The Road to Drag Week 2016 - July 17, 2016

[jayb]

I don't know what to say about this week except, holy crap I was not expecting this! 

Friday I went back to my machine shop to pick up the short block so I could get it assembled over the weekend.  The good news was the honing on the cylinder bores came out pretty well.  The #4 hole, which had the dings in it from the air cleaner stud incident last year, came out looking pretty good; there are only two small areas that didn't hone out.  See the small dark areas in the picture below:



Those dark areas used to be about an inch wide and half inch high, so going 0.008" oversize cleaned the bore right up.  All the other bores also honed nicely with almost no material removed.

Then I got some completely unexpected bad news.  I had brought the rods in to get checked out of an abundance of caution.  These were new rods in the spring of 2015, and heavier than the standard Crower rods, just to avoid any potential issues like the one I had in 2014, when the #5 rod broke at the Drag Week test and tune.  Well, my machinist informed me that I had a cracked rod!  Not only that, but it was the same rod, #5, as the one that broke the last time!  I just couldn't believe it.  The rod was cracked so badly that I'll bet it would have let go in one or two more passes down the track.  I guess I was lucky this time, but it sure doesn't feel that way.  Here are a couple of close up pictures of the rod:





Both sides of the rod were cracked, and the cracks extended through the edges all the way to the center section of the rod.  That center section was the only thing holding the rod together.

The news wasn't much better after that.  My machinist also pointed out that on most of the pistons there was evidence of contact with the exhaust valve.  I had completely missed this when I took the engine apart, probably because I was so focused on what I found with the oil ring support rail.  But he was right; here's a picture of one of the pistons:



Well, at least the piston to valve contact was explainable.  On the dyno I didn't have any indication that there was a valvetrain problem, but I only ran the engine to 7200 RPM on the dyno.  At the track, I was going through the lights at 7700, and I must have just run out of spring.  This was unexpected but probably not too serious, and a set of upgraded valve springs should solve the problem.

The connecting rod situation, on the other hand, is completely baffling to me.  Why this one rod is taking so much abuse is a mystery.  I ran this engine from 2008 through 2012 and didn't have this issue, so something must have changed after that.  I spoke with Blair Patrick about this on Saturday, and it was his opinion that there is some kind of resonance or harmonic in this one cylinder that is causing the problem.  He thought I should focus on upgrading the valve springs to change any resonant frequency that may be causing a problem.  Also, last year at Drag Week I had not been real careful about maintaining the timing chain tension, and it had gotten rather loose by the end of the event.  Blair thought I should try to monitor that more closely this year.  Finally, he suggested a call to ATI to see if a larger or heavier harmonic balancer might be in order.  My balancer is several years old anyway, so maybe rebuilding it might help.  Also ATI suggests bolting any accessories to the harmonic balancer, rather than using a long bolt to the crank.  It just so happens that I am using a long crank bolt to hold the arbor and drive pulley for the dry sump in place, so getting one of ATI's drive arbors that bolts to the balancer might be a good improvement to make.

But in any case, when I get this thing back together I'm going to minimize the dyno time, take it as easy as possible at Drag Week, and then when I tear the engine back down to look at the pistons, I'm going to have to look at the rods again too.  Fortunately for me Blair has a replacement rod that I can get my hands on next week, so this won't hold me up too much.  But, back to the assembly, the piston rings didn't make it on Friday, so I wasn't able to assemble the rest of the short block.  Looks like it will be next week before I can get that done.  I did get the block cleaned up, main bearing clearances checked, and the crank installed this weekend; pic below:



Right now I'm wondering what else could possibly go wrong with this project in the next eight weeks, before I hit the road for Drag Week.  I'm still hoping I can make it with this car and engine...

[427Fastback]

Is the crack on the same side of the rod ?

[jayb]

There are cracks on both sides of the rod, you just can't see them very well in the photos.  To be a little clearer, all four thick areas on the rod, front and back, and left side / right side, show the cracks that you can see in the photo.  The only thing holding that rod together is the center portion of the I-beam.

[cjshaker]

Wow, talk about dodging a MAJOR bullet! That crack is visible to the eye so I'm amazed it was still holding. It's a darn good thing you didn't try one last run for the fun of it!

It seems odd to me that harmonics would affect #5 while not doing the same on #1. Is there a working hypothesis as to why harmonics in the valvetrain would affect the rod, or was that just in relation to the piston contact? The contact doesn't seem very severe, so it's hard to imagine the relation between the two.

I have to say, you're shaking my confidence in the Crower rods a bit; the rod of choice in my next engine. The larger balancer and drive arbor certainly seem like good ideas, as does a vigilant maintenance of the timing chain tension. I had mentioned before that chain and belt harmonics can get brutal, and I imagine that to be even worse on the unsupported lengths of the SOHC chain. Are there any signs of abnormal wear on the nylon guides?

[jayb]

I think I'd be looking at a different set of rods also, if there were time.  But having the failure on the same rod twice in a row makes me think that its not the rods, its something else. 

Blair thought that since the front of the engine is different from side to side, relative to the timing chain configuration, this may explain why only one rod is affected.  His suggestion was to start changing things up, and since resonances can appear in the valvetrain, plus I have a P-V contact issue, that was the first place to start.

Just got off the phone with ATI and the guy I spoke to said that going to a larger harmonic balancer (they make an 8" diameter, 14 pound balancer) was not necessary, that a 585" engine at 7700 RPM would be just fine with the 7" balancer.  He said I should rebuild it though, since the O-rings are old (balancer was new in 2008).  Not sure that Blair agrees with his assessment regarding the larger balancer LOL!  But in any case, getting a custom balancer is not in the cards for this engine because of the lead time required to get one (6+ weeks). 

Chain guide wear looks normal...

[Hemi Joel]

Sorry to hear of all these problems Professor Brown. 2014 was the year that you busted the rod on Drag Week, and if I remember right, that was the first year that you ran the dry sump. So maybe the harmonics are coming from the oil pump?

[jayb]

I was thinking the same thing, Captain Stabbin'.  It could at least be a contributing factor.  Getting the drive pulley mounted to the harmonic balancer, rather than through the long bolt to the crank, will be a good step I think.

I was also thinking about the crank target I am using, also new in 2014, which is 3/8" plate steel, 8" in diameter, with 36 teeth.  But one tooth is missing, to allow the EFI computer to sync up once each revolution.  So, that piece of steel is not balanced.  I think I'm going to drill some holes to try to lighten that wheel, and also balance it...

[Barry_R]

I'm having a hard time blaming the mid-beam rod failure on the balance/harmonics stuff.  Just seems like a really long reach.  Have you discussed this with Crower yet?  That almost looks like a fatigue/flex location for a break.  How do the bearings look?  Pin fit in the pistons?

[machoneman]

Rod stretch is my guess, maybe induced by slamming the throttle closed at the line and using heavy engine braking to slow the car, stretching the rods. Still, why only #5? Checked on the rod centers for the other seven rods? 

[jayb]

I'm having a hard time blaming the mid-beam rod failure on the balance/harmonics stuff.  Just seems like a really long reach.  Have you discussed this with Crower yet?  That almost looks like a fatigue/flex location for a break.  How do the bearings look?  Pin fit in the pistons?

Haven't talked to Crower yet, but I plan to.  Rod bearings were beautiful on #5; no significant issues, the coating was still intact.  I haven't checked pin fit or rod length, but I will...

[jayb]

Still, why only #5?

This, to me, is the key question.  Why the #5 rod, twice in a row?  If it was engine braking and rod stretch, what are the odds it would affect #5 and no others?  None of the other rods show any evidence of problems.  The harmonic/resonance theory seems unlikely to me too, but what else is there?

[MRadke]

With your block being offset bored, is there simply more angle load on 5 than on the other cylinders?

[jayb]

Nope, #1, #4, #5, and #8 all have the same offset bore (0.105").  #2, #3, #6, and #7 are all offset 0.035".

[cjshaker]

It's certainly possible that it was a coincidence that it was #5 both times, but that just leads to a Quality Control or materials issue. I'd certainly be interested in what Crower has to say, but I'd guess they would place the blame somewhere else, and with all the successful racers out there running bigger power it'd be hard to argue against.

With such a long stroke, and running nearly 8000 rpm, I wonder if the side loading of the rod is just too much? It would also explain the piston coating scuffing, and possibly even the ring issues. Maybe a slight gear change to keep the RPMs down in the traps would be a good call?

[jayb]

After Drag Week last year I knew I needed less gear, so I've already gone down to 4.11s (from 4.29s).  Should keep the engine in the powerband I want.  Last year peak power was at 6600 RPM, and fell off rapidly after 7000, so I definitely had too much gear.  I'm also considering dropping down to 3.89 gears, depending on how things look for this engine on the dyno.  I've got to believe that RPM exaggerates this problem, whatever it is that is causing it.  I never intended to run the kind of RPM that I did at Drag Week last year, but who wants to let off in the last 100 feet LOL!