Engine: Fitting KB Hypereutectic Pistons & Rings

[JoeHall]

I am ready to install the KB hyper pistons in the 289 block, so reviewed KB recommendations for bore clearance and ring gap in "street - normally aspirated" engines. If <4.1" bore, piston clearance is to be .0015" to.002"; if >4.1", it is .002" to .0025". So the .002" I told the machinist was spot on, and I STILL cannot believe he suggested .0005".

RE ring gap, the top ring runs much hotter in KB hypers, so needs extra gap, which is calculated at bore inches X .0065". So the 3.6245" bore X .0065" = .024" gap. The 2nd ring runs cooler, about same as OEM cast pistons, and is calculated at bore inches X .004", so 3.6245" X .004" = .0145" gap (OEM Stude spec is .008" to .012"). Currently, the new rings have .012" gap when slipped into the cylinders, so looks like I have some "sizing" to do.

I decided to do this separate post on fitting pistons and rings, due to so many members reporting overheating problems with Stude rebuilds. Most pay a "professional" to do the work, but it's getting hard to find someone who'll even follow Stude Shop Manual procedures, let alone a special app, like fitting modern pistons in a Stude motor. So I suspect some of the botched Stude motor rebuilds are due to improper assembly; there are several pitfalls, and fitting hyper pistons has a few worth mentioning. Per KB, if their rings do not have sufficient end gap, they may "lock tight in the cylinder" and break the ring lands on the piston. I am sure, prior to that, the motor would likely run hot, and seem excessively tight, especially upon shut down (near instant stop), and when cranking during hot restarts. Maybe this post will help someone else down the road, come time for an engine rebuild.

[Bud]

The last few sets of pistons have the required bore diameter printed on the box. I also go by the .004 inches of end gap for every inch of bore diameter and haven't had problems with hot running engines, broken rings oil consumption, blow by etc. I can see increasing the ring end gap and a bit of extra piston to wall clearance if the engine will run with higher compression or supercharged- turbocharged as that will raise combustion temperatures. I believe is best to follow the piston and ring manufacturers specs when installing pistons and rings. If in doubt about specifications, call the part manufacturers tech line for answers. Bud

[JoeHall]

Bud, that's exactly what I did was go to KB for their specific instructions, on THEIR pistons, specifically their hyper eutectics, which is different from other type pistons. If using regular cast pistons, I'd just use the Stude Shop Manual specs, but again it does not apply to these hypers. I did the same with the last set of KB hypers, which I installed about 10 years and 60,000 miles ago in the other GT's 289 and all went well - and still well, so gonna stay with success. I figured, when all else fails, read the instructions. LOL

[JoeHall]

I plan to set ring gap tomorrow, so today did extensive reading on the internet on hyper pistons and ring gap, to determine if I should second guess KB's ring gap specs. Early on (1990s - early 2000s), there were lotsa complaints about KBs being "brittle" and lots of them broke, often shortly after initial startup, mostly above the oil ring. The main culprit was eventually found to be insufficient top ring gap, and the secondary was detonation. RE ring gap, many installers simply did not follow KB's instructions; other hyper pistons are beefier and have tighter ring gap specs than KBs, and OEM and forged pistons are apples to oranges. KB listed several reasons why their top rings run hotter: thermal conductivity of materials used; top ring located higher than OEM pistons (does not apply to Stude, they are identical), and "varied end use", i.e. gapped for stock application, but later raced. So the KBs got a bad rep, but most who follow KB specific instructions report no problems, which has been my experience too, with the other 289 mentioned above. So again, I agree with you Bud, when all else fails read the instructions, or call the manufacturer's tech line.

Reading on the internet I also learned (if I knew it before, I'd forgotten it) the KB hypers were brought to the Studebaker world thanks to our long recognized guru John Erb (R.I.P.), who had an inside connection with KB. He also brought us the shallow dish version KB, which is a compromise between the standard deep dish and R1 flat top.

[PackardV8]

Hi, Joe,

Too bad shipping costs have gotten so exhorbitant or I would have offered to loan you my power ring filer. Makes it a lot easier.



jack

[JoeHall]

Jack, that machine sure looks purdy, and I bet it would make the job easy. But I'll just do it the old fashion way with a flat file, steady hands, and frequent size checking.

With patience and perspiration, old school methods can be OK, and sometimes it's all we have. One of the best/worst examples of old school I ever heard was from an old friend, John Bryan, in SoCal in the 1980s. He was a lifelong Packard specialist and, in his 80s, still worked a 5+ day work week in his Packard specific shop. When 55-56 Packard V8 rod bearings became all but extinct, he used straight 8 Packard bearings, which were about .100" wider, but could be narrowed to fit. (IIRC the tang must also be relocated.) I asked how he narrowed them without overheating the metals, and he said by hand, on thick pane glass, topped with sandpaper. I tried his method, and gave up before even completing the first bearing half. His shop and yard was always full of Packards from all over. His phone rang often, and he always answered, "Bryan's Packard service, John speaking". Once he laughingly told me, "I tell'em when they can drop them off, but don't tell'em when they can pick them up". LOL