3.2 Rebuild & Modify Thread

[Coultl]

I'm restoring my '84 911 3.2 and building it back up as street tuned turbo. I figured I'd start a thread on the engine rebuild as this is my first air cooled rebuild and I could really benefit from your expertise. The engine has 130k on the clock, has good compression, and seems to be in good shape overall.

The goal of this build is to refresh the engine and strengthen where needed. I will be running about 7 psi of boost through a custom turbo and standalone ECU. My goal is about 320hp and a 7k redline. Key parts of the build plan:

- (hopefully) reuse the cylinders and pistons
- Pauter rods
- Aasco valve spring and titanium retainers
- Regrind cams to 964 spec
- Twin plug heads w/ coil on plug
- ARP head studs
- Patrick 60-2 lightweight flywheel
- ECU Master Black ECU

I have a separate thread HERE where I will detail the development of the turbo system.

The rust repair, body work, suspension, etc. are all happening in parallel so this isn't going to go very quickly...

[targa72e]

Save some money and use your stock springs and retainers. You do not need Aasco valve spring and titanium retainers base on your build specs, they might even be considered a detriment for a street car.

john

[mikedsilva]

What's different about this thread, compared to the other well established thread?

[Coultl]

This thread is about the engine rebuild, not about the turbo. The goal here is to share the process of rebuilding the engine and get pointers along the way.

The other thread is focused on the development of the turbo system. That's a huge project on it's own.

That's my thinking anyway.

[Coultl]

targa72e, I went back and forth on the Aasco springs. The general sense I got is that the stock springs are questionable at 7k and I'd really like to have that redline. I also like that they give some insurance against an over rev causing piston to valve contact.

All that said, I don't like titanium retainers in a street engine. They don't last forever like steel does...and dropping a valve is a nightmare. I also don't love the additional wear on the camshafts and rockers.

No right answer but I already bought them so no going back now!

[kamaro]

Originally Posted by Coultl

targa72e, I went back and forth on the Aasco springs. The general sense I got is that the stock springs are questionable at 7k and I'd really like to have that redline. I also like that they give some insurance against an over rev causing piston to valve contact.

All that said, I don't like titanium retainers in a street engine. They don't last forever like steel does...and dropping a valve is a nightmare. I also don't love the additional wear on the camshafts and rockers.

No right answer but I already bought them so no going back now!

I had the same thoughts when I was doing my boosted 3.4, I decided to go with AASCO springs kit with the titanium retainers after speaking with them on the phone, they will last at least 30K miles before replacing them and as I'm in my mid 50s I don't think I will ever reach that mileage anyway if I'm doing about 20 miles a week max

[Coultl]

The teardown is happening. Such a treat to work on this engine.

A few notes:
- Disassembly has been pretty straightforward. I eventually upgraded my engine stand as it felt insane to have a $20k engine sitting on an unstable $50 harbor freight stand.
- The dots on the engine are there bc I 3D scanned it.
- I cannot believe how clean the inside of this engine is. 130k on the clock and almost no varnish. The cylinder heads are about 30% bare aluminum…like the carbon just chips off. I’ve never seen that before. An air cooled thing?
- The cams are pretty wrecked. Pitting on 4 or 5 lobes. Planning to send to Dougherty to regrind to 964 profile and get the rockers redone too.
- The bores look really good, but we’ll see how they measure out.
- As others have suggested, an oxy-acetylene torch made removing the exhaust manifold bolts easy. This is a northeast car and all other exhaust bolts had to be cut.
- The tins are pretty toast. Lots of rust. So expensive to replace… Somethung to figure out.
- The heads will be sent out to be rebuilt, but I’m not sure where. Ideas?

I’m posting a bunch of photos in case it’s helpful

[Coultl]

More photos

[Coultl]

More photos

[Coultl]

More photos

[Coultl]

More photos

[Coultl]

More photos

[Coultl]

Originally Posted by kamaro

I had the same thoughts when I was doing my boosted 3.4, I decided to go with AASCO springs kit with the titanium retainers after speaking with them on the phone, they will last at least 30K miles before replacing them and as I'm in my mid 50s I don't think I will ever reach that mileage anyway if I'm doing about 20 miles a week max

Sounds like beast of build Kamaro! Awesome. Photos?

[ian c2]

You eat a lot of bananas .
What engine stand did you buy ?

[Coultl]

Ha, I get those boxes at Costco. They are the best for parts.

I bought a “bid red” 1,500 lb engine stand on Amazon. Four wheels and much more stable. The yoke that mounts to the back of the engine came from eBay. For $240 it was surprisingly well made. It did require some grinding to clear the exhaust though.

[Coultl]

Engine fully torn down and looking good.

I cleaned the pistons with B12 which is my go to. It doesn’t corrode aluminum like most degreasers and it’s incredibly good at dissolving carbon.

This engine made nearly zero oil pressure at idle, but I found nothing that would have caused that inside the engine. Low oil pressure at idle seems common I guess. I can also say that the low oil pressure did not result in any bearing damage.

The main and rod bearings looked great. #7 showed the most wear but it’s not bad. All journals are nice and clean. The pistons and cylinders look really good. Very happy about that. The intermediate shaft gear has pitting on the teeth so that will need to be replaced. The gear in the crank looks good and hopefully that can be used.

Next up will be measuring everything and sending the heads to the machine shop.

[Coultl]

More photos

[mikedsilva]

Originally Posted by Coultl

This engine made nearly zero oil pressure at idle, but I found nothing that would have caused that inside the engine. Low oil pressure at idle seems common I guess. I can also say that the low oil pressure did not result in any bearing damage.

If it made nearly zero at idle, you need to check carefully. You either have a faulty pump (pull it apart) or lots of little oil leaks (large clearances on main and big end bearings).

Bolt the case together with the nose bearing, torque to spec and measure the journal sizes. Should be 65.00-65.019mm.. I see lots much larger than that....

[Coultl]

I agree Mike. I was actually hoping to find something obvious but didn't. I tore the pump down and it looks mint inside.

Before I tore the engine down I confirmed nearly no oil pressure at idle with an external gauge. Installing cam box oil restrictors solved it, but I'd rather than run the restrictors.

I am going to run a GT3 pump which has a pressure side that's 30% larger (I think) but I still need to figure out why I had low oil pressure.

I will be measuring everything and will share back here.

[Coultl]

I started measuring tonight and have some indication on where the oil might have been going. The crank journals (main and rod) are all on the low end of the spec range. Thankfully within spec but right on the bottom end.

The journals all look so clean and bearings show so little wear that I suspect that the crank started life on the low side of the spec.

I did a quick plastigauge check with the old bearings and the mains showed 0.002" to 0.003" of clearance. Impossible to be precise with plastigauge but it's definitely up near 3 thousandths on a few journals.

I suspect that I'll end up going to a coating to get the main bearing clearances down to 1.5 to 2 thousandths. I'm okay running ~2.5 thousandths on the con rods but I think the mains need to be tighter.

Next I'll measure the case bores and see how they compare to spec. Once I get the new bearings I'll also compare those to the old ones.