Engine rebuild question...

[M491]

I have a question after a bit of a long story... I bought a 1972 911T that was embroiled in a mechanic's lien situation, and had been sitting for about 18 years. When I found the car, it was outside and had no intake on then engine. It had been raining that day, and I noted that some water had been dripping into the intake ports. I stuck my finger into a port and found dirt and tree droppings inside. So, I figured that this was an engine that was hopeless as it was. I finally got the title to the car and had it flat-bedded home.

In the meantime, I bought another 1972 911T engine, complete with MFI, from a long-distance member of this forum (and the 356 registry too). The seller told me the engine had very good provenance and was "running sweet".

At this point, I have to say something... The Porsche community has been one in which I have been ripped off about 90% of the time. I'm a trusting type and , I guess, there are a lot of people out there who would rather get as much money from anyone at any cost. Zero integrity.

As you may have guessed, the "sweet running" engine has leakdown figures of under 10% on cylinders 1-4, a bit higher on cylinder 6, and 40% on cylinder 5. Long story short: This engine is no good. It basically has a dead cylinder and very little power. I know it was rebuilt, but has either a burnt or bent valve, or a broken ring. Oh well. Why am I not surprised. Why my ex-mechanic bothered to install this engine at all is a question I ask myself daily. That mechanic was German Auto Service of Jessup Maryland. He charged me through the nose to install a a crappy engine, put in a 914 fuel pump (I had to go buy another correct MFI electric fuel pump), charged to swap clutches, clean the fuel tank, and many other things, all of which he never did. I removed the fuel tank he had "cleaned" and it weighed about 50 pounds--all sludge. He never even removed the level sender. I know for a fact because when I tried to look inside for my self, the screws securing the sender were seized and snapped. Now, I have a solid and straight but limping 1972 911T sitting in my garage leaking oil, and the original engine dismantled and on an engine stand being rebuilt.

On to my question (finally), regarding the original engine (the one that had dirt and water in the intakes). I dismantled this engine, and it actually came apart quite easily, The PO had converted this engine to Webers, so the heads were plugged. I was pleasantly surprised to find that this engine had been rebuilt with 2.4 911S pistons and cylinders. The cylinders, particularly number 4 and 5 had a layer of rusty colored sludge (dirt and debris) on the bottom inside surface outside of the pistons. Question one: Can dirty S Nikasil cylinders be honed by a machine shop to clean them for reuse?

The heads are currently out being rebuilt by a pro. I have a new set of 911E cams. I have a choice of 2.2 911E pistons and cylinders, a second set of 2.4 911S pistons and cylinders, and the dirty 2.4 911S pistons and cylinders. I have a new set of Goetz piston rings to use on whatever pistons I go with. I also have a complete and good 2.2 911E MFI setup I want to use instead of the Webers.

Now, the main question... I split the case and found it surprisingly clean inside. I know for sure it as rebuilt because of the 911S P/Cs, and I know the engine can't have been run much because it sat since 1989. I am going to bring the case to a local machine shop to clean it up, verify tolerances, and ensure the mating surfaces are straight, and install case savers. The main bearings are STD with a date code of 5-82. The crank looks perfect to me. I see no scoring or pitting anywhere. Because I have been so ripped off and so bled of money by the extra engine seller and by German Auto Service, I want to spend as little as possible and come out with a strong and reliable engine. I'm wondering if it is absolutely necessary to remove the connecting rods, have them resized, have the crank micropolished, renew bearings, etc.? Obviously, I have to renew all of the gaskets and seals, I know.

My hope is to be able to not disturb the crank and rods setup, install all new seals and chains, re-mate the case halves, install a set of pistons and cylinders, install the rebuilt heads and E cams, and be done with it. Does this sound OK? Would it be false economy to neglect the crank and rods that have been sitting for almost two decades but not run much since the previous rebuild?

Finally, considering the price of gas today, would the use of the higher compression 2.2 E pistons be worthwhile over the lower compression 2.4 S pistons? I mean, with the S pistons, I could run any gas, I guess.

Thanks for reading this far. It's a long story and a lot of words, but I need some good advice, and appreciate it in advance. Thanks...

[66S]

If the mains look like new then the rods should be just as good but there is only one way to know- then you must get new rod bolts and nuts. Id spend the $300-400 and renew all if needed. You gotta ask yourself- Do I feel lucky? Id use the S pistons for street, dont use base gasket for a little more compression. 2.2 E pistons will give a high compression ratio but will probably need valve pocket machining and they arent forged like the S pist.

[Tom F.]

Here's my two cents' worth.

I would skip the case savers - they're really only needed for the 2.7s, which have a lot less metal between the cylinder head studs and the holes where the cylinders go.

I would not hone Nikasils. I thought that Nikasils wouldn't rust. Maybe the rust is the piston rings, which is bad news. Or, maybe you got lucky, and the rust is just corrosion that dripped off the valves.

Why not leave the crankcase alone? The main thing to worry about in a 2.4 engine, in my opinion, is an out of round #1 main bearing. (I have seen that they tighten up, which I believe to be caused by the compression of the through bolts, and the expansion and shrinkage caused by heating and cooling cycles.) If the bearings are new, and the crank measures up okay and turns freely, then I would be inclined not to spend money on the crankcase, especially where it sounds like you may have to spend lots of money on new valves.

Good luck.

[Tom F.]

P.S. I wouldn't waste money on having the crank polished. Besides, it's a good way to put flat spots on your crank. Also, why put in new chains. Check them - the ingenious timing arrangement on 911s leads to exceptionally long timing chain life.

[304065]

Do not let prior bad experiences force you into compromises that could potentially be problems down the road.

First of all, when you take a magnesium case apart, it may or may not go back together without being surfaced. Unlike an aluminum case, these things tend to warp, hence the resizing process. If you split the case, be prepared to have it surfaced. If it were me, I would absolutely check on the condition of the crank and rods-- no point doing a bunch of work only to experience problems down the line. You should consider the oil bypass modification, this is not expensive, and any other machine work necessary to bring it back to spec.

I would NOT trust this work to the local machine shop unless their name is Ollies, German Precision, Competition Engineering, etc. Shipping a mag case to the experienced shops is not an expensive proposition.

Nikasil cylinders should NOT be honed. Consider a red scotch-brite pad and some motor oil as a lubrican to remove the ring of crud. If they are too far gone, they can be bored and replated, but this is very expensive.

If you want to use 2,2E MFI, fine, but remember that if the pump needs a rebuild it's $1600 and if the stacks are worn out it's about $1200, and without these services it's hard to make 40 year old stuff work right. That said, I have a 2,2E that I absolutely love-- the E cams should be used to match the fuel delivery curve of the E pump unless you have many, many hours to dyno and AFR test the fuel curves and adjust the pump.

Anyway back to the main question, the only way to tell whether your crank is in spec is to MEASURE it. This isn't hard if you have an outside micrometer and are willing to invest the time to learn the "feel" of how the mic works. If not, the same shop that will check out your case can check the crank, costs a little more in freight but good to do. Bearing sets aren't that expensive and again, good cheap insurance for the future. Ditto the rods, check out the small ends and measure to see if they are in spec, rebuilding the rods is worthwhile once you are in there. Excess play between the rod bearing and the pin is not likely to lead to long-term longevity.

The chains stretch with time. Check the sprockets also, the teeth wear to a point. If the chains are too long, the tensioners won't take up the slack.

Hope this helps, let me know if you have additional questions.

[M491]

Thanks for your input everybody. I will likely make few or no compromises. I just have to have more time and money, both of which come with patience. The crank looks like new. It doesn't have a scratch. So, I'll have it measured with the rods and have the rods reworked if needed. (The heads are presently being completely rebuilt). I do still have a couple of questions. John Cramer, is rebuilding or refurbishing the rocker arms essential? I have a newly ground E cam from John Dougherty. I plan to use RS O-rings on the rocker shafts. Refurbishing the rocker arms costs $360. Second question: 66S suggested not using cylinder base gaskets to raise compression a bit (these are the thin copper gaskets?). Sounds good, but don't these gaskets have a function? I mean, if I were to leave them out, wouldn't the engine possibly leak oil and/or lose compression there?

Regarding the cylinders, they look very much like much of what seems to be rust in them is really deposits of junk that dripped in from the environment, and some rust from the heads. A fingernail can affect this stuff, so I think it's sitting on the Nikasil surface, not eating into it. I think I'll try the red Scotchbrite pad here. If not, I'll set them aside and use another set of pistons and cylinders I have stored.

Thanks!

[304065]

Mauro,

Resurfacing the rockers is essential-- the face of the rocker that rubs on the camshaft will develop a wear pattern that is uneven across the face. If this is allowed to rub on a new cam, the wear on the cam lobe will be uneven. For this reason the rocker face is always ground when a new cam is used. John (Camgrinder) can handle this for you or any of the other shops, I used Ollies for mine, it's not complicated and I think $360 is high.

It's not a good idea to alter compression ratio with cylinder height. The base gaskets serve to prevent the cylinders from leaking and galling against one another, as well as spacing the cylinders up so the heads are at the right height, so the cam boxes are at the right height.

Unless you have the ability to measure precisely the height of the heads and cam towers (to the centerline of the cam) and then remove .25mm of material so the height matches, then the cams will be off-center in the seals. Enough of this tolerance buildup from this and other sources (like surfacing the heads, which your rebuilder is probably doing) and flattening the bottom of the cam tower and pretty soon your cam seals are leaking. OK, so Bruce Anderson says you can take 1mm off the heads to bump compression on the IMSA 2,5 and the chain tensioners will take up the slack, but why push your luck when there are better approaches that will allow you to retain target 1mm deck?

If you want to alter compression you can have the rod bushings offset bored, or change the pistons-- there are many alternatives that keep the geometry the same.

Hmm here is some math a 2,2E has 9.1:1 compression so with a 1mmm deck height and 68cc chamber that's a dome of 28.4cc-- using that same piston in the 2,4 (70.4) with the 2,4 rods, compression and deck height the same gets you 9.6:1. If you use a thinner spacer you would be at 9.9:1 BUT I would be absolutely certain to check piston-to-head and camshaft clearance and consider twin plugs if you want to use street gas.

[Tom F.]

Mauro,

I had thought that you were trying to do a budget rebuild. If you're going for gold, then you should probably have the heads altered to the E intake port size, which is a couple of millimeters larger than the T heads that you have. Send the case and connecting rods to German Precision or Ollies, like John says. Send the FI system out, too. Include the fuel injectors, so they can test them, too. If you do new chains, put in new sprockets, too.

I wasn't advocating the shortcuts, except to save $$.

Tom

P.S. If you're going to give the crankcase a try as is, you should Plastigage the mains, to make sure that the #1 isn't tight.

[M491]

Thanks. Yesterday, I sent off my rockers to John Dougherty to have them refurbished. He told me he'd do them for $30 each. Multiplied by 12, this comes out to $360. I thought this was really high too, but since he did such a good job on my cams, I figured I'd just take the pain. I wonder if he might consider a bit of a discount. I hope so.

I may decide to just prepare all of my parts, to include rebuilt heads, etc., and bring them to a local expert named Taylor Chapman to put together for me. He's a good guy and a super Porsche mechanic. I truly believe building this engine myself is within my personal capabilities, but I feel like I want to be able to drive this car with full knowledge of its reliability. I've never done this before, so I worry that I might make a simple but ruinous mistake, causing the engine to fail after a relatively short time. I go back and forth on this thought constantly.

[66S]

I run a bead of silicone sealant in the corner of the mating flange of the cyl., dont use too much, just enough to seal. Ive done this with 2.0s and have had no problems with sealing , chains, deck height or anything. And it costs $0, my favorite price. The 2.4 MFI head has 30mm intake ports, too small? My 2.4 T ran strong but if you want more top end power then port them. Magnesium cases often become tight on the main bearing webs, these need a ream to std. or some hand work [you guys would laugh if I told you how I do this]