You won't believe why it blew up...........

asphaltgambler · 06-05-2005, 07:29 AM

Readers Digest of my story. Last year we were in the market for our first 911. Being a European tech by trade with many years under my belt AND good advice from P-car exclusive techs I was ready to "git one"

After many dissapointments, decided on a nice '85 Targa w/95K that was not perfect, but was priced under market with small items I could address along the way.

After @1200 mile and two months, no issues until one Sunday road trip the engine gave way in a serious manner. Now I'm bummed out big-time. Spare time and $$ got in the way until recently when I dropped the engine for a complete rebuild / hop-up.

Split the cases Friday night and much to my surprise the rod cap was off and bent beyond belief; piston, cylinder, layshaft ruined. The case and crank were damaged, but repairable.

The cause???????? Believe it or not the connecting rod nuts FELL OFF allowing the rod cap to progressively work loose and parts went flying!! At first I thought the rod bolts had failed. Closer inspection revealed what was perfect threads on the nuts and the bolts. They had just backed off until they fell off!! UN-F__KING BELIEVABLE !!!

That issue destroyed a really good 3.2. The prior leak down was good and the bearings looked almost new.

Anyone else seen this?? I'm baffled

Pics of the carnage will follow soon.

Jeff Alton · 06-05-2005, 09:44 AM

This may have been cuased by an over rev earlier in the cars life causing the rod bolts to stretch. The nuts would then not be torqued and could possibly come loose?? Maybe? Just a possibility

Jeff

Romy · Romy's Garage

I know how you feel. About a month ago I did a cross country trip from Texas, where I bought the car. I initially thought of having my new purchase shipped back to Cali., but I decided to drive it back instead, in order to "bond" with my baby. Everything went well, the 915 tranny though sluggish in the city performs well on the freeways. The K-27 upgrade, which I paid the PO to upgrade before title sign over, allowed the 3.3 to breath and spool up quicker. I cruised I-10 through New Mexico and Arizona enjoying the pre-summer desert weather when just 30 miles outside the California - Arizona border, I heard a pop/clunk from he back and i see from my side mirrors black smoke eminating from the rear. My dream car has become my nightmare. How was this so? The PO provided paperwork to doument the rebuild from TRE about 10K miles ago. Didnt expect the engine to go out so soon. To make a long story short, I had found a carrier and had shipped back to NorCal to begin the engine rebuild. Heck, I was only behind the steering wheel for about 18 hours, now I gotta spend months in the garage before i can get back behind the wheel. Needless to say, my wife was livid when her first images of the car was on a flatbed. Once i got over the initial shock and heartache, I actually look forward to dropping the engine and working on it. I guess in some perverse way, it's all about the car. Driving it or working on it, it's all the same, you gotta love it. He he he, just got to convince my boss for some overtime......I want my parts! I will be documenting my rebuild on another thread.

adomakin · adomakin's Garage

I think Jeff hit the nail on the head. 3.2's have got a rep for rod bolt faliure. over revs are a real danger as the bolt stretches, then the nut is effectively backed off and loose. ends up either failing though a floating rod cap or because the nut comes off. nitemare. what else is mangled? have you got any pics?

Andy

350HP930 · 06-05-2005, 02:05 PM

If the nuts had time to back off I am surpised you didn't hear it knocking before it threw the rod.

Jeff Alton · 06-05-2005, 04:37 PM

350 has a good point. It would seem they would be loose for a little while and there should be a small reduction in oil pressure as well I would think.

Jeff

asphaltgambler · 06-05-2005, 06:06 PM

Oh it was knocking alright, but at that moment we were in the middle of deliverance-ville, no shoulder to pull off on, it was a old 4 lane divided hwy. Initially it sounded just like the timing chain tensioner had collasped, but quickly grew worse, then........pop just as we found a place to pull over.

Just the stuff I listed above was damaged. I was planning up a 3.4 build so the ruined piston is no big deal. I've already puchased one good used rod and found a useable cylinder this weekend. The case damage was contained where the web between mains 3-4 join. I can have it Tig-welded back. It broke the laysahft and bent the connecting drive tube to the oil pump. So basically could have STILL been a lot worse. That crank is just slightly damaged on # 5 rod throw, it's fixable most likely 1st undersize.

I'll try to have pics next week.

asphaltgambler · 06-05-2005, 06:08 PM

By the way ROMY.............that REALLY sucks!!

Wayne 962 · Wayne 962's Garage

You need a copy of my Engine Rebuild book, where I document this problem, and recommend ARP rod bolts instead of the factory ones. This is a very common problem...

-Wayne

adomakin · adomakin's Garage

i know someone in the states who has a good used layshaft if you need one

Andy

ChrisBennet · ChrisBennet's Garage

Quote:

Originally posted by catca
350 has a good point. It would seem they would be loose for a little while and there should be a small reduction in oil pressure as well I would think.

Jeff

I lost a rod bearing once and to my surprise the oil pressure didn't seem to drop at all. "Oil pump, strong like bull!"
-Chris

asphaltgambler · 06-06-2005, 04:44 PM

Wayne, WAAAY ahead here. Your book is my bible and this build will be my P-car term final. This board has been extremely helpful to me in the planning stages.

Jeff Alton · 06-06-2005, 05:27 PM

Chris, wow, that surprises me, but I am easily surprised!!

Jeff

David · David's Garage

I see another Loctite on rod bolts thread starting

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by 125shifter
I see another Loctite on rod bolts thread starting

Hmm, thanks for bringing that up. I really feel that putting the Loctite on the rod bolts buys you some extra miles when you might need it. This is a perfect example, where the torque was lost on the bolts and the dang thing fell right off. That probably would not have happened if the bolts were tightened with some Loctite...

-Wayne

stevepaa · 06-07-2005, 08:47 AM

Well, just a simple question. How do you put Loctite on ARP rod bolts with the lube applied to the threads?

1fastredsc · 06-07-2005, 09:38 AM

According to the book written by wayne, your not supposed to put any lube on the threads, just the locktite. Therefore the locktite acts like a thread lube.

ChrisBennet · ChrisBennet's Garage

Quote:

Originally posted by stevepaa
Well, just a simple question. How do you put Loctite on ARP rod bolts with the lube applied to the threads?

Not that I'm advocating Loctite on rod bolts but if you were worried about getting proper fastener tension you could use the bolt stretch method instead of using torque angle method.

Unlike the factory bolts, the ARP's may be reused. Of course if you Loctite them that might be a problem...

I don't know what the stretch spec is for factory rod bolts or even if there is one. I suppose one could come up with a rough value by measuring the stretch on few rod bolts tightened using the factory method.

The 9mm factory rod bolts have a well know reputation for stretch-leading-to-failure and this perhaps justifies the Loctite "solution". I am unaware/ignorant of any problems with ARP rod bolts in this regard.

-Chris

stevepaa · 06-07-2005, 12:13 PM

Yeah, I used the stretch method after trying the torque method. Stretch is the way to go. So I guess you could use loctite if one did the stretch method.

triplesn8s · 06-10-2005, 06:12 AM

OK, so which Loctite is recommended? Is this problem common on the 2.4L motors? I am about to start assembly with new rod bolts & will use the stretch method. Thanks.