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Rich H

Just pulled the head off my 1980 '24 N/A due to excessive sooting up of the plugs and oil consumption. I did a compression test before I started ad it was 165/165/165/160 cold and 185/185/185/185 warm (and I assume oily) So there might be a little bit of wear on the rings on No4 but I'm going to leave them for now.

Turns out all the exhaust stem seals are shot, the just fell off the top of the guides, got to get measuring tomorrow but everything looks fine and the guides don't seem to be very worn (85k miles)

so apart from re-lapping in the valves and changing all the gaskets and seals is there anything else worth doing now while it's all in bits?

TIA
Rich
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

Smoothie · Posted: Mon Aug 20, 2007 8:37 am Post subject:

Those are the most consistent compression readings I've seen - I'd consider your rings and valves to be in excellent shape..

If/when I'm in your position, with the head removed, I'll be converting over to air-shrouded injectors. The conversion would involve the new injectors, upper and lower holders, and modification to the head to fit the slightly larger diameter lower holders and air tubes to let air in near the upper holders. -But first, I have to figure out which ones to use.
Vaughan, if you're out there, can your Bosch buddies help with that (info on which injectors to use, that is)? I thought I was on the right track by looking at a similar HP'ered Audi 5000 Turbo (which uses air-shrouded injectors), but then it occured to me that they have 5 cylinders, so 4 injectors from a 5 cyl car may not deliver enough to produce the same power in 4 cyls., if you know what I mean. In other words, I might be left with only 4/5ths of the injector capacity needed..
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

scottc · Posted: Mon Aug 20, 2007 9:30 am Post subject:

Whats the advantage of air shrouded injectors smoothie?

I don't think you need to worry. using 4 injectors from a 5 cylinder car will give you approximately the same fuel. The 5 cylinder was a 2.2, Therefore each cylinder is only slightly smaller. I Suppose it really comes down to what pressure they open at. But you could probably overcome that with a twist of the mixture screw.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Make sure you replace the cam oiler elbow. If you don't go the "smoothie" route on injectors

I'd strongly recommend replacing the plastic injector inserts...no better time to do it than when the head is out, as they can be a bit tricky to remove...that way if one breaks during removal, it's no big deal (unlike if you change them while the head is still on).

When I did my head rebuild, I did a complete top-end restoration...ALL gaskets from the head up, timing belt & tensioner, plugs, wires, rotor, cap, coil, air/oil/fuel filters, and ALL engine rubber (heating & cooling hoses, as well as vacuum lines; you can get all the silicone vac lines from HoseTechniques.com). I also did some decorative painting

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erstwhile owner of just about every 924 variant ever made

Smoothie · Posted: Mon Aug 20, 2007 10:26 am Post subject:

Air shrouded injectors improve the fuel atomization, which should translate to smoother running, improved fuel economy and lower emissions. Here's a pic that tells the story -

Here I "borrowed" Endwrench's cutaway view and Photoshopped-in an air-shrouded injector to see what would have to be done -

-and a couple more showing the parts (click for larger views) -

BTW, talking about the plastic upper injector holders - I believe you could use the brass holders from another car such as the Audi 5000. I'm pretty sure at least that they have the same thread size, plus they are the o-ringed push-in design like the 924NA.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

scottc · Posted: Mon Aug 20, 2007 10:34 am Post subject:

Thanks Smoothie.

How do you make sure the air is metered and filtered? Just run a tube to the manifold?

Smoothie · Posted: Mon Aug 20, 2007 12:02 pm Post subject:

No, actually air for the shrouding is taken from upstream of the throttle plate - of course it's already been filtered and metered at that point as well.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Rich H · Posted: Mon Aug 20, 2007 5:37 pm Post subject:

Cheers for that but I forgot to add I'll be enlarging the injector holes to take my EFI injectors

I'm going to bore them out to take the O rings leaving a lip to retain them (Thats the theory anyway) The plastic bungs came out ok, but left all their threads in the head :? Don't need them but its annoying.

Did I mention I like German Engineering? Everything came apart ok even the exhaust manifold came off the head! The only casualties being a banjo bolt (My fault, working back-to-front and the damn ratchet was the wrong way!

) and a valve collet fired itself across the shed last night when the valve swpring compressor slipped, I'll find it later it was too dark last night. (I have spares anyway)

The exhaust valves are heavilty contaminated with alot of oil build up on the bottom of the stems. I'll scrape it all off and clean them up in brake fluid. The inlets are like new.

I'm also going to clean out the crank breather filter as access should be better.

Anythign else?

Cheers
Rich
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Rich H · Posted: Tue Aug 21, 2007 5:19 pm Post subject:

Head is now cleaned up fine, looks like its been rebuilt before, the valves are stamped with dots to id the cylinder. The valves and guides are not very worn at all just looks like the stem seals on the exhausts have failed.

Going to refit the CIS and get it running (And hopefully not burning so much oil!) Then I'll rip it apart again and fir the EFI

_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Smoothie · Posted: Wed Aug 22, 2007 3:05 am Post subject:

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Thanks, Smoothie.

I'm OK with the idea of cutting the end off, I'm OK with the cost for something that will outlast the rest of the car, I'm even OK with "why would they need to go to different sizes for different applications" and "they look the same in pictures", (close enough t for me!

)

But...I'm not keen on the idea of wobbly injectors and I'm a little confused with how the brass ones seal against air. They seem to have grooves down the hex section and I don't see where the rubber do(ugh)-nut goes... (unless it's further down relative to the plastic ones; in which case, what does this do for injector depth location?)

If I'm feeling flush some day I'll order one just to have a look at it for compatibility, etc.
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1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

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