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

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.

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

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.

http://forums.pelicanparts.com/uploa...1117997424.jpg

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

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

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

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.

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

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

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

Andy

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

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.

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

Jeff

I see another Loctite on rod bolts thread starting :D

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

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

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.

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

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.

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.

Wasnt locktite used at the factory? if so it didnot sound like it helped
Like Chris said has anybody ever herd of an ARP nut coming off ?
I spoke with ARP last week they recommend there lube for both
methods.But using locktite is a smart saftey net for the torque turn method with stock bolts. Palmer

I've built / modified a lot of different types of engines in last 30 yrs and I never heard of or had been reccomended to put Loctite red on the rod bolts. Guess what?? I will now.

Besides this build, my drag Harley is the next most time consuming and costly to do. I cannot afford a mistake from a techincal or parts standpoint.

I'm thinking out of the box more on this build because Porsche engineering is so precise compared to other types of engines. In most circumstances for other engine builds you usually throw most everything away execpt the block, maybe the head castings and start fresh.

These engines are so well thought out and (for the most part) have very good quaility components in there from the beginning so the focus is more on using whats there already and working with it.

Just buy some good aftermarket rod bolts instead of doing something half a$$ed like putting locktite on the threads of an OEM set.

With you there. ARP.

Just fire up the welder and tack them.;)

Tom

Actually, I'm d@mn good at oxy-acetylene / coat hanger welding!