2.7 Rebuid on Budget

[jgparker]

I've started rebuilding my '76 2.7 911S engine and times being what they are, I'm on a budget. The plan is to go with Early S-Cams, early dual sports exhaust, Webbers, and maybe raise the compression a little. I would like to do as much as possible myself, so my questions are:

1) The connecting rods all measures in-spec and the bushings look great, so can I get away with just replace the big end bearings and rod bolts or do I really need to have them professionally rebuilt?

2) The crank shaft measures well within spec. Is it reasonable to have it magnifluxed and micro-polished locally, or should I send it out to a Porsche specialist for expert evaluation? One rod bearing was down to copper, but there is no measurable or perceivable damage to the crank.

3) All of my intake valve stems measured below spec nearest to the heads. (~8.920 mm) They were in-spec in the middle and closer to the retainer. Is this how they normally wear, and should all the intake valves be replaced? several measure a little long too.

4) The exhaust valves all measured with-in spec. I get the impression the exhaust valves and guides were replaced in the last rebuild, but the intakes were not. Should the exhaust valves still be replaced? The valve guides are all worn-out, and will be replaced.

5) before I started the rebuild, the oil pressure would drop abruptly when I let off the accelerator at very high RPM. There was no obvious cause on engine disassembly. What could cause this odd oil pressure behavior? Worn oil pump, very worn bearings, or pressure relief springs and pistons?

6) Is there a reliable way to raise the compression when using 2.7 Euro RS P/C from 8.5:1 to 9.8:1? (lengthening the rods or decking the case?) By my calculations, It should take about 1.4 mm to raise the compression this much, but I would think this would reduce the piston to head clearance and valve to piston clearance down to near-zero. I know a cleaner option is the Mahle 93mm 9.8:1 P/C set, but they are close to $3k, which is a bit pricey for me. The old P/C set are Alusil, and are used-up.

Any help would be greatly appreciated. By the way, Wayne's new book is great. A must have if you are doing a 911 engine rebuild.

[Britwrench]

You haven't mentioned the most important part of 2.7 rebuilding; having the case properly machined.

[jgparker]

I'm sending the case, heads and rockers to Ollie's for machining. I hear they are good form local PCA people. Freight from FL to CA is going to be a little high though.

[Roland Kunz]

Hello

The question is on what level and budget will you work. There is a big difference between slaping a engine togehter or rebuild one.
Finally they look the same way and both work.

1.) have them checked ( truiness ) and renew the upper end as well. Also you can polish the I beam and shave some wight off.

2.) Check the rockwell hardness on that failed bearing and have the oil bores extensivley cleaned.

3.) Why making compromisses ?

4.) see abouve, the thing is if you have no datas or feedback from a trustworthy previous rebuilder then you can´t say thats a solid fundament.
You can check the parts and decide if you save money and bear the risk. If you consider to rise the poweroutput then you either have the budget to do it right or you make a "intermediate" and make a solid base engine and save some money for a later upgrade. But don´t spend your budget on tuning stuff sacrificing the basics. Thats just wastet money, time and parts. Plus you can run into some serious frustration.

5.) maybe all that had a influence but on mag cases you loos pressure trough the main bearing galery. Have also all the oilsquirterers checked or replaced.
Have the case prepared to accept the new generation oilpumps. Case savers are a must as well ( reuse your steelstuds they are fine ). If your mains have to be bored up make sure you get a suiting main galery set ( including #8 ).

6.) I can´t follow your thoughts on rising compression. You can´t deck anything on 911 engines to rise the compression. The only way is to get a set high compression pistons. Other way would be to use heads with a smaller dome-chamber or you can regrind the crank to a slightly higher stroke and use suiting rods ( Carillo ).

Grüsse

[jgparker]

Thanks for the feedback. I have no problem replacing the valves. I just need reassurance that I'm not throwing away $400 worth of serviceable parts. The case already has time-serts and Dilavar studs, which I plan to keep.

[Bobboloo]

Just a little note on Dilivar. Some people advise against them because they can break. However, they do help you in not overstressing the case. The problem is that they are an alloy that contains alluminum and alluminum breaks down over time from stress loads. If they are old you might want to consider replacing them because they are most prone to breaking when re-torqued. If you don't mind going back into the motor then you might take the gamble and see what happens. Just check on them at tune up intervals.

[911pcars]

I'm not going to condemn Dilavar head studs as they seem work on some (my 2.7, so far) but not on others. Maybe the lifespan has something to do with the version of Dilavar and environmental issues. What color Dilavar studs do you have? I have a theory that the breakage frequency is higher with the silver or gold-finished versions than the later, black, epoxy painted ones. Just MHO, I could be wrong. Ideally, the breakage frequency should be zero. I've even heard of Raceware studs breaking though not as frequently - maybe because of the comparatively small number of these aftermarket studs in use versus the thousands of engines using Dilavar.

According to Racer's Encyclopedia of Metals, Fibers and Materials, Dilavar contains:
13% nickel
5-6% manganese
3-4% chromium
"dashes" of other alloying metals (nothing said about aluminum)

The trick part of this material is the thermal coefficient of 11.3 ppm which closely matches aluminum and magnesium. It has the same density and elastic modulus as other steels, and most importantly, in the same temper chosen by Porsche, delivers a UTS (ultimate tensil strength) of up to 180 ksi, a yield strength of at least 116 ksi and with more than 12% elongation (whew).

As far as fasteners go, that's fairly high-end metallurgy.

As for your engine, the regular RS pistons won't provide enough CR you're looking for. You may have to bite the bullet for the 9.8:1 Mahles or find some Nikasil cylinders and fit them with JE pistons with the compression of your choice. There's another thread on this forum where a builder ordered the incorrect JEs for his customer and may have a set of 10-11:1 pistons for sale. With a set of S cams (or wilder) and the correct set of circumstances (twin plugs, etc.), these may work. If they're 3 liter pistons (I forget), they won't. Anytime you deviate from stock dimensions, I suggest you double-check the piston-to-head and valve clearance and machine accordingly. Replace all out of spec engine parts. There's only so much you can do to make a correct 911 rebuild a budget proposition. Scrounging for deals on good parts and providing the skilled labor delivers the most impact.

Sherwood Lee
http://members.rennlist.org/911pcars

[jgparker]

My Dilavar Studs are the old black, coated versions. They appear to be in like-new condition. They've held up through one rebuild cycle so it is hard to justify throwing them away.

The exhaust valves are within spec, but I have heard recommendations to always replace them anyway. I was just wondering if this was the consensus.

[J P Stein]

I dunno if there is a consenus.
I put the latest full thread black coated Divilars (24 of em' and case savers) in my 2.7L ....with malice and forethought. It was the lesser of 2 evils deal. I would rather break studs than pull em'.

I also went to extra lenghts to keep the motor cool.....now it takes forever to get it warm (sigh).

[911pcars]

JP,
I say reuse the exhaust valves if they are within spec. The person doing the valve job may have more of an educated opinion after inspecting them as well. I'm not sure there is a consensus, just MHO.

Sherwood Lee
http://members.rennlist.org/911pcars

[J P Stein]

I concur with Mr. Lee.
I disassembled my heads then checked all the valve stems for taper using a certified mic, accurate to .00005...that's half a tenth in the trade. All appeared well.
Off they went to EBS....back they came with all new intake valves. No grind stock left on em'....rats. At least the intakes are the cheep ones.

[jgparker]

I have access to a real good set of digital micrometers too. Not only will they read to .00005", they'll read .001mm and you won't have to do the conversion. Makes the measuring a breeze. Wish I had a digital bore gauge to go with it. I'm afraid I'm loosing to much accuracy using telescoping gauges.

[PorschePilot]

Good choice on using Ollie's. I had them do my cases, rods, rockers and heads with outstanding results. Be prepared to spend $2400 to $2800 on the machine work. Don't forget to upgrade your tensioners.