2.7 Crankshaft journal advice

[SunburntLobster]

2.7 Crankshaft journal advice

I have torn down my 1976 911S (2.7) due to low compression on cylinder 1 - turned out to be broken ring(s) and smashed skirt! The car has done 183k miles or had done when the odometer stopped clicking around.

Due to extremely tight budget I am looking for opinions on what to do with my crank.

Realistically it will always be a fair weather car, doing 2-3k per year. I am the sole driver so will always be warmed up and not used for short hops.

It won’t be doing any track work and will have the oil dropped every year and an oil analysis done so I don’t need an engine capable of another 100k+ miles

The readings are:



Due to the low cost of over-sized rod bearings I intend to get those journals reground to first over size (0.25).

Due to the high cost / unavailability of over-size main journal shells I intend to leave them and have new standard shells coated with HM Elliott HM-30 or similar to add a little meat – this is subject to the journal polish not taking them out of spec.

Any other thoughts / recommendations?

[dannobee]

It's a little late at this point, but splitting the case on the mag case engines often results in the case distorting (banana shaped). When you reassemble the case, often the crank will not turn by hand, necessitating the case to be line bored. I'd be more worried about that than any crank or bearing work at this point, as it's costly to correctly line bore the case.

[tx93086]

The rod bearings have much higher loads on them, and your 1 journal is well past the spec wear limit of 51.960, but your main journals are all under the wear limit of 56.960 so given your situation, there is no need to do anything with the mains. Warpage of the case may be a bigger concern, but there are ways to deal with it (though not ideal) that will allow you to avoid line boring.

[Walt Fricke]

I'd send the case to a shop which has experience line boring these cases, but back to standard and not oversized. Those larger OD bearings are expensive, and the #8 really so (or it was 20 years ago). These shops A) figure out if the case will bolt back together with these openings in good shape, and B), if on rebolting the bores are out of whack, they can line bore back to standard. They do this by shaving a little bit off the case mating faces, then line boring to standard. It appears this works pretty well. The case does not end up significantly narrower than it was, so you don't run into issues there. It is also a time to true the tops of the cylinder spigots, if they will benefit from that.

[colingreene]

Plan for around 3k for machine work on the case.