3.2 Rebuild & Modify Thread

[Magyar Kiwi]

Hi
The link below discusses bearing crush, clearance and housing bore displacement.
Measurements to calculate bearing clearance must be made with the shells installed in the crankcase or conrod to account for the additional clearance from bearing crush and bore displacement.
https://enginepro.com/bearing-crush-and-vertical-clearance/
Best regards

[Coultl]

Really interesting! It makes sense that the bearing crush would open up the rod end a little. I’m surprised is that’s much. Good to know!

[Veeveessees]

The heads look amazing!

[Coultl]

I finally got to my buddies place to machine the pistons. This engine is going to be turbo charged and I’ll run pretty conservative boost. I’d guess I could get away with the stock compression but lowering it will make it less likely to blow up. (Turbo system posts here: https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/1165542-3-2-turbo-build-5.html)

I ended up pulling exactly 10 grams off each piston. I would have liked to take a little more off but it felt like I should quit while I was ahead. To get those 10 grams I pulled 0.225” off the top of the piston.

With Aluminum’s density of 2.75 grams per cc, the 10 grams I pulled off is equivalent to 3.6cc of aluminum…removed from the combustion chamber. This lowers the compression ratio from 9.5:1 to 9:1.

I think 9:1 will be passible for my modest power goals. That’s said I can get it down to 8.6:1 if I run cylinder base gaskets that are 0.5mm thicker. I might do that…

I have not seen anyone else cut these pistons down for this purpose but there’s a lot of aluminum up top. I think they will be fine. On that note, are these (Mahle 3.2 pistons) forged or cast?

[Coultl]

The rebuild is moving along. I had to pause the case work because I forgot to order the intermediate shaft bearings.

The rods are all on the crank and the crank is test fit in the case. I measured bolt stretch after torquing the rod bolts to make sure everything was properly tight. All came in right at 0.005” of stretch at 50 lbft of torque.

The intermediate shaft was rebuilt with a new gear. This was pretty straightforward.

Lastly I measured all cylinders, pistons, and ring gaps. All are in good shape. I 3D printed a tool to set the rings in the proper location to check gap. All of the gaps with new Goetze rings came in right around 0.4mm. I think that is plenty even with boost.

[Coultl]

Making more progress. The cam towers were vapor blasted…they looked awesome but what a pain…

I’m huge fan of this process but I now know it’s just not worth it for hard to clean parts. I pulled the oil spray bar plugs and cleaned that out…and yes, there was media in there. Then I realized that there were other difficult to reach areas inside the cam towers that needed to be cleaned.

The wife was out of town so naturally I used the dishwasher. I’ve done this on other parts and as it always does, it gave the aluminum a very dull / gray finish.

Last step was to use aluminum brightener to bring them back. Yeah, a lot of work…

[Coultl]

The IMS also got a rebuild since the aluminum gear had pitting. I ended up tearing it fully down and cleaning the inside really well. The YouTube channel Klassik Automotive has a great video on the process and on checking for proper gear lash.

[Coultl]

The case is closed! After a whole lot of double checking, it feels great to cross this milestone.

I used Loctite 574. I tried to keep it within 15 minutes but it ended up more like 30 by the time I was done. 15 would be a feat. The Loctite gooped out when tightening so I think I was fast enough.

The case bolt o-rings are viton and they were greased liberally. I 3D printed a little o-ring guide to minimize the o-ring to thread contact when installing. Overkill…

On to cylinders and heads next.

[mikedsilva]

all looks really good!

Yes, the vapour blasting does need a LOT of cleaning afterwards... I pull the plugs AND the tubes before they get done.
No matter many times you think you've cleaned it, I bet there is still more residue. I run them through my ultrasonic tank maybe a DOZEN times and you will still see little parts of blast media on the bottom of the tank...

This is why i don't get the case halves blasted (I cannot get to all the nooks and crannies inside the oil galleries to clean)

[Coultl]

An ultrasonic tank big enough for the cam houses would be awesome. I cleaned them maybe 10 times and hopefully I got it all!

I totally agree. Now that’s I’ve seen what it takes to clean, I’d never vapor blast the case halves.

[Coultl]

Some updates:

- I ended up using 1.3mm cylinder base gaskets. I think that’s about as thick as you can go without causing issues. The material pulled off the piston and the thick base shims got my compression ratio down to 8.4:1.
- I somehow forgot to put the air deflectors on and had to crush and remove the oil return tubes. The 574 was already dry on the cam houses and there was no way I was taking them off. I put some collapsible ones on.
- Timing the engine went well. I set it at 1.28mm for the 964 cams. Before the heads were on I did scribe TDC on the flywheel. I used a dial gauge on the piston and this gave me a very accurate TDC.
- The rockers went in without issue. I used the RSR seals on the rocker shafts. I had no way to get a torque wrench on the rocker shaft bolts and the torque seems fairly critical. I ended up using a luggage scale on my 6” allen key. 28lb of force equates to 14 lbft of torque.
- I did a leak down test just to make sure there are no major issues. The leak down ranged from 10% to 4%. The rings are brand new so I’m okay with those numbers. Hopefully that 10% gets down to 5% or so after break in.

[Coultl]

More photos

[Coultl]

Some more photos showing the luggage scale torque wrench and the prototyped section of an intake manifold I’m working on.

[mikedsilva]

loving the updates

[Okiikee911s]

The heads look amazing!

[Coultl]

The engine build is wrapping up, so I’m gonna move over to the turbo thread here:

https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/1165542-3-2-turbo-build.html

I didn’t realize this until the build was done, but for twin plug you need to ground down one of the chain boxes. After taping up and covering everything with extreme care, I took care of. It doesn’t feel great to grind metal on a new motor, but I kept it clean.