advice needed on rebuild

brianc944 · 01:11 PM

Hello everyone. I've been lurkin' on this board for about a year now an try not to ask some stupid questions to annoy you guys but perhaps now I'm gonna. Here's my story. My mechanical level is average. I'm good with external things an such but when it comes to internal I have no hands on experience. Only what I've read in Chilton's manuals an such.

I have a 86 951 that is near mint, she's not the problem , it's my 1985.5 na. This is the first Porsche I ever sat in so she's kinda special to me to take her back to her original beauty an let her live out her life in peace. Okay, okay, I'm getting there. Here's her problems, part of my problem is I don't know which job I should be doing first. First the problems I know I can't do by myself: I would like to rebuild the head (she needs it)or maybe put a four valve head in her, how much more would that be in parts vs a rebuild of my 2 valve head? This would be the first job correct? ballpark figure, labor on old head vs new 4 valve head? . An the second is she needs a new water pump/timing belt. Another job that I'm just a lil to afraid to do by myself on fear of messing her up good. If anyone around Albany/Saratoga region knows how an wants to show me an make some $$$, I'm down, I'd pay ya good to show me. This would be the second job?

Now for the stuff I probably can do myself: new clutch( with help from another friend), exhaust, power steering pump, new alt. No order right? minor things from there. I've already put new shocks, struts,new control arms, new radiator an probably a few other things I can't think of right now. Thanks for your time everyone, I really do appreciate it. If I've forgot any info you need do hesitate to ask . Thanks again.

brian c

Tishabet · 06-15-2005, 01:32 PM

What is it that you need to do to the existing head? Did you break a timing belt?
As far as I know, the difficulty (both technical and $) of installing an S head into an NA is not even approachable in terms of the performance gains you will realize...very small gains, very difficult modification. I think the S head has different water jacket ports or something like that.
As far as doing your own water pump and belts, it's not very difficult, check out clarks-garage.com for some great tutorials. Doing your own clucth on the otehr hand......

Zero10 · 06-15-2005, 01:39 PM

The first problem that I see with the 16V head, is the combustion chamber volume in the head is MUCH lower on the 16V head. your 85.5NA will have a 9.6:1 compression ratio, the 16V's will have a 10.9:1 (IIRC) compression ratio. In order to bring this down, to help prevent detonation, Porsche dished the 16V pistons deeper than the 8V pistons, so, if you use 8V pistons, and a 16V head, I would imagine it could bump your compression ratio has high as 13:1, which we all know usually means bad news.
On top of that, you would have to change your fuel mapping and spark timing to manage such a high compression ratio, just not worth the trouble.

IMO, go with a 16V engine, or stick with your 8V head. No huge gains to be had by swapping the 16V head on. I also believe Tshabet is correct on the water jackets being different, but I am not 100% sure on that.

If nothing is bent on the 8V head, figure about $200 for a rebuild, plus valve guides and seals (~$40?), which isn't too bad. Then (of course) you'll need a head gasket set, which is about $100.

Rebuilding a 16V head, I don't know, never had one done.

ae1969 · 06-15-2005, 03:18 PM

Forget the 4 valve conversion. (if you have been lurking this comes up every 3 months or so, not as often as can I turbo my NA....... but you get the picture)

- Buy a headgasket set/water pump/rollers/belts/front seals

Pull the head. Have it rebuilt if you wish. I have seen some high mile heads and the only ones that I have ever seen being a problem are the turbo heads. The exhaust side get quite a pounding. The seats are usually worn. On your NA .......check for valve guide play/ seats......... if it looks OK. Throw in some new valve stem seals and call it a day.

- Replace the waterpump, front seals and belts and have someone check your tension.

The only places I see you getting IN real trouble if you are new to this.

1. The waterpump studs. Odds are you will break some.

2. Tensioning the belt. It would be nice if someone in your are a would help you out on this.

The rest is pretty much tear down/replace/put back together. As long as you are familiar with the torque specs, steps involved it should go ok.

brianc944 · 06-15-2005, 05:00 PM

Thanks alot guys, I'll scrap that whole idea about the 16 valve head. Seems much eaiser to rebuild the head. This should be fun. Any more advice or suggestion are appreciated.

I've seen many a turbo swap post but missed the 4 valve swap post, must not be lurking enough.

Thanks again.
bc

Zero10 · 06-15-2005, 07:36 PM

It comes up here and there, but it doesn't get as much attention as the turbo-my-N/A posts do. Although, I'm about to go down that road, lol.

Anyhoo, is there anything wrong with the head that's on there right now? Just curious about the motivation for this.

brianc944 · 12:42 PM

a good amount of black smoke when I 'get on her'. Sluggish performance compared to what I remember her being like. What would be good signs to rebuild a head besides that? There's no rattling going on . I guess we all could say this IS an assumption.n The car supposedly has 80,000 on her but....i really can't say it does. Thanks for the reply.

bc

Tishabet · 06-16-2005, 12:34 PM

Black smoke all the time, or just on start up?

brianc944 · 06-16-2005, 12:36 PM

on start up an, again, when 'I get on her,' every now an again, I'm not abusing this car, to bad.

b

Zero10 · 06-16-2005, 12:37 PM

Black smoke, so it's running rich. You might get out of this one cheap. I'd start by checking the fuel injection system out, AFM, TPS, temp sensors, etc. Once you get it running right, any carbon build-up on the valves/combustion chambers will burn off pretty quickly.

If you had blue smoke on startup, I'd say valve seals, and pull the head for certain, but given what I've heard thus-far, I would say leave the head on.

brianc944 · 06-16-2005, 12:44 PM

Well actually now that you meantion it, it is more like a blue smoke on start up an more black when 'I get on it.'

bc