2.7 Rebuild – To bore or not to bore and other questions

[draw]

Originally Posted by LukasM

Hi Ward,

Nice progress indeed, almost ready for case assembly!

And good to hear that the coating helped enough to get the clearances within tolerance. How durable is the coating, compared to regular bearing shells?

What is your view on the case, did Olli's do a good job? I would have thought that they would align bore to the minimum specified size, since wear just opens up the bore over time, and you want to maximize service life. However I'm a novice when it comes to engine building so maybe I'm overlooking something.

Cheers,
Lukas

The coating is supposed to be pretty durable. HM Elliott does these coatings for NASCAR and MAHLE.

As for the case, Ollie's did great work considering how twisted it was. They had to take 0.035" off to get it back to standard. They did align bore, but couldn't get it back to the minimum size.

Originally Posted by Rosco_NZ

Seems Ollies bore to spec … my case was STD but on the high side, crank was STD but on the low side .. net result too much clearance.

Yes, exactly my situation.

Originally Posted by dedyplay

Fabulous engine! Make sure the intake and exhaust ports are well opened!

Thanks, I debated this for quite a while but decided to open the intake to 37mm and kept the exhaust at the stock 35mm.

Originally Posted by SiracHaile

I had my case align bored and pined by Ollie’s. I measured my clearances with a dial gauge and plastigauge and they were loose across all mains. I called Ollie’s about it and they assured me it’s fine. So it’s together and once I get it running we’ll see what the oil pressure is at. But I thought I was the only one looks like it’s common.

I'm no expert, but I've talked to a few during my rebuild and this sounds like it's becoming very common...even the guy who coated my bearings said he's seeing a lot of these.

Originally Posted by Herb_911_76

Draw, thanks for your detailed report, very informative as I'm also working on a 2.7. FYI: Previous owner had Dilavar studs on exhaust side. All but 3 Dilavars had snapped while all steelies on the intake side were fine and tight, despite a lot of rust. Novice advice requested: Your bearing trouble has me reconsidering splitting the case. It wasn't leaking, except a bit of sweat around both shaft seals. Are there any pointers that can help me make a decision? I don't know the exact mileage (intermittent odometer), but should be around 80k miles. Cylinders still have cross hash and also Pistons are dead nuts in spec, valve guides are worn... Sorry didn't mean to hijack your thread.

Thanks! This is my first engine rebuild, so I'm not really qualified to give any advice except for what not to do...That said, I think that most people would agree that the mag cases need work no matter what.

[draw]

Bolted on some of the ancillaries...

Got the chain rails installed and a titanium RSR crank pulley from EB Motorsport. I'm a sucker for titanium!



Updated oil pressure reliefs, oil connection, and sump plate with titanium drain plug from EB Motorsport bolted on with PVD coated titanium M6 socket cap screws and washers...



Breather cover, oil thermostat, and oil pressure switch. I got a little sloppy with the paint pen, but at least I know they are torqued...



Question...I'm installing carbs, so is there any good reason to keep these three studs installed? I'm thinking I'll remove these...



Onward...

[Veeveessees]

Are the intakes and exhaust ports wide open ? Fab engine!

[Vavavoom]

Are the ports wide open ?

[draw]

Preparing for the next phase of assembly, I moved on to measuring the cylinder to piston clearances, ring gaps, and installing the pistons in the cylinders.

First measured the cylinders...



Then each of the pistons...



Per MAHLE's spec sheet, clearance is 0.0254mm to 0.046mm. Did a little mixing and matching to get them as even as possible. All came out within range.



Moved on to checking the ring gaps...



The spec for the top ring is 0.017" and they all started with a gap of about 0.007". About 200 turns on the manual ring file and test fitting 20 times each, got them done. Fortunately, only the top rings needed filing.



Cleaned and prepped for assembly...



Rings installed on the piston...



Insert using a tapered spring compressor...



Say a prayer, then BINGO! Installed and ready to go...



Onward...

[draw]

Now to check actual deck height...

Back in post #48, I measured the case and other parts and, using a 1mm base shim in my spreadsheet, I calculated the deck height to be 0.79mm (0.031"). Let's see how things look in reality...

Started with a 1mm shim supplied by Ollie's...



Installed the piston and cylinder and found TDC...



Deck height turned out to be 0.85mm (0.0335"). Pretty close to what I expected...



When I measured on the opposite side of the piston, I got 0.029". This is a little too close for my comfort.

I could stack a 0.25mm and a 1mm shim together to get a better deck height, but this would be about 1.14mm and would lower my compression ratio to 9.98. So doing some googling, I found Hussey Performance who makes custom gaskets in any thickness in 0.001" increments. I gave them a call, sent them one of my shims from Ollie's, and two weeks later got a pack of 6 shims for $150...



I ordered the shims in a 0.047" thickness, which measured out to be 1.204mm...



Put everything back together and got a deck height of 0.042" or 1.07mm...



It took a lot of futzing around, but I think this is a good result. I could have ordered the shims in a 0.046" thickness, but I decided I'd rather err on the side of caution.
With this deck height, the calculated compression ratio is 10.06.

In case anyone is wondering, I've checked the Harbor Freight caliper against my feeler gauges, and it is surprisingly accurate.

Onward...

[PeteKz]

Ward and others: FYI, I'm currently running a 103mm forged piston in a motorcycle engine with iron sleeve and .025" clearance and no contact with the head up to 7000 RPM. Per David Vizard, in small block American V8 engines, you can get down to .018" before contact if your pistons don't rock much (e.g., hyper-eutectic cast pistons). The clearances of pistons to aluminum cylinders in Porsche air-cooled engines are pretty tight, therefore they don't rock much either, so I would not be concerned with a .029" piston/head clearance. I have around .030" in my current engine.

[draw]

After ruining two rear main seals using the "PVC pipe" technique, I opted for the "proper" P215 tool...







That was much easier!

Ready to install the pistons and cylinders. Everything prepped and a little bead of Curil T on the base gaskets...



Using the Supertec head studs makes attaching them to the connecting rods much easier. However, a word of caution...My casesavers were not perfectly perpendicular to the case, which caused the studs to "porcupine". This became a real nightmare getting a few of the studs screwed into the case. When I do this again, I will install the studs first.



Seeing that threaded hole in the adapter on the crankshaft gave me an idea...looks like a great place to mount a degree wheel...

Bought a degree wheel and positive stop to find TDC...



Attached the degree wheel to the flywheel side using the RMS tool and made a pointer out of a coat hanger with a little yellow paint on the end.



I realize that the wheel turns "backwards," but I really just need an accurate TDC for when I get to the cam timing. Cheap and hopefully effective!

Onward...

[75 911s]

Ward,

Amazing attention to detail on this build.

You asked about the three studs for carbs. I would remove those and plug the holes in the shroud. For the back two holes I just put a nice Bolt and washer in. I used a rubber plug for the 3rd hole where the spacer sits.

[draw]

This is my engine. There are many like it, but this one is mine...

I like the look of the 906 cooling tins, so I bought a set from EB Motorsport. When I went to install them, it became obvious that the 906 cylinder is not the same size as my 93mm cylinders from LN. The hole for the spring retainer was about a half inch past the barrel...



Drew up a modified version in CAD and had SendCutSend laser cut them out of Grade 2 titanium...



The part as delivered...



And installed...





Onward...

[ian c2]

Nice
I believe Henry and the guys at Supertek make/sell them .

[ian c2]

Nice
I believe Henry and the guys at Supertek make/sell them .

[LukasM]

It sure is a cool time to live when you have Fusion 360 (and tons of Youtube tutorials) available for free, and then a service like SCS to make custom parts like that for you for a very reasonable price!

Great work as usual!

[draw]

Time to install the heads and cam housings...

Heads refurbished, intakes ported, and twin plugged by CGarr...



Intakes opened up to 37mm...



Installed on the cylinders...



Loctite 574 (over) applied to the cam housing...



And installed...



Starbase, we have a problem (or two)...

[draw]

I ran into a couple of issues.

The first problem was that I'm a doofus...

My 15mm 12-point deep socket didn't fit through the cam housing, preventing me from getting to the head stud nuts to torque them down. Figuring that a semi-deep socket would work, I bought a Snap-on socket off ebay. When it arrived, I could get past the housing and down into the hole. At this point I realized that the nut was 14mm and my deep socket that I already had would fit great. Not a big deal, really. I'm just out $50 for a socket that I'll probably never use. Anyone need a Snap-on 15mm 12-point semi-deep socket? I'll make you a deal...



My second problem was a little more serious. When torquing down the cam housing to the heads, this nut wouldn't tighten past 15NM...



The only way to assess the situation and repair the damage was to tear everything apart...





Threads on the stud basically disintegrated...



Removed all the Loctite 574 and replaced the stud with an extra one I had in my stash...



All back together...



Onward...

[draw]

Originally Posted by PeteKz

Ward and others: FYI, I'm currently running a 103mm forged piston in a motorcycle engine with iron sleeve and .025" clearance and no contact with the head up to 7000 RPM. Per David Vizard, in small block American V8 engines, you can get down to .018" before contact if your pistons don't rock much (e.g., hyper-eutectic cast pistons). The clearances of pistons to aluminum cylinders in Porsche air-cooled engines are pretty tight, therefore they don't rock much either, so I would not be concerned with a .029" piston/head clearance. I have around .030" in my current engine.

Pete, I appreciate your experience here and I did seriously consider going with a tighter clearance. Maybe on my next build...

Originally Posted by 75 911s

Ward,

Amazing attention to detail on this build.

You asked about the three studs for carbs. I would remove those and plug the holes in the shroud. For the back two holes I just put a nice Bolt and washer in. I used a rubber plug for the 3rd hole where the spacer sits.

Thanks Duane! I'm going to remove those studs before I install the shroud.

Originally Posted by ian c2

Nice
I believe Henry and the guys at Supertek make/sell them .

Thanks, Ian. Yes, I think Supertec does sell them as well.

Originally Posted by LukasM

It sure is a cool time to live when you have Fusion 360 (and tons of Youtube tutorials) available for free, and then a service like SCS to make custom parts like that for you for a very reasonable price!

Great work as usual!

Thanks Lukas! Absolutely! It’s amazing how accessible high-quality design and manufacturing tools have become. Between the tools, the wealth of tutorials online, and services like SCS, the barrier to turning an idea into a real, custom part is lower than ever. Definitely a great time to be a maker!

[snbush67]

Nice build. Were the deck heights on each cylinder the same?

[Jesse911]

This is a very nice build! Also all the photos and info are great as I will be rebuilding my engine soon too. Thanks!

What oil pump did you use btw?

[mikedsilva]

Originally Posted by draw

My second problem was a little more serious. When torquing down the cam housing to the heads, this nut wouldn't tighten past 15NM...


The only way to assess the situation and repair the damage was to tear everything apart...


Threads on the stud basically disintegrated...



Removed all the Loctite 574 and replaced the stud with an extra one I had in my stash...



All back together...



Onward...

Interesting.. never had a strud strip like that before....

I see you have those vertical marks in your barrels...

[draw]

Time to prep the chain housings for installation.

Apply Dykem...





Sanded flat...





Apply Loctite EA 9340 epoxy...



Found a "worm hole" in the magnesium...



Not the best picture, but filled it up with the Loctite EA 9340 epoxy and sanded smooth...



Onward...