Mopar Rod Failures

S

splats

New member
I have been having a problem with our 2.2's. We have thrown 3 rods, 2 in cyl#3 & 1 in cyl#4. One was a street motor w/approx 80-90k miles, two of the motors were fresh rebuilds. Nothing has been the same, 2 different heads, different cranks, etc. One blew after 10mins track-time, second blew after 2 schools & 2 week-ends (old motor), and the other after a Dbl weekend (Moroso) & practice at Daytona. It is fuel-injected with a factory rev-limiter (6k). Sorry for this BOOK.

HELP!! Is there anyone that can help. We are at a lost. We didn't have a problem with the 2.5's that we ran in circle tracks. We can't afford to run ITA, so for now we are going to try & stay with the 2.2's.

Thanks for any help you can give.
 
What revs are you trying to run? Also, what style rod? There is an early style and late style (after '85). The later style rods are lightweight and therefore a little more prone to problems. Still, I rarely have seen rod problems unless you zing the motor past 7000. What motor/body combination are you running?

------------------
~Matt Rowe
ITA Shelby Charger
MARRS #96
 
Matt,
We are running an '88 Daytona, the blocks were '85 (short deck). Two of the cranks are early style (6 bolt), & one late style (8 bolt). We are trying to keep the revs around 5k. Moroso bounced-off the rev-limiter (6k) at the END of the straight for a split-second & Daytona was 5500. The motors have blown with a stock exhaust manifold & headers. Bone-stock TBI & pressure regulator. And just a bit of trivia, the car is an ex-circle track car that my son ran. It was the only Mopar & it was number 96. Thought you might get a kick out of that. Back to business. Will a 8 bolt 2.2 crank fit in the 2.5 block using the 2.5 rods and pistons? The block is an '88. If I remove the counter-balancers (never used in a 2.2) & plugged the oilers for the c/b's, will it work? I'm learning as I go with these "Baby-Hemi's". We don't want to build a new motor until we find out what is going on.

Mark
 
My guess is detonation--Perhaps insufficient fueling at high revs or too much ignition advance or insufficient octane.

Detonation causes a lot more problems than melted pistons...
 
Two of them were on 93 oct, the other on 100 oct. Two were at 12* btdc, the other at 28*. On two of the motors we were running 2 fuel pumps in-line. One high-volume/low-pressure self-priming, the other high-pressure (45psi). On one motor we were running the stock fuel tank with a new in-tank pump. Plugs were all perfect. And the ECM is stock, as is the the ignition (except the coil).
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[This message has been edited by splats (edited May 10, 2005).]
 
If you are thinking to eliminate detonation as the culpirt (I haven't), then also look at oiling (periodic loss of pressure). Is the oil pan well baffled? Have you considered an accusump?

Good luck!
 
I broke a rod in the stock engine in my '85 ITB Daytona at my first driver's school. That engine had at least 70,000 miles on it and I think it was caused by a spun bearing. The engines I've built after that have used ARP rod bolts, a baffled oil pan, an Accusump and an oil restrictor (that keeps too much oil from going to the head). I haven't had any rod related problems even with the lightweight rods. I have, however, blown a couple of engines due to missed shifts leading to broken valves.

Bob Clifton
Dodge Daytona ITB #85
 
I'll second Joeg's assessment.

Since all the rods have been on one "end" of the engine, it's possible that you have an oil starvation problem under hard cornering. I lost a couple of #4 rods in my old Honda before I figured it out - and an Accusump fixed it.

I also have a rod failure that was traced to a crank that was improperly ground, causing excess tolerance in the #3 main journal - which is where the oil was pumped into the crank. The result was that most of the ooil ran out of the bearing and back into the pan instead of pressurizing the crank properly.
 
We are looking at putting an oil-cooler on next motor. We start out with 65psi (oil)at idle, then it drops to 10psi when it heats up. At full throttle, its 'bout 20psi. From what I've been told, this is typical with these engines. Using Mobil-1 helps.
 
Mark,

Check the rod bearings for signs of abuse due to detonation and oiling issues. The mains will also give you some indication of oiling. That assumes you can get the thing shut off before contamination from the failures. In my experience these motors can develop oiling issues in cylinders 2 and 3 from high cornering loads. A baffled pan will help some, but I also run an accusump to make sure. 10 psi hot oil pressure is a little low, you should be able to maintain about 15-20 at idle while hot and 30-40 while at speed. Higher volume oil pumps are out there and a good idea, I also run an oil cooler. The big question is what are you oil temps?

The ARP rod bolts are definitely a good idea. Also, even with the 6k rev limiter make sure you aren't over reving on downshifts. Spinning beyond 6500 doesn't really do much in my 2.2, the 2.5 is even lower, but 5k seems a little low to use as a redline.

------------------
~Matt Rowe
ITA Shelby Charger
MARRS #96
 
Originally posted by splats:
... Will a 8 bolt 2.2 crank fit in the 2.5 block using the 2.5 rods and pistons? The block is an '88. If I remove the counter-balancers (never used in a 2.2) & plugged the oilers for the c/b's, will it work? ...
Click to expand...

Not to be a buzz-kill or anything but, since this is an IT site and I'm assuming we are talking about IT cars, your friendly, nieghborhood rules NERD needs to remind the assembled that the up- and back-date rule doesn't allow mix-and-match engine assemblies, or use of parts from cars on other spec lines.

If you do have two engine options among years/models on a spec line - like we do with the Golf - you can use one or the other. I'd LOVE to use the forged crank out of the early OBDI cars with the slightly better head of the later OBDII ones. But I can't.

K
 
10 lbs of pressure hot for every 1,000 rpm is the old rule of thumb. 7,000 rpm = 70 lbs of pressure. Some engines may get along with a little less, but not 20 lbs hot at revs. With 65 lbs cold and 10 lbs hot I think that you have major bearing clearance problems or a bad pump.
 
Is your problem in the big end, or the small end of the rod? I'm assuming the big end.

Does the bearing snip in the journal?

What do the bearings look like on the rods that don't spin?

What do the mains look like?

What direction does the galley flow and which mains support which rods?

What do the backs of the bearing shells look like after installation on a fresh engine? Have you ever checked the contact pattern?

Do you have any photos you could send or post?

Knowing this will make it more clear.

But, from what you've said, you've lost your MOFT (minimum oil film thickness).

As others have stated... this can be due to cornering and a loss of pick-up, or due to the pumps inability to supply the rods at high rpms. The pump may be cavitating, or you may be aerating the oil due to the temperature and duty cycle.

Take some care with an oil cooler, as it will lower your oil pressure further.
 
This is off topic, but I am curious about the two fuel pump set up. Why did you go to that set up and what pumps are you using?

Bob Clifton
85 Dodge Daytona ITB
 
Bob,
When we switched-out the stock-tank for the cell, we started having a pick-up problem. If the high-pressure pump sucked air, the car would either die or fall-on-its-face. We couldn't figure-out how to put in a sump tank into my cell. So, we got a low-pressure high-volume self-priming pump and just put it in-line between the cell & high-pressure pump. Its only there to feed that pump. Some of the long vans use a booster-pump in the same way. That is were we got the idea. As far as the pumps, the high-pressure is a universal EFI pump (Master brand part #E2000, from Autozone). The other pump is one we bought at the track. I don't know the brand or model of it, but it was for a carb (something like 8-10psi). Both pumps are wired together on one switch (easy-on, easy-off). I hope this helps.
Where are you getting your parts? I've been having trouble finding things.
 
Well, I went to the Pocono double regional this past weekend and broke a rod (#3 cyl) on the 3rd lap of Saturday's practice. I pulled the oil pan last night and there's less damage than I would have guessed. I'm hoping it broke on the down stoke and the head isn't messed up. I'll get the head off tonight and find out.

Anyway...parts suppliers:
www.fwdperformance.com
www.forwardmotioninc.com
They tend to favor the drag and turbo crowd but they have some stuff for us as well.

Bob Clifton
#85 ITB Dodge Daytona
 
Bob,
Sorry to send you my luck!!!! I haven't pulled-down the last blow-up, but the next to last one didn't hurt the head. The rod broke on the large side (crank). It broke were the rod joins the journal, not the cap side. The bolts were still attached. Let me know how yours blew. GOOD LUCK!!
 
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