924Board.org

[seanski44]

Hi all. VERY VERY LONG!!

Some of you may have seen my ramblings on this topic before, so apologies, but have been to try to get the car looked at in my desparation and annoyance and it threw up some questions. For those who haven't seen this topic before, it concerns my NA.

BACKGROUND: When I first got her on the road (exactly a year ago) I had a problem whereby I couldn't adjust the tappet on number4 exhaust. You could see daylight between the bucket and the cam. In the process of trying to fix her I replaced the tappet adjuster with a 3notch (no noticeable difference, can't remember the exact clearance, but think it was still off the scale) I also replaced the cam with a spare I had from a 931, no joy.

so I started thinking it was either a bent valve or broken spring. Chap in the garage I took it to the other day said it couldn't be a bent valve - not a chance or it wouldn't run on 4 cyls. He also said it couldn't be a broken spring as there would still be enough force to close up the tappet. He said in his experience it would either be a worn bucket or a worn valve tip - reckoned that if the valve tip is worn the valve would be shorter. Someone else on this forum has mentioned that if a turbo valve was used by mistake that they are shorter, this could be the fault.

So, what are the opinions of you guys? - could this all be down to the bucket? should I rule out the 'bent valve' theory? should I rule out the broken spring theory?

I am intending to compression test the engine when I can either a/ find the time to buy a tool and check or b/ find a garage who can be bothered to accept my business (long story)

btw, there are a few issues with simply pulling the lot to check - namely 1/ when refitting the head, money and time was tight and we managed to break the electrical connector on the back of the head, so used a little glue - I'd expect this to be a bodge that will come back to bite me if the head needs pulling again.
2/ when swapping the cam out I managed to thread most of the threads on the dissy drive housing, meaning I had to get a garage to fix her (which they did by using slightly longer bolts and being very careful!) - I'm anxious not to cock this up again as it feels like I could kill the head!

anyway, sorry for the long post, but please help any way you can (and for the mo, I'm keeping hold of the na!)
_________________
1998 BMW Z3 2.8 arctic silver & red

1981 168HP 931 S2 blue/tan leather - SOLD
1985 121HP 924 2.0l na modded - SOLD!
1992 968 lux SOLD
1989 944 2.7 lux SOLD

[Mike924]

I think your mechanic's right in ruling out the bent valve (which would stick long before opening a noticable gap at the tappet) and the broken valve spring (our cars have double valve springs, either of which is capable of closing the gap with the engine stopped).

A worn valve-top is a possibility. I have seen the ends 'mushroom' on other engines (non-Porsche) and this can open the tappet gap if severe enough.

You should be able to inspect the ends of the valves if you take the cam out. (Be careful with the dizzy housing bolts!) But, of course, if you need to change a valve, the head has to come off. Another problem with a mushroomed valve end is that it often doesn't fit though the valve guide without damaging it (the guide, that is).
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[seanski44]

[Mike924]

Even if you strip the dizzy housing threads completely, there should always be scope for re-tapping new threads for over-size bolts; not to be recommended, but better than junking the head! Still, be as careful as you can.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[seanski44]

[Mike924]

Let us know how you get on, Sean.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[Porscheaddiction]

Have you tried swapping in a different tappet and adjuster?
I just went through this but mine was the opposite my exhaust clearance was not enough. by moving them around I was able to get them set right.
just an idea and worth a try..and make sure you use a proper feeler guage to check your clearnances.
Chris.
_________________
1981 924 NA (Restoring mode)
1984 928S (Enjoying the driving season)

[seanski44]

[seanski44]

also, I guess it'd be an idea once I have the cam off and am able to check these things, to just torque the cam back down each time I change something with just the bearing caps without putting all the dissy drive back on and everything, so I can check what difference each change makes..
_________________
1998 BMW Z3 2.8 arctic silver & red

1981 168HP 931 S2 blue/tan leather - SOLD
1985 121HP 924 2.0l na modded - SOLD!
1992 968 lux SOLD
1989 944 2.7 lux SOLD

[Mike924]

[seanski44]

[seanski44]

OK, all this chat got me thinking about it, so as I have this afternoon off, I've whipped the cam cover off to have another look and re-aquaint myself with my old foe (no.4 exhaust tappet)

first surprise is that the oil spray bar as snapped! - pics to follow, but broke off at the end, just before after the last bearing cap which it is bolted to. it was lying in the back corner of the head looking battle scarred. Very angry as I bought this spray bar only a year ago new from the main dealer. also thinking m engine might not be quite as rattly now I've fished it out.

other than that, I went to measure the exact tappet clearance at no.4 exhaust and I was able to get a 0.8 feeler in there. I also turned the adjuster another notch (though I feel I'm approaching sag!)

anyway, I'm not much clearer on the problem for doing it, but at least I'm possibly on the road to sorting it.

Does anyone know offhand if a 931 bucket is the same as a 924?
_________________
1998 BMW Z3 2.8 arctic silver & red

1981 168HP 931 S2 blue/tan leather - SOLD
1985 121HP 924 2.0l na modded - SOLD!
1992 968 lux SOLD
1989 944 2.7 lux SOLD

[Mike924]

[Lizard]

same for all, tappets that is.
_________________
3 928s,

[seanski44]

OK, pics of oil spray tube nightmare...:




_________________
1998 BMW Z3 2.8 arctic silver & red

1981 168HP 931 S2 blue/tan leather - SOLD
1985 121HP 924 2.0l na modded - SOLD!
1992 968 lux SOLD
1989 944 2.7 lux SOLD