[dataway]

Attached in an image of the #4 connecting rod, as it sits between the pin bosses in an assembled engine. Note the difference in pin showing on one side compared to the other.

Is there a reason for this?

And

Keep in mind ... the pin being pressed in on center has nothing to do with this ... the pin floats in the piston ... it does not control where the rod sits in relation to the center line of the piston from front to back.

Stock crank, rpm rods, 400 block, nothing fancy.

The other picture shows the rod/pin on the same journal, other bank. Centered much better.

Most of the rods on the passenger bank are offset like this to varying degrees, the rods on the Driver side bank are closer to center, but not all perfect.

Yes: Rods are installed correctly, ie: chamfers, tangs, pistons pointing in the right direction.

What I would like to know, is first of all ... how many of you have actually peered inside the assembled engine to assess how the rods are centered between the bosses .... and if you have, what did yours look like? I have never heard of any spec, measurement or guideline as to if the rod should "appear" to be centered.

And of course this is not a matter of a few thousands ... it's closer to 1/8 - 3/16". So it would be a MAJOR problem (assuming it is a problem and not normal), not one that would require a micrometer.

And this engine assembly turns nice as it should, no binding, no problems, all clearances good.

(photos have been altered to remove any "distractions")

[Tom Vaught]

I have a 455 engine on the stand with pressed on Eagle Rods on TRW Pistons.

Pan is off, just need to remove engine bag and I will look at #4 on my engine as well as the other pistons and rods. No pics but can tell you if close to your deal.

Tomorrow.

Tom V.

[dataway]

Thanks bro,

[Squidward]

1. Your rods weren't heated enough during pin pressing, as evidenced by the color.

2. I have seen a slight amount of off centering of rod/pin in the piston, but figured that was a design condition, and that was why the pin would slide left & right in the piston. I always figured that as long as it didn't scrape the wall and the rod wasn't obviously defective, then I called it good. The rod manufacturer is waaay better at doing his business than I am at building engines. Call it my newbishness or whatever, I never put that detail under the microscope very hard.

Sorry about #1. Couldn't resist!

[dataway]

Here is some added information.

A composite photo showing, as best as I can, the rod position on all eight cylinders. Numbered as if you are looking at the engine upside down on the stand.

On the number 2 bank, all the rods are shifted slightly towards the front of the engine.

On the number 1 bank, all the rods are close to centered, perhaps a bit to the rear of the engine.

Also a picture of the compete lower end.

This can't be by mistake IMHO, looks like it's by design. If the rods were somehow, so out of whack to do this (first it would very visible looking at one) then the number 1 bank would be offset the same amount as number 2 bank.

[dataway]

Originally Posted by Squidward

1. Your rods weren't heated enough during pin pressing, as evidenced by the color.

2. I have seen a slight amount of off centering of rod/pin in the piston, but figured that was a design condition, and that was why the pin would slide left & right in the piston. I always figured that as long as it didn't scrape the wall and the rod wasn't obviously defective, then I called it good. The rod manufacturer is waaay better at doing his business than I am at building engines. Call it my newbishness or whatever, I never put that detail under the microscope very hard.

Sorry about #1. Couldn't resist!

Exactly! What I was thinking, a design quirk/feature/whatever

And ... I almost burst a vessel till I read your whole message

[STEELCITYFIREBIRD]

Holy chit, your block is blue too!

Was this balanced? Perhaps they removed material from the side of the small end instead of the balance pad?

[dataway]

Yes it was balanced, but when I look at the small ends they look pretty symmetrical side to side.

Took another very close look, all the rods are offset in the cylinder bore to the chamfer side of the rod. The small end is on the same center as the big end ... meaning if you laid them on the side the small end is the same width as the big end and it would lay flat ... near as I can measure with them installed, so the rods are "straight", with no appreciable offset.

If I was an engineer ... I would almost say that the cylinder bores, and rods, were designed with this spacing to make the engine block shorter for some reason. Imagine if you kept moving the cylinder bores on each bank, closer and closer to being lined up with each other ... the block would get shorter, but the rods would have to be offset in the bores farther and farther to one side to get both rods on the same journal. Until ... as seen in a "perfect" V type two cylinder ... you end up with a male and female rod on the same journal, that both have the same center point. I think Harley did it that way.

PS. While I'm at it ... does the dipstick tube look correct?

[STEELCITYFIREBIRD]

Windage tray?

[dataway]

Yep, tray slides down on it just like that. Had to remove the oil pump to remove the tray because of that.

You're up late. I keep running down to the shop to look at this thing.

[STEELCITYFIREBIRD]

Yeah I got up late too! Your problem was my problem.
Find any resolve?

[STEELCITYFIREBIRD]

Looking at the composite picture that you posted,. It sure looks to me like quite a few of those wrist pins have been pressed. The tattle tale is the straight score marks on the pins, running with the long dimension.
Can't think of any other way for those marks to get on virgin pins.
6,2,5,3 and possibly 7 are pretty evident.
Not trying to light your lamp, just calling it like I see it.

[dataway]

Yes ... they are all pressed. The rods are press pin type.

A point I've tried to make is that a pin pressed into a rod, that floats in the piston, does not determine rod position, it could be pressed 1/2" off and still not effect where the rod is centered in the bore, the pin is close to 1" narrower than the cylinder bore, the pin will just slide in the piston to wherever the crank journal puts it, there are no circlips, so the pin can move wherever it wants so long as it doesn't contact a cylinder wall. So .. pressed pins, or pins not pressed in perfectly is not the problem here.

The problem is, that the rods are not centered in the cylinder bore, therefore not centered in the piston. The rods have no offset that I can see, the crank can obviously only fit in one way, and I would assume the cylinder bores are in the right place.

So that leaves the question, why are rods about 1/8-3/16" off the center of the cylinder bore. On every rod, it is off center towards the chamfer side of the rod.

Personally, I think this is the way the engine is designed, and since there is no spec at all for where a rod is centered in the bore, no one ever thinks to look at it. Might be specific to certain 400 castings, might be universal. But I see no way an assembly error, or part defect would cause this. The rods are NOT manufactured with the offset ... it's evident to look at them that there is no offset.

How many people, assemble their Pontiac V8, and then look underneath the pistons to see where the rod lies in the hole? And what the heck would a person do about it if they did not lie in the center.

[STEELCITYFIREBIRD]

If your ok believing pressing pins in is proper procedure, go with it. If they heated them, then pressed them, someone stuck them.... something screwy went on here.!
I close my eyes


(BTW I completely understand the small end will fall where the crank pin and /or rod offset puts it, is your crank end play in spec?).

[Bluesugar]

This is normal,the way the casting of the block was done determines this.The crank
will sit in the engine saddles only one way(of course the thrust bearing has its
tolerances).Pressed or floating pins will let the pistons find their on centerline.
Some engines are cast so badly around the lifter bores you see more metal on
one side of the hole than the other!...I'm curious if someone will chime in that
has an after market(aluminum)block and tell us what they see looking down at
an assembled bottom end...dataway,your build looks good,don't worry about it.

[dataway]

Yep, crank end play is right at .006.

Laid a straight edge along a counterweight and rod ... no offset, small end is a tad wider than the big end on each side. Absolutely typical RPM forged rod.


Bluesugar ... I know that castings can be far enough off that it affects cylinder wall thickness, cooling jackets etc. There is certainly some go-no-go spec at the factory. I can't think of anything else that would cause this, unless that's just the way they were designed. Evidently the cylinder bank offset is less than the centerline distance from one rod big end to the adjacent rod (same as the thickness of one rod big end, plus half rod side clearance) I could draw a picture ... but it's pretty simple ... the cylinder banks ideally are offset the width of one rod big end, plus half rod side play ... that puts both rods in the center of the bores. If the bank offset is less than that, then the rods will end up off center in the bores to compensate.

[johnta1]

Hard to see for sure on the crank throws, but it appears that half of your rods are backwards?

The 'wider' side of the big end of rod should go to the cheek of the crank throws.
(for the chamfer of the crank bearing surface)

What are the clearances between the rod big ends?

Also did you assemble the engine?

[STEELCITYFIREBIRD]

http://www3.telus.net/68bird/engine_mistake.htm

Sharp eye johnta1!

[Tom Vaught]

Originally Posted by STEELCITYFIREBIRD

http://www3.telus.net/68bird/engine_mistake.htm

DATAWAY, I INSPECTED EVER ROD/PISTON TODAY ON MY TRW PISTON/EAGLE ROD (PRESSED PIN) ENGINE AND THEY ARE ALL PERFECTLY CENTERED ROD TO PIN BOSSES.

Great link, I specifically took the engine I took in 'in Trade" (for a centrifugal Supercharger kit) apart to verify this possibility.

You could tell where originally the pistons and tods were mounted for the wrong numbered holes but fortunately the machine shop years ago caught their mistake and reinstalled the
pistons and rods correctly before he swapped it to me.

I just had to know that the parts were installed correctly which is why I removed it from storage and inspected everything.

As many have posted WIDE CHAMFERS go to cheeks of the crank and the piston "Arrow"
on the top of the piston must face the front of the engine on each cylinder.

Good that you are inspecting your engine too and asking questions NOW!
Maybe that bit of interference saved your engine project.

Tom V.

[Engine-Ear]

DAMN! Great thread.

I will be going thru the 428 short block I assembled in '04 but haven't had the $ to finish.

I will definitely check this out.

Thanks, all you SMART guys!