SwayBar

Erik, no, no rod failures at all with the 928's, NA or FI.

Here's Carrillo stating it's typically 'installation mistakes' when a rod fails.

Download and open the link below:

Carrillo Rod Failure pdf

Rob Edwards

Statistically I'm sure that Carrillo is correct that the majority of rod failures are installation mistakes. But in these two cases the big end of the rod was still mounted on the crank journal, no damage to the bearing or crank, so it's not a bearing installation issue, nor a rod bolt failure. Not sure what other part of installation could be responsible for a rod failure like this.

If you hop back to post #53, Carrillo did examine the other 7 rods from the Zombie motor. They didn't see anything wrong with the metallurgy, and they said they were ok to re-use. I sold them to another local 928er for a project motor.

hacker-pschorr

Wrist pin issue?

How were they inspected (referring to Catorce's post above)? Not questioning it, just curious.


Honestly this whole situation has my head spinning. We've all read over and over and over again how necessary it is to build these engines with harder Chevy rod bearings since the stock ones are too soft. And here we find out how successful the Zombie was with custom rods made to use stock 928 rod bearings.... maybe I'm the only one just now realizing this.

Yes I know the bearing and the bearing end of the rod isn't what failed here. But all this talk over the years about the correct and incorrect way to have Chevy rods made for a 928 block......why bother?

If one desires for whatever reason to still use a harder rod bearings, build the engine around one that is smaller in diameter & wider (not skinnier and larger like SBC units). It's common in the BBC world to build cranks around SBC bearings since they are wider and smaller than BBC units....while 928 motors are being built going the other direction.

Is this because the SBC parts are so inexpensive? I understand every build has a budget, but this may not be the best place to cut corners considering the possible issue with rod offset fitting SBC bearings into a 928 block.

It's common for NASCAR and other circle track SBC race engines to be built using custom cranks around the smaller Honda rod bearings.
They don't even use the SBC bearing:

https://www.chevydiy.com/build-chevy...ssembly-guide/

mark kibort

So, could it be a rod design issue, as i believe we are talking about the newest of the GB rod designs? What about the original designed rod. the one that lasted many seasons?
do rods break under stress of over-rev? And where do they typically break? as Erik showed, its not uncommon to spin these motors up to 8,000 for a fraction of a second. marks rev limiter (and joes) were set at 6800rpm, and this can be verified by the sound of the engine. (with mine being a template, verified via the dyno a few months ago) even a mishift of our motors at 6000rpm would take the RPM to 8500rpm, where bad things could happen. ) but the sound of that would be pretty obvious on the video.

mark kibort

Can you give me the 30 second overview of the rod bearing size variants of the strokers vs stock S4 engines? so my Todd engine was made with "chevy" rods meaning they are bigger diameter, meaning the modex crank has larger diameter journals than a stock crank which uses stock smaller diameter bearings? GB engines have traditionally used the stock sized bearings, which means the journal on the modex crank is smaller? and that has worked well on marks engine, and joes that lasted for many years.
what about the bearing width? how do you fit larger bearings on a rod big end.. i would imagine the rod has to be wider at the bottom and the crank has to have a wider journal as well. has that been done, or is this part of the chevy rod end change?
what did Devek strokers use when using the Scat crank, which i believe Joe's might have had that crank to start, and maybe even has it now...did that have smaller, 928 sized bearings?

hacker-pschorr

SBC rod bearings are slightly larger in diameter and narrower. Lager means they are spinning faster and narrower means less surface area. Neither option is very ideal.
That is why Nascar is using a Honda rod bearing which is smaller diameter and wider.

Yes
Two reasons why people would do this:
1. More options of bearings to choose from (harder, stronger etc... is the mentality)
2. Lower cost - many "off the shelf" rods available in this bearing size

The rods in your motor are "off the shelf" SBC 6" Carrillo severe or heavy duty rods with 7/8" Carr rod bolts. Most rods have 3/8" ARP rod bolts.

The wrist pin is also smaller in the "Chevy" rod compared to a stock 928 unit.

In your motor are Clevite 77 rod bearings and the H-11 Tool Steel Wrist Pins. In Todd's opinion the best wrist pins money can buy.

The engine which lasted 5 years in the Zombie was assembled by Greg, using a custom rod / crank setup Mark A purchased from someone else using stock 928 rod bearings.

The two motors in question which failed are using the same size Chevy small block rod bearings that are in your motor. I cannot comment on which particular bearing was used in these motors, only Greg can speak to that.

Strokers have custom cranks built around the bearing size.

No idea, I've been told & read over the years those too used the Chevy rod bearings.

William A

Nothing new here.

Rod maker/machinist blames assembly/builder, Builder blames an unskilled/careless driver (racing history is rich with examples of this in professional racing, sometimes justified sometimes not). Again very common in racing history, in this thread there is accusation of the driver blaming the builder, though for the record he posts that he does not blame the builder.

Regardless, it is just a circular firing squad with each player entrenched and blaming other(s). Isn't the whole point of discussing this to discover the source of the failure and learn something?

I know I am not the only crazy one to want to see an objective discussion of the problem(s) contributing to an ultimate improvement for the community. Doubtful since a few have dragged this into cringe worthy territory, but please wake me if this reverts to a constructive discussion.

Such a shame, this thread began to celebrate 928s on the track.

hacker-pschorr

Some dust always gets kicked up in such threads, plow through and eventually on the other side we find good discussions, which it appears is already happening..... Assuming everyone just plays nice, which we know will never happen, but we can try!!!

Bigfoot928

this is pretty heated territory and this thread needs a fork in it. So would that mean we are forked? For the record, my stroker has the scat crank which was made for sbc rods. Here is my history of rods:



Stock rods on the left, 1st set of rods in the middle and the Oliver titanium rods on the right. The reason for the rod change was that the rods in the middle were 5.700 and the longer rods on the right are 5.850 The middle rods needed tons of clearance and the rods on the right were pretty much a bolt in. I don't remember what bearings I used. I believe they were clevite 77 dlc coated iirc.

Below are the piston versions:



Stock on the left with stock bores. Middle is JE coated but I don't remember with what on steel pressed in liners. Liners rotated in the bores and the block was toast. Piston on the right is current with the rod on the right in the above pic
Bore is nikasil and the piston have coatings on the skirts but I don't remember what. Engines were same displacement used same crank, cams and heads. Engine on the right made about 50HP more, the only difference being pistons, rods and balancer.

This was my deed to turn this thread back toward something technical. I'm guessing everyone will start taking pot shots at me now.

Bigfoot928

forgot wrist pins...




Left are stock at 180 grams. Middle are who knows what at 120 grams, On the right are 9310 tool steel taper wall wrist pins at 90 grams each.

hacker-pschorr

Here is the rod, & piston in Kiborts motor. I don't seem to have a photo of the wrist pin.

mark kibort

staying techincal.... how did you get 50hp out of changing from the JE pistons in nicasil block (middle items) vs the right items ? (balancer, pistons and rods)???? the rotating mass change, and more importantly the rate at which the rotating mass rpm changed in a dyno test could not be responsible for 50hp change in power for those items alone. since i have the same components as the middle group, thats like saying i could change to the Right group and gain 50hp and that doesnt seem at all likely .

mark kibort

Now i feel even MORE guilty racing this engine... it's like jewelry!

GregBBRD

While I really do appreciate all of the very positive thoughts, suggestions, and support, I do not believe that anyone that hasn't been anywhere near this car...or engine...is going to figure out the cause of the failure, sitting in their armchair at work or home.

I've made arrangements to remove the engine and take it apart, to determine what failed, if possible. Joseph Fan is a fantastic human (and a great friend) and I feel badly for his loss. That being said, I've offered to buy the car, from Joseph, at the full price Mark Anderson was going to pay for the car, before the engine blew. (They had a gentleman's agreement for Mark to buy the car, before the car went onto the track at Fontana, which Joseph released Mark from.)

The Carrillo connecting rods that are in Kibort's engine, that our helpful, independent moderator has provided pictures of, show that these rods are of the same EXACT design that Carrillo now uses on all 928 connecting rods.....including the ones I have made. This design was done, after Carrillo discovered that people had been foolishly using "Chevy" offset connecting rods in 928 engines, which have a completely different cylinder head offset. These rods have the "square" side beam machining that Carrillo now uses on some of their connecting rods, instead of the older "one pass ball end radius" that they used in the past. This was done to make these rods lighter. Although here is, without doubt, a higher percentage of material removed from the beam, Carrillo uses this design on many connecting rods for many different engines.

I have or will have access to the computers from these two engines, Mr. Kibort, and I will download the rev limiter settings.....although I'm certain that your finely tuned ear is far more accurate than any data about the actual rev limiter setting will somehow be moot.

Mark Anderson

Not exactly true. I bought the car for $35k and he bought it back for $20k as is.