Groves cut into the crankshaft main journals

[Doug Thomson]

I am getting nervous about the cost of this 1964 356SC engine I am rebuilding. The 912 heads seem to be no good. One has been fly cut and the Depth of cylinder seats are 6.0mm. The bottom fin is pretty thin. The other head seems to have been cut unevenly, in that, the embossed area on one side is present and not on the other. The Depth of cylinder seats are 6.5mm.

The crankshaft main jourvals have groves cut into them which I have never seen. I am concerned they too may be unusable.

[Doug Thomson]

I forgot to mention that all three main bearings are not groved.

[Vic Skirmants]

#1 main journal appears to be the 55mm S-90 size.

[Doug Thomson]

Zim, I measure #1 49.72mm #2 54.65mm and #3 54.70mm. It seams to be correct for sc:912. Just the grove is on the journals instead of the bearings? Thanks you, retroactively, for your post on Feb 13,2017 about exhaust port size being noticeably larger on 30 degree heads.

[Vic Skirmants]

I mistook the image size; and PLEASE don't call me zim!

[Doug Thomson]

I am really sorry Vic! I am losing my mind. I read you posts all the time and ... No excuse. I am embarased.

[Doug Thomson]

As embarrassed as saying the "Just the groove is on the journals instead of the bearings". The bearings are groove-less. Not my day.

[Jacques Lefriant]

Hi Doug
i have no issue with the grooves on the journals. the crank is .25mm already which means it has been ground at least once before. From your measurements i would grind to .50 the cost of having this done pulling the plugs and renitriding and the fatigue factor. you may consider another crank. A SCAT crank is probably overkill. there are other options each with their plus and minuses. Check with Olivier he may be able to help you.
j

[Doug Thomson]

Thank you Jacques.

[Mike Horton]

Doug, search for the "AA Performance Products" Asian forged C/SC/912 clone crank, new manufacture, I know 2 912ers who have used these lately.

Note of caution: The oil journal plugs, to which Jacques refers, on these Asian clone cranks, are not the factory type driven in soft plugs, but they come already drilled, threaded, with the screw in plugs installed...

"LOOSE!"

They are only installed finger tight, as the Scat cranks, I presume under the assumption, that any competent engine builder, will remove them, perform a final cleaning, and reinstall, and tighten, likely with Loctite.

[Doug Thomson]

Thanks Mike, I will. What are the plugs for? Cleaning?

[Mike Horton]

Yes...

[Vic Skirmants]

The plugs are for plugging the hole required to do the proper drilling of the crank oil supply holes.

[Doug Thomson]

Thank you Vic

[Mike Horton]

To complete the thoughts of Vic & I, without the plugs, as Vic said, these drillings are to correctly tie in the other improved oil passage cross drillings, and, for later proper cleaning of the centrifuged particulates from the oil, thrown there in service. Without the plugs, the oil pressure would leak out into the case, and not build the "life blood", of the needed oil pressure to lubricate the engine's bearings, and journals. The "spin off oil" spray, out of the bearing, and crank journal interface, also "splash" lubes the cylinder bores, and ultimately, the piston & rings, which have a big job to do in the process.

We tend to hurriedly answer these questions, but the "rest of the story", which seems easily understood, for those of us who have been around these engines for a long time, may not be so obvious, to the newer of our number, so forgive us in our brevity, and keep asking questions, until we fully answer your inquiry...