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otto_kretschmer's Avatar
 
Join Date: Jun 2010
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it's a mag mag mag world

Hi folks,

I'm in the (slow) process of moving back to Arizona. Currently reside in California.

When I eventually get home and have my garage set up I'll be working on the car to get it on the road. I can register the car with historic vehicle plates and avoid a smog test so I have a lot of options open.

option 1: stock rebuild of the 2.7 in the car. Its a magnesium block and will need an align bore if I split the case.

option 2: I have a 2.2 that came out of a 1970 911t. Magnesium case and Zenith carbs. This maybe a step backwards but if I can use it with just a top end, this may be a viable solution.

option 3: find a 3.0 or 3.2 with an aluminum block and build a motor. This is the most expensive; core, rebuild and maybe PMOs

Are oversize bearings unobtanium for mag cases? Bearing availability may be the ultimate driver of my choice.
Old 04-07-2019, 09:32 AM
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Why do you think it will need align-boring? Some do, but many get bored that didn't need to be.
Old 04-07-2019, 10:48 AM
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Quote:
Originally Posted by Daves911L View Post
Why do you think it will need align-boring? Some do, but many get bored that didn't need to be.

I'm just going with the worst possible scenario. If I split the case, I'm committed. If the case doesn't warp then I'll be lucky. I won't know the condition of the bottom end until I split the case. I may get by with just a top end of the 2.7. New pistons/cylinder kit and a valve job and slap the thing together.

If I split the case and it does need a align bore and the bearings are no longer available then what do I do? Machine the case faces and rebore to the original bearings?

I just want a daily driver. I plan on taking the car on road trips to Vermont, California and Washington so I don't need a hot rod engine. A stock engine is preferable.
Old 04-07-2019, 11:08 AM
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Location: Fallbrook, Ca. 92028
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Every 75-77 2.7 911 sold in California came from the factory running too hot.
This was the nature of the smog equipment.
Almost every engine ran in excess of 245 degrees. Because of the thermal reactors, they actually got hotter after the engine was shut off.
Heat is the death knell of magnesium cases.
What happens is that expansion causes the crank bore to distort. They get oblong from top to bottom with the center actually getting smaller.
Over the years I've seen inexperienced builders, go cheap on the rebuild by refusing to split the case.
What would happen is they would notice the case through bolts were loose so it seemed reasonable to replace the o-rings on the bolts and re-torque to factory specs. The result more often than not was the crank would seize up.
Is it guaranteed that a 2.7 case will need align bore? no, but I would bet on it and give odds.
As for bearing availability, Supertec has most of the odd ball bearing available.
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Old 04-07-2019, 11:50 AM
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Hi Henry,

This is a California car. I bought it about 15 years ago and it was on its last legs, ready to get parted out. I drove it a little and then parked it.

The thermal reactors are long gone. When I get back to Arizona I'm going to drop the motor and do a partial tear down/inspection. If I see signs of a rebuild (case savers) I may just do a top end. If the bearings are available and priced within my reach then I'll probably do a complete rebuild.

I think I should go close my garage door before another lookyloo shows up
Old 04-07-2019, 12:44 PM
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First under Undersized bearings, for when you have to turn the crank, aren't that expensive. Oversized od bearings, if you do an old style align bore, are a much different matter, and I'm pretty sure that the extra cost of a proper align bore, where a bit is shaved off the case mating surfaces, and the case bored back to standard, is a money saver.

A first under/first over bearing would be quite tough to find, I suspect. But one probably ought not to underestimate what Henry has tucked away.
Old 04-07-2019, 08:34 PM
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I expect the crank will not need to be ground. I've only rebuilt 5 engines: 2 BMW airheads, a vw type 1, a type 4 and a 152 for a IHC Scout. Only the 152 needed work on the crank. That engine was beyond belief how worn it was. The other 4 were fairly well treated with proper oil changes.

Most likely I'll only need oversize on the case side. I'll only know when I get the crank out and measure the journals and look at the overall condition of all the parts.
Old 04-07-2019, 08:58 PM
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It would be worth checking with Ollies or whoever you would have align bore your case how much extra it costs to have them do it right so you end up with stock standard dimensions. Twenty-five years ago I'm not sure how to do this was broadly known - Bruce Anderson's first handbook on the 911 didn't mention it. But now we all know, and at least in the abstract it is easy enough to understand, and probably to do with the right equipment. You do have to pull all the perimeter studs, and maybe the head studs, but a guy could to that himself easily enough before shipping the case halves off.

My biggest mistake back when was not specifying that the #8 bearing bore be left alone. Look around to see what a first over #8 nose bearing costs. Maybe it is less now than then, as the regular #8 isn't super expensive these days (because there is an aftermarket source?), but they don't wear much.
Old 04-08-2019, 07:22 PM
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I did a leak-down

#1 90/92
#2 90/92
#3 91/92
#4 101/105
#5 96/98
#6 55/90

blah, almost perfect

#6 may have some crud on one of the valves

Maybe my thoughts on needing to do a rebuild are premature.
Old 04-09-2019, 12:44 PM
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Update

In a similar situation, interested, and following! Any Update?
Old 04-28-2019, 06:17 AM
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Quote:
Originally Posted by Left_coast*9 View Post
In a similar situation, interested, and following! Any Update?
nope,

I got my 911 running to the point I can drive it in and out of my garage and onto a trailer and that's all I wanted right now.

I was always thinking that I would need an overhaul because it seemed like the oil pressure was on the low side when the engine was hot. So I finally did a leak down after owning the car for 14 odd years and I was really surprised of the results. The engine is in a lot better shape that I was expecting so I'm going to hold off on the rebuild until I figure out what is wrong with #6. If its a valve then I'll just fix that but if its the rings then I may have to do more.

Right now I'm knee deep in my new-to-me suburban. I just finished cleaning off all the mud on the undercarriage and I'm having buyers remorse.
Old 04-28-2019, 02:09 PM
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911

Time to focus on the Porsche!
Old 04-29-2019, 03:37 PM
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