paste off when you finshed. wash it good with white spirit or something.
as for nelly (think you mean termostat housing) if you can get it off try the molegrips, maybe put a little heat to the stud first
good luck

[Bluemini]

To free up the valves, take off the compressor and tap the end of the valve with a hammer and also tap the spring cap a few times around it with a hammer.

Therm bolt, try and get the therm cover off then use mole grips to get the stud out, or smash the therm cover and get the molies on the stud or try plenty of heat and penetrating oil.

Valve seats you have 2 choices, firstly is just get the valves and seats re-cut at an engineers (around £20 max) if they are really bad, or just re-lap them yourself if its only mild. Lapping is easy but boring
Second choice would be to get the head converted to unleaded (if it isn't already) which would mean having an engineers machining out the old exhaust seats and fitting hardened ones. This should cost around £100 but depends how far your budget will stretch.

[The Matt]

Sorry to hi-jack a thread, but is there a restriction on valve sizes for unleaded seats? If so, what is the biggest you can go?

[Bluemini]

You can fit larger exhaust valves to an unleaded head, but the bigger they are, the more the seat needs to be cut and more forces being put on it, which may result in a seat falling out.

[stormduck]

ian - i understand that it's not difficult, just time consuming, but that's cool in the attempt of doing things myself and saving money! I did see the wooden stick and paste in halfords - £2.99 bargain!

nelly = thermostat housing - i wasn't 100% what it's called!

bluemini - i did wallop all of the valves when i was having trouble and tried again but no joy. If that's the only way then i'll persavere and try tomorrow. I sprayed them generously in WD40, dunno if that's guna make a difference.

The head already runs on unleaded (an 89 mayfair) so the 2nd option need not apply. Is it possible to re-use the old valves and seats then? They don't look that bad to me, i'll have to get some photos when i've finished stripping it. You say an engineers could re-cut them - is that just taking a skim of metal off them? And is lapping them name for using the stick with paste? And that will remove the imperfections in the metal? This is sounding better by the minute if i'm understanding this right!

Cheers!

[Bluemini]

Yeah re-cutting them is just 'skimming' the face of the valve and seat, you will still need to lap the valve in after tho so that you get a good seal, altho I have not bothered lapping them before after having them re-cut and had no probs, but it is best to do it.

Lapping is the boring bit with the stick with a suction cup on the end, you stick it to the vavle, put a bead of paste around the valve contact area where it sits against the seat and role the stick between your hands (like your trying to start a fire). There will be 2 types of paste - coarse and fine, use the coarse first until the seat and valve go a dull gray colour, then wipe all the paste off both surfaces and start again with the fine paste. You'll be able to tell when they are done because there will be uniform dullness around the valve and seat.

[stormduck]

Sweet! Diamond, cheers fella! So i take it there are no side effects of taking a slight amount of metal off the surface by lapping? Like the valve sitting slightly further into the head? Even if it is very very very slightly? I'd be chuffed at just lapping them, my budget is fast diminishing!

[Bluemini]

The amount taken off by lapping would be so small you could hardly measure it. Even when re-cutting, you have a fair bit of seat and valve that you can cut away before you get probs, the valve springs are plenty long enough to to take up the extra .00001mm or whatever it amounts to of the valve.

[stormduck]

Allo fela, right, i got the inlet valves out, and got the thermostat housing off and the stud out without any problems :grin: how happy am i!



Here's a pic of probably the worst looking valve seats:



Does that look cool to you for just lapping them?

All the valves look good bar one inlet, that has a sharp lip of metal that's looks like it would sit just inside the valve seat, almost as if the valve's been squashed to one side and pushed the metal up creating a lip. I think it's only a few quid for a new valve, would it be wise to just replace this one and keep all the others?

How about the springs, collets and retainers? Are they all sweet to re-use? There doesn't seem anything wrong with them, although i might, hopefully, get a new cam or a regrind to something a little livelier than standard, but wouldn't go higher than 276. In this instance should i be looking to get double springs?

Cheers geez! dave.

[Bluemini]

Damit, just spent ages typing out a reply in fast reply and clicked the wrong button by mistake and lost it all

The seats look saveable with a bit of time and effort, the best thing to do it lap them all in and see how they look after. If they are still badly pitted then you'll need to get them re-cut, if there is only the odd pit then you can get away with it although its not ideal, but ok... Post up a pic after you've done it and we can tell you if they are ok, the valves and seats should be a nice dull gray colour by the time you finnish.

As for the valve, I think I know what you mean but its hard to say without seeing it. Post up a pic so we can take a look, it might be saveable or you could just have that one valve and seat re-cut.

The cloots, springs and top caps are all re-usable, check the collets in the valves before you put them back in the head. You want to make sure there isnt eccesive play in the collet as sometimes they wear the locating groove on the valve causing play. They should be a snug fit with little or no movement.

Did you keep each valve together with its own spring, collets and top cap and mark which valve it was in relation to the head??? Unless your having a full overhaul with new guides and re-cuts then they need to go back into the port they came out of idealy.

If you plan on getting a different cam then now is the time to change the springs to something a little stronger. Either go for double springs or the uprated single ones. If your only going for a mild cam like a 276 then its not imperative that you get new springs, but it will make a little improvement and its easier to do it now than take the head apart again later. Another thing to considder is wether you plan on using high lift rockers like 1.5 roller tips with your new cam, standard springs can 'crush' (when all the coils of the spring touch) because of too much lift and bend valves or as Bungle found out, rocker shafts. Better rated springs often have less coils in them for this reason, but confirm this with the suplier if you buy any to make sure you get the ones you need.

[stormduck]

Cheers fella, I'll get a pic sorted of the dodgy valve.

Yeah i kept each valve, collet, spring, oil seal and cap together and labelled in a nice freezer bag for each set :grin: They'll all go back the same way they came out. The collets seemed perfect when i took them out, no noticeable play, but i'll make sure when i put them back. The engine's a 1990 998 with 87k, and so far seems good.

Are the guides the slight stem that the valves go into (rocker side of the head)? I don't think they'll be worn enough to warrant a complete rebuild, besides, i'd rather do it later using a decent head when i can afford it.

I don't intend to use high lift rockers, i don't see the advantage within a tight budget. But i know the original rockers can be replaced, minispares sell them for about £8 a piece if i really need to, i know it's hard to judge, but these are the rockers, the wear on them are that i can feel a definate dip where they touch the valve:



These adjust anyway don't they to set the clearence, so is there any need to worry about a bit of wear?

I can't find anything on minispares but minisport sell extra strong single set for £11 or a double set cooper style for £22, they even do extra strong doubles (200lb) for £22 aswell. I'll see how it goes. Oooh, just one more for today! What's the best way to clean the head? Cheers!! Top man.

[Bluemini]

When you put the head back together, fit new stem seals (they should come as part of the head gasket set).

If the rockers dont feel too bad then re-use them as like you say, you can take the slack out when you adjust them.

I use white spirit and a tooth brush to clean stuff up, takes a while but you get good results. If your gonna paint it after, dont use hi temp engine paint because its horrid stuff. Go to Halfords and buy some paint called Jenolite Re-Paint, its an enamel bases paint and take heat realy well and is only about £6 for a normal size (1L?) tin and there are lots of colours to choose from.