Engine: Piston orientation - why?

[M-Webb]

Working on rebuilding a Stude V8 right now. Anybody know the technical or theoretical reason why the pistons have an orientation, the notch facing to the front? Just curious more than anything as my motor now actually has new custom made pistons and the place that made them told me they can go either way, don't have a "front" direction.





None of the typical factory Studebaker V8 pistons that I am aware of have notches in the tops for valve clearance, so I don't think that would be it, maybe R3/R4 do, not sure about those.

Just trying to understand things as I'm learning how to properly rebuild this motor after a couple pro shops did some sloppy work and I now need to fix it.

Also, while at it, I was checking the torque on the pinch bolts to see if that had been done correctly. The odd pinch bolts were put in backwards, not according to the shop manual. So I need to switch those. But in doing so, I ended up stripping the threads on the 1st one. I was trying to check for the 28ft-lbs of torque, but it stripped before I got there, or at least I think it did. Using an early 2000's USA made Craftsman wrench, so guessing it is good. I'm not sure if it is great to reuse old pinch bolts or better to just always use fresh new ones. I ordered a new set of 8 just in case since they are available and not that expensive considering how critical they are. Anybody have any thoughts on those?

[StudeRich]

Where in the heck did someone get a ("Auto Tec")? Piston with swirl marks on top ?
This IS for a 289 right ?
Are there even Three Rings ? Looks like some Late model racing piston with a short skirt.

The "notch forward thing" has always bugged me, because the original idea was that SOME Pistons have Offset Wrist Pins, so they need a notch to face forward, I don't believe a Studebaker is that way.

When the original pistons had the expansion Slot on one side called a "T Slot" that WAS a good reason to put that side UP (inboard) BUT that would mean that on one side of the block the Notch faces REAR, since all pistons are alike !
I think on a correct Piston, it does Not matter, but yours do not appear to be Studebaker Vendor Pistons.

[PackardV8]

Most all OEM pistons, including Studebakers, do have offset pin bores for quieter operation.

Many custom pistons have centered pins, which supposedly make slightly more power.

jack vines

[IndStudenut]

What Jack said. It was always my understanding the notch was to orient the piston in the correct fashion when they were designed with an offset wristpin. if the the pin is neutral then I do not see why it would make a difference.

[M-Webb]

Yes, it is for a 289, with block fully sleeved back down to standard bore. Intention is for lower compression so can be driven comfortably on cheap pump gas, hence the dished tops.

The 2nd shop which was helping with this motor had the pistons custom made to fit the block after they said the block was previously over-bored and sonic checking it showed it questionably thin on a few of the cylinders due to casting core shift. I told them OK, just sleeve the whole block, but down to +.060" to keep a few extra cubic inches and to use standard Studebaker pistons. They were a race shop, so they said it wasn't that much more for custom pistons and would really prefer to go with those. I said OK, if it is only a little more, fine but it is pretty easy to just get the standard pistons. So anyway, they had those made because I was paying, not them obviously. Well, they actually ended up about 3-4 times the price of the standard pistons of course. Plus apparently they didn't listen to me and just had the block sleeved back down to standard bore for some unknown reason which they had no excuse for. They said "Why not?" I said "Because it would have been the exact same price to get the extra ci and a little extra hp out of it." I thought they were a race shop, should have known that by default. Didn't listen, poor attention to detail, sloppy work, took forever and to top it off, just could never manage to get it done after a full year.

But anyway, looking at the bottom of the pistons, I saw that they were made by this company, Race-tec / AutoTec:

https://www.racetecpistons.com/autotec/c10

Seems like a reasonable company, good stuff from what little I know about pistons. From website info and the casting marks, it appears to be an Auto-Tec forged piston with their "2618" alloy, for higher horsepower racing applications, for better or worse given that this will be a street driven truck with less than 300hp. I called them and they looked up the order and told me the pistons I have can go in either way, do not have a front/back. It seemed to be mostly based on the fact that they do not have any asymmetrical notches for valve clearances from what I gathered. I wasn't aware of wrist pin asymmetry, so didn't ask about that. But he said the ones I have could go in either way.

Partly the reason I'm asking is because I'm trying to make double and triple sure as I put this motor back together, it is correct and as needed - unlike the 3 previous 'pro' attempts. This is my first time trying to build a motor, so having to learn a lot of everything along the way, including all the odd Studebaker specific stuff. After all the previous problems I've had to deal with on this build, I'm just trying to understand as much as I can to try to get this right. I mostly trust that they told me they can go either way. But to be 100% honest, I'm not sure what I can trust or not at this point, at least not without understanding the actual technical issues to some degree and deciding for myself. Just the guy telling me they can go either way, still gives me a little bit of doubt without knowing why they might not be and checking on it.

Sounds like one reason would be the wrist pins and that could be measured on the bottom of the piston, being slightly asymmetrical vs. perfectly symmetrical? I just measured that, and it seems like it is the same both sides, so I don't think that is it.

As you can see on the photo of the bottom of the piston above, it has had some asymmetrical machine work done to it. I assume for balancing of some sort. Oddly, 4 of the pistons do not seem to have any of that extra machine work done on them, but the other 4 do and each one is different. #'s 2, 3, 5 and 7 have extra machine work, 1, 4, 6 and 8 do not.

I do now also see this extra little casting bump up in the inside of the piston that is on the one side of the casting, but not the other. Not sure what that is for or if means anything critical.

[M-Webb]

I will add that all the full piston - rod assemblies put together with the rings and bearings all weigh pretty close to the same at 127.3 - 127.5 grams each. So as they are, they all seem pretty tightly balanced for overall weight.

[PackardV8]

In a technical discussion, correct terminology helps. Those are forgings, not castings.

The positive is your RaceTec forged pistons are as good as money can buy.

The only bad news about them is your street engine does not benefit from their strength and they require additional clearance; thus they'll be noisier on cold startup.

Well, that plus the price. You'd have been much better off with the Silvolite hypereutectic cast pistons from our vendors. They can be run with less bore clearance and will be quieter

jack vines

[M-Webb]

Sounds about right Jack. Yes, I would have just used the standard typical pistons our vendors have, like I told them to do. But they didn't listen, thought they knew better, which is one reason I lost confidence in them finishing the motor correctly and gave up on them. But that's water under the bridge, time and money long ago wasted already at this point.

Believe it our not, the 3rd shop tried to convince me to toss these pistons and replace them with flat top higher compression pistons so we could max out the power on the motor. I said no, that is not what I want. I don't want to totally waste the money spent on these pistons that I already have and I don't want max compression and hp either, like I told them to begin with. I told them from the very beginning that I wanted a low stressed, smooth running, good reliable driver motor that would run well on just cheap pump gas. But they tried to convince me that was a mistake. I told them it will be a big mistake I will be extremely unhappy about if we did swap the pistons and the motor ended up needing premium gas or additives and had to be always be tuned perfectly to keep it from pinging, etc. In the end, they claimed I wasn't listening to them. I was apparently the problem, not them.

I also told them I wanted a motor that was sealed up as well as could be to minimize oil leaks. What I got from them was dry over torqued squished corked gaskets, a literal gap at the front pan filler block, arguing about how to do the timing cover oil seal even after I gave them the info on how exactly to do it, not to mention the sealant in the head bolt passage that feeds the oil up to the rockers. So no sealant where it should have been, but some where it literally would have ruined those rockers in short order. But yes, it was me not listening to their expert advice. Plus they couldn't finish a job in 6 months that shouldn't really have taken more than 1 month if they actually knew what they were doing and put even 1/2-ass effort into it. Given what I got from them, I'm actually lucky they couldn't finish it.

It is shocking how unprofessional professional engine building help seems to be these days, if you can even find it. And quite frankly, it might be best if you can't find it given what I have encountered.

But yes, I should have long ago decided to just learn how to rebuild the motor myself and done it myself and used the standard available Studebaker pistons like I would have if doing it myself. If I could go back in time and start over again from scratch, that is exactly what I would do. But at this point, I'm just trying to salvage things as best I can and live with it, lessons learned, many lessons, most of them the hard and expensive way so far.

[M-Webb]

I called back and spoke with an AutoTec rep again just now to get 100% clarification on things as far as the wrist pin off-set and orientation of the pistons, etc. He confirmed again that these pistons do not have an offset and can be installed in either direction, doesn't matter. He said the notches on the bottoms would not have been done by them, so must have been done by the machine shop during assembly to balance the entire assembly. He also said that because these have AutoTec indicated on them, that they are for sure the 4032 "street" motor pistons, not the 2618 "race" pistons. He said all AutoTec pistons are the 4032 and all RaceTec are the 2618. The other number on the piston is the forging number of the piston, not an indication of the alloy. That clears that up. So these are fortunately actually the better piston for this motor.

So I again called the machine shop that actually did the machine work and core assembly work for the 2nd shop. He answered this time and was very helpful. He seems like a good guy, knows his stuff. He confirmed that he was the one who trimmed 4 of the pistons to get them weight balanced. He also said it would not matter if the pistons were rotated, but there is no need for it since these pistons do not have a front/back orientation, no reason to do it. So I think that is enough checking on that and will just leave them as is, well enough alone for that. Check that off the list.

He did also confirm on the pinch bolts, remembers doing those. He said he did use all new pinch bolts because some of the ones it had on it when he got it from the 1st build attempt were stripped. He said that when he redid them, he did do the tightening and tapping and re-tightening bit on them as standard good engine work practice. He did not recall the part where Studebaker says to orient the nuts to the same direction on all pistons verses mirrored as they were installed. I told him Studebaker says to put them all on the same direction for some reason, but that I have yet to find out an explanation why. He said that he could not think of a good reason and doubts that with a well balanced motor that it would make any difference. And he might be right on that, not sure. But since I've got it apart and now have a new fresh set of pinch bolts as of today, I will just redo all of them anyway to be 100% sure on those and do it the way Studebaker says to do it, whatever the mysterious reason might be.

Couple questions:

1. should I put some Loctite on the threads just as a little extra insurance, or just oil things up extra good during assembly so get proper torque and go with that?

2. Guessing I should use fresh lock washers too instead of reusing these, which honestly look like were new from the previous assembly. If so, any typical ones OK or should I use Grade 8 or stainless specifically?

3. Confirm that 28ft-lbs is the proper torque spec. on the pinch bolts. Since I stripped the 1st one attempting to do that, guess it is good to double confirm that for sure before I start on them again.

[enjenjo]

Use grade 8 lock washers. They are made from a better quality steel. I don't think Loctite is needed with properly torqued bolts.

[M-Webb]

Went to the local hardware store today that has a great selection of fasteners. The pinch bolts are 3/8"-24 fine thread fyi. They did not have any Grade 8 lock washers. But they did have them in regular zinc steel and also stainless, both outside and inside type. They also had SS nuts with integral lock surface and regular zinc with an integral lock washer. They did not have just plain steel 3/8"-24 for some reason, or even zinc plated.

My concern is I do not have the original steel Studebaker nuts, and the lock washers look new as well. But in looking at it closely, I don't see that the lock washer is getting a lot of grip on the nut to prevent it from backing off. And I'm wondering if the nut the shop used is too hard of a material and it isn't allowing the lock washer to grip into it as would be needed. So maybe a softer plain steel nut is really what should be used. Or some other type of locking nut and washer might be as good or better.

I could also maybe use 2 thinner nuts and double nut it.

I might be just over thinking the whole thing. But obviously I don't want to chance these coming loose and then off. If I had the original Studebaker parts, I probably would just reuse them and not be concerned about it. But given that both the nut and lock washer I have is not factory correct, I want to be sure whatever it is, it won't be coming off.

I'm going to go to a local fastener store tomorrow and ask them what they think might be best, if not just try to find regular steel nuts to try to match what Studebaker used.

In the meant time, if anyone has any other thoughts on what they've done besides just reusing original nuts and lock washers, feel free to chime in here, good or bad.

Maybe a hardened alum. flanged nut might be best? A little less weight and lock washer will grip into it better?

[PackardV8]

I might be just over thinking the whole thing. But obviously I don't want to chance these coming loose and then off. If I had the original Studebaker parts, I probably would just reuse them and not be concerned about it. But given that both the nut and lock washer I have is not factory correct, I want to be sure whatever it is, it won't be coming off . . . . . In the meant time, if anyone has any other thoughts on what they've done besides just reusing original nuts and lock washers, feel free to chime in here, good or bad.]

Yes, way overthinking it. Once properly installed, there's very little shear or tensile stress on the pinch bolt fasteners.

I just installed a set this week. If one only pulls torque to spec, as one would do with say the rod cap nuts, is guaranteed to fail. Use a screwdriver to align the taper on the bolt with the flat of the wrist pin and insert the pin, install the lock washer and nut. Tighten by hand with a box end wrench, whack on the back side with the brass hammer; the wrench will then find a bit of slack, tighten, whack, tighten, whack and when the nut no longer moves by hand, verify with a torque wrench.

jack vines

[Buzzard]

I can attest to what Jack stated about piston noise. In the 70"s I was building my R4 High Compression 304.5 CID utilizing Jahns Forged pistons. Jahns stated the piston to bore clearance at 9.5 thou and my machinist insisted on knurling the skirts to retain some lubrication when cold. You can still hear the pistons slap until they warm up. It does make pretty good power however.
Bill

[altair]

About the notch, I think the notch is there for when a mild clean up is done eg. rings, bearings and hone only, the piston can be returned the same way. If rebored it wouldn't matter.

[PackardV8]

About the notch, I think the notch is there for when a mild clean up is done eg. rings, bearings and hone only, the piston can be returned the same way. If rebored it wouldn't matter.

Maybe rethink that. The notch is an important orientation, because the pin bore in Studebaker pistons is offset and they would make a lot of noise if installed backwards.

jack vines

[altair]

On a Studebaker engine where is the clearance applied, to the block or the piston? When the Model T Ford engine was built the bore was 3.75 and the clearance was applied to the piston, however when rebored by one of hundreds of machine shops with various methods of boring and honing and new pistons installed usually aluminum from a host of manufacturers, who knows where the clearance was applied. Some rattled some smoked and some seized after a "rebuild". I have talked with machinists and honing alone has advanced greatly over the years, some believe lots of scratches are good to hold oil while others believe that polished smooth is better. Engine break-in is all things to all people some baby their engines and some don't. Is the clearance applied, standard in the industry either to the block or the pistons?