The real red story

It seems a lot of people don’t understand what goes into making an engine or what manufacturers do to control clearances (ie: bearing and piston sizes). Let’s look at piston sizes in a Holden si x or V8: These could go from size one to size 25 wit h one through 16 being `Standard’ and 21 to 25 being 0.005” or 0.006” oversize. From what I can remember there was no si ze 17-20.

Pistons were placed in a controlled-temperature room for 24 hours before being graded for size. The dif ference in size was measured in microns and t hat’s why t here were so many variations. If you look at t he pan ra il of any of these engines you will see t hat t he piston size is stamped adjacent to t he bore so t hat t he pistons could be selected and prepared long before insertion on t he production line. As fa r as I can remember there were no oversize rings to go wit h t he 0.005” or 0.006” oversize pistons.

Now for the bearings: If you look at t he pan ra il again, you will see t hat there are centre punch marks adjacent to ever y main bearing cap. One dot equalled a standard bearing, t wo dots indicated a 0.001” bearing in t hat location in t he block only.

Then, the crankshaft will have coloured daubs of paint next to each main journa l indicating standard or 0.001” on t hat particula r journa l a llow ing for t he correct bearing to be insta lled into t he main cap. I don’t ever reca ll seeing 0.010” bearings being insta lled in t he block (as one of your prev ious respondents claimed). This was to ensure that the assembly process went ahead without too much conf usion over selection or placement of t hat bearing.

Remember that one 0.001” bearing ta kes up 0.0005” of clearance and t wo shells ta ke up 0.001”. All of t his extra selection was done to ensure correct oil clearance and tolerance.

As for t he crank pins, they were a lways standard or a ll re-machined to an undersize. This was done to again avoid conf usion on t he line. Yes, t he old engine plant was getting long in t he tooth but even new engines built in new plants with new machines st ill have select-f it bearings.

Rule number-one of engine building: Always build it to spec and build it clea n.

WC,

Email. Morley Says

JEEZ, WC, if I didn’t know any better, I’d say you’ve been inside your fair

share of Holden engines over the years. And in a more-than-cursory way. It’s interesting that you claim all the big-ends were either standard or, if one measured up a bit small, the whole lot were reground to the first undersize. That makes all sorts of sense to me, as it would eliminate somebody putting the wrong bearing in the wrong crankpin on a hazy Monday morning after the Grand Final.

Meantime, I’m off to the shed to check my current red-six build for the punch-marks and stamps indicating piston size. I never knew these marks existed, but clearly, you know what you’re talking about. I guess I’m just like any other workshop dufus: I tend to focus on what I have in front of me, and forget about the history of the thing that could actually be telling me a whole lot more.

And it won’t be just me, WC; that sound you can hear right now is that of UC readers pushing back their chairs and heading out to the shed to take a close look at that old 186 block in the corner.