Newbie '73T 2.4 MFI Engine Rebuild

[Neil Harvey]

Not everyone has the ability to map their cams and calculate the lift at the different crank positions in software, so here’s a way you can do it at home.

After doing the valve drop as I described above, disassemble the moch up and remove the rod and piston. Re fit the head with the valves installed with soft checking springs. Hardware store will have something. Just strong enough to hold the weight of the valve and retainer.

Fit the cam deck, cam and 2 rocker arms, Intake and Exhaust, (set the required lash) time the cam at whatever position you have decided to run it. You can move it as many times as you like to do the same measurement to find the lifts. With the “cam timed”, you may have used your dial indictor to set the cams, so with the indicator in place, position the pointer onto the retainer and make sure it will not be interfered with by the rocker arm and has enough travel. Rotate the crankshaft so the rocker pad is off the ramp and on the backside of the lobe. On the base circle. Zero out the indictor.

Remember you timed the cams at overlapping TDC turn the crank backwards well past 20° BTDC and turn the crank clockwise until you reach 20° BTDC. You can also turn the crank all the way around clockwise too, just make sure you know where to stop. At 20° BTDC, measure the indictor travel. Record this number. Do the same at every position through to 20° ATDC. These values need to be less that what you measure doing the valve drop. Plus the clearance you want to run.
For example, maybe the valve drop at 20° BTDC was 0.450”. The valve lift at 20° BTDC was measured at 0.490”. Not really but to make the point I’m using these numbers. And you want to run 0.040” piston clearance. Well on paper you have 450” – ( 0.490” +0.040”), which would give you 0.080” interference on paper only. You haven’t crashed the valves into the piston and you have a absolute interference number. Typically the closet the valves will come will be at 10° either side of TDC.

You should expect the lift numbers to always be smaller than the valve drop numbers. The clearance can often show up as an issue. Changing the cam timing often is required to obtain the clearance you want or your cutting pockets deeper.

You can see now why getting the valve lift numbers from your cam supplier makes it a lot easier.

I hope stuff helps and makes it clearer and an idea there are short cuts in doing some of the stuff. When you understand what you are doing and why, its really simple stuff. Hell if I can do it, anyone can.

[Inkblot]

I weighed all of my rods, rod caps, bearings, bolts, nuts, pistons and pins to create the most matched sets possible. It's a bit of a (fun) puzzle to mix and match each component to find the optimum balance.

I started with the rods, caps and bearings, and arranged them from lowest to highest. A dry erase marker worked well on the metal pan work surface for writing everything down.




I then worked through the rest of the components, placing them wherever they would preserve the best equilibrium. Finally, I marked each set with the position it will go in (1-6).




It helped me to put it all into a quick spreadsheet, to make sure the pairs were as close as possible, and that the heaviest pair would be closest to the flywheel (pair 3-6).




I ended up with each pair being matched to within 0.1g (I believe the spec is 0.5g), and the sum of the left side (1-2-3) being equal to the sum of the right side (4-5-6).

I'm trusting my machinist's work on balancing each rod itself; everything else he's done has checked out so far. All in all, I think it's pretty well balanced!


Next, I went ahead and measured the unstretched length of each rod bolt, and recorded that along with its location (rod 4a,b, etc.). I marked each "stamp" side bolt, so that I'd remember to put it back in the right place. This will allow me to measure the stretch after I've torqued them down, and adjust as necessary.

The new bolts were a tight fit, and required some fairly strong whacks to seat in place. I didn't want to damage or mar any of the surfaces, so I found some washers just large enough for the bolts to pass through, and set it up on my vise. The vise is just giving me something to whack against; it's not clamping the bolts.






Next up, I'll assemble the rods onto the crank.

- Jake

[Inkblot]

@Neil thanks- very nice write up. Makes good sense- at least as I sit now, before actually trying it

And:

Originally Posted by Neil Harvey

Hell if I can do it, anyone can.

I think you're being *just a bit* modest!

Best,

Jake

[Trackrash]

I'm guessing your machinist also checked the end to end balance as well.

[Inkblot]

@Gordon I think so... Jay at German Precision reconditioned and "balanced" them... I'm assuming that's the same thing as checking the end to end balance... or ?

[Inkblot]

So, moving on to the assembly of the rods onto the crank. If you've been following along here, or if you've seen any of the many threads on the subject, you'll know that there is a lot of debate/confusion out there regarding how best to treat your rod bolts; i.e., torque to spec, torque to stretch, how many times they can be stretched, how far to stretch 'em, etc. etc... It's confusing.

The clearest path seems to be to use ARP rod bolts, which have a clear spec for how much to stretch them. For better or worse, I'm using OEM bolts, which don't have a stretch spec, only a torque spec- but then the question is which torque spec to use. Wayne's book says torque to 14.7ft lbs then add 90 degrees, the Woods/Anderson handbook says 40ft lbs, and the tech bulletin for the newer "12.9" bolts says torque to 10.5 ft lbs, + 90 deg, and + 90 deg again. I've also seen 40-55nm, with 55nm being just over 40 ft lbs.

Based on some of the great feedback in this thread, I did measure the bolt lengths prior to assembly. My plan is to combine the first two specs, then measure the lengths to compare stretch from bolt to bolt. Then, I'll add torque to any of the bolts that are noticeably shorter than the others.

I lubed up the bearings with assembly lube, and applied some of the lube to the threads of each rod bolt. I did not use any thread lock.

I started by just finger tightening everything, to make sure that I had everything in the right place, making sure that my rods were in the proper locations, based on the balancing I had previously done, and that each rod bolt was where I wanted it to be, so that I could easily reference its pre-stretch length. In other words, get everything arranged, and double check it, before starting to torque anything.




Then I went through and tightened everything to 14.7 ft lbs. Made sense to me to do them all in each step, instead of getting to final torque on one and then moving to the next, as this would limit the number of setting and re-setting I'd have to do on my torque wrench.

Next, I set my wrench to 40 ft lbs, and started to turn each nut the additional 90 deg. If I hit 40 ft lbs first, I'd stop, and make a mental note of how many degrees short of 90 i was. I found it pretty easy to do both of these steps in a "sweep" kinda way, thus avoiding any issues with standing friction on my torque readings. Turns out, I hit 40 on all of them before getting to 90 degrees, and they were all reasonably close to 45 degrees from the previous (14.7 ft lbs) position. This would indicate that my torque wrench is a little light, and/or that the 14.7+90 spec is intended to get you a little over 40 ft lbs total.

From there I measured every bolt and recorded its length into a spreadsheet to easily calculate the stretch. The idea was twofold: make sure that none of the bolts were stretched noticeably more than another (indicating a bad bolt), and to find any under-stretched bolts and torque them a bit more.




The idea was good, but, in practice, measuring the length of the rod bolts was tough. The OEM bolts aren't designed to be measured like this, so the surfaces of the bolt head and bolt bottom aren't perfectly flat or parallel to each other. This makes it really fiddly to use a micrometer, as you might be on a high spot, for example, which you weren't on during the original measurement. I found that consistency really helped; e.g., I tried to measure each bolt in exactly the same orientation every time. Even then, it was typical for me to see deviations of up to 0.0020" within repeated measurements of the same bolt. This is why the ARP bolts are designed with a little dimple in the head, so that you can use a pointy-tipped stretch gauge and get much more repeatable measurements. My solution was to take 3-4 measurements per bolt and average them together.

With that, I was able to calculate the stretch of each bolt. All of my bolts had stretched about 0.0053", with the lowest stretch being only 0.0027" lower than the highest (which is only just over my worst measurement deviation). So, looking pretty good!

That said, I decided to try to bring the most under-stretched bolts up closer to the most stretched bolts. I did a rough calculation, based on the thread pitch, to relate the desired additional stretch in length to degrees I'd need to additionally crank the nut. I also added the target measurement, so that I'd know what measurement I was shooting for after applying the additional degrees of turn. You can see those values in my spreadsheet.




I then marked my 14mm socket with 2 10-deg markings, at 90 deg intervals. This was not very precise, but would at least give me a visual reference for how far to crank the nut. I'd seat the socket onto the rod nut, find the closest set of markings on my socket, then draw a little line on the rod to align with my first marking. From there it was pretty easy to get down to 5 deg increments, as I could easily eyeball halfway between my marks.






In practice, I found that trying to torque anywhere less than 5 deg didn't work with any reliability; that's just too small to overcome the standing friction with any precision. But, for the bolts which required more than 10 deg, the system worked like a champ! I was able to bring increase the stretch of my shortest bolts to within 0.0011" of the longest ones. Again, this well under my previous measurement's margin of error; so you'd be right if you said this was a bit overkill

Now that I've gone through all of this, if I had it to do again, I'd probably get the ARP bolts, and do the proper stretch spec. If I were to do the OEM bolts again, I'd definitely measure their lengths pre and post torque, but only with an eye towards catching any obvious outliers. Regarding the different torque specs for the OEM bolts, the experience with my bolts would suggest that it doesn't really matter- they're all very similar to each other. Most of my bolts ended up at somewhere just slightly north of 40 ft lbs (and likely within a margin of error for any typical torque wrench), and also right around 90 deg over the initial 14.7 ft lb torque.

Good times!

-Jake

[Inkblot]

Slightly off topic- but if any of you like this kind of project, and are looking for a semi-professional workspace to work on your own stuff, the shared shop space I work in has an opening. Check out my other post here:
https://forums.pelicanparts.com/off-topic-discussions/1032886-shared-shop-space-available-sf-bay-area.html
PM me if you're interested!

Jake

[Inkblot]

Some slow progress here at the shop.

I cleaned up and test fit the oil pump and IMS assembly:




... then I remembered that I did have new IMS gears in my parts box. A quick trip to the hydraulic press and the old gears came right off.




Here's the assembly with the new gears. Anyone notice what's wrong?




Yeah, I put the drive gear on backwards! Dumb. No damage though, just a pain to get back off.



That's better.


Ok, everything's as it should be- fits well and turns smoothly.





The old gears actually look pretty good, after a quick media blast. I'm not going to reuse them, but if I were, I suppose I'd need to somehow polish the teeth (as the new gears appear to be).





Any schools of thought out there on reconditioning/reusing gears like this? I don't need to, but I'm curious...

Jake

[Inkblot]

I'm getting ready to seal up the case halves, but first, I thought I'd make up a quick set of the metal rod and chain holders:











I wouldn't call these professional grade, by any stretch... but they'll do the trick.

Jake

[Inkblot]

In prepping for closing up the case, I've read a bunch of the threads here about which sealants and techniques to use. The grandaddy of them all is here:

The Complete Engine Sealant Thread...

Yes, it's 31 pages (and counting) on sealants. Not because it's such an interesting topic, but because everyone seems to have a different opinion on how to do it! Anyway, I'll be going with a slightly modified/updated version of Henry Schmidt's recommendations:

Outer Case Halves: Threebond 1184 (was 1104)

Bearing Saddle Surfaces: Loctite 574 (super light coat for sheer strength)

#8 Bearing (balancer end) O-Ring: Threebond 1211 (1215 is the new version, but 1211 is still out there)

Case Thru Bolts: Dow Corning 111 on Green Viton O-Rings

Flywheel Seal: DRY

Balancer Seal: DRY

Intermediate Shaft Cover to Case: ThreeBond 1211

Oil Breather Cover to Case: ThreeBond 1211

Cylinders to Case: Curil K-2

Cam Towers to Cylinder Heads: Threebond 1184

Cam Chain Housings to Case: Threebond 1184

Cam Chain Housings to Cam Towers: 1184

Cam Chain Housing Cover to Cam Chain Housing: 1184

Gaskets: Thin coat of Loctite 574

I've amassed all of those goops, and more, so I think I'm almost ready. I'm still open to suggestions on the sealant front, however, I definitely don't need to re-hash any of the (religious) arguments from the previous thread




Having never sealed a 911 case before, I've got a fair bit of anxiety around getting it right; or, at least, as good as it can be. I think part of what makes it nerve-wracking is that you have to move quickly (before the 1184 sets up), and that you probably won't know you've screwed it up until you've got the whole rest of the motor together and driving for a while.

The best advice seems to be to stay organized, and to rehearse the routine. A such, I'm double-checking that I have all of the gaskets, hardware, and sealants at the ready. Going through the hardware, I found my original case bolts, bevel washers and nuts. They appear to be in good shape, so I'm inclined to reuse them. I'm tempted to re-plate them, so that they'll look amazing before quickly getting covered in oil because I've botched my sealant job - ha

On that note, all of my local plating shops have minimum orders, so it doesn't make sense to just send the case bolts and hardware. If I do go down that path, it would be best to send everything I might need re-plated, which means looking into the future a little bit. Any recommendations out there as to what other engine hardware I should send to the platers as a "while I'm there" kinda thing? I already bought a set of new hardware for the engine tin, so I'm mostly asking about structural stuff around the case and top end.

Here are some pics of my cleaned up case through-bolts.

Fresh out of the parts washer:








Hit with a wire brush:










Jake

[Inkblot]

Oh, and the bolts:

[1980 SC Targa]

This is a great thread thanks

[47silver]

yes very nice thanks

[Richey]

Has your case really been measured by someone ? I can't believe the main bores are still round , they become oval shaped and when the case is bolted together again the crankshaft will not turn so well . How are the cylinder decks ? #2 is always low on a high mileage engine . The camshaft housing will be warped and the camshaft may bind .

[manbridge 74]

Put a straight edge on the spigots and using a light from behind you will know right away. Last two mag cases I did still measured out great, but they were low stress T engines not the later heat affected t-reactor 2.7 type.

A tip for good sealing: there are a lot of stud holes as you can see. Make sure there is no debris in them or studs will scrape it off causing it to land on sealant below as you are lowering case half or cam towers.

[Richey]

I am working on an original '71 with 90,000 miles . #2 cylinder deck was .005" low .
Good luck with your project .

[Inkblot]

@1980, @47silver Thanks for the feedback!

@Richey Yes, my machinist (Ted @ German Precision) measured the case. That said, I did not receive a list of those measurements- just the "thumbs up" from a reputable, old-school Porsche guy. He's human, so mistakes are certainly possible- but normally his a-ok is good enough for me.

@Richey + @Jeff Can you guys clarify re. the measurements you're talking about? I understand the issue about the roundness of the main bores, and as mentioned, I'm trusting Ted on that one. I do have a bore gauge, so I may try to check it out myself as well; but I think it'll be hard for me to reach the innermost bearings.

What exactly do you mean by "cylinder deck"? I'm assuming you mean the surface on the case upon which the cylinder sits? If so, these were resurfaced by Ted (see above re. human infallibility )

Put a straight edge on the spigots and using a light from behind you will know right away.

Can you elaborate? What would I be checking for here?

Thanks guys!

Jake

[Inkblot]

Got a bunch of hardware back from the local plating shop, HyTech. They were great; recognized the parts as from a 911 right away. I don't have a lot to compare to, but the quality seems great to my eye. I had my parts back in 3 days. The biggest issue is that they normally do things in bulk, so there are minimum charges per process, which means you have to have enough parts to make it worth it. Also, staying organized is a challenge, as all of the parts get thrown together; so I made sure to take lots of pictures to help me remember which parts go where.

Here's a few pics of the engine through-bolts, you can compare with the pics from the earlier post:






I really like the idea of a DIY plating setup. This thread has been awesome- check it out:

https://forums.pelicanparts.com/porsche-911-technical-forum/1023138-zinc-plating-diy.html

I may still go the DIY route for future stuff, as I really like the possibility of doing a few parts at a time when you need to. But, despite my workspace being within a semi-pro shop (or maybe because of it...), I have yet to convince my stable mates that having those chemicals laying around here is a good idea... Until then, it's batch 'em up and send them to HyTech.

With all the hardware back, it's almost time to seal up the case!

Jake

[manbridge 74]

Ted did my cylinder heads, pretty sure you’ve nothing to worry about in regards to case warp if GP were assessing it.

[Richey]

If Ted resurfaced the cylinder decks , seems your good to go .