Just my luck...

[3400-95-Modified]

Thats the one downfall of a fractured cap rod, as you noted there is no smooth machined surface for the tang to touch.

[Superdave]

Yep, i noticed that as well.


BTW, as of right now i'll be picking up another 3500 on Friday/Saturday to steal the crank and bearings out of. the machine shop is lost and can't get me bearings so i'm going to let them hold onto the crank untill they can.

[project89]

since u guys seem to be haning problems have u thought about dowlpinning the beearings into place?
im not sure if its even possible but all the race motors we build have a small dowl pin in the cap or on the rod side that locks the bearing positivly into place.

is this issue just with the 3500's?
ive been taking my motor as high as 7,800 repeatedly and havent had an issues,though i do run extra clearance in the rods and i also run 65 psi hot at idle and 105+ psi hot at redline oil presure with a standard volume pump

ive been runnoing rotella-t 15-40 in this new motor but in the old motor i ran 20-50 or just stright sae 50 wieght and that motor saw alot of 7k rpm pulls over its lifetime and i never had an issue

heres a picture of the bearings of my old motor when it came apart





high milage motor i actually goofed and did an oil change and started the car without oil in it it ran for 2 mins before i relized what i did, once i filled it with oil it only had 5-10 psi hot at idle and 30 at redline hot.thats prolly were all the bearing damage came from

[Joseph Upson]

Not sure who to believe but I'm favoring the forum source that gave me these values a few months ago, not sure if they were loose weigh ins or very close but I was told by a member 420 gm on the 3900 piston and 585 gm on the rod. The post office digital scale measured 422.4 gm on the piston which did have one spiral lock still in place and 632.1 gm for the rod, maybe the other measurement was without the bolts. The pin weighs 155.9 gm for a estimated grand total of about 56 grams heavier than the Forged piston and pin assembly.

This link shows how significant that is;

http://www.perpetualbalance.com/balance/main.html

[Barry]

Project89, how did you acheive those oil pressures with a stock pump?

[project89]

3 an washers behind the pressure relief valve spring

edit it might have been 4 nextime im at the shop ill grab one of the washers and measure the thickness, i actually want to pull one of the washers out and drop the oil presure slightly but i refuse to pull the motor out just to do that

[ForcedFirebird]

3 an washers behind the pressure relief valve spring

edit it might have been 4 nextime im at the shop ill grab one of the washers and measure the thickness, i actually want to pull one of the washers out and drop the oil presure slightly but i refuse to pull the motor out just to do that

The pan can come off with the motor in the car. I have done it about four times now

Yep, i noticed that as well.


BTW, as of right now i'll be picking up another 3500 on Friday/Saturday to steal the crank and bearings out of. the machine shop is lost and can't get me bearings so i'm going to let them hold onto the crank untill they can.

Good move

[project89]

yeah i know the pan can come off with the motor in the car ive done it before as well.
i just dont feel like fighting with it much simpler to just pull the whole thing.prolly do it at the end of the season and throw new main and rod bearings in the motor while im at it

[ForcedFirebird]

Thats the one downfall of a fractured cap rod, as you noted there is no smooth machined surface for the tang to touch.

There's actually more to it than that. The not only is there no flt for the tang to touch, but there is a notch on both the cap and rod. From a machinist's standpoint, I don't see why this was necessary other than saving very little time on the complete machining process. All they had to do was remove the cap and put the divot in each part individually, instead they used a slot cutter to mill both the rod and cap together.

[3400-95-Modified]

eek... Horrible idea if you ask me...

its just like setup to push the tang right back in and make it flat....

I have my reasons for liking my 3400 bottom end

[Joseph Upson]

There's actually more to it than that. The not only is there no flt for the tang to touch, but there is a notch on both the cap and rod. From a machinist's standpoint, I don't see why this was necessary other than saving very little time on the complete machining process. All they had to do was remove the cap and put the divot in each part individually, instead they used a slot cutter to mill both the rod and cap together.


[ATTACH]2011[/ATTACH]

That's what I was saying earlier, I just took to long to post a picture of the rod. What 3400-95-.. is probably saying is that since it is a fractured cap rod that maybe the only sure way to notch it for the bearings without a possible more expensive process for GM, as the slightest deformation in the caps fractured intermeshing surfaces may result in an incomplete seat of the cap.

I nearly ruined one of my rods by putting the cap on 180 degrees rotated and starting to snug the bolts down, once those jagged surfaces are deformed, you can pretty much forget saving the rod.

[3400-95-Modified]

Yup... pretty much.

Gotta be careful putting those together, you need to stamp the rod number on the same side of the caps so you can line up the numbers to be sure you have the fracture lined up properly.

[Joseph Upson]

While looking for someone near home in Tampa Florida to do an offset crankshaft grind, I mentioned the rod notch that might be constributing to bearing spin and was told the notches were only there to center the bearing in the rod and that it is the cap pressure that keeps it from spinning which suggests that the cause of Superdave's bearing spinning is likely a reduced cap pressure from rod stretch. Perhaps a little roughing of the contact surfaces and some loctite might really help after all.

[3400-95-Modified]

Yeah but at the same time you can't argue that the tangs touching a flat surface that in-fact will stop them from rotating would help preventing a bearing from spinning.

I also cant imagine that a centering tool would be on ONE side of the rod only... it almost seems like if they wanted it to center the bearing the would put it on both sides...

Title:CONNECTING ROD BEARING
Document Type and Number:United States Patent 3576353
Abstract:A connecting rod bearing providing with V-shaped tabs for accurately aligning and locking the bearing half shells to a strap type bearing cap and connecting rod end.

[gectek]

f all that, just have the rod/cap machined straight, rotate the cap, then use the ARP bolts that I found for the rods that will work...oh yah forgot to update everyone on that.

I found ARP bolts that will work for the cracked rods, 3500/3900/3600 all the same bolts, all the same rod pretty much...they are the cap screw type and are ARP PRO 2000 series, and actually come in a set of 12...
who could ask for anything more